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Efficient synthesis of 2-oxazolidinones and quinazoline-2,4(1H,3H)-diones from CO2 catalyzed by tetrabutylammonium fluoride
Tetrahedron 74 (2018) 2914e2920
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Efficient synthesis of 2-oxazolidinones and quinazoline-2,4(1H,3H)diones from CO2 catalyzed by tetrabutylammonium fluoride Akira Fujii, Hideaki Matsuo, Jun-Chul Choi, Tadahiro Fujitani, Ken-ichi Fujita* National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki, 305-8565, Japan
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 March 2018 Received in revised form 16 April 2018 Accepted 18 April 2018 Available online 21 April 2018
By employing tetrabutylammonium fluoride (TBAF) as a catalyst, the various carboxylative cyclizations of the propargylic amines having internal alkynes with CO2 proceeded to afford the corresponding 2oxazolidinones. In this case, it was also found that the generated 2-oxazolidinones were tautomerized into the corresponding 2-oxazolones due to the basicity of TBAF. In addition, we performed the synthesis of quinazoline-2,4(1H,3H)-dione from 2-aminobenzonitrile and CO2 by using TBAF as a catalyst. © 2018 Elsevier Ltd. All rights reserved.
Keywords: Carbon dioxide Catalysis Tetrabutylammonium fluoride
1. Introduction The chemistry of carbon dioxide (CO2) has drawn much attention in the last two decades because CO2 is abundant, nontoxic, non-flammable, and easily available. Moreover, CO2 is one of the most attractive C1 building blocks to displace toxic reagents such as phosgene and carbon monoxide.1 CO2 also has great potential as a renewable resource for the production of value-added chemicals, and thus much effort has been expended to incorporate CO2 in fine chemical synthesis.2 However, because CO2 is thermodynamically stable and kinetically inert due to its high oxidation state, organometallic complexes of noble metals must often be used as catalysts for the chemical fixations of CO2.3 Recently, transformations of CO2 have also been achieved by metal-free organocatalysts through the activation of CO2 or substrates.4 Previously, as an example of organocatalysts, tetrabutylammonium fluoride (TBAF) was reported to catalyze the cyclization reaction of b-alkynyl hydrazines to give the corresponding azaproline derivatives.5 This transformation appeared to be caused by a quaternary ammonium cationep interaction with the triple bond of alkynes.6 In addition, several other TBAF-catalyzed cyclization reactions of alkynyl compounds have been reported.7 Recently, we discovered that the carboxylative cyclization of a propargylic amine having a terminal alkyne with CO2 is catalyzed by the quaternary
* Corresponding author. E-mail address: [email protected] (K. Fujita). https://doi.org/10.1016/j.tet.2018.04.059 0040-4020/© 2018 Elsevier Ltd. All rights reserved.
ammonium salts to provide the corresponding 2-oxazolidinone.8 Among the quaternary ammonium salts applied to the carboxylative cyclization, TBAF was found to be the most effective. We report herein the TBAF-catalyzed carboxylative cyclization of various propargylic amines with CO2 to provide 2-oxazolidinones, and the quaternary ammonium salt-catalyzed tautomerization of a 2-oxazolidinone into the corresponding 2-oxazolone. Moreover, we found that TBAF was the most effective quaternary ammonium salt for the synthesis of quinazoline-2,4(1H,3H)-diones from 2aminobenzonitriles and CO2.9 2. Results and discussion 2.1. Synthesis of 2-oxazolidinones from propargylic amines and CO2 2-Oxazolidinones are important heterocyclic compounds in many applications in organic synthesis and pharmaceutical chemistry. For example, they can be used as cholesteryl ester transfer protein inhibitors and monoamine oxidase inhibitors.10 Syntheses of 2-oxazolidinones by the carboxylative cyclization of propargylic amines with CO2 have been reported to be catalyzed by organometallic complexes of noble metals11 such as silver12 and gold.13 Recently, a number of metal-free catalysts, such as superbases,14 N-heterocyclic carbenes,15 triethanolamine,16 and cyanuric acid,17 which are less expensive and environmentally benign, have been used for the carboxylative cyclization of propargylic amines with CO2 as alternatives to organometallic catalysts. Very recently, we found that 1 mol% of TBAF catalyzes the carboxylative
A. Fujii et al. / Tetrahedron 74 (2018) 2914e2920
Scheme 1. Carboxylative cyclization of a propargylic amine 1a with CO2.
