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Efficient asymmetric transfer hydrogenation of N-sulfonylimines on water
Tetrahedron 69 (2013) 6500e6506
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Efficient asymmetric transfer hydrogenation of N-sulfonylimines on water Lei Wang a, c, Qi Zhou a, c, Chuanhua Qu b, Qiwei Wang a, Linfeng Cun a, Jin Zhu a, Jingen Deng a, b, * a
Key Laboratory of Asymmetric Synthesis & Chirotechnology of Sichuan Province, Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences, Chengdu, 610041, China Key Laboratory of Drug-Targeting of Education Ministry, Department of Medicinal Chemistry, West China School of Pharmacy, Sichuan University, Chengdu, 610041, China c The University of Chinese Academy of Sciences, Beijing, 100049, China b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 25 December 2012 Received in revised form 2 May 2013 Accepted 17 May 2013 Available online 28 May 2013
An efficient and green approach for synthesis of optically active amines was developed via asymmetric transfer hydrogenation of N-sulfonyl ketimines catalyzed by the chiral and lipophilic rhodium-amido complex on water. Higher reactivity and enantioselectivity were observed on the hydrogenation of the solid substrate in an aqueous suspension compared to organic homogeneous phases. In the heterogeneous aqueous reaction, the reactivity depends on stirring speed and the recrystallized conditions of the solid substrate. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: Asymmetric transfer hydrogenation Rhodium-amido complex N-Sulfonyl ketimines On water
1. Introduction Presently, there is an intense interest in developing greener chemistry for both laboratory and industrial applications. Replacement of organic solvents and especially chlorinated ones, with greener ones is an important question for green chemistry.1 Water is an attractive solvent for organic reactions because it is low cost, safer to operate (non-flammable, non-toxic), and negligible impact for the environment, and often shows interesting features like enhanced reaction rate and selectivity (chemo-, regio-, stereo-, even enantio-) if compared to organic media used in the same process.2,3 As a result, great effort has been inspired to this field and effective aqueous phase organic reactions have been documented.3 Among the aqueous catalytic approaches, asymmetric transfer hydrogenation (ATH) presents several advantages.4e8 The hydrogen source, sodium formate (HCO2Na), is water-soluble and produces the volatile co-product, carbon dioxide (CO2), which facilitates the purification of the reduction products. The transition metalcatalysts are insensitive to water as well as air oxidation, and stable in aqueous media.5b Particularly, in the comparison to organic media, the ATH of ketones was performed in water to exhibit * Corresponding author. Tel./fax: þ86 28 85238597; e-mail address: jgdeng@ cioc.ac.cn (J. Deng). 0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.tet.2013.05.064
significantly higher reactivity,5 better chemoselectivity,6 and regioselectivity,7 even higher enantioselectivity in the presence of surfactants.3f,6,8a Optically active amines are important building blocks for bioactive molecules and natural products, and have also extensively been used as chiral auxiliaries and resolving agents in asymmetric synthesis.9 Asymmetric reduction of ketimines is the most direct and efficient method for preparation of chiral amines.9,10 Because ATH possesses an operational simplicity and avoids the handling of hazardous chemicals such as metallic hydrides or molecular hydrogen, recently, the ATH has widely been applied to reduction of ketimines.11 However, the water-mediated ATH was rarely investigated probably because of the instability of ketimines, especially acyclic ketimines.4 Previous works indicated that ATH of cyclic ketimines and even ketiminiums was well performed in aqueous media, but the acyclic N-sulfonylimines did not work under the same conditions.8 Since optically active a-arylethylamines are key constituents of chiral drugs and bioactive compounds, such as Rivastigmine, Cinacalcet, and oxazolone derivative (Fig. 1),9a we herein like to report the preliminary results on the successful ATH of N-sulfonyl arylketimines catalyzed by lipophilic diaminetransition metal-catalysts in the aqueous suspension, which also shows that the recrystallized conditions greatly affect the reactivity of the solid substrates in the heterogeneous aqueous reactions.
L. Wang et al. / Tetrahedron 69 (2013) 6500e6506
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Fig. 1. Structures of pharmaceuticals and bioactive compound with chiral amine moieties.
2. Results and discussion The previous reports show that N-tosyl ketimines are more stable and efficient substrates for highly selective asymmetric hydrogenation in halogenated solvents.12 However, the development of efficient especially environmental friendly process or catalyzed system for the asymmetric reduction with higher enantioselectivity and more abroad scope of ketimine substrates is still an important research field. Initially, the ATH of N-tosyl ketimine 1a was tried by using 1 mol % of metal-complex prepared via treating (R,R)-TsDPEN (2a) and [RhCl2(Cp*)]2 in situ.4,13 Table 1 shows that the reactivities and enantioselectivities significantly depend on reaction media (entries 1e7). Interestingly, although 1a was well dissolved in the common organic solvents, the best yield (98.7%) and enantioselectivity (96.5% ee) were obtained with solid suspensions of 1a in water (Fig. 2) by using water-soluble HCO2Na as a hydrogen source after 1 h at 40 C (entry 7).14 Vigorous stirring promotes the
reactions (entry 8 vs entries 9 and 10), most likely by increasing the area of surface contact between the solid particles and aqueous phases. However, the reaction rate obviously decreased under sonication conditions (entry 11).14a The results suggest that the reaction proceeds at the interface between the solid substrates and water in other words ‘on water’. Although solid 1a and Rh-2a catalyst produced in situ are only sparingly soluble in water (Fig. 2),5b,13 the hydrophobic interactions and trans-phase hydrogen-bonding might contribute to accelerate the reactivity.2c,3b,e Various types of transition metal complexes were also investigated as catalyst precursors (entries 12e14). Excellent yields were obtained with both [RhCl2(Cp*)]2 and [IrCl2(Cp*)]2 as the precursors after 5 h, but slightly poor enantioselectivity was observed with [IrCl2(Cp*)]2. However, poor yield and low ee value were provided by using [RuCl2(p-cymene)]2 as a metal precursor, which is obviously different to the results of the imines catalyzed by the water-soluble ligands.8a,b Decreasing the reaction temperature
Table 1 Scanning of different solvent, metal precursor, and stirring speeda
Entry
Solventb
Metal complex
T ( C)
t (h)
Yieldc (%)
ee (%)
1 2 3 4 5 6 7 8 9e 10f 11g 12 13 14 15 16 17h
CH2Cl2 CH3CN MeOH EtOH THF EtOAc H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O
[RhCl2(Cp*)]2 [RhCl2(Cp*)]2 [RhCl2(Cp*)]2 [RhCl2(Cp*)]2 [RhCl2(Cp*)]2 [RhCl2(Cp*)]2 [RhCl2(Cp*)]2 [RhCl2(Cp*)]2 [RhCl2(Cp*)]2 [RhCl2(Cp*)]2 [RhCl2(Cp*)]2 [RhCl2(Cp*)]2 [IrCl2(Cp*)]2 [RuCl2(p-cymene)]2 [RhCl2(Cp*)]2 [IrCl2(Cp*)]2 [RhCl2(Cp*)]2
40 40 40 40 40 40 40 40 40 40 40 40 40 40 28 28 40
1 1 1 1 1 1 1 0.5 0.5 0.5 1 5 5 5 27 27 5
Trace Trace 44.6 47.3 83.5 91.4 98.7 96.7 35.4 29.1 17.2 99.1 99.0 21.8 57.1 30.3 82.6
n.d.d n.d. 82.2 83.6 90.1 94.2 96.5 96.4 96.6 96.6 n.d. 96.9 94.3 50.8 97.6 95.8 95.2
a The reaction in organic media was carried out in 1 mL of solvent under argon atmosphere using 0.4 mmol 1a. [Rh-(R,R)-2a]/[1a]¼1:100 and 0.2 mL of a mixture of formic acid and triethyl amine (TEAF, v/v¼5:2) as hydrogen source; the reaction in water was carried out in 1 mL of H2O under argon atmosphere using 0.4 mmol 1a. [M-(R,R)-2a]/ [1a]/[HCO2Na]¼1:100:750; stirring speed is 1200 rpm. b Organic solvent was dried before use. c Isolated yield. d n.d.¼not detected. e Stirring speed is 700 rpm. f Stirring speed is 300 rpm. g Under sonication conditions. h The reaction was carried out in 1 mL of H2O under argon atmosphere using 0.8 mmol 1a. [M-(R,R)-2a]/[1a]/[HCO2Na]¼1:200:1500.
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Fig. 2. Reaction process of 1a on water by using Rh-2a complex as a catalyst. (a) Precatalyst prepared in situ; (b) after adding 1a; (c) after adding HCO2Na and 1a; (d) reaction completed.
from 40 C to 28 C, a significant decline of yield was observed even prolong the reaction time to 27 h but the enantioselectivity slightly increased (entries 15 and 16). The different catalyst loading was also tested. When 0.5 mol % catalyst was used, only 82.6% yield was obtained with 95.2% enantioselectivity after 5 h (entry 17). Using N-Ts-imine 1a as the standard substrate, we screened a wide range of chiral diamine ligands. The results were summarized in Table 2. Most of these chiral sulfonyl diamine-complexes of [RhCl2(Cp*)]2 could provide a good to excellent enantioselectivity. Lipophilic ligands Ts-DPEN (2a) and 30 -NO2 substituted Ts-DPEN (2j) exhibited the highest yields with excellent ee values (entries 1 and 10). However, water-soluble ligands 2l8c and 2o8d did not
afford better results (entries 12 and 15). It indicated that various substituents on the benzene rings as well as sulfonyl group of 2a (entries 4e11), even with another chiral auxiliary group (entries 13 and 14) showed slight effect to the enantioselectivity of the product. Considering the similar enantioselectivities (entries 1 and 10) and the inconvenient preparation of 2j, we chose easily available 2a as the ligand for further research. The pH value is another important factor to the ATH of ketones and imines in water.5a,b,8a,b,15 Thus, the pH value of the reaction was carefully examined (Table 3). The conversion and enantioselectivity of 1a increased with elevated pH value by adjusting the ratio of HCO2Na and HCO2H. When the initial pH value achieved about 4,
Table 2 Scanning of ligand scopea
Entry
Ligand
Yieldb (%)
eec (%)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
2a 2b 2c 2d 2e 2f 2g 2h 2i 2j 2k 2l 2m 2n 2o
78.2 33.3 62.1 41.7 55.2 47.6 7.46 7.24 32.9 87.5 27.9 36.4 44.4 33.9 22.1
96.8 88.2 96.2 93.3 95.5 93.8 n.d. n.d. 94.8 96.1 96.5 94.5 96.3 95.8d 88.6
a b c d
All reactions were stirred at 1200 rpm. Determined by 1H NMR of the crude mixture in CDCl3, using 0.06 N mesitylene solution in CDCl3 as internal standard. (R)-3a was obtained. Detected as (S)-form product by comparing the sign of rotation with the data from literatures.11d,12
L. Wang et al. / Tetrahedron 69 (2013) 6500e6506 Table 3 Effect of the pH valuea
Entry
Amount (mmol) HCO2HþHCO2Na
pHb
pHc
Yieldd (%)
eee (%)
1 2 3 4 5 6 7
2þ0 3þ0 0.75þ2.25 0.5þ2.5 0.143þ2.857 0þ3 0þ3f
1.60 1.29 3.94 4.46 5.03 7.40 11.18
1.92 1.62 5.95 6.84 7.25 8.23 10.76
11.0 30.8 90.7 89.2 95.9 96.1 42.3
n.d. 87.7 93.2 94.6 96.3 96.3 97.0
a Reaction conditions: 0.002 mmol [RhCl2(Cp*)]2, 0.004 mmol (R,R)-2a, 0.4 mmol 1a, 1 mL of degassed water, stirring speed at 1200 rpm for 1 h. b Initial pH value. c pH value after reaction. d Determined by 1H NMR analysis of the crude mixture. e Detected as R isomer by comparing the sign of rotation with the data from literatures.11d,12 f Extra 0.5 mmol Na2CO3 was added.
