Mannich-type reaction of (1-methoxy-2-methylpropenyloxy)trimethylsilane with arylaldehydes and aromatic amines catalyzed by perfluorinated rare earth metal salts in fluorous phase

Tetrahedron 61 (2005) 4965–4970

Mannich-type reaction of (1-methoxy-2-methylpropenyloxy)trimethylsilane with arylaldehydes and aromatic amines catalyzed by perfluorinated rare earth metal salts in fluorous phase Min Shi,* Shi-Cong Cui and Ying-Hao Liu State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Lu, Shanghai 200032, China Received 4 January 2005; revised 8 March 2005; accepted 10 March 2005 Available online 2 April 2005

Abstract—In this paper, we describe a useful Mannich-type reaction in fluorous phase. By use of perfluorodecalin (C10F18, cis- and transmixture) as a fluorous solvent and perfluorinated rare earth metal salts such as Sc(OSO2C8F17)3 or Yb(OSO2C8F17)3 (2.0 mol%) as a catalyst, the Mannich-type reaction of arylaldehydes with aromatic amines and (1-methoxy-2-methylpropenyloxy)trimethylsilane can be performed for many times without reloading the catalyst and the fluorous solvent. q 2005 Elsevier Ltd. All rights reserved.

1. Introduction Mannich reaction is one of the most important fundamental reactions in organic chemistry. It is a powerful tool in the routes for the synthesis of various b-amino ketones or esters, which are versatile synthetic building blocks for the preparation of many nitrogen-containing, biologically important compounds.1 In the bimolecular version of the classical Mannich reaction the use of preformed or in situ generated iminium2 or N-acyliminium ions3 and carbon nucleophiles has greatly expanded the versatility of this methodology allowing the use of milder reaction conditions. Recently, some significant progresses have been made in a number of Lewis acid or transition metal catalyzed Mannich reactions of (1-methoxy-2-methylpropenyloxy) trimethylsilane with imines in organic solvents. For example, the application of zirconium [Zr(OPri)4], palladium complexes, and rare earth metal triflates [Ln(OTf)n, LnZYb, Sc, Y, La] in Mannich reaction has enlarged its utility in organic synthesis.4 On the other hand, perfluorocarbon fluids, especially Keywords: Mannich-type reaction; Perfluorinated rare earth metal salt; Perfluorinated alkali metal salt; (1-Methoxy-2-methylpropenyloxy)trimethylsilane; Perfluorodecalin (C10F18 cis- and trans-mixture); Fluorous biphase system. * Corresponding author. Tel.: C86 21 5492 5137; fax: C86 21 64166128; e-mail: [email protected] 0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.tet.2005.03.059

perfluoro-alkanes, have some unique properties that make them attractive alternatives for conventional organic solvents.5 They have limited miscibility with conventional organic solvents. Compounds functionalized with perfluorinated groups often dissolve preferentially in fluorous solvents. This character can be used to extract fluorous components from reaction mixtures.6 The ‘Fluorous Biphase System’ (FBS) technique was first reported by Horvath and Rabai.6a It allows the catalysis to be performed in a two-phase reaction mixture consisting of a perfluorinated solvent and an organic solvent. Therefore, by introducing a perfluorinated catalyst in a catalytic reaction system, the catalyst is solubilized and simultaneously immobilized in the ‘Fluorous Phase’. By elevating the temperature the biphasic system forms a homogenous solution and the catalytic process can take place. Cooling down the reaction mixture leads to the reformation of two separate phases. Afterwards, easy product isolation and the recovery of the perfluoro-tagged metal catalyst can be achieved by simple phase separation.7 The isolation and recovery of perfluorinated components can be accomplished not only by a phase separation of immiscible liquid layers but also by solid–liquid extraction using a perfluorinated non-polar stationary phase.6a Based on this concept, we attempted the application of fluorous phase separation techniques to the one-pot ‘threecomponent’ Mannich reaction of (1-methoxy-2-methylpropenyloxy)trimethylsilane with arylaldehydes and

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Scheme 1.