cyclization of propargylic amine 1a, which has a terminal alkyne, to provide the corresponding 2-oxazolidinone 2a under CO2 pressure of 0.5 MPa at 110 C, as shown in Scheme 1. This reaction was considered that the propargylic amine 1a reacted with CO2 to form the corresponding carbamic acid, then the carbamic acid was dually activated by a quaternary ammonium cationep interaction with the triple bond and a fluoride ionehydrogen interaction with OH of the carbamic acid.8
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First, we performed the TBAFecatalyzed carboxylative cyclization of propargylic amine 1b, which has an internal alkyne, with CO2 as shown in Table 1. A t-butanol solution of propargylic amine 1b and 1 mol% of TBAF as a catalyst were stirred for 12e24 h in a sealed autoclave under a CO2 atmosphere of 0.5 MPa at 90e110 C. By carrying out the carboxylative cyclization of 1b at 110 C for 12 h, the corresponding 2-oxazolidinone 2b was obtained in an 83% chemical yield along with a small amount of a 2-oxazolone 3b (3%; Table 1, entry 1). Similarly, in our previous report using an N-heterocyclic carbene as a catalyst, a small amount of 2-oxazolidinone was obtained in the carboxylative cyclization of a propargylic amine.15a Then, by carrying out the carboxylative cyclization of 1b at 90 C for 24 h, the corresponding 2-oxazolidinone 2b was obtained in an 85% chemical yield and the formation of 2-oxazolone 3b was suppressed, probably due to the low reaction temperature (1%; Table 1, entry 3). We subsequently examined the time-course of the carboxylative cyclization of propargylic amine 1b at 90 C (Fig. 1). The results showed that the chemical yield of 2-oxazolidinone 2b increased till
Table 1 Carboxylative cyclization of propargylic amine 1b with CO2.a
Entry
Temp ( C)
Time (h)
Yield of 2b (%)b
Yield of 3b (%)b
Recovery of 1b (%)b
1 2 3
110 90 90
12 12 24
83 55 85
3 1 1
0 44 9
a b
Reaction conditions: 1b (1 equiv.), TBAF (1 mol%), t-BuOH (1 M based on 1b), carried out at 90e110 C for 12e24 h in a sealed autoclave under a CO2 atmosphere of 0.5 MPa. Determined by the integration of 1H NMR with reference to an internal standard.
Fig. 1. Time-course curves of the carboxylative cyclization of propargylic amine 1b.
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48 h, then mildly decreased thereafter. On the other hand, the formation of 2-oxazolone 3b was observed with a decrease in the yield of 2-oxazolidinone 2b. Fig. 1 suggests that the carboxylative cyclization of propargylic amine 1b with CO2 proceeds to initially provide 2-oxazolidinone 2b, and that the generated 2oxazolidinone 2b is tautomerized into the corresponding 2oxazolone 3b, the tautomerization into which was also reported in a case using an N-heterocyclic carbene as a catalyst.15a Next, we examined the tautomerization of 2-oxazolidinone 2b into 2-oxazolone 3b through the use of various tetrabutylammonium salts as catalysts, as shown in Table 2.18 First, by the stirring of a t-butanol solution of 2-oxazolidinone 2b at 80 C for 6 h under an argon atmosphere through the use of 5 mol% of TBAF, 2b was tautomerized to afford 2-oxazolone 3b in a 55% chemical yield (Table 2, entry 1). In contrast, when tetrabutylammonium chloride, bromide, or acetate was used as a catalyst, no 2-oxazolone 3b was obtained (Table 2, entries 2e4). On the other hand, when tetrabutylammonium hydroxide was employed as a catalyst, 2-oxazolone 3b was obtained in a 67% chemical yield (Table 2, entry 5), which was higher than the yield in the case using TBAF. From these results, it is assumed that the tautomerization of 2-oxazolidinone 2b into 2oxazolone 3b was caused by the deprotonation of CH2N in 2b due to the basicity of the catalyst.