significant acceleration of the reaction rate was observed (entries 1e3). It is notable that the best result was obtained in the basic media (entry 6),8a,b however, in an organic media, the ATH of imines is performed on acidic activation.16 The conversion decreased obviously as further increasing of pH value by adding Na2CO3 (entry 7). The results also indicate that the ATH of N-sulfonyl ketimine 1a may be activated by water via trans-phase hydrogen-bonding in this aqueous suspension.2c,3b Our previous works indicated that both the reactivity and enantioselectivity could be promoted by the addition of micelleforming agents.3f,6b,d,,8a In this study, either the cationic surfactants (CTAB) or anionic surfactant (SDS) showed significant decrease in both the yield and enantioselectivity (Table 4, entries 2 and 3) because of difficult solubilization of solid substrate in the micellar media but easy transport of the catalyst in micellar phase,6b,17 while the addition of nonionic surfactant Triton X-100 accelerated the reaction effectively (entries 4e8). The different amount of Triton X-100 was also screened, and it was showed that with the addition of 10% Triton X-100, the reaction gave the best results (entries 6 and 8). Here, Triton X-100 may play possibly the Table 4 Scanning of surfactantsa
Entry
Additive
Amount (mol %)
t (min)
Yieldb (%)
ee (%)
1 2 3 4 5 6 7 8
d CTABc SDSd Triton Triton Triton Triton Triton
d 50 50 50 30 10 4 10
10 10 10 10 10 10 10 30
76.9 13.4 10.5 84.7 85.7 91.6 40.7 99.8
96.8 89.9 n.d. 97.0 97.2 97.9 97.2 97.8
X-100e X-100 X-100 X-100 X-100
a Reaction conditions: 0.002 mmol [RhCl2(Cp*)]2, 0.004 mmol (R,R)-2a, 0.4 mmol 1a, 1 mL degassed water, stirring speed at 1200 rpm. b Isolated yield. c CTAB¼hexadecyl trimethyl ammonium bromide. d SDS¼sodium dodecyl sulfate. e Triton X-100¼octyl phenoxy poly ethoxy ethanol.
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role of a phase-transfer catalyst (PTC).3f,15 The results also suggest that the reduction occurs on the surface of the solid particles. After the optimal conditions had been established, the generality of the ATH processes of N-sulfonylimines (1aeq) was explored. As shown in Table 5, the reactions proceeded with high yields and good to excellent enantioselectivities. For N-tosyl arylimines (1aem), electronic effects of substituents on the aryl group largely affected the reactivities (entries 1e13). Ketimines 1def bearing strong electron-donating methoxyl group on the benzene ring proceeded in longer time (24 h) than 1aec (entries 4e6 vs 1e3). By adding Triton X-100, the rate of para- and meta-methoxyl substituted ketimines 1d and 1e were greatly increased. Amines 3d with 84.8% yield and 95.5% ee in 7 h and amine 3e, which is a key intermediate of chiral drug Rivastigmine (Fig. 1), with 92.2% yield and 96.3% ee in 3 h were obtained, respectively. However, only a little orthomethoxyl substituted amine 3f was produced, even prolonging the reaction time to 24 h (entry 6). Interestingly, ortho-trifluoromethyl ketimine 1g could be smoothly reduced with 98% yield and 96.1% ee in 24 h.17 Although the reduction of 1g was performed with Triton X-100 in 7 h, lower ee value (93.9%) was provided (entry 7). The chiral amine obtained from deprotection of 3g is a structural motif of biologically active oxazolone derivative,18 and to the best of our knowledge, this is the first asymmetric synthesis for optically active 1-(2-trifluoromethylphenyl)ethylamine via catalyzed asymmetric reduction. Moreover, chiral amine 3h, which is an important intermediate of chiral drug, Cinacalcet, could be obtained in 96.2% yield with 98.8% ee in the presence of 10 mol % of Triton X-100 in 8 h (entry 8). It is interesting that the additional Triton X-100 could slow down the reaction rate of hetero cyclic ketimines 1k and 1l (entries 11 and 12). On the contrast, the reaction rate of benzothien2-yl imine 1m could be accelerated in the presence of Triton X-100 (entry 13). To further examine the efficiency of this catalyst system, more N-sulfonyl ketimines were also tested. We found that cyclic sulfonylimine 1n was only reduced well with [RuCl2(p-cymene)]2 as a metal precursor in 98.3% yield and 96.1% ee (entries 15 vs 14).8a,19b N-tert-Butylsulfonyl ketimines 1o and 1p, as well as N-p-methoxylphenylsulfonyl ketimine 1q were hydrogenated in high yields and enantioselectivities in the absence of Triton X-100 (entries 16e18). It is notable that hindered N-sulfonyl ketimines, such as 1g and 1h, can be smoothly reduced with good yields and excellent enantioselectivities in this heterogeneous system.17 We sometimes found that the result of ATH of the model substrate 1a is not reproducible and speculated on a change in the crystallized conditions after the purification of 1a by chromatography on silica gel, such as the ratio of EtOAc and petrol ether (PE), which are the eluents. Thus, we recrystallized 1a under different conditions. The highest yield (96.7%) was obtained in 0.5 h with 1a recrystallized from a mixture of EtOAc and PE in 1:20 ratio (v/v) at 28 C. Decreased yields (79e87%) were observed with changing the ratio of EtOAc and PE for the recrystallization of 1a. Compound 1a recrystallized from a mixture of EtOAc and PE (1:20, v/v) at 0 C gave lower yield (58%). Only 16% yield of 3a was provided by using PE alone as recrystallized solvent at 28 C. However, quantitative yield could be obtained by prolonging the reaction time to 6 h for 1a obtained under all recrystallized conditions. These results showed that the recrystallized condition is an important factor for the reduction of solid substrates in the heterogeneous aqueous phases, which would lead to different dispersity of substrates in water. 3. Conclusion Asymmetric transfer hydrogenation of a wide range of N-sulfonyl ketimines has successfully been performed in high yields (82e>99%) and enantioselectivities (91e99%) on water by employing the chiral and lipophilic rhodium-amido complex as a catalyst and using HCO2Na as a hydrogen source. In the
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L. Wang et al. / Tetrahedron 69 (2013) 6500e6506
Table 5 Substrate scope of ATH of N-sulfonyl ketiminesa
Entry
Imine
R1
R2
t (h)
Yieldb (%)
eec (%)
Conf.d
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15f 16 17 18
1a 1b 1c 1d 1e 1f 1g 1h 1i 1j 1k 1l 1m 1n 1n 1o 1p 1q
C6H5 4-MeC6H4 4-FeC6H4 4-MeOC6H4 3-MeOC6H4 2-MeOC6H4 2-CF3C6H4 1-Naph 2-Naph C6H5 2-Fury 2-Thienyl 2-Benzothienyl
Me Me Me Me Me Me Me Me Me Et Me Me Me
1 (0.5) 5 (1) 5(2) 24 (7) 24 (3) 24 (24) 24 (7) 21 (8) 23 (2) 8(6) 19 (19) 8 (7) 24 (4) 12 (24) 10 14 5 24
99.1 (99.8) 92.0 (99.2) 92.4(92.5) 95.1 (84.8) 55.7 (92.2) 10.2 (12.7) 98.0 (95.0) 69.2 (96.2) 95.5 (99.6) 92.9 (87.0) 82.1 (67.2) 97.3(94.0) 39.9 (99.0) n.r. (89.2) 98.3 93.8 60.0 99.1
96.9 (98.0) 96.5 (97.7) 96.0(96.5) 96.4 (95.5) 95.4 (96.3) n.d. (n.d.)e 96.1 (93.9) 91.4 (98.8) 95.4 (97.4) 96.0 (96.7) 91.0 (90.4) 95.5(95.9) 82.5 (96.4) n.d. (70.8) 96.1 96.7 86.0 95.7
R R R R R n.d. (þ) () R R R R R R R R () (þ)
a b c d e f
Reaction conditions: 0.002 mmol [RhCl2(Cp*)]2, 0.004 mmol (R,R)-2a, 0.4 mmol N-sulfonyl imine, 3 mmol HCO2Na, 1 mL degassed water. Isolated yield and the data in the parenthesis were obtained by the addition of 0.04 mmol Triton X-100. Determined by chiral HPLC analysis. The absolute configuration was determined by comparing the sign of rotation with the data from literature.11d,12,19,20 n.d.¼not detected. Reaction conditions: 0.002 mmol [RuCl2(p-cymene)]2, 0.004 mmol (R,R)-2a, 0.4 mmol 1n, 3 mmol HCO2Na, 1 mL degassed water, 0.04 mmol Triton X-100.
heterogeneous aqueous reaction, reactivity depends on stirring speed and the recrystallized conditions of the solid substrates. Moreover, a significant enhancement of rate and ee value in the reduction was observed by adding nonionic surfactant Triton X100. It is worth to note that the ATH of hindered N-sulfonyl ketimines was well performed in the aqueous suspension compared to organic homogeneous phases. Thereby, a green approach for the synthesis of key intermediates of bioactive compounds including chiral drugs has been developed. 4. Experimental section 4.1. General information All commercially available reagents were used as received without further purification. 1H NMR and 13C NMR were acquired at 300 MHz and 75 MHz, respectively. Enantiomeric excess was determined by HPLC analysis on Chiralcel AD, OD, or OJ column (Daicel Chemical Industries, LTD). Electrospray ionization highresolution mass spectra (ESI-HRMS) were recorded on a Bruke PSIMS-Gly FT-ICR mass spectrometer. 4.2. General procedure for the asymmetric transfer hydrogenation of imines 1 and characterizations A mixture of [RhCl2(Cp*)]2 (1.3 mg, 0.002 mmol), ligand 2a (1.5 mg, 0.004 mmol) in 1 mL of degassed water was heated up to
40 C for 1 h. N-Sulfonylimine 1 (0.4 mmol), HCO2Na (204 mg, 3 mmol)/and Triton X-100 (26 mg, 0.04 mmol) were successively added. The solid suspension was stirred vigorously at 40 C. After completion of the reaction (monitored by TLC), the reaction mixture was extracted with EtOAc (5 mL) for three times. The combined organic phases were dried over anhydrous Na2SO4 and evaporated under reduced pressure. The crude product was dissolved in 1 mL of CDCl3, and the yield was determined by 1H NMR analysis using 1,3,5-trimethylbenzene or dimethyl malate as an internal standard. Isolated yield was obtained by using flash chromatography. 4.2.1. (R)-4-Methyl-N-(1-phenylethyl)benzenesulfonamide (3a).11d,12 White solid, mp: 78e80 C, 98.0% ee, determined by HPLC, Chiral AD-H column, 254 nm, i-PrOH/hexane¼20:80, 1.0 mL/min, tmajor¼7.75 min, tminor¼8.59 min. [a]23 D þ64.6 (c 0.41, CHCl3). 1H NMR (CDCl3, 300 MHz) d 1.42 (d, J¼6.9 Hz, 3H), 2.38 (s, 3H), 4.42e4.51 (m, 1H), 4.84 (br d, J¼6.7 Hz, 1H), 7.09e7.11 (m, 2H), 7.17e7.19 (m, 5H), 7.62 (d, J¼8.3 Hz, 2H). 4.2.2. (R)-4-Methyl-N-(1-p-tolylethyl)benzenesulfonamide (3b).19a White solid, mp: 111e113 C, 97.7% ee, determined by HPLC, Chiral OJ-H column, 254 nm, i-PrOH/hexane¼30:70, 1.0 mL/min, tminor¼9.56 min, tmajor¼10.99 min. [a]23 D þ74.5 (c 0.40, CHCl3). 1H NMR (CDCl3, 300 MHz) d 1.41 (d, J¼6.8 Hz, 3H), 2.28 (s, 3H), 2.39 (s, 3H), 4.36e4.45 (m, 1H), 4.90
L. Wang et al. / Tetrahedron 69 (2013) 6500e6506
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(d, J¼6.6 Hz, 1H), 6.96e7.02 (m, 4H), 7.19 (d, J¼8.0 Hz, 2H), 7.62 (d, J¼8.2 Hz, 2H).