Table 1. Mannich-type reaction of 1a, 2a, and 3 in hexane and fluorous phase per fluorodecalin for 2 h Entry

Catalyst

1 2 3 4 5 6 7 8 9

HOSO2CF3 HOSOC8F17 Yb(OSO2CF3)3 Yb(OSO2C8F17)3 Sc(OSO2CF3)3 Sc(OSO2C8F17)3 Na(OSO2C8F17) Na(OSO2CF3) Li(OSO2C8F17)

a

Yield (%)a 4a 50 63 47 65 55 71 24 14 28

Isolated yields.

aromatic amines using perfluorinated rare earth metal salts or other metal salts as catalysts. By this technology, the efficiency of the synthetic process of this Mannich-type reaction can be increased because the recovery of perfluorinated rare earth metal salt or other metal salt catalysts from the reaction solution can be avoided. In order to perform this Mannich-type reaction in fluorous phase, we prepared several perfluorinated rare earth metal salts [Ln(OSO2CF3)3 and Ln(OSO2C8F17)3, LnZYb, Sc]8 and perfluorinated alkali metal salts [M(OSO2CF3) and

M(OSO2C8F17), MZLi, Na]9 and used them as catalysts in the one-pot ‘three-component’ Mannich-type reaction of (1-methoxy-2-methyl propenyloxy)trimethylsilane 3 with benzaldehyde 1a and aniline 2a in hexane10 and perfluorodecalin (C10F18, cis- and trans-mixture) fluorous solvent (Scheme 1). At 60 8C (upon heating), the organic phase is miscible with fluorous phase to give a homogeneous phase. At 20 8C (room temperature), it becomes a biphasic system. The results are summarized in Table 1 and as can be seen, Ln(OSO2C8F17)3 Lewis acid catalysts are more effective than Ln(OSO2CF3)3 (Table 1, entries 3–6) while perfluorinated alkali metal salts are ineffective in this FBS catalytic reaction system (Table 1, entries 7–9). It should be emphasized here that no reaction occurred in the absence of catalyst. In addition, the Bronsted acids HOSO2CF3 and HOSO2C8F17 themselves can catalyze this reaction as well, with HOSO2C8F17 being more effective than HOSO2CF3 under identical conditions (Table 1, entries 1 and 2). These results suggest that a long perfluorinated alkyl chain, so called ‘pony tail’, could indeed allow more efficient transfer of the catalyst into the fluorous phase. Overall, Sc(OSO2C8F17)3 is the most active catalyst in this reaction. Although HOSO2C8F17 itself can effectively catalyze this reaction as well, its salt Sc(OSO2C8F17)3 is more stable under ambient atmosphere and can be easily handled (Table 1, entries 1 and 2). It should be noted that in consideration of cost of

Table 2. Mannich-type reaction of 1a, 2a, and 3 in different fluorous solvents for 2 h

Entry

Fluorous phase

Yield (%)a 4a

1

71

2

54

3

40

4

CF3(CF2)4CF3

46

b

5

72

6b

71

7b

65

a b

Isolated yields. The catalyst in fluorous phase was reused.

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catalyst, Yb(OSO2C8F17)3 is also an active and cheap catalyst in this reaction.

could be recovered during the purification of the adducts by column chromatography.

Next, we screened several other fluorous solvents, such as perfluoroheptane (C7F8), perfluoro (methylcyclohexane) (C7F14) and perfluorohexane (C6F14) in this FBS catalytic system. The results are summarized in Table 2. We found that during the Mannich-type reaction process, the loss of fluorous solvent is very serious at 60 8C when using perfluorohexane (C 7F8), perfluoro(methylcyclohexane) (C7F14) and perfluorohexane (C6F14) as solvent because they are volatile (bp 58–76 8C). Perfluorodecalin (C10F18, cis- and trans-mixture) is the best fluorous solvent for this reaction (Table 2, entries 1–4). This new fluorous phase is not volatile because it has higher boiling point (bp 142 8C). Based on the 19F NMR spectroscopic data and GC–MS, no loss of catalyst or perfluorodecalin to the organic and water phase during workup can be detected.

In addition, we utilized relatively cheaper Yb(OSO2C8F17)3 as a Lewis acid to catalyze the reaction of (1-methoxy-2methylpropenyloxy)trimethylsilane 3 with arylaldehydes 1 and 2-aminophenol 5 in a biphasic way of hexane and perfluorodecalin. The results are summarized in Table 4. The initial examination of this reaction was performed at 60 8C using arylaldehyde 1a as the substrate under the same conditions as those described above. Unfortunately, the corresponding Mannich-type adduct 6a was formed in lower yield (40%) because of the oxidization of 2-aminophenol 5 at this high temperature (60 8C) (Table 4, entry 1). We found that with the addition of tetrahydrofuran (THF) (0.5 mL) into this hexane (1.0 mL) and perfluorodecalin (1.0 mL) system to dissolve the solid powders of 2-aminophenol 5, the reactions proceeded smoothly at 20 8C to give 6a in higher yield (Table 4, entry 2), although this catalytic reaction system is not a homogenous phase at 20 8C. For other arylaldehydes, these reactions proceeded smoothly under the same conditions to give the corresponding Mannich-type adducts 6 in good yields (Table 4, entries 3–6). The fluorous phase containing the employed Lewis acid Yb(OSO2C8F17)3 can also be easily recovered and reused for three times to give the adduct 6a in similar yields without reloading the catalyst and fluorous solvent (Table 4, entries 7–9).