Table 2 Tautomerization of 2-oxazolidinone 2b using various tetrabutylammonium salts as catalysts.a.
In order to prevent the tautomerization of 2-oxazolidinone 2b into 2-oxazolone 3b under the carboxylative cyclization of propargylic amine 1b with CO2, we carried out the carboxylative cyclization of 1b catalyzed by tetrabutylammonium acetate (Table 3). However, the formation of 2-oxazolone 3b was detected under the reaction conditions for the carboxylative cyclization of 1b (1%; Table 3, entry 4). In addition, for the purpose of catalyzing the carboxylative cyclization of 1b, TBAF was more effective than tetrabutylammonium acetate (Table 3, entries 1 and 2). Finally, we performed the carboxylative cyclizations of various propargylic amines 1 to provide the corresponding 2-oxazolidinone 2 by employing TBAF as a catalyst under controlled reaction conditions, as shown in Table 4. The introduction of a methoxy or a methyl group at the phenyl group in R1 decreased the reactivity of the triple bond, as in our previous report.15 In these cases, by carrying out the reaction for 48 h, the corresponding 2-oxazolidinone 2 was mainly obtained (Table 4, entries 2 and 4). In contrast, when a trifluoromethyl or a cyano group was introduced at the phenyl group in R1, the initial carboxylative cyclization of 1 appeared to proceed smoothly due to the high reactivity of the triple bond, and the generated 2-oxazolidinone 2 appeared to be tautomerized into the corresponding 2-oxazolone 3 at 110 C. As a result, 2-oxazolone 3 was mainly obtained by carrying out the reaction at 110 C for 24 h (Table 4, entries 5 and 7). In these cases, by carrying out the reaction at 70 C, the corresponding 2-oxazolidinone 2 was mainly obtained (Table 4, entries 6 and 8). In the case of the methyl group in R1, even by employing 5 mol% of TBAF as a catalyst, the corresponding 2-oxazolidinone 2h was obtained in an only 8% chemical yield (Table 4, entry 12).19
2.2. Synthesis of quinazoline-2,4(1H,3H)-diones from 2-aminobenzonitriles and CO2 Entry
Catalyst
Yield of 3b (%)b
1 2 3 4 5
Bu4NF Bu4NCl Bu4NBr Bu4NOAc Bu4NOH
55 0 0 0 67
a Reaction conditions: catalyst (5 mol%), 2b (1 equiv.), t-BuOH (0.2 M based on 2b), carried out at 80 C for 6 h in glassware. b Determined by the integration of 1H NMR with reference to an internal standard.
Quinazoline-2,4(1H,3H)-diones and their derivatives have attracted much attention due to their wide range of biological and pharmacological activities.20 The reaction of CO2 with 2aminobenzonitriles is an environmentally benign process with 100% atom efficiency, and it has been widely investigated by use of various catalysts21 including DBU,22 imidazolium salt,23 and guanidine.24 Very recently, Dyson et al. reported that 10 mol% of TBAF or tetramethylphosphonium salts catalyzed the formation of quinazoline-2,4(1H,3H)-dione from 2-aminobenzonitrile under atmospheric pressure of CO2 at 90 C and proposed its
Table 3 Carboxylative cyclization of propargylic amine 1b with CO2.a
Entry c
1 2 3c 4 a b c
Catalyst
Time (h)
Yield of 2b (%)b
Yield of 3b (%)b
Bu4NF Bu4NOAc Bu4NF Bu4NOAc
12 12 48 48
55 36 89 86
1 0 2 1
The reaction conditions were identical to those in Table 1. Determined by the integration of 1H NMR with reference to an internal standard. Cited from Fig. 1.