(m, 2H), 2.35 (s, 3H), 4.18 (q, J¼7.2 Hz, 1H), 4.84 (d, J¼7.0 Hz, 1H), 6.99e7.01 (m, 2H), 7.10e7.16 (m, 5H), 7.53 (d, J¼8.1 Hz, 2H).
4.2.3. (R)-N-(1-(4-Fluorophenyl)ethyl)-4-methyl-benzenesulfonamide (3c).12,19a White solid, mp: 127e129 C, 96.5% ee, determined by HPLC, Chiral OJ-H column, 254 nm, i-PrOH/hexane¼30:70, 1.0 mL/min, tminor¼8.83 min, tmajor¼10.00 min. [a]23 D þ52.9 (c 0.54, CHCl3). 1H NMR (CDCl3, 300 MHz) d 1.38 (d, J¼6.9 Hz, 3H), 2.39 (s, 3H), 4.40e4.49 (m, 1H), 4.99 (d, J¼6.7 Hz, 1H), 6.83e6.89 (m, 2H), 7.04e7.09 (m, 2H), 7.18 (d, J¼8.3 Hz, 2H), 7.59 (d, J¼8.2 Hz, 2H).
4.2.10. (R)-N-(1-(Furan-2-yl)ethyl)-4-methyl-benzenesulfonamide (3k).11d White solid, mp: 72e74 C, 91.0% ee, determined by HPLC, Chiral OJ-H column, 254 nm, i-PrOH/hexane¼20:80, 0.8 mL/min, 1 tminor¼13.06 min, tmajor¼15.45 min. [a]23 D þ81.6 (c 0.39, CHCl3). H NMR (CDCl3, 300 MHz) d 1.44 (d, J¼6.9 Hz, 3H), 2.39 (s, 3H), 4.49e4.58 (m, 1H), 4.97 (d, J¼5.1 Hz, 1H), 5.98 (d, J¼3.2 Hz, 1H), 6.15 (dd, J¼3.0 Hz, 1.8 Hz, 1H), 7.16 (d, J¼0.9 Hz, 1H), 7.22 (d, J¼8.1 Hz, 2H), 7.68 (d, J¼8.2 Hz, 2H). 13C NMR (CDCl3, 75 MHz) d 20.8, 21.5, 47.3, 106.1, 110.0, 127.0, 129.4, 137.6, 141.9, 143.1, 154.0.
4.2.4. (R)-N-(1-(4-Methoxyphenyl)ethyl)-4-methyl-benzenesulfonamide (3d).12 White solid, mp: 116e118 C. 96.4% ee, determined by HPLC, Chiral OJ-H column, 254 nm, i-PrOH/hexane¼30:70, 1.0 mL/ min, tminor¼13.40 min, tmajor¼15.11 min. [a]23 D þ75.4 (c 0.47, CHCl3). 1 H NMR (CDCl3, 300 MHz) d 1.40 (d, J¼6.8 Hz, 3H), 2.39 (s, 3H), 3.76 (s, 3H), 4.36e4.45 (m, 1H), 4.68 (d, J¼6.8 Hz, 1H), 6.73 (d, J¼8.6 Hz, 2H), 7.01 (d, J¼8.7 Hz, 2H), 7.20 (d, J¼8.2 Hz, 2H), 7.62 (d, J¼8.2 Hz, 2H). 4.2.5. (R)-N-(1-(3-Methoxyphenyl)ethyl)-4-methyl-benzenesulfonamide (3e).11d,12,19a White solid, mp: 62e64 C, 96.3% ee, determined by HPLC, Chiral OJ-H column, 254 nm, i-PrOH/ hexane¼30:70, 1.0 mL/min, tminor¼10.53 min, tmajor¼11.80 min. 1 [a]23 D þ68.0 (c 0.12, CHCl3). H NMR (CDCl3, 300 MHz) d 1.40 (d, J¼6.8 Hz, 3H), 2.37 (s, 3H), 3.68 (s, 3H), 4.37e4.46 (m, 1H), 5.24 (d, J¼6.6 Hz, 1H), 6.59 (s, 1H), 6.69 (d, J¼7.8 Hz, 2H), 7.07e7.18 (m, 3H), 7.61 (d, J¼8.0 Hz, 2H). 4.2.6. (þ)-4-Methyl-N-(1-(2-trifluoromethylphenyl)ethyl)benzenesulfonamide (3g). White solid, mp: 151e153 C, 96.1% ee, determined by HPLC, Chiral OD-H column, 254 nm, i-PrOH/ hexane¼20:80, 1.0 mL/min, tmajor¼6.22 min, tminor¼7.80 min. [a]20 D þ93.1 (c 1.0, CHCl3). 1H NMR (CDCl3, 300 MHz) d 1.38 (d, J¼6.7 Hz, 3H), 2.36 (s, 3H), 4.82e4.86 (m, 1H), 5.95 (d, J¼4.5 Hz, 1H), 7.15 (d, J¼8.1 Hz, 2H), 7.20e7.26 (m, 1H), 7.31e7.36 (m, 1H), 7.45e7.51 (m, 2H), 7.65 (d, J¼8.2 Hz, 2H). 13C NMR (CDCl3, 75 MHz) d 21.4, 24.8, 49.3, 125.1 (q, JCeF¼272.6 Hz), 125.3 (q, JCeF¼5.8 Hz), 126.9 (q, JCeF¼30.0 Hz), 126.9, 127.1, 127.6, 129.3, 132.2, 136.9, 142.0, 143.2. HRMS (ESI) calcd for C16H16F3NNaO2S [MþNa]þ: 366.0746, found: 366.0741. 4.2.7. ()-4-Methyl-N-(1-(naphthalen-1-yl)ethyl)benzenesulfonamide (3h).12a White solid, mp: 92e94 C, 98.8% ee, determined by HPLC, Chiral OJ-H column, 254 nm, i-PrOH/hexane¼10:90, 1.0 mL/ 1 min, tminor¼7.83 min, tmajor¼9.93 min. [a]23 D 14.8 (c 0.12, CHCl3). H NMR (CDCl3, 300 MHz) d 1.54 (d, J¼6.5 Hz, 3H), 2.17 (s, 3H), 5.14e5.23 (m, 1H), 5.60 (d, J¼7.1 Hz, 1H), 6.88 (d, J¼8.0 Hz, 2H), 7.14 (t, J¼7.7 Hz, 1H), 7.26e7.33 (m, 3H), 7.45 (d, J¼8.0 Hz, 2H), 7.53 (d, J¼8.1 Hz, 1H), 7.64e7.66 (m, 1H), 7.80e7.83 (m, 1H).
4.2.11. (R)-4-Methyl-N-(1-(thiophen-2-yl)ethyl)benzenesulfonamide (3l).11d White solid, mp: 92e94 C, 95.9% ee, determined by HPLC, Chiral OD-H column, 254 nm, i-PrOH/hexane¼10:90, 1.0 mL/min, 1 tmajor¼9.55 min, tminor¼11.21 min. [a]20 D þ70.0 (c 0.51, CHCl3). H NMR (CDCl3, 300 MHz) d 1.52 (d, J¼6.8 Hz, 3H), 2.41 (s, 3H), 4.69e4.78 (m, 1H), 5.01 (d, J¼7.6 Hz, 1H), 6.76 (d, J¼3.3 Hz, 1H), 6.81e6.83 (m, 1H), 7.11 (d, J¼5.0 Hz, 1H), 7.24 (d, J¼8.0 Hz, 2H), 7.71 (d, J¼8.1 Hz, 2H). 13C NMR (CDCl3, 75 MHz) d 21.5, 23.8, 49.2, 124.3, 124.7, 126.6, 127.1, 129.5, 137.6, 143.3, 146.0. 4.2.12. (R)-N-(1-(Benzothiophen-2-yl)ethyl)-4-methyl-benzenesulfonamide (3m).11d White solid, mp: 139e141 C, 96.4% ee, determined by HPLC, Chiral AD-H column, 254 nm, i-PrOH/ hexane¼20:80, 1.0 mL/min, tminor¼13.74 min, tmajor¼16.16 min. 1 [a]20 D þ90.3 (c 1.0, CHCl3). H NMR (CDCl3, 300 MHz) d 1.58 (d, J¼6.6 Hz, 3H), 2.32 (s, 3H), 4.79e4.90 (m, 2H), 6.95 (s, 1H), 7.15 (d, J¼8.0 Hz, 2H), 7.28e7.33 (m, 2H), 7.59 (dd, J¼1.6, 8.6 Hz, 1H), 7.69 (dd, J¼3.5, 8.4 Hz, 3H). 13C NMR (CDCl3, 75 MHz) d 21.4, 23.4, 49.8, 121.1, 122.2, 123.4, 124.21, 124.23, 127.0, 129.3, 137.3, 139.1, 143.3, 146.4. 4.2.13. (R)-3-tert-Butyl-2,3-dihydrobenzoisothiazoline 1,1-dioxide (3n).8a,19b White solid, mp: 124e126 C, 96.1% ee, determined by HPLC, Chiral OD column, 254 nm, i-PrOH/hexane¼20:80, 1.0 mL/ 1 min, tminor¼6.73 min, tmajor¼17.51 min. [a]20 D þ53.4 (c 0.4, CHCl3). H NMR (CDCl3, 300 MHz) d 1.00 (s, 9H), 4.35 (d, J¼4.9 Hz, 1H), 5.55 (br s, 1H), 7.43e7.55 (m, 3H), 7.72 (d, J¼7.3 Hz, 1H). 13C NMR (CDCl3, 75 MHz) d 26.4, 36.5, 67.2, 121.2, 125.9, 129.0, 132.2, 135.8, 138.1. 4.2.14. (R)-2-Methyl-N-(1-phenylethyl)propane-2-sulfonamide (3o).11d,19b White solid, mp: 79e81 C, 96.7% ee, determined by HPLC, Chiral AD-H column, 254 nm, i-PrOH/hexane¼10:90, 1.0 mL/ min, tmajor¼7.08 min, tminor¼8.56 min. [a]23 D þ32.6 (c 0.31, CHCl3). 1 H NMR (CDCl3, 300 MHz) d 1.32 (s, 9H), 1.58 (d, J¼6.7 Hz, 3H), 4.25 (d, J¼8.6 Hz, 1H), 4.63e4.72 (m, 1H), 7.27e7.38 (m, 5H).