The perfluorodecalin fluorous phase containing Sc(OSO2C8F17)3 catalyst can be easily isolated by simple separation of the fluorous phase. This catalytic phase can be reused for three times to give similar results without reloading fluorous solvent and the catalyst (Table 2, entries 5–7). Using Sc(OSO2C8F17)3 as a catalyst and perfluorodecalin (C10F18, cis- and trans-mixture) as the fluorous solvent in a biphasic way, Mannich-type reaction of (1-methoxy-2methylpropenyloxy)trimethylsilane 3 with other arylaldehydes 1 and aromatic amines 2 were examined as well. The results are shown in Table 3. These Mannich-type reactions proceeded smoothly at 60 8C to give the corresponding adducts 4b-f in good yields (Table 3, entries 1–5). Thus, a novel FAB catalytic process of Mannich reaction of (1-methoxy-2-methylpropenyloxy)trimethylsilane with arylaldehydes and aromatic amines has been explored. This is the first example of an Mannich reaction of arylaldehydes with aromatic amines and (1-methoxy-2methylpropenyloxy)trimethylsilane in a fluorous phase. It should be also emphasized here that no reaction occurred when using aliphatic aldehydes as substrates with aromatic amines in this reaction under the same conditions. This is because the corresponding imines formed in situ are not stable in the presence of Lewis acids. In these cases, the reactions gave no other by-products. The starting materials

In summary, we reported in this paper a new process to carry out the Mannich-type reaction of (1-methoxy-2-methylpropenyloxy)trimethylsilane, arylaldehydes and aromatic amines in fluorous phase. Using perfluorodecalin (C10F18, cis- and trans-mixture) as a fluorous solvent and Sc(OSO2C8F17)3 or Yb(OSO2C8F17)3 as a catalyst, this Mannich reactions can be repeated several times without reloading fluorous solvent and the catalyst. By the conventional Lewis acid catalyzed reaction, the water-stable Lewis acids, Yb(OPf)3, Sc(OTf)3 or Sc(OPf)3 could be recovered from the water phase after the usual workup. Obviously, the water must be evaporated and this will consume a lot of energy. By this technology, the catalytic phase can be easily recovered and can be reused for the next reaction without any treatment. Further investigations to develop other types

Table 3. Results of Mannich-type reaction of aryladehyde 1, aromatic amine 2, and 3 in fluorous phase for 2 h

Entry

R1

R2

Yield (%)a 4

1 2 3 4 5

1b, R1Zp-Cl 1c, R1Zp-NO2 1d, R1Zp-Ome 1a, R1ZH 1a, R1ZH

2a, R2ZH 2a, R2ZH 2a, R2ZH 2b, R2Zp-F 2c, R2Zo-CF3

4b, 65 4c, 65 4d, 70 4e, 66 4f, 58

a

Isolated yields.

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Table 4. Results of Mannich-type reaction of arylaldehydes 1, 2-aminophenol 5 and 3 in fluorous phase for 8 h

Entry

R1

Yield (%)a 6

1b 2 3 4 5 6 7c 8c 9c

1a, R1ZH 1a, R1ZH 1b, R1Zp-Me 1c, R1Zp-OMe 1d, R1Zp-Cl 1e, R1Zp-Br 1a, R1ZH 1a, R1ZH 1a, R1ZH

6a, 40 6a, 93 6b, 73 6c, 63 6d, 79 6e, 66 6a, 60 6a, 64 6a, 68

a b c

Isolated yields. The reaction was performed at 60 8C. The recovered catalyst in fluorous phase was used.

of reactions in fluorous phase with perfluorinated metal salt are now in progress.