A. Fujii et al. / Tetrahedron 74 (2018) 2914e2920
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Table 4 Carboxylative cyclizations of various propargylic amines 1 for the synthesis of 2-oxazolidinones 2.a
Entry
1 2 3 4 5 6 7 8 9 10 11 12 a b
1 R1
R2
4-CH3OC6H4 4-CH3OC6H4 4-CH3C6H4 4-CH3C6H4 4-CF3C6H4 4-CF3C6H4 4-CNC6H4 4-CNC6H4 C6H5 C6H5 CH3 CH3
CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH2C6H5 CH2C6H5 CH2C6H5 CH2C6H5
1c 1c 1d 1d 1e 1e 1f 1f 1g 1g 1h 1h
Yield (%)b
Bu4NF
Temp.
Time
(mol%)
(ºC)
(h)
2c-h
3c-h
1 2 1 1 1 1 1 1 1 1 1 5
110 110 110 110 110 70 110 70 110 110 110 110
24 48 24 48 24 24 24 3 24 18 24 24
22 78 77 89 12 84 2 88 84 91 1 8
0 5 1 3 57 6 64 12 9 3 0 0
The reaction conditions were identical to those in Table 1. Determined by the integration of 1H NMR with reference to an internal standard.
catalytic cycle.9 On the other hand, in this paper, by employing 1 mol% of various quaternary ammonium salts, which is similar to the amount of catalysts used for the synthesis of 2oxazolidinones 2, we examined the synthesis of quinazoline2,4(1H,3H)-diones from 2-aminobenzonitriles under a pressurized CO2 atmosphere. In order to optimize the catalyst, we examined the synthesis of quinazoline-2,4(1H,3H)-dione 5a from 2-aminobenzonitrile 4a with CO2 through the use of 1 mol% of various catalysts, such as quaternary ammonium salts and organic bases, as shown in Table 5. First, we confirmed that stirring of a DMSO solution of 2aminobenzonitrile 4a at 110 C for 3 h under a CO2 atmosphere of 2 MPa in the absence of catalysts yielded none of the corresponding quinazoline-2,4(1H,3H)-dione 5a (Table 5, entry 1). Next, by a screening of the catalytic activity of various tetraalkylammonium halides (Table 5, entries 2e7), TBAF was found to afford the highest chemical yield among them (55%; Table 5, entry 4). This result suggests that the higher basicity of the counter anion of the tetraalkylammonium salt facilitates the carboxylative cyclization of 4a with CO2. It was also found that a tetraalkylammonium fluoride with longer alkyl groups afforded a higher chemical yield (Table 5, entries 2e4). In addition, tetrabutylammonium acetate afforded a 40% chemical yield (Table 5, entry 8). On the other hand, by employing quaternary ammonium hydroxides with various structures, the chemical yields of 5a were low in all cases (1e6%; Table 5, entries 9e12). This may have been due to the formation of bicarbonate ion from the hydroxide ion in the presence of CO2.25 Although cesium fluoride moderately catalyzed the reaction to afford 5a in a 45% chemical yield (Table 5, entry 13), organic bases such as 1,1,3,3tetramethylguanidine (TMG) and triethanolamine did not catalyze the reaction effectively (11% and 0%; Table 5, entries 14 and 15, respectively).
Table 5 Optimization of the catalyst for the synthesis of quinazoline-2,4(1H,3H)-dione 5a.a
Entry
Catalyst
Yield of 5 (%)b
Recovery of 4 (%)b
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
none Me4NF Et4NF Bu4NF Bu4NCl Bu4NBr Bu4NI Bu4NOAc Me4NOH Bu4NOH (C6H13)4NOH (C16H33)Me3NOH CsF TMG triethanolamine
0 38 41 55 0 0 0 40 3 5 6 1 45 11 0
99 61 59 45 >99 >99 99 60 90 91 93 98 54 88 >99
a Reaction conditions: 4a (1 equiv.), catalyst (1 mol%), DMSO (1 M based on 4a), carried out at 110 C for 3 h in a sealed autoclave under a CO2 atmosphere of 2 MPa. b Determined by the integration of 1H NMR with reference to an internal standard.