4.2.8. (R)-4-Methyl-N-(1-(naphthalen-2-yl)ethyl)benzenesulfonamide (3i).11d,12,19a White solid, mp: 111e113 C, 97.4% ee, determined by HPLC, Chiral OJ-H column, 254 nm, i-PrOH/ hexane¼30:70, 1.0 mL/min, tminor¼14.67 min, tmajor¼16.68 min. 1 [a]20 D þ74.1 (c 0.50, CHCl3). H NMR (CDCl3, 300 MHz) d 1.50 (d, J¼6.8 Hz, 3H), 2.21 (s, 3H), 4.61e4.66 (m, 1H), 5.43 (d, J¼7.2 Hz, 1H), 6.99 (d, J¼8.0 Hz, 2H), 7.21e7.26 (m, 1H), 7.42e7.47 (m, 3H), 7.58 (d, J¼8.1 Hz, 2H), 7.64 (d, J¼8.2 Hz, 2H), 7.73e7.76 (m, 1H).
4.2.15. ()-2-Methyl-N-(1-(naphthalen-1-yl)ethyl)propane-2sulfonamide (3p). White solid, mp: 99e101 C, 86.0% ee, determined by HPLC, Chiral AD-H column, 254 nm, i-PrOH/ hexane¼20:80, 1.0 mL/min, tmajor¼5.42 min, tminor¼6.97 min. 1 [a]23 D 5.7 (c 0.34, CHCl3). H NMR (CDCl3, 300 MHz) d 1.28 (s, 9H), 1.70 (d, J¼6.8 Hz, 3H), 4.39 (d, J¼8.3 Hz, 1H), 5.46e5.56 (m, 1H), 7.47e7.58 (m, 4H), 7.78e7.82 (m, 1H), 7.87e7.90 (m, 1H), 8.08 (d, J¼8.3 Hz, 1H). 13C NMR (CDCl3, 75 MHz) d 24.2, 26.0, 53.6, 59.8, 122.6, 122.7, 125.5, 125.8, 126.5, 128.0, 129.0, 129.8, 133.9, 139.6. HRMS (ESI) calcd for C16H25N2O2S [MþNH4]þ: 309.1631, found: 309.1625.
4.2.9. (R)-4-Methyl-N-(1-phenylpropyl)benzenesulfonamide (3j).11d,12 White solid, mp: 115e117 C, 96.7% ee, determined by HPLC, Chiral OJ-H column, 254 nm, i-PrOH/hexane¼30:70, 1.0 mL/ min, tminor¼7.15 min, tmajor¼10.94 min. [a]23 D þ48.1 (c 0.52, CHCl3). 1 H NMR (CDCl3, 300 MHz) d 0.78 (t, J¼7.4 Hz, 3H), 1.66e1.86
4.2.16. (þ)-4-Methoxy-N-(1-phenylethyl)benzenesulfonamide (3q).20 White solid, mp: 96e98 C, 95.7% ee, determined by HPLC, Chiral AD-H column, 254 nm, i-PrOH/hexane¼20:80, 1.0 mL/min, 1 tmajor¼10.39 min, tminor¼11.97 min. [a]23 D þ7.0 (c 0.22, CHCl3). H NMR (300 MHz, CDCl3) d 1.43 (d, J¼6.9 Hz, 2H), 3.84 (s, 3H),
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4.40e4.49 (m, 1H), 4.76 (d, J¼6.6 Hz, 1H), 6.85 (d, J¼8.9 Hz, 2H), 7.08e7.11 (m, 2H), 7.16e7.24 (m, 3H), 7.65 (dd, J¼2.0, 8.9 Hz, 2H). Acknowledgements We thank National Science Foundation of China (Grant Nos. 20972154 and 21172152), National Basic Research Program of China (973 Program, No. 2010CB833300), and Sichuan University for financial support. Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences, and West China School of Pharmacy, Sichuan University, contributed equally to this work. Supplementary data NMR, HPLC, and HRMS spectra of products. Supplementary data associated with this article can be found in the online version, at http://dx.doi.org/10.1016/j.tet.2013.05.064. References and notes 1. (a) Sheldon, R. A. Green Chem. 2007, 9, 1273e1283; (b) Sheldon, R. A. Chem. Commun. 2008, 3352e3365. 2. (a) Narayan, S.; Muldoon, J.; Finn, M. G.; Fokin, V. V.; Kolb, H. C.; Sharpless, K. B. Angew. Chem., Int. Ed. 2005, 44, 3275e3279; (b) Pirrung, M. C. Chem.dEur. J. 2006, 12, 1312e1317; (c) Jung, Y.; Marcus, R. A. J. Am. Chem. Soc. 2007, 129, 5492e5502. 3. For recent reviews on organic synthesis ‘in water’ and ‘on water’, see: (a) Simon, M.-O.; Li, C.-J. Chem. Soc. Rev. 2012, 41, 1415e1427; (b) Butler, R. N.; Coyne, A. G. Chem. Rev. 2010, 110, 6302e6337; (c) Shaughnessy, K. H. Chem. Rev. 2009, 109, 643e710; (d) Chanda, A.; Fokin, V. V. Chem. Rev. 2009, 109, 725e748; (e) € m, U. M.; Andersson, F. Angew. Chem., Int. Ed. 2006, 45, 548e551; (f) Lindstro Dwars, T.; Paetzold, E.; Oehme, G. Angew. Chem., Int. Ed. 2005, 44, 7174e7199. 4. For reviews on asymmetric transfer hydrogenation in water, see: (a) Tang, Y.; Deng, J. Prog. Chem. 2010, 22, 1242e1253; (b) Wu, X.; Xiao, J. Chem. Commun. 2007, 2449e2466; (c) Ikariya, T.; Blacker, A. J. Acc. Chem. Res. 2007, 40, 1300e1308. 5. (a) Wu, X.; Li, X.; Zanotti-Gerosa, A.; Pettman, A.; Liu, J.; Mills, A. J.; Xiao, J. Chem.dEur. J. 2008, 14, 2209e2222; (b) Wu, X.; Liu, J.; Tommaso, D. D.; Iggo, J. A.; Catlow, C. R. A.; Bacsa, J.; Xiao, J. Chem.dEur. J. 2008, 14, 7699e7715; (c) Wu, X.; Li, X.; Hems, W.; King, F.; Xiao, J. Org. Biomol. Chem. 2004, 2, 1818e1821. 6. (a) Ma, Y.; Liu, H.; Chen, L.; Cui, X.; Zhu, J.; Deng, J. Org. Lett. 2003, 5, 2103e2106; (b) Wang, F.; Liu, H.; Cun, L.; Zhu, J.; Deng, J.; Jiang, Y. J. Org. Chem. 2005, 70, 9424e9429; (c) Tang, Y.; Xiang, J.; Cun, L.; Wang, Y.; Zhu, J.; Liao, J.; Deng, J. Tetrahedron: Asymmetry 2010, 21, 1900e1905; (d) Li, J.; Li, X.; Ma, Y.; Wu, J.; Wang, F.; Xiang, J.; Zhu, J.; Wang, Q.; Deng, J. RCS Adv. 2013, 3, 1825e1834. 7. (a) Li, X.; Li, L.; Tang, Y.; Zhong, L.; Cun, L.; Zhu, J.; Liao, J.; Deng, J. J. Org. Chem. 2010, 75, 2981e2988; (b) Tang, L.; Lin, Z.; Wang, Q.; Wang, X.; Cun, L.; Yuan, W.; Zhu, J.; Deng, J. Tetrahedron Lett. 2012, 53, 3828e3830.