2. Experimental 2.1. General remarks MPs were obtained with a Yanagimoto micro melting point apparatus and are uncorrected. 1H NMR spectra were recorded on a Bruker AM-300 spectrometer for solution in CDCl3 with tetramethylsilane (TMS) as internal standard; J-values are in Hz. All of the solid compounds reported in this paper gave satisfactory CHN microannalyses with a Carlo–Erba 1106 analyzer. Mass spectra were recorded with a HP-5989 instrument and HRMS was measured by a Finnigan MAC mass spectrometer. Organic solvents were dried by standard methods when necessary. Commercially obtained reagents were used without further purification. All reactions were monitored by TLC with Huanghai GF254 silica gel coated plates. The orientation of nitration was determined by NMR analysis. Flash column chromatography was carried out using 300–400 mesh silica gel. 2.2. Preparation of perfluorinated rare earth metal catalysts [Ln(OSO2C8F17)3, LnZYb, Sc] The reaction procedure: an excess amount of a lanthanide(III) oxide (99.9% purity) was added to an aqueous solution of C8F17SO3H (50% v/v) and heating at boiling for 30 min to 1 h. The mixture was filtered to remove the unreacted oxide. The water was then removed from the filtrate under reduced pressure. The resulting hydrate was dried by heating under vacuum at 180–200 8C for 48 h. 2.3. Preparation of perfluorinated alkali metal salt catalysts [M(OSO2C8F17), MZLi, Na, K] The reaction procedure: trifluoromethanesulfonic acid was added dropwise to a solution of the carbonate salt in

methanol at 0 8C. The reaction mixture was stirred at room temperature for 30 min, then at reflux for 2 h. The clear solution concentrated under reduced pressure. The resulting white cake was dried at 125 8C for 2 h. The production was recrystallized from methanol or ethanol/diethyl ether. 2.4. Typical reaction procedure for the Mannich-type reaction in fluorous phase To a solution of Sc(OPf)3 [(C8F17SO3)3Sc] (10 mg, 0.006 mmol) in perfluorodecalin (C10F18, cis- and transmixture) (solvent, 1.0 mL) was added a solution of aniline (27 mL, 0.3 mmol) and benzaldehyde (30 mL, 0.3 mmol) in toluene (solvent, 1.0 mL). Then, (1-methoxy-2-methylpropenyloxy)trimethylsilane (90 mL, 0.45 mmol) was added in the mixture under stirring. The mixture was stirred at 60 8C for 20 h. The fluorous layer was separated for the next reaction. The reaction mixture (organic layer) was washed by water (5 mL) and extracted with dichloromethane (2!15 mL). The combined organic layers were dried over anhydrous Na2SO4. The solvent was removed under reduced pressure and the residue was purified by column chromatography on silica gel (EtOAc–hexaneZ 1:10) to give the product as a colorless solid 60 mg, yield 71%. 2.4.1. 2,2-Dimethyl-3-phenyl-3-phenylaminopropionic acid methyl ester 4a. A white solid, 60 mg, yield 71%; This is a known compound. Its 1H NMR spectroscopic data are in consistent with those reported in literature (Ref. Loh, T.-P.; Liung, S. B. K. W.; Tan, K.-L.; Wei, L.-L. Tetrahedron 2000, 56, 3227–3238). 1H NMR (CDCl3, TMS, 300 MHz): d 1.16 (3H, s, CH3), 1.27 (3H, s, CH3), 3.65 (3H, s, OCH3), 4.49 (1H, s, CH), 4.79 (1H, s, NH), 6.49 (2H, dd, JZ1.2, 8.7 Hz, ArH), 6.59 (1H, t, JZ7.5 Hz, ArH), 7.04 (2H, dd, JZ7.5, 8.7 Hz, ArH), 7.17–7.29 (5H, m, ArH). 2.4.2. 3-(4-Chlorophenyl)-2,2-dimethyl-3-phenylaminopropionic acid methyl ester 4b. A white solid, 62 mg, yield 65%. Mp 108–110 8C. IR (CHCl3): n 1732, 1613,