Finally, we performed the synthesis of various quinazoline2,4(1H,3H)-diones 5 at 110 C for 24 h under a CO2 atmosphere of
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2 MPa by employing 1 mol% of TBAF as a catalyst, as shown in Table 6. 2-Aminobenzonitrile derivatives with electronwithdrawing or electron-donating groups at benzene 4b-f could react with CO2 to provide the corresponding quinazoline2,4(1H,3H)-diones 5b-f in excellent chemical yields in all cases (96e99%; Table 6, entries 2e6). On the other hand, 2-amino-3cyanopyridine 4g with CO2 provided 5g in a moderate chemical yield under the present reaction conditions (59%; Table 6, entry 7).
Table 6 Syntheses of various quinazoline-2,4(1H,3H)-diones 5.a
3. Conclusion In the case of the TBAFecatalyzed carboxylative cyclization of a propargylic amine having an internal alkyne with CO2, it was found that a 2-oxazolone is obtained by the tautomerization of the generated 2-oxazolidinone, which was similar to the result obtained using an N-heterocyclic carbene as a catalyst. By optimization of the reaction conditions, including the reaction temperature and the reaction time, we could perform the TBAFecatalyzed carboxylative cyclization of a propargylic amine to provide the corresponding 2-oxazolidinone selectively. Further, it was found that TBAF is the most effective quaternary ammonium salt for catalyzing the carboxylative cyclization of 2-aminobenzonitriles when using a catalyst concentration of 1 mol% under a pressurized CO2 atmosphere. 4. Experimental 4.1. General
Entry
Substrate
Yield (%)b
Product
1
4a
5a
97
2
4b
5b
98
3
4c
5c
96
Kieselgel 60 F254 (Merck) was used for TLC, and Wakogel C-300 (Wako) was used for silica gel column chromatography. Degassed solvent was prepared by freeze-pump-thaw cycling of commercially available dry solvents for the carboxylative cyclization of propargylic amines 1, the tautomerization of 2-oxazolidinone 2b, and the synthesis of quinazoline-2,4(1H,3H)-diones 5. Propargylic amines 1b-h and 2-oxazolidinone 2b were prepared by the methods reported in the literature (1b,13e 1c, e,26 1d,13a 1f,15b 1g,27 1h,12e 2b15b). The other reagents, and the dry solvents were commercially available and were used as received. Carbon dioxide (Showa Denko Gas Products Co., Ltd., purity > 99.99%) was used without further purification. 1 H and 13C NMR spectra were measured with a Bruker Avance III 400 spectrometer (1H: 400 MHz; 13C: 100 MHz). Chemical shifts were reported as ppm downfield from TMS as an internal standard in d units. Coupling constants (J) were given in hertz (Hz). 4.2. Carboxylative cyclization of a propargylic amine 1 with CO2: general procedure
4
4d
5d
>99
5
4e
5e
>99
6
4f
5f
98
7
4g
5g
59
To a t-butanol solution (0.6 mL) of a propargylic amine 1 (0.6 mmol) in a stainless steel autoclave was added a quaternary ammonium salt (0.006e0.03 mmol) under an argon atmosphere. The autoclave was sealed, heated at 70e110 C and then pressurized with CO2 of 0.5 MPa. The carboxylative cyclization of 1 proceeded by the magnetic stirring of the resulting mixture at 70e110 C for the indicated time. After the reaction the autoclave was cooled in an ice bath and depressurized. The chemical yields of the 2-oxazolidinone 2 and the 2-oxazolone 3 were determined by integrating 1H NMR with reference to an internal standard (3hydroxybenzyl alcohol except in the case of 1b, when benzoin methyl ether was used instead), a dichloromethane solution (2 mL) of which was added to the reaction mixture. 2-Oxazolidinones 2b-h are known compounds, and their NMR spectra were found to agree with the values reported in the literature (2b-d, f, g,15b 2e,28 2h14). 2-Oxazolones 3b-g are known compounds, and their NMR spectra also agreed with the values reported in the literature.18a 4.3. Tautomerization of 2-oxazolidinone 2b into 2-oxazolone 3b: general procedure
a b
The reaction conditions were identical to those in Table 5. Isolated yield.