8. (a) Wu, J.; Wang, F.; Ma, Y.; Cui, X.; Cun, L.; Zhu, J.; Deng, J.; Yu, B. Chem. € ss-Fink, G. Green Chem. 2007, 9, Commun. 2006, 1766e1768; (b) Canivet, J.; Su 391e397; (c) Li, L.; Wu, J.; Wang, F.; Liao, J.; Zhang, H.; Lian, C.; Zhu, J.; Deng, J. Green Chem. 2007, 9, 23e25; (d) Tang, Y.; Li, X.; Lian, C.; Zhu, J.; Deng, J. Tetrahedron: Asymmetry 2011, 22, 1530e1535. €hne, M.; Bornscheuer, U. T. ChemCatChem 2009, 1, 42e51; (b) Breuer, M.; 9. (a) Ho € rmer, R.; Zelinski, T. Angew. Ditrich, K.; Habicher, T.; Hauer, B.; Kebeler, M.; Stu Chem., Int. Ed. 2004, 43, 788e824. 10. For reviews on the asymmetric reduction of imines, see: (a) Kobayashi, S.; Ishitani, H. Chem. Rev. 1999, 99, 1069e1094; (b) Blaser, H. U.; Malan, C.; Pugin, B.; Spindler, F.; Steiner, H.; Studer, M. Adv. Synth. Catal. 2003, 345, 103e151; (c) Cho, B. T. Tetrahedron 2006, 62, 7621e7643; (d) Nugent, T. C.; El-Shazly, M. Adv. Synth. Catal. 2010, 352, 753e819; (e) Rueping, M.; Sugiono, E.; Schoepke, F. R. geot, N.; de la Fuente, V.; Castillo n, S.; Synlett 2010, 852e865; (f) Fleury-Bre Claver, C. ChemCatChem 2010, 2, 1346e1371; (g) Xie, J.-H.; Zhu, S.-F.; Zhou, Q.-L. Chem. Rev. 2011, 111, 1713e1760; (h) Wang, C.; Villa-Marcos, B.; Xiao, J. Chem. Commun. 2011, 9773e9785. 11. For recent examples on the asymmetric transfer hydrogenation of imines, see: (a) Martins, J. E. D.; Clarkson, G. J.; Wills, M. Org. Lett. 2009, 11, 847e850; (b) Haraguchi, N.; Tsuru, K.; Arakawa, Y.; Itsuno, S. Org. Biomol. Chem. 2009, 7, Yus, M. Tetrahedron Lett. 2009, 50, 69e75; (c) Guijarro, D.; Pablo, O.; 5386e5388; (d) Kwak, S. H.; Lee, S. A.; Lee, K.-I. Tetrahedron: Asymmetry 2010, Yus, M. J. Org. Chem. 2010, 75, 21, 800e804; (e) Guijarro, D.; Pablo, O.; 5265e5270; (f) Zhou, S.; Fleischer, S.; Junge, K.; Das, S.; Addis, D.; Beller, M. Angew. Chem., Int. Ed. 2010, 49, 8121e8125; (g) Strotman, N. A.; Baxter, C. A.; Brands, K. M. J.; Cleator, E.; Krska, S. W.; Reamer, R. A.; Wallace, D. J.; Wright, T. J. J. Am. Chem. Soc. 2011, 133, 8362e8371. 12. (a) Yang, Q.; Shang, G.; Gao, W.; Deng, J.; Zhang, X. Angew. Chem., Int. Ed. 2006, 45, 3832e3835; (b) Wang, Y.-Q.; Lu, S.-M.; Zhou, Y.-G. J. Org. Chem. 2007, 72, 3729e3734. 13. (a) Mashima, K.; Abe, T.; Tani, K. Chem. Lett. 1998, 1199e1200; (b) Murata, K.; Ikariya, T.; Noyori, R. J. Org. Chem. 1999, 64, 2186e2187; (c) Mao, J.; Baker, D. C. Org. Lett. 1999, 1, 841e843. ska, M.; Adamkiewicz, A.; Mlynarski, J. Green Chem. 2011, 13, 14. (a) Rogozin 1155e1157 and references therein; (b) Klijn, J. E.; Engberts, J. B. F. N. Nature 2005, 435, 746e747. cs, J.; Fuhrmann, H.; Oehme, G. Adv. Synth. Catal. 2002, 344, 15. Grassert, I.; Kova 312e318. 16. (a) Aberg, J. B.; Samec, J. S. M.; B€ ackvall, J.-E. Chem. Commun. 2006, 2771e2773; (b) Blackmond, D. G.; Ropic, M.; Stefinovic, M. Org. Process Res. Dev. 2006, 10, 457e463. 17. 1-(2-Trifluoromethylphenyl)-N-tosylethanimine (1g) is only liquid substrate in this study, and the reduction was performed well in the presence of 10 mol % SDS and CTAB in 7 h with 48.8% (91.8% ee) and 76.5% (93.6% ee) yields, respectively. After 7 h, 3g was obtained with 56.8% yield and 97.3% ee in neat water. For comparison, 3g and 1-(1-naphthyl)-N-tosylethanimine (3h) were reduced under Lee’s conditions,11d however, no reaction was observed for 3g and 3h only gave 31.8% yield (99.8% ee) after 8 h. 18. Sutin, L.; Andersson, S.; Bergquist, L.; Castro, V. M.; Danielsson, E.; James, S.; n, K.; Williams, M. Bioorg. Med. Henriksson, M.; Johansson, L.; Kaiser, C.; Flyre Chem. Lett. 2007, 17, 4837e4840. 19. (a) Nishimura, T.; Yasuhara, Y.; Hayashi, T. Org. Lett. 2006, 8, 979e981; (b) Chen, Y.-C.; Wu, T.-F.; Deng, J.-G.; Liu, H.; Cui, X.; Zhu, J.; Jiang, Y.-Z.; Choi, M. C. K.; Chan, A. S. C. J. Org. Chem. 2002, 67, 5301e5306. 20. Ye, Y.-H.; Zhang, J.; Wang, G.; Chen, S.-Y.; Yu, X.-Q. Tetrahedron 2011, 67, 4649e4654.
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Efficient asymmetric transfer hydrogenation of N-sulfonylimines on water Lei Wang a, c, Qi Zhou a, c, Chuanhua Qu b, Qiwei Wang a, Linfeng Cun a, Jin Zhu a, Jingen Deng a, b, * a
Key Laboratory of Asymmetric Synthesis & Chirotechnology of Sichuan Province, Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences, Chengdu, 610041, China Key Laboratory of Drug-Targeting of Education Ministry, Department of Medicinal Chemistry, West China School of Pharmacy, Sichuan University, Chengdu, 610041, China c The University of Chinese Academy of Sciences, Beijing, 100049, China b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 25 December 2012 Received in revised form 2 May 2013 Accepted 17 May 2013 Available online 28 May 2013
An efficient and green approach for synthesis of optically active amines was developed via asymmetric transfer hydrogenation of N-sulfonyl ketimines catalyzed by the chiral and lipophilic rhodium-amido complex on water. Higher reactivity and enantioselectivity were observed on the hydrogenation of the solid substrate in an aqueous suspension compared to organic homogeneous phases. In the heterogeneous aqueous reaction, the reactivity depends on stirring speed and the recrystallized conditions of the solid substrate. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: Asymmetric transfer hydrogenation Rhodium-amido complex N-Sulfonyl ketimines On water
1. Introduction Presently, there is an intense interest in developing greener chemistry for both laboratory and industrial applications. Replacement of organic solvents and especially chlorinated ones, with greener ones is an important question for green chemistry.1 Water is an attractive solvent for organic reactions because it is low cost, safer to operate (non-flammable, non-toxic), and negligible impact for the environment, and often shows interesting features like enhanced reaction rate and selectivity (chemo-, regio-, stereo-, even enantio-) if compared to organic media used in the same process.2,3 As a result, great effort has been inspired to this field and effective aqueous phase organic reactions have been documented.3 Among the aqueous catalytic approaches, asymmetric transfer hydrogenation (ATH) presents several advantages.4e8 The hydrogen source, sodium formate (HCO2Na), is water-soluble and produces the volatile co-product, carbon dioxide (CO2), which facilitates the purification of the reduction products. The transition metalcatalysts are insensitive to water as well as air oxidation, and stable in aqueous media.5b Particularly, in the comparison to organic media, the ATH of ketones was performed in water to exhibit * Corresponding author. Tel./fax: þ86 28 85238597; e-mail address: jgdeng@ cioc.ac.cn (J. Deng). 0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.tet.2013.05.064
significantly higher reactivity,5 better chemoselectivity,6 and regioselectivity,7 even higher enantioselectivity in the presence of surfactants.3f,6,8a Optically active amines are important building blocks for bioactive molecules and natural products, and have also extensively been used as chiral auxiliaries and resolving agents in asymmetric synthesis.9 Asymmetric reduction of ketimines is the most direct and efficient method for preparation of chiral amines.9,10 Because ATH possesses an operational simplicity and avoids the handling of hazardous chemicals such as metallic hydrides or molecular hydrogen, recently, the ATH has widely been applied to reduction of ketimines.11 However, the water-mediated ATH was rarely investigated probably because of the instability of ketimines, especially acyclic ketimines.4 Previous works indicated that ATH of cyclic ketimines and even ketiminiums was well performed in aqueous media, but the acyclic N-sulfonylimines did not work under the same conditions.8 Since optically active a-arylethylamines are key constituents of chiral drugs and bioactive compounds, such as Rivastigmine, Cinacalcet, and oxazolone derivative (Fig. 1),9a we herein like to report the preliminary results on the successful ATH of N-sulfonyl arylketimines catalyzed by lipophilic diaminetransition metal-catalysts in the aqueous suspension, which also shows that the recrystallized conditions greatly affect the reactivity of the solid substrates in the heterogeneous aqueous reactions.
L. Wang et al. / Tetrahedron 69 (2013) 6500e6506
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Fig. 1. Structures of pharmaceuticals and bioactive compound with chiral amine moieties.
2. Results and discussion The previous reports show that N-tosyl ketimines are more stable and efficient substrates for highly selective asymmetric hydrogenation in halogenated solvents.12 However, the development of efficient especially environmental friendly process or catalyzed system for the asymmetric reduction with higher enantioselectivity and more abroad scope of ketimine substrates is still an important research field. Initially, the ATH of N-tosyl ketimine 1a was tried by using 1 mol % of metal-complex prepared via treating (R,R)-TsDPEN (2a) and [RhCl2(Cp*)]2 in situ.4,13 Table 1 shows that the reactivities and enantioselectivities significantly depend on reaction media (entries 1e7). Interestingly, although 1a was well dissolved in the common organic solvents, the best yield (98.7%) and enantioselectivity (96.5% ee) were obtained with solid suspensions of 1a in water (Fig. 2) by using water-soluble HCO2Na as a hydrogen source after 1 h at 40 C (entry 7).14 Vigorous stirring promotes the
reactions (entry 8 vs entries 9 and 10), most likely by increasing the area of surface contact between the solid particles and aqueous phases. However, the reaction rate obviously decreased under sonication conditions (entry 11).14a The results suggest that the reaction proceeds at the interface between the solid substrates and water in other words ‘on water’. Although solid 1a and Rh-2a catalyst produced in situ are only sparingly soluble in water (Fig. 2),5b,13 the hydrophobic interactions and trans-phase hydrogen-bonding might contribute to accelerate the reactivity.2c,3b,e Various types of transition metal complexes were also investigated as catalyst precursors (entries 12e14). Excellent yields were obtained with both [RhCl2(Cp*)]2 and [IrCl2(Cp*)]2 as the precursors after 5 h, but slightly poor enantioselectivity was observed with [IrCl2(Cp*)]2. However, poor yield and low ee value were provided by using [RuCl2(p-cymene)]2 as a metal precursor, which is obviously different to the results of the imines catalyzed by the water-soluble ligands.8a,b Decreasing the reaction temperature
Table 1 Scanning of different solvent, metal precursor, and stirring speeda
Entry
Solventb
Metal complex
T ( C)
t (h)
Yieldc (%)
ee (%)
1 2 3 4 5 6 7 8 9e 10f 11g 12 13 14 15 16 17h
CH2Cl2 CH3CN MeOH EtOH THF EtOAc H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O
[RhCl2(Cp*)]2 [RhCl2(Cp*)]2 [RhCl2(Cp*)]2 [RhCl2(Cp*)]2 [RhCl2(Cp*)]2 [RhCl2(Cp*)]2 [RhCl2(Cp*)]2 [RhCl2(Cp*)]2 [RhCl2(Cp*)]2 [RhCl2(Cp*)]2 [RhCl2(Cp*)]2 [RhCl2(Cp*)]2 [IrCl2(Cp*)]2 [RuCl2(p-cymene)]2 [RhCl2(Cp*)]2 [IrCl2(Cp*)]2 [RhCl2(Cp*)]2
40 40 40 40 40 40 40 40 40 40 40 40 40 40 28 28 40
1 1 1 1 1 1 1 0.5 0.5 0.5 1 5 5 5 27 27 5
Trace Trace 44.6 47.3 83.5 91.4 98.7 96.7 35.4 29.1 17.2 99.1 99.0 21.8 57.1 30.3 82.6
n.d.d n.d. 82.2 83.6 90.1 94.2 96.5 96.4 96.6 96.6 n.d. 96.9 94.3 50.8 97.6 95.8 95.2
a The reaction in organic media was carried out in 1 mL of solvent under argon atmosphere using 0.4 mmol 1a. [Rh-(R,R)-2a]/[1a]¼1:100 and 0.2 mL of a mixture of formic acid and triethyl amine (TEAF, v/v¼5:2) as hydrogen source; the reaction in water was carried out in 1 mL of H2O under argon atmosphere using 0.4 mmol 1a. [M-(R,R)-2a]/ [1a]/[HCO2Na]¼1:100:750; stirring speed is 1200 rpm. b Organic solvent was dried before use. c Isolated yield. d n.d.¼not detected. e Stirring speed is 700 rpm. f Stirring speed is 300 rpm. g Under sonication conditions. h The reaction was carried out in 1 mL of H2O under argon atmosphere using 0.8 mmol 1a. [M-(R,R)-2a]/[1a]/[HCO2Na]¼1:200:1500.