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1510, 1533, 1442, 1149, 873 cmK1. 1H NMR (CDCl3, TMS, 300 MHz): d 1.15 (3H, s, CH3), 1.27 (3H, s, CH3), 3.65 (3H, s, OCH3), 4.45 (1H, s, CH), 4.79 (1H, s, NH), 6.46 (2H, dd, JZ1.0, 8.8 Hz, ArH), 6.62 (1H, t, JZ7.4 Hz, ArH), 7.05 (2H, dd, JZ7.4, 8.8 Hz, ArH), 7.20–7.28 (4H, m, ArH). 13C NMR (CDCl3, 75 MHz): d 20.8, 24.4, 46.9, 52.1, 65.8, 113.3, 117.5, 128.2, 129.0, 129.6, 133.2, 137.9, 146.6, 176.7. MS (EI) m/z: 317 (MC, 4.63), 216 (MCK101, 100), 180 (MCK137, 4.27), 104 (MCK213, 13.22), 77 (MCK 240, 19.37). Anal. Calcd for C18H20ClNO2 requires C, 68.03; H, 6.34; N, 4.41. Found: C, 68.26; H, 6.33; N, 4.40%. 2.4.3. 2,2-Dimethyl-3-(4-nitrophenyl)-3-phenylaminopropionic acid methyl ester 4c. A yellow solid, 64 mg, yield 65%. Mp 103–105 8C. IR (CHCl3): n 1728, 1603, 1507, 1523, 1438, 1266, 1139, 853 cmK1. 1H NMR (CDCl3, TMS, 300 MHz): d 1.18 (3H, s, CH3), 1.32 (3H, s, CH3), 3.67 (3H, s, OCH3), 4.57 (1H, d, JZ7.1 Hz, CH), 4.90 (1H, d, JZ7.1 Hz, NH), 6.45 (2H, d, JZ8.6 Hz, ArH), 6.64 (1H, t, JZ7.5 Hz, ArH), 7.06 (2H, dd, JZ7.5, 8.6 Hz, ArH), 7.49 (2H, d, JZ8.9 Hz, ArH), 8.16 (2H, d, JZ8.9 Hz, ArH). 13C NMR (CDCl3, 75 MHz): d 21.1, 24.5, 46.8, 52.3, 64.2, 113.3, 118.0, 123.3, 129.1, 129.2, 146.1, 147.4, 147.5, 176.2. MS (EI) m/z: 328 (MC, 5.74), 227 (MCK101, 100), 181 (MCK147, 37.21), 168 (MCK160, 8.99), 77 (MCK 251, 19.42). Anal. Calcd for C18H20N2O4 requires C, 65.84; H, 6.14. N, 8.53. Found: C, 65.99; H, 6.14; N, 8.44%. 2.4.4. 3-(4-Methoxyphenyl)-2,2-dimethyl-3-phenylaminopropionic acid methyl ester 4d. A yellowish oil, 66 mg, yield 70%. IR (CHCl3): n 1727, 1603, 1510, 1265, 1178, 1034 cmK1. 1H NMR (CDCl3, TMS, 300 MHz): d 1.15 (3H, s, CH3), 1.25 (3H, s, CH3), 3.65 (3H, s, OCH3), 3.76 (3H, s, OCH3), 4.44 (1H, s, CH), 4.74 (1H, s, NH), 6.49 (2H, d, JZ8.4 Hz, ArH), 6.59 (1H, t, JZ7.4 Hz, ArH), 6.81 (2H, d, JZ8.7 Hz, ArH), 7.04 (2H, dd, JZ7.4, 8.4 Hz, ArH), 7.18 (2H, d, JZ8.7 Hz, ArH). 13C NMR (CDCl3, 75 MHz): d 20.9, 24.7, 47.4, 52.3, 55.4, 64.0, 113.6, 113.7, 117.4, 129.2, 129.5, 131.4, 147.2, 159.1, 177.3; MS (EI) m/z: 313 (MC, 3.08), 212 (MCK101, 100), 168 (MCK145, 6.10), 104 (MCK209, 15.95), 77 (MCK236, 14.87). HRMS (Maldi) calcd for C19H24O3N (MCC1) requires 314.1756. Found: 314.1751. 2.4.5. 3-(4-Fluorophenylamino)-2,2-dimethyl-3-phenylpropionic acid methyl ester 4e. A white solid, 59 mg, yield 66%. Mp 89–91 8C. IR (CHCl3): n 1727, 1591, 1493, 1265, 1150 cmK1. 1H NMR (CDCl3, TMS, 300 MHz): d 1.15 (3H, s, CH3), 1.28 (3H, s, CH3), 3.66 (3H, s, OCH3), 4.41 (1H, d, JZ7.3 Hz, CH), 5.02 (1H, d, JZ7.3 Hz, NH), 6.15 (1H, dt, JZ2.8, 11.8 Hz, ArH), 6.25–6.31 (2H, m, ArH), 6.96 (1H, dd, JZ8.1, 15.0 Hz, ArH), 7.23–7.29 (5H, m, ArH). 13C NMR (CDCl3, 75 MHz): d 21.1, 24.9, 47.1, 52.3, 64.6, 100.3 (d, JZ25.5 Hz), 104.0 (d, JZ22.1 Hz), 109.5 (d, JZ2.4 Hz), 127.9, 128.4 (d, JZ3.6 Hz), 130.2, 130.3, 139.0, 149.0 (d, JZ11.0 Hz), 164.0 (d, JZ 254.7 Hz), 177.1. MS (EI) m/z: 301 (MC, 3.40), 200 (MCK101, 100), 122 (MCK179, 21.75), 95 (MCK206, 20.93), 77 (MCK224, 9.22). Anal. Calcd for C18H20FNO2 requires C, 71.74; H, 6.69; N, 4.65. Found: C, 71.80; H, 6.40; N, 4.53%. 2.4.6.