To a t-butanol solution (0.8 mL) of 2-oxazolidinone 2b (0.16 mmol) in glassware was added tetrabutylammonium salt (0.008 mmol) under an argon atmosphere. Tautomerization of 2b
A. Fujii et al. / Tetrahedron 74 (2018) 2914e2920
proceeded by the stirring of the resulting mixture at 80 C for 6 h. After the filtration of the reaction mixture through a silica gel pad, the chemical yield of 2-oxazolone 3b was determined by integrating 1H NMR with reference to an internal standard (3hydroxybenzyl alcohol), a dichloromethane solution (2 mL) of which was added to the filtrate. 4.4. Synthesis of quinazoline-2,4(1H,3H)-diones 5 from 2-aminobenzonitriles 4 and CO2: general procedure
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8.7 Hz, 1H, ArH), 7.13 (d, J ¼ 8.7 Hz, 1H, ArH); 13C NMR (100 MHz; DMSO‑d6) d 161.7, 150.0, 140.1, 137.5, 128.9, 117.8, 116.2, 113.8. 4.4.7. Pyrido[2,3-d]pyrimidine-2,4(1H,3H)-dione (5g)30 Pale yellow solid; 1H NMR (400 MHz; DMSO‑d6) d 11.68 (s, 1H, NH), 11.47 (s, 1H, NH), 8.60 (dd, J ¼ 1.8, 4.8 Hz, 1H, ArH), 8.26 (dd, J ¼ 1.8, 7.8 Hz, 1H, ArH), 7.25 (dd, J ¼ 4.8, 7.7 Hz, 1H, ArH); 13C NMR (100 MHz; DMSO‑d6) d 162.4, 154.6, 152.4, 150.4, 136.4, 118.9, 109.9. Acknowledgment
Table 5: To a DMSO‑d6 solution (1 mL) of 2-aminobenzonitrile 4a (1 mmol) in a stainless steel autoclave was added a catalyst (0.01 mmol) under an argon atmosphere. The autoclave was sealed, heated at 110 C and then pressurized with CO2 of 2 MPa. The cyclization reaction of 4a proceeded by the magnetic stirring of the resulting mixture at 110 C for 3 h. After the reaction the autoclave was cooled in an ice bath and depressurized. The chemical yield of quinazoline-2,4(1H,3H)-dione 5a was determined by integrating 1H NMR with reference to an internal standard (3,5-dimethoxybenzyl alcohol), which was added to the reaction mixture. Table 6: DMSO solution (6 mL) of 4 (6 mmol) was treated for the carboxylative cyclization of 4 with CO2 according to the procedure of Table 5. After the reaction, the autoclave was cooled in an ice bath and depressurized, and the reaction mixture was added to water (60 mL). The precipitation was collected by filtration, washed with water and diethyl ether, and then dried in vacuo at 35 C for 15 h to give the pure product 5. Quinazoline-2,4(1H,3H)-diones 5a-g are known compounds, and their NMR spectra were found to agree with the values reported in the literature. 