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Fig. 2. Reaction process of 1a on water by using Rh-2a complex as a catalyst. (a) Precatalyst prepared in situ; (b) after adding 1a; (c) after adding HCO2Na and 1a; (d) reaction completed.
from 40 C to 28 C, a significant decline of yield was observed even prolong the reaction time to 27 h but the enantioselectivity slightly increased (entries 15 and 16). The different catalyst loading was also tested. When 0.5 mol % catalyst was used, only 82.6% yield was obtained with 95.2% enantioselectivity after 5 h (entry 17). Using N-Ts-imine 1a as the standard substrate, we screened a wide range of chiral diamine ligands. The results were summarized in Table 2. Most of these chiral sulfonyl diamine-complexes of [RhCl2(Cp*)]2 could provide a good to excellent enantioselectivity. Lipophilic ligands Ts-DPEN (2a) and 30 -NO2 substituted Ts-DPEN (2j) exhibited the highest yields with excellent ee values (entries 1 and 10). However, water-soluble ligands 2l8c and 2o8d did not
afford better results (entries 12 and 15). It indicated that various substituents on the benzene rings as well as sulfonyl group of 2a (entries 4e11), even with another chiral auxiliary group (entries 13 and 14) showed slight effect to the enantioselectivity of the product. Considering the similar enantioselectivities (entries 1 and 10) and the inconvenient preparation of 2j, we chose easily available 2a as the ligand for further research. The pH value is another important factor to the ATH of ketones and imines in water.5a,b,8a,b,15 Thus, the pH value of the reaction was carefully examined (Table 3). The conversion and enantioselectivity of 1a increased with elevated pH value by adjusting the ratio of HCO2Na and HCO2H. When the initial pH value achieved about 4,
Table 2 Scanning of ligand scopea
Entry
Ligand
Yieldb (%)
eec (%)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
2a 2b 2c 2d 2e 2f 2g 2h 2i 2j 2k 2l 2m 2n 2o
78.2 33.3 62.1 41.7 55.2 47.6 7.46 7.24 32.9 87.5 27.9 36.4 44.4 33.9 22.1
96.8 88.2 96.2 93.3 95.5 93.8 n.d. n.d. 94.8 96.1 96.5 94.5 96.3 95.8d 88.6
a b c d
All reactions were stirred at 1200 rpm. Determined by 1H NMR of the crude mixture in CDCl3, using 0.06 N mesitylene solution in CDCl3 as internal standard. (R)-3a was obtained. Detected as (S)-form product by comparing the sign of rotation with the data from literatures.11d,12
L. Wang et al. / Tetrahedron 69 (2013) 6500e6506 Table 3 Effect of the pH valuea
Entry
Amount (mmol) HCO2HþHCO2Na
pHb
pHc
Yieldd (%)
eee (%)
1 2 3 4 5 6 7
2þ0 3þ0 0.75þ2.25 0.5þ2.5 0.143þ2.857 0þ3 0þ3f
1.60 1.29 3.94 4.46 5.03 7.40 11.18
1.92 1.62 5.95 6.84 7.25 8.23 10.76
11.0 30.8 90.7 89.2 95.9 96.1 42.3
n.d. 87.7 93.2 94.6 96.3 96.3 97.0
a Reaction conditions: 0.002 mmol [RhCl2(Cp*)]2, 0.004 mmol (R,R)-2a, 0.4 mmol 1a, 1 mL of degassed water, stirring speed at 1200 rpm for 1 h. b Initial pH value. c pH value after reaction. d Determined by 1H NMR analysis of the crude mixture. e Detected as R isomer by comparing the sign of rotation with the data from literatures.11d,12 f Extra 0.5 mmol Na2CO3 was added.
significant acceleration of the reaction rate was observed (entries 1e3). It is notable that the best result was obtained in the basic media (entry 6),8a,b however, in an organic media, the ATH of imines is performed on acidic activation.16 The conversion decreased obviously as further increasing of pH value by adding Na2CO3 (entry 7). The results also indicate that the ATH of N-sulfonyl ketimine 1a may be activated by water via trans-phase hydrogen-bonding in this aqueous suspension.2c,3b Our previous works indicated that both the reactivity and enantioselectivity could be promoted by the addition of micelleforming agents.3f,6b,d,,8a In this study, either the cationic surfactants (CTAB) or anionic surfactant (SDS) showed significant decrease in both the yield and enantioselectivity (Table 4, entries 2 and 3) because of difficult solubilization of solid substrate in the micellar media but easy transport of the catalyst in micellar phase,6b,17 while the addition of nonionic surfactant Triton X-100 accelerated the reaction effectively (entries 4e8). The different amount of Triton X-100 was also screened, and it was showed that with the addition of 10% Triton X-100, the reaction gave the best results (entries 6 and 8). Here, Triton X-100 may play possibly the Table 4 Scanning of surfactantsa
Entry
Additive
Amount (mol %)
t (min)
Yieldb (%)
ee (%)
1 2 3 4 5 6 7 8
d CTABc SDSd Triton Triton Triton Triton Triton
d 50 50 50 30 10 4 10
10 10 10 10 10 10 10 30
76.9 13.4 10.5 84.7 85.7 91.6 40.7 99.8
96.8 89.9 n.d. 97.0 97.2 97.9 97.2 97.8
X-100e X-100 X-100 X-100 X-100
a Reaction conditions: 0.002 mmol [RhCl2(Cp*)]2, 0.004 mmol (R,R)-2a, 0.4 mmol 1a, 1 mL degassed water, stirring speed at 1200 rpm. b Isolated yield. c CTAB¼hexadecyl trimethyl ammonium bromide. d SDS¼sodium dodecyl sulfate. e Triton X-100¼octyl phenoxy poly ethoxy ethanol.
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role of a phase-transfer catalyst (PTC).3f,15 The results also suggest that the reduction occurs on the surface of the solid particles. After the optimal conditions had been established, the generality of the ATH processes of N-sulfonylimines (1aeq) was explored. As shown in Table 5, the reactions proceeded with high yields and good to excellent enantioselectivities. For N-tosyl arylimines (1aem), electronic effects of substituents on the aryl group largely affected the reactivities (entries 1e13). Ketimines 1def bearing strong electron-donating methoxyl group on the benzene ring proceeded in longer time (24 h) than 1aec (entries 4e6 vs 1e3). By adding Triton X-100, the rate of para- and meta-methoxyl substituted ketimines 1d and 1e were greatly increased. Amines 3d with 84.8% yield and 95.5% ee in 7 h and amine 3e, which is a key intermediate of chiral drug Rivastigmine (Fig. 1), with 92.2% yield and 96.3% ee in 3 h were obtained, respectively. However, only a little orthomethoxyl substituted amine 3f was produced, even prolonging the reaction time to 24 h (entry 6). Interestingly, ortho-trifluoromethyl ketimine 1g could be smoothly reduced with 98% yield and 96.1% ee in 24 h.17 Although the reduction of 1g was performed with Triton X-100 in 7 h, lower ee value (93.9%) was provided (entry 7). The chiral amine obtained from deprotection of 3g is a structural motif of biologically active oxazolone derivative,18 and to the best of our knowledge, this is the first asymmetric synthesis for optically active 1-(2-trifluoromethylphenyl)ethylamine via catalyzed asymmetric reduction. Moreover, chiral amine 3h, which is an important intermediate of chiral drug, Cinacalcet, could be obtained in 96.2% yield with 98.8% ee in the presence of 10 mol % of Triton X-100 in 8 h (entry 8). It is interesting that the additional Triton X-100 could slow down the reaction rate of hetero cyclic ketimines 1k and 1l (entries 11 and 12). On the contrast, the reaction rate of benzothien2-yl imine 1m could be accelerated in the presence of Triton X-100 (entry 13). To further examine the efficiency of this catalyst system, more N-sulfonyl ketimines were also tested. We found that cyclic sulfonylimine 1n was only reduced well with [RuCl2(p-cymene)]2 as a metal precursor in 98.3% yield and 96.1% ee (entries 15 vs 14).8a,19b N-tert-Butylsulfonyl ketimines 1o and 1p, as well as N-p-methoxylphenylsulfonyl ketimine 1q were hydrogenated in high yields and enantioselectivities in the absence of Triton X-100 (entries 16e18). It is notable that hindered N-sulfonyl ketimines, such as 1g and 1h, can be smoothly reduced with good yields and excellent enantioselectivities in this heterogeneous system.17 We sometimes found that the result of ATH of the model substrate 1a is not reproducible and speculated on a change in the crystallized conditions after the purification of 1a by chromatography on silica gel, such as the ratio of EtOAc and petrol ether (PE), which are the eluents. Thus, we recrystallized 1a under different conditions. The highest yield (96.7%) was obtained in 0.5 h with 1a recrystallized from a mixture of EtOAc and PE in 1:20 ratio (v/v) at 28 C. Decreased yields (79e87%) were observed with changing the ratio of EtOAc and PE for the recrystallization of 1a. Compound 1a recrystallized from a mixture of EtOAc and PE (1:20, v/v) at 0 C gave lower yield (58%). Only 16% yield of 3a was provided by using PE alone as recrystallized solvent at 28 C. However, quantitative yield could be obtained by prolonging the reaction time to 6 h for 1a obtained under all recrystallized conditions. These results showed that the recrystallized condition is an important factor for the reduction of solid substrates in the heterogeneous aqueous phases, which would lead to different dispersity of substrates in water. 3. Conclusion Asymmetric transfer hydrogenation of a wide range of N-sulfonyl ketimines has successfully been performed in high yields (82e>99%) and enantioselectivities (91e99%) on water by employing the chiral and lipophilic rhodium-amido complex as a catalyst and using HCO2Na as a hydrogen source. In the
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Table 5 Substrate scope of ATH of N-sulfonyl ketiminesa
Entry
Imine
R1
R2
t (h)
Yieldb (%)
eec (%)
Conf.d
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15f 16 17 18
1a 1b 1c 1d 1e 1f 1g 1h 1i 1j 1k 1l 1m 1n 1n 1o 1p 1q
C6H5 4-MeC6H4 4-FeC6H4 4-MeOC6H4 3-MeOC6H4 2-MeOC6H4 2-CF3C6H4 1-Naph 2-Naph C6H5 2-Fury 2-Thienyl 2-Benzothienyl
Me Me Me Me Me Me Me Me Me Et Me Me Me
1 (0.5) 5 (1) 5(2) 24 (7) 24 (3) 24 (24) 24 (7) 21 (8) 23 (2) 8(6) 19 (19) 8 (7) 24 (4) 12 (24) 10 14 5 24
99.1 (99.8) 92.0 (99.2) 92.4(92.5) 95.1 (84.8) 55.7 (92.2) 10.2 (12.7) 98.0 (95.0) 69.2 (96.2) 95.5 (99.6) 92.9 (87.0) 82.1 (67.2) 97.3(94.0) 39.9 (99.0) n.r. (89.2) 98.3 93.8 60.0 99.1
96.9 (98.0) 96.5 (97.7) 96.0(96.5) 96.4 (95.5) 95.4 (96.3) n.d. (n.d.)e 96.1 (93.9) 91.4 (98.8) 95.4 (97.4) 96.0 (96.7) 91.0 (90.4) 95.5(95.9) 82.5 (96.4) n.d. (70.8) 96.1 96.7 86.0 95.7
R R R R R n.d. (þ) () R R R R R R R R () (þ)
a b c d e f
Reaction conditions: 0.002 mmol [RhCl2(Cp*)]2, 0.004 mmol (R,R)-2a, 0.4 mmol N-sulfonyl imine, 3 mmol HCO2Na, 1 mL degassed water. Isolated yield and the data in the parenthesis were obtained by the addition of 0.04 mmol Triton X-100. Determined by chiral HPLC analysis. The absolute configuration was determined by comparing the sign of rotation with the data from literature.11d,12,19,20 n.d.¼not detected. Reaction conditions: 0.002 mmol [RuCl2(p-cymene)]2, 0.004 mmol (R,R)-2a, 0.4 mmol 1n, 3 mmol HCO2Na, 1 mL degassed water, 0.04 mmol Triton X-100.
heterogeneous aqueous reaction, reactivity depends on stirring speed and the recrystallized conditions of the solid substrates. Moreover, a significant enhancement of rate and ee value in the reduction was observed by adding nonionic surfactant Triton X100. It is worth to note that the ATH of hindered N-sulfonyl ketimines was well performed in the aqueous suspension compared to organic homogeneous phases. Thereby, a green approach for the synthesis of key intermediates of bioactive compounds including chiral drugs has been developed. 4. Experimental section 4.1. General information All commercially available reagents were used as received without further purification. 1H NMR and 13C NMR were acquired at 300 MHz and 75 MHz, respectively. Enantiomeric excess was determined by HPLC analysis on Chiralcel AD, OD, or OJ column (Daicel Chemical Industries, LTD). Electrospray ionization highresolution mass spectra (ESI-HRMS) were recorded on a Bruke PSIMS-Gly FT-ICR mass spectrometer. 4.2. General procedure for the asymmetric transfer hydrogenation of imines 1 and characterizations A mixture of [RhCl2(Cp*)]2 (1.3 mg, 0.002 mmol), ligand 2a (1.5 mg, 0.004 mmol) in 1 mL of degassed water was heated up to
40 C for 1 h. N-Sulfonylimine 1 (0.4 mmol), HCO2Na (204 mg, 3 mmol)/and Triton X-100 (26 mg, 0.04 mmol) were successively added. The solid suspension was stirred vigorously at 40 C. After completion of the reaction (monitored by TLC), the reaction mixture was extracted with EtOAc (5 mL) for three times. The combined organic phases were dried over anhydrous Na2SO4 and evaporated under reduced pressure. The crude product was dissolved in 1 mL of CDCl3, and the yield was determined by 1H NMR analysis using 1,3,5-trimethylbenzene or dimethyl malate as an internal standard. Isolated yield was obtained by using flash chromatography. 4.2.1. (R)-4-Methyl-N-(1-phenylethyl)benzenesulfonamide (3a).11d,12 White solid, mp: 78e80 C, 98.0% ee, determined by HPLC, Chiral AD-H column, 254 nm, i-PrOH/hexane¼20:80, 1.0 mL/min, tmajor¼7.75 min, tminor¼8.59 min. [a]23 D þ64.6 (c 0.41, CHCl3). 1H NMR (CDCl3, 300 MHz) d 1.42 (d, J¼6.9 Hz, 3H), 2.38 (s, 3H), 4.42e4.51 (m, 1H), 4.84 (br d, J¼6.7 Hz, 1H), 7.09e7.11 (m, 2H), 7.17e7.19 (m, 5H), 7.62 (d, J¼8.3 Hz, 2H). 4.2.2. (R)-4-Methyl-N-(1-p-tolylethyl)benzenesulfonamide (3b).19a White solid, mp: 111e113 C, 97.7% ee, determined by HPLC, Chiral OJ-H column, 254 nm, i-PrOH/hexane¼30:70, 1.0 mL/min, tminor¼9.56 min, tmajor¼10.99 min. [a]23 D þ74.5 (c 0.40, CHCl3). 1H NMR (CDCl3, 300 MHz) d 1.41 (d, J¼6.8 Hz, 3H), 2.28 (s, 3H), 2.39 (s, 3H), 4.36e4.45 (m, 1H), 4.90
L. Wang et al. / Tetrahedron 69 (2013) 6500e6506
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(d, J¼6.6 Hz, 1H), 6.96e7.02 (m, 4H), 7.19 (d, J¼8.0 Hz, 2H), 7.62 (d, J¼8.2 Hz, 2H).
(m, 2H), 2.35 (s, 3H), 4.18 (q, J¼7.2 Hz, 1H), 4.84 (d, J¼7.0 Hz, 1H), 6.99e7.01 (m, 2H), 7.10e7.16 (m, 5H), 7.53 (d, J¼8.1 Hz, 2H).
4.2.3. (R)-N-(1-(4-Fluorophenyl)ethyl)-4-methyl-benzenesulfonamide (3c).12,19a White solid, mp: 127e129 C, 96.5% ee, determined by HPLC, Chiral OJ-H column, 254 nm, i-PrOH/hexane¼30:70, 1.0 mL/min, tminor¼8.83 min, tmajor¼10.00 min. [a]23 D þ52.9 (c 0.54, CHCl3). 1H NMR (CDCl3, 300 MHz) d 1.38 (d, J¼6.9 Hz, 3H), 2.39 (s, 3H), 4.40e4.49 (m, 1H), 4.99 (d, J¼6.7 Hz, 1H), 6.83e6.89 (m, 2H), 7.04e7.09 (m, 2H), 7.18 (d, J¼8.3 Hz, 2H), 7.59 (d, J¼8.2 Hz, 2H).
4.2.10. (R)-N-(1-(Furan-2-yl)ethyl)-4-methyl-benzenesulfonamide (3k).11d White solid, mp: 72e74 C, 91.0% ee, determined by HPLC, Chiral OJ-H column, 254 nm, i-PrOH/hexane¼20:80, 0.8 mL/min, 1 tminor¼13.06 min, tmajor¼15.45 min. [a]23 D þ81.6 (c 0.39, CHCl3). H NMR (CDCl3, 300 MHz) d 1.44 (d, J¼6.9 Hz, 3H), 2.39 (s, 3H), 4.49e4.58 (m, 1H), 4.97 (d, J¼5.1 Hz, 1H), 5.98 (d, J¼3.2 Hz, 1H), 6.15 (dd, J¼3.0 Hz, 1.8 Hz, 1H), 7.16 (d, J¼0.9 Hz, 1H), 7.22 (d, J¼8.1 Hz, 2H), 7.68 (d, J¼8.2 Hz, 2H). 13C NMR (CDCl3, 75 MHz) d 20.8, 21.5, 47.3, 106.1, 110.0, 127.0, 129.4, 137.6, 141.9, 143.1, 154.0.
4.2.4. (R)-N-(1-(4-Methoxyphenyl)ethyl)-4-methyl-benzenesulfonamide (3d).12 White solid, mp: 116e118 C. 96.4% ee, determined by HPLC, Chiral OJ-H column, 254 nm, i-PrOH/hexane¼30:70, 1.0 mL/ min, tminor¼13.40 min, tmajor¼15.11 min. [a]23 D þ75.4 (c 0.47, CHCl3). 1 H NMR (CDCl3, 300 MHz) d 1.40 (d, J¼6.8 Hz, 3H), 2.39 (s, 3H), 3.76 (s, 3H), 4.36e4.45 (m, 1H), 4.68 (d, J¼6.8 Hz, 1H), 6.73 (d, J¼8.6 Hz, 2H), 7.01 (d, J¼8.7 Hz, 2H), 7.20 (d, J¼8.2 Hz, 2H), 7.62 (d, J¼8.2 Hz, 2H). 4.2.5. (R)-N-(1-(3-Methoxyphenyl)ethyl)-4-methyl-benzenesulfonamide (3e).11d,12,19a White solid, mp: 62e64 C, 96.3% ee, determined by HPLC, Chiral OJ-H column, 254 nm, i-PrOH/ hexane¼30:70, 1.0 mL/min, tminor¼10.53 min, tmajor¼11.80 min. 1 [a]23 D þ68.0 (c 0.12, CHCl3). H NMR (CDCl3, 300 MHz) d 1.40 (d, J¼6.8 Hz, 3H), 2.37 (s, 3H), 3.68 (s, 3H), 4.37e4.46 (m, 1H), 5.24 (d, J¼6.6 Hz, 1H), 6.59 (s, 1H), 6.69 (d, J¼7.8 Hz, 2H), 7.07e7.18 (m, 3H), 7.61 (d, J¼8.0 Hz, 2H). 4.2.6. (þ)-4-Methyl-N-(1-(2-trifluoromethylphenyl)ethyl)benzenesulfonamide (3g). White solid, mp: 151e153 C, 96.1% ee, determined by HPLC, Chiral OD-H column, 254 nm, i-PrOH/ hexane¼20:80, 1.0 mL/min, tmajor¼6.22 min, tminor¼7.80 min. [a]20 D þ93.1 (c 1.0, CHCl3). 1H NMR (CDCl3, 300 MHz) d 1.38 (d, J¼6.7 Hz, 3H), 2.36 (s, 3H), 4.82e4.86 (m, 1H), 5.95 (d, J¼4.5 Hz, 1H), 7.15 (d, J¼8.1 Hz, 2H), 7.20e7.26 (m, 1H), 7.31e7.36 (m, 1H), 7.45e7.51 (m, 2H), 7.65 (d, J¼8.2 Hz, 2H). 13C NMR (CDCl3, 75 MHz) d 21.4, 24.8, 49.3, 125.1 (q, JCeF¼272.6 Hz), 125.3 (q, JCeF¼5.8 Hz), 126.9 (q, JCeF¼30.0 Hz), 126.9, 127.1, 127.6, 129.3, 132.2, 136.9, 142.0, 143.2. HRMS (ESI) calcd for C16H16F3NNaO2S [MþNa]þ: 366.0746, found: 366.0741. 4.2.7. ()-4-Methyl-N-(1-(naphthalen-1-yl)ethyl)benzenesulfonamide (3h).12a White solid, mp: 92e94 C, 98.8% ee, determined by HPLC, Chiral OJ-H column, 254 nm, i-PrOH/hexane¼10:90, 1.0 mL/ 1 min, tminor¼7.83 min, tmajor¼9.93 min. [a]23 D 14.8 (c 0.12, CHCl3). H NMR (CDCl3, 300 MHz) d 1.54 (d, J¼6.5 Hz, 3H), 2.17 (s, 3H), 5.14e5.23 (m, 1H), 5.60 (d, J¼7.1 Hz, 1H), 6.88 (d, J¼8.0 Hz, 2H), 7.14 (t, J¼7.7 Hz, 1H), 7.26e7.33 (m, 3H), 7.45 (d, J¼8.0 Hz, 2H), 7.53 (d, J¼8.1 Hz, 1H), 7.64e7.66 (m, 1H), 7.80e7.83 (m, 1H).
4.2.11. (R)-4-Methyl-N-(1-(thiophen-2-yl)ethyl)benzenesulfonamide (3l).11d White solid, mp: 92e94 C, 95.9% ee, determined by HPLC, Chiral OD-H column, 254 nm, i-PrOH/hexane¼10:90, 1.0 mL/min, 1 tmajor¼9.55 min, tminor¼11.21 min. [a]20 D þ70.0 (c 0.51, CHCl3). H NMR (CDCl3, 300 MHz) d 1.52 (d, J¼6.8 Hz, 3H), 2.41 (s, 3H), 4.69e4.78 (m, 1H), 5.01 (d, J¼7.6 Hz, 1H), 6.76 (d, J¼3.3 Hz, 1H), 6.81e6.83 (m, 1H), 7.11 (d, J¼5.0 Hz, 1H), 7.24 (d, J¼8.0 Hz, 2H), 7.71 (d, J¼8.1 Hz, 2H). 13C NMR (CDCl3, 75 MHz) d 21.5, 23.8, 49.2, 124.3, 124.7, 126.6, 127.1, 129.5, 137.6, 143.3, 146.0. 4.2.12. (R)-N-(1-(Benzothiophen-2-yl)ethyl)-4-methyl-benzenesulfonamide (3m).11d White solid, mp: 139e141 C, 96.4% ee, determined by HPLC, Chiral AD-H column, 254 nm, i-PrOH/ hexane¼20:80, 1.0 mL/min, tminor¼13.74 min, tmajor¼16.16 min. 1 [a]20 D þ90.3 (c 1.0, CHCl3). H NMR (CDCl3, 300 MHz) d 1.58 (d, J¼6.6 Hz, 3H), 2.32 (s, 3H), 4.79e4.90 (m, 2H), 6.95 (s, 1H), 7.15 (d, J¼8.0 Hz, 2H), 7.28e7.33 (m, 2H), 7.59 (dd, J¼1.6, 8.6 Hz, 1H), 7.69 (dd, J¼3.5, 8.4 Hz, 3H). 13C NMR (CDCl3, 75 MHz) d 21.4, 23.4, 49.8, 121.1, 122.2, 123.4, 124.21, 124.23, 127.0, 129.3, 137.3, 139.1, 143.3, 146.4. 4.2.13. (R)-3-tert-Butyl-2,3-dihydrobenzoisothiazoline 1,1-dioxide (3n).8a,19b White solid, mp: 124e126 C, 96.1% ee, determined by HPLC, Chiral OD column, 254 nm, i-PrOH/hexane¼20:80, 1.0 mL/ 1 min, tminor¼6.73 min, tmajor¼17.51 min. [a]20 D þ53.4 (c 0.4, CHCl3). H NMR (CDCl3, 300 MHz) d 1.00 (s, 9H), 4.35 (d, J¼4.9 Hz, 1H), 5.55 (br s, 1H), 7.43e7.55 (m, 3H), 7.72 (d, J¼7.3 Hz, 1H). 13C NMR (CDCl3, 75 MHz) d 26.4, 36.5, 67.2, 121.2, 125.9, 129.0, 132.2, 135.8, 138.1. 4.2.14. (R)-2-Methyl-N-(1-phenylethyl)propane-2-sulfonamide (3o).11d,19b White solid, mp: 79e81 C, 96.7% ee, determined by HPLC, Chiral AD-H column, 254 nm, i-PrOH/hexane¼10:90, 1.0 mL/ min, tmajor¼7.08 min, tminor¼8.56 min. [a]23 D þ32.6 (c 0.31, CHCl3). 1 H NMR (CDCl3, 300 MHz) d 1.32 (s, 9H), 1.58 (d, J¼6.7 Hz, 3H), 4.25 (d, J¼8.6 Hz, 1H), 4.63e4.72 (m, 1H), 7.27e7.38 (m, 5H).
4.2.8. (R)-4-Methyl-N-(1-(naphthalen-2-yl)ethyl)benzenesulfonamide (3i).11d,12,19a White solid, mp: 111e113 C, 97.4% ee, determined by HPLC, Chiral OJ-H column, 254 nm, i-PrOH/ hexane¼30:70, 1.0 mL/min, tminor¼14.67 min, tmajor¼16.68 min. 1 [a]20 D þ74.1 (c 0.50, CHCl3). H NMR (CDCl3, 300 MHz) d 1.50 (d, J¼6.8 Hz, 3H), 2.21 (s, 3H), 4.61e4.66 (m, 1H), 5.43 (d, J¼7.2 Hz, 1H), 6.99 (d, J¼8.0 Hz, 2H), 7.21e7.26 (m, 1H), 7.42e7.47 (m, 3H), 7.58 (d, J¼8.1 Hz, 2H), 7.64 (d, J¼8.2 Hz, 2H), 7.73e7.76 (m, 1H).
4.2.15. ()-2-Methyl-N-(1-(naphthalen-1-yl)ethyl)propane-2sulfonamide (3p). White solid, mp: 99e101 C, 86.0% ee, determined by HPLC, Chiral AD-H column, 254 nm, i-PrOH/ hexane¼20:80, 1.0 mL/min, tmajor¼5.42 min, tminor¼6.97 min. 1 [a]23 D 5.7 (c 0.34, CHCl3). H NMR (CDCl3, 300 MHz) d 1.28 (s, 9H), 1.70 (d, J¼6.8 Hz, 3H), 4.39 (d, J¼8.3 Hz, 1H), 5.46e5.56 (m, 1H), 7.47e7.58 (m, 4H), 7.78e7.82 (m, 1H), 7.87e7.90 (m, 1H), 8.08 (d, J¼8.3 Hz, 1H). 13C NMR (CDCl3, 75 MHz) d 24.2, 26.0, 53.6, 59.8, 122.6, 122.7, 125.5, 125.8, 126.5, 128.0, 129.0, 129.8, 133.9, 139.6. HRMS (ESI) calcd for C16H25N2O2S [MþNH4]þ: 309.1631, found: 309.1625.
4.2.9. (R)-4-Methyl-N-(1-phenylpropyl)benzenesulfonamide (3j).11d,12 White solid, mp: 115e117 C, 96.7% ee, determined by HPLC, Chiral OJ-H column, 254 nm, i-PrOH/hexane¼30:70, 1.0 mL/ min, tminor¼7.15 min, tmajor¼10.94 min. [a]23 D þ48.1 (c 0.52, CHCl3). 1 H NMR (CDCl3, 300 MHz) d 0.78 (t, J¼7.4 Hz, 3H), 1.66e1.86
4.2.16. (þ)-4-Methoxy-N-(1-phenylethyl)benzenesulfonamide (3q).20 White solid, mp: 96e98 C, 95.7% ee, determined by HPLC, Chiral AD-H column, 254 nm, i-PrOH/hexane¼20:80, 1.0 mL/min, 1 tmajor¼10.39 min, tminor¼11.97 min. [a]23 D þ7.0 (c 0.22, CHCl3). H NMR (300 MHz, CDCl3) d 1.43 (d, J¼6.9 Hz, 2H), 3.84 (s, 3H),
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4.40e4.49 (m, 1H), 4.76 (d, J¼6.6 Hz, 1H), 6.85 (d, J¼8.9 Hz, 2H), 7.08e7.11 (m, 2H), 7.16e7.24 (m, 3H), 7.65 (dd, J¼2.0, 8.9 Hz, 2H). Acknowledgements We thank National Science Foundation of China (Grant Nos. 20972154 and 21172152), National Basic Research Program of China (973 Program, No. 2010CB833300), and Sichuan University for financial support. Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences, and West China School of Pharmacy, Sichuan University, contributed equally to this work. Supplementary data NMR, HPLC, and HRMS spectra of products. Supplementary data associated with this article can be found in the online version, at http://dx.doi.org/10.1016/j.tet.2013.05.064. References and notes 1. (a) Sheldon, R. A. Green Chem. 2007, 9, 1273e1283; (b) Sheldon, R. A. Chem. Commun. 2008, 3352e3365. 2. (a) Narayan, S.; Muldoon, J.; Finn, M. G.; Fokin, V. V.; Kolb, H. C.; Sharpless, K. B. Angew. Chem., Int. Ed. 2005, 44, 3275e3279; (b) Pirrung, M. C. Chem.dEur. J. 2006, 12, 1312e1317; (c) Jung, Y.; Marcus, R. A. J. Am. Chem. Soc. 2007, 129, 5492e5502. 3. For recent reviews on organic synthesis ‘in water’ and ‘on water’, see: (a) Simon, M.-O.; Li, C.-J. Chem. Soc. Rev. 2012, 41, 1415e1427; (b) Butler, R. N.; Coyne, A. G. Chem. Rev. 2010, 110, 6302e6337; (c) Shaughnessy, K. H. Chem. Rev. 2009, 109, 643e710; (d) Chanda, A.; Fokin, V. V. Chem. Rev. 2009, 109, 725e748; (e) € m, U. M.; Andersson, F. Angew. Chem., Int. Ed. 2006, 45, 548e551; (f) Lindstro Dwars, T.; Paetzold, E.; Oehme, G. Angew. Chem., Int. Ed. 2005, 44, 7174e7199. 4. For reviews on asymmetric transfer hydrogenation in water, see: (a) Tang, Y.; Deng, J. Prog. Chem. 2010, 22, 1242e1253; (b) Wu, X.; Xiao, J. Chem. Commun. 2007, 2449e2466; (c) Ikariya, T.; Blacker, A. J. Acc. Chem. Res. 2007, 40, 1300e1308. 5. (a) Wu, X.; Li, X.; Zanotti-Gerosa, A.; Pettman, A.; Liu, J.; Mills, A. J.; Xiao, J. Chem.dEur. J. 2008, 14, 2209e2222; (b) Wu, X.; Liu, J.; Tommaso, D. D.; Iggo, J. A.; Catlow, C. R. A.; Bacsa, J.; Xiao, J. Chem.dEur. J. 2008, 14, 7699e7715; (c) Wu, X.; Li, X.; Hems, W.; King, F.; Xiao, J. Org. Biomol. Chem. 2004, 2, 1818e1821. 6. (a) Ma, Y.; Liu, H.; Chen, L.; Cui, X.; Zhu, J.; Deng, J. Org. Lett. 2003, 5, 2103e2106; (b) Wang, F.; Liu, H.; Cun, L.; Zhu, J.; Deng, J.; Jiang, Y. J. Org. Chem. 2005, 70, 9424e9429; (c) Tang, Y.; Xiang, J.; Cun, L.; Wang, Y.; Zhu, J.; Liao, J.; Deng, J. Tetrahedron: Asymmetry 2010, 21, 1900e1905; (d) Li, J.; Li, X.; Ma, Y.; Wu, J.; Wang, F.; Xiang, J.; Zhu, J.; Wang, Q.; Deng, J. RCS Adv. 2013, 3, 1825e1834. 7. (a) Li, X.; Li, L.; Tang, Y.; Zhong, L.; Cun, L.; Zhu, J.; Liao, J.; Deng, J. J. Org. Chem. 2010, 75, 2981e2988; (b) Tang, L.; Lin, Z.; Wang, Q.; Wang, X.; Cun, L.; Yuan, W.; Zhu, J.; Deng, J. Tetrahedron Lett. 2012, 53, 3828e3830.
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