2,2-Dimethyl-3-phenyl-3-(3-trifluoromethyl-

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phenylamino)propionic acid methyl ester 4f. A white solid, 61 mg, yield 58%. Mp 108–110 8C. IR (CHCl3): n 1714, 1616, 1519, 1495, 1437, 1266, 1124, 785 cmK1. 1H NMR (CDCl3, TMS, 300 MHz): d 1.17 (3H, s, CH3), 1.30 (3H, s, CH3), 3.66 (3H, s, OCH3), 4.46 (1H, s, CH), 5.14 (1H, s, NH), 6.60 (1H, d, JZ8.1 Hz, ArH), 6.72 (1H, s, ArH), 6.82 (1H, d, JZ8.1 Hz, ArH), 7.11 (1H, t, JZ8.1 Hz, ArH), 7.21–7.33 (5H, m, ArH). 13C NMR (CDCl3, 75 MHz): d 21.1, 25.0, 47.1, 52.4, 64.9, 110.0 (q, JZ 4.1 Hz), 114.1 (q, JZ4.2 Hz), 116.2, 117.7 (q, JZ 277.5 Hz), 127.9, 128.4, 128.4, 129.7, 129.9 (q, JZ 10.1 Hz), 138.7, 147.3, 177.1. MS (EI) m/z: 351 (MC, 2.16), 250 (MCK101, 100), 172 (MCK179, 11.97), 145 (MCK206, 15.63). Anal. Calcd for C19H20F3NO2 requires C, 64.95; H, 5.74; N, 3.99. Found: C, 65.06; H, 5.88; N, 3.95%. 2.5. Typical reaction procedure for the Mannich-type reaction in fluorous phase A solution of Yb(OPf) 3 [(C8F 17SO 3) 3Yb] (25 mg, 0.025 mmol) in perfluorodecalin (C10F18, cis- and transmixture) (1.0 mL) was added to a solution of 2-aminophenol (33 mg, 0.3 mmol) and benzaldehyde (31 mL, 0.3 mmol) in a mixture solvent of hexane (1.0 mL) and tetrahydrofuran (0.5 mL). Then, (1-methoxy-2-methyl-propenyloxy)trimethylsilane (90 mL, 0.45 mmol) was added to the reaction mixture under stirring. The mixture was stirred at 20 8C for 8 h. Then, the reaction mixture was washed by dichloromethane (3!2 mL). And the fluorous phase was separated for the next reaction. The solvent of organic layer was removed under reduced pressure and the residue was purified by column chromatography on silica gel (EtOAc– hexaneZ1:10) to give the product. 2.5.1. 3-(2-Hydroxyphenylamino)-2,2-dimethyl-3phenyl-propionic acid methyl ester 6a. A white solid; 84 mg, yield 93%. This is a known compound. Its 1H NMR spectroscopic data are in consistent with those reported in literature (Ref. Ishitani, H.; Ueno, M.; Kobayashi, S. J. Am. Chem. Soc. 2000, 122, 34, 8180–8186). 1H NMR (CDCl3, TMS, 300 MHz): d 1.21 (3H, s, CH3), 1.24 (3H, s, CH3), 3.69 (3H, s, OCH3), 4.55 (1H, s, CH), 4.87 (1H, s, NH), 5.21 (1H, s, OH), 6.38–6.70 (4H, m, ArH), 7.22–7.29 (4H, m, ArH). 2.5.2. 3-(4-Methylphenyl)-3-(2-hydroxyphenylamino)2,2-dimethylpropionic acid methyl ester 6b. A white solid; 68 mg, yield 73%. This is a known compound. Its 1H NMR spectroscopic data are in consistent with those reported in literature (Ref. Yamashita, Y.; Ueno, M.; Kuriyama, Y.; Kobayashi, S. Adv. Synth. Catal. 2002, 344, 929–931). 1H NMR (CDCl3, TMS, 300 MHz): d 1.20 (3H, s, CH3), 1.24 (3H, s, CH3), 2.28 (3H, s, CH3), 3.68 (3H, s, OCH3), 4.55 (1H, s, CH), 4.99 (1H, s, NH), 6.31–6.70 (4H, m, ArH), 7.20–7.26 (4H, m, ArH). 2.5.3. 3-(4-Methoxyphenyl)-3-(2-hydroxyphenylamino)2,2-dimethyl-propionic acid methyl ester 6c. A yellow solid; 62 mg, yield 63%. IR (thin film): n 3421, 2954, 2926, 2853, 1712, 1610, 1514, 1487, 1448, 1392, 1369, 1269, 1193, 1140, 1120, 1104, 1010 cmK1. 1H NMR (CDCl3, TMS, 300 MHz): d 1.20 (3H, s, CH3), 1.23 (3H, s, CH3),

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3.68 (3H, s, OCH3), 3.75 (3H, s, OCH3), 4.53 (1H, s, CH), 4.98 (1H, s, NH), 5.76 (1H, s, OH), 6.36–6.70 (4H, m, ArH), 7.17–7.24 (4H, m, ArH). 13C NMR (CDCl3, 75 MHz): d 19.9, 24.3, 47.4, 52., 55.1, 63.9, 113.3, 113.7, 114.1, 117.7, 120.9, 129.3, 130.9, 135.6, 144.2, 158.7, 177.9. MS (EI) m/z: 65 (11.32), 73 (16.81), 80 (10.75), 115 (12.65), 120 (27.24), 197 (14.72), 276 (100), 277 (16.98), 278 (96.68), 279 (14.45), 377 (MC, 2.11). HRMS (MALDI): calcd for C 18H 21 NO 3 Br (M CC1) requires 378.0704, found: 378.0699. 2.5.4. 3-(4-Chlorophenyl)-3-(2-hydroxyphenylamino)2,2-dimethylpropionic acid methyl ester 6d. A white solid; 78 mg, yield 79%. This is a known compound. Its 1H NMR spectroscopic data are in consistent with those reported in literature (Ref. Ishitani, H.; Ueno, M.; Kobayashi, S. J. Am. Chem. Soc. 2000, 122, 8180–8186). 1 H NMR (CDCl3, TMS, 300 MHz): d 1.19 (3H, s, CH3), 1.24 (3H, s, CH3), 3.68 (3H, s, OCH3), 4.55 (1H, s, CH), 4.99 (1H, s, NH), 6.31–6.70 (4H, m, ArH), 7.20–7.26 (4H, m, ArH). 2.5.5. 3-(4-Bromophenyl)-3-(2-hydroxyphenylamino)2,2-dimethylpropionic acid methyl ester 6e. A yellow solid; 74 mg, yield 66%. IR (thin film): n 3415, 2955, 2925, 1713, 1610, 1512, 1451, 1248, 1178, 1139, 1107, 1036 cmK1. 1 H NMR (CDCl3, TMS, 300 MHz): d 1.20 (3H, s, CH3), 1.24 (3H, s, CH3), 3.68 (3H, s, OCH3), 4.54 (1H, s, CH), 4.98 (1H, s, NH), 5.75 (1H, s, OH), 6.31–6.70 (4H, m, ArH), 7.15–7.41 (4H, m, ArH). 13C NMR (CDCl3, 75 MHz): d 20.0, 24.2, 47.1, 52.4, 63.9, 113.3, 114.2, 117.9, 121.1, 121.3, 130.0, 131.1, 135.3, 138.2, 143.9, 177.5. MS (EI) m/z: 65 (1.99), 73 (4), 80 (2.01), 109 (3.07), 151 (3.60), 161 (2.45), 221 (2.46), 228 (100), 229 (17.11), 329 (MC, 2.11). HRMS (MALDI): calcd for C19H24NO4(MCC1) requires 330.1705, found: 330.1708.

2. 3.

4.

5. 6.

7.

8.

Acknowledgements We thank the State Key Project of Basic Research (Project 973) (No. G2000048007), Chinese Academy of Sciences (KGCX2-210-01), Shanghai Municipal Committee of Science and Technology, and the National Natural Science Foundation of China for financial support (20025206, 203900502, and 20272069).

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References and notes 1. (a) Kleinman, E. F. In Trost, B. M., Fleming, I., Eds.; Comprehensive Organic Synthesis; Pergamon: Oxford, 1991; Vol. 2, pp 893–951. (b) Tramontini, M.; Angiolini, L. In Mannich Bases. Chemistry and Uses; CRC: Boca Raton, FL,

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1994. (c) Pilli, R. A.; Russowsky, D. Trends Org. Chem. 1997, 6, 101. (d) Risch, N.; Arend, M.; Westermann, B. Angew. Chem., Ind. Ed. 1998, 37, 1044–1070. (e) Speckamp, W. N.; Moolenaar, M. J. Tetrahedron 2000, 56, 3817–3856. Pilli, R. A.; Russowsky, D. J. Chem. Commun. 1987, 1053–1054. (a) Pilli, R. A.; Dias, L. C.; Maldaner, A. O. J. Org. Chem. 1995, 60, 717–722. (b) Pilli, R. A.; Russowsky, D. J. Org. Chem. 1996, 61, 3187–3190. (a) Kobayashi, S.; Ishitani, H.; Nagayama, S. Chem. Lett. 1995, 423–424. (b) Kobayashi, S.; Busujima, T.; Nagayama, S. Synlett 1999, 545–546. (c) Ali, T.; Chauham, K. K.; Frost, C. G. Tetrahedron Lett. 1999, 40, 5621–5624. (d) Iimura, S.; Nobutou, D.; Manabe, K.; Kobayashi, S. Chem. Commun. 2003, 1644–1645. (e) Yamashita, Y.; Kobayashi, S. J. Am. Chem. Soc. 2002, 124, 3292–3392. (f) Ueno, M.; Kobayashi, S. Org. Lett. 2002, 4, 3395–3397. (a) Zhu, D. W. Synthesis 1993, 953–954. (b) Wolf, E. D.; Koten, G. V.; Deelman, B. Chem. Soc. Rev. 1999, 28, 37–41. (a) Horvath, I. T.; Rabai, J. Science 1994, 266, 72–75. (b) Horvath, I. T.; Kiss, G.; Cook, R. A.; Bond, J. E.; Stevens, P. A.; Rabai, J.; Mozeliski, E. J. J. Am. Chem. Soc. 1998, 120, 3133–3143. (c) Fawcett, J.; Hope, E. G.; Kemmitt, R. D. W.; Paige, D. R.; Russell, D. R.; Stuart, A. M.; Cole-Hamilton, D. J.; Payne, M. J. Chem. Commun. 1997, 1127–1128. (d) Curran, D. P. Angew. Chem. Int. Ed. 1998, 37, 1174–1196. (e) Nakamura, H.; Linclau, B.; Curran, D. P. J. Am. Chem. Soc. 2001, 123, 10119–10120. (a) Schneider, S.; Bannwarth, W. Angew. Chem. 2000, 112, 4292–4295. (b) Schneider, S.; Bannwarth, W. Helv. Chim. Acta 2001, 84, 735–742. For the preparation of perfluorinated rare earth metal catalysts [Ln(OSO2C8F17)3, LnZYb, Sc], please see: Hanamoto, Y.; Sugimoto, Y.; Jin, Y. Z.; Imanaga, J. Bull. Chem. Soc. Jpn. 1997, 70, 1239–1244. The reaction procedure: an excess amount of a lanthanide(III) oxide (99.9% purity) was added to an aqueous solution of C8F17SO3H (50% v/v) and the mixture was heated at boiling temperature for 30 min to 1 h. The mixture was filtered to remove the unreacted oxide. The water was then removed from the filtrate under reduced pressure. The resulting hydrate was dried by heating under vacuum at 180 to 200 8C for 48 h. For the preparation of perfluorinated alkali metal salt catalysts [M(OSO2C8F17), MZLi, Na, K], please see: Corey, E. J.; Shimoji, K. Tetrahedron Lett. 1983, 24, 169–172. The reaction procedure: trifluoromethanesulfonic or heptadecafluorooctanesulfonic acid was added dropwise to a solution of the carbonate salt in methanol at 0 8C. The reaction mixture was stirred at room temperature for 30 min, then it was refluxed for 2 h. The clear solution was concentrated under reduced pressure. The resulting white cake was dried at 125 8C for 2 h. The obtained product was recrystallized from methanol or ethanol/diethyl ether. The organic substrates in hexane is miscible with various fluorous solvents upon heating at 60 8C.