4.4.1. Quinazoline-2,4(1H,3H)-dione (5a)29 White solid; 1H NMR (400 MHz; DMSO‑d6) d 11.28 (s, 1H, NH), 11.14 (s, 1H, NH), 7.89 (d, J ¼ 7.4 Hz, 1H, ArH), 7.64 (t, J ¼ 7.6 Hz, 1H, ArH), 7.20e7.16 (m, 2H, ArH); 13C NMR (100 MHz; DMSO‑d6) d 162.9, 150.4, 140.9, 135.0, 127.0, 122.3, 115.4, 114.4. 4.4.2. 6,7-Dimethoxyquinazoline-2,4(1H,3H)-dione (5b)29 White solid; 1H NMR (400 MHz; DMSO‑d6) d 11.09 (s, 1H, NH), 10.91 (s, 1H, NH), 7.26 (s, 1H, ArH), 6.68 (s, 1H, ArH), 3.83 (s, 3H, CH3), 3.79 (s, 3H, CH3); 13C NMR (100 MHz; DMSO‑d6) d 162.4, 154.9, 150.4, 145.0, 136.5, 107.2, 106.2, 97.8. 55.8, 55.7. 4.4.3. 6-Methylquinazoline-2,4(1H,3H)-dione (5c)24 White solid; 1H NMR (400 MHz; DMSO‑d6) d 11.20 (s, 1H, NH), 11.04 (s, 1H, NH), 7.69 (s, 1H, ArH), 7.46 (dd, J ¼ 1.7, 8.3 Hz, 1H, ArH), 7.07 (d, J ¼ 8.3 Hz, 1H, ArH) 2.32 (s, 3H, CH3); 13C NMR (100 MHz; DMSO‑d6) d 162.8, 150.3, 138.7, 135.9, 131.5, 126.5, 115.3, 114.2, 20.2. 4.4.4. 6-Fluoroquinazoline-2,4(1H,3H)-dione (5d)24 Pale yellow solid; 1H NMR (400 MHz; DMSO‑d6) d 11.43 (s, 1H, NH), 11.21 (s, 1H, NH), 7.61e7.53 (m, 2H, ArH), 7.22e7.19 (m, 1H, ArH); 13C NMR (100 MHz; DMSO‑d6) d 162.2 (4JC-F ¼ 2.8 Hz), 157.3 (1JC-F ¼ 238.2 Hz), 150.1, 137.6, 122.9 (2JC-F ¼ 24.1 Hz), 117.6 (3JC3 2 F ¼ 7.8 Hz), 115.4 ( JC-F ¼ 7.5 Hz), 112.0 ( JC-F ¼ 23.7 Hz). 4.4.5. 6-Chloroquinazoline-2,4(1H,3H)-dione (5e)24 Pale yellow solid; 1H NMR (400 MHz; DMSO‑d6) d 11.36 (brs, 2H, NH), 7.82 (d, J ¼ 2.3 Hz, 1H, ArH), 7.69 (dd, J ¼ 2.5, 8.7 Hz, 1H, ArH), 7.18 (d, J ¼ 8.8 Hz, 1H, ArH); 13C NMR (100 MHz; DMSO‑d6) d 161.8, 150.1, 139.7, 134.8, 126.3, 125.9, 117.5, 115.8. 4.4.6. 6-Bromoquinazoline-2,4(1H,3H)-dione (5f)24 Pale yellow solid; 1H NMR (400 MHz; DMSO‑d6) d 11.44 (s, 1H, NH), 11.27 (s, 1H, NH), 7.94 (d, J ¼ 2.3 Hz, 1H, ArH), 7.80 (dd, J ¼ 2.4,
This work was based on results obtained from a project (P16010) commissioned by the New Energy and Industrial Technology Development Organization (NEDO). References 1. Sakakura T, Choi J-C, Yasuda H. Chem Rev. 2007;107:2365. 2. (a) Vessally E, Babazadeh M, Hosseinian A, Arshadi S, Edjlali L. J CO2 Util. 2017;21:491; (b) Yu B, He L-N. ChemSusChem. 2015;8:52; (c) Omae I. Coord Chem Rev. 2012;256:1384; (d) Riduan SN, Zhang Y. Dalton Trans. 2010;39:3347. 3. (a) Arshadi S, Vessally E, Sobati M, Hosseinian A, Bekhradnia A. J CO2 Util. 2017;19:120; (b) Huang K, Sun C-L, Shi Z-J. Chem Soc Rev. 2011;40:2435; (c) Cokoja M, Bruckmeier C, Rieger B, Herrmann WA, Kuhn FE. Angew Chem Int Ed. 2011;50:8510. 4. (a) Fiorani G, Guo W, Kleij AW. Green Chem. 2015;17:1375; (b) Maeda C, Miyazaki Y, Ema T. Catal Sci Technol. 2014;4:1482. 5. (a) Nagy E, Lepore SD. Org Lett. 2017;19:3695; (b) Maity P, Lepore SD. Angew Chem Int Ed. 2011;50:8338. 6. Nagy E, St Germain E, Cosme P, Maity P, Terentis AC, Lepore SD. Chem Commun. 2016;52:2311. 7. (a) De Nisi A, Sierra S, Ferrara M, Monari M, Bandini M. Org Chem Front. 2017;4: 1849; (b) Huguenot F, Delalande C, Vidal M. Tetrahedron Lett. 2014;55:4632; (c) Wang XQ, Jia PJ, Liu SP, Yu W. Chin Chem Lett. 2011;22:931; (d) Hiroya K, Jouka R, Kameda M, Yasuhara A, Sakamoto T. Tetrahedron. 2001;57:9697. 8. Fujii A, Choi J-C, Fujita K. Tetrahedron Lett. 2017;58:4483. 9. Previous reported TBAFecatalyzed synthesis of quinazoline-2,4(1H,3H)-diones from 2-aminobenzonitriles and CO2 Hulla M, Chaman SMA, Laurenczy G, Das S, Dyson PJ. Angew Chem Int Ed. 2017;56:10559. 10. (a) Smith CJ, Ali A, Hammond ML, et al. J Med Chem. 2011;54:4880; (b) Valente S, Tomassi S, Tempera G, Saccoccio S, Agostinelli E, Mai A. J Med Chem. 2011;54:8228. 11. (a) Zhao D, Liu X-H, Zhu C, et al. ChemCatChem. 2017;9:4598; (b) Brunel P, Monot J, Kefalidis CE, Maron L, Martin-Vaca B, Bourissou D. ACS Catal. 2017;7:2652; (c) Liu X, Wang M-Y, Wang S-Y, Wang Q, He L-N. ChemSusChem. 2017;10:1210; (d) Zhao Y, Qiu J, Tian L, Li Z, Fan M, Wang J. ACS Sustainable Chem Eng. 2016;4: 5553; (e) Shi M, Shen Y-M. J Org Chem. 2002;67:16; (f) Mitsudo T, Hori Y, Yamakawa Y, Watanabe Y. Tetrahedron Lett. 1987;28: 4417. 12. (a) Zhang G, Yang H, Fei H. ACS Catal. 2018;8:2519; (b) Chang Z, Jing X, He C, Liu X, Duan C. ACS Catal. 2018;8:1384; (c) Yoshida M, Mizuguchi T, Shishido K. Chem Eur J. 2012;18:15578; (d) Kikuchi S, Yoshida S, Sugawara Y, et al. Bull Chem Soc Jpn. 2011;84:698; (e) Yoshida S, Fukui K, Kikuchi S, Yamada T. Chem Lett. 2009;38:786. 13. (a) Fujita K, Inoue K, Sato J, Tsuchimoto T, Yasuda H. Tetrahedron. 2016;72: 1205; (b) Hase S, Kayaki Y, Ikariya T. ACS Catal. 2015;5:5135; (c) Yuan R, Lin Z. ACS Catal. 2015;5:2866; (d) Fujita K, Sato J, Inoue K, Tsuchimoto T, Yasuda H. Tetrahedron Lett. 2014;55: 3013; (e) Hase S, Kayaki Y, Ikariya T. Organometallics. 2013;32:5285. 14. Costa M, Chiusoli GP, Taffurelli D, Dalmonego G. J Chem Soc Perkin Trans. 1998;1:1541. 15. (a) Fujita K, Sato J, Fujii A, Onozawa S, Yasuda H. Asian J Org Chem. 2016;5:828; (b) Fujita K, Fujii A, Sato J, Onozawa S, Yasuda H. Tetrahedron Lett. 2016;57: 1282. 16. Zhao Y, Qiu J, Li Z, Wang H, Fan M, Wang J. ChemSusChem. 2017;10:2001. 17. Yu B, Kim D, Kim S, Hong SH. ChemSusChem. 2017;10:1080. 18. (a) Fujita K, Sato J, Yasuda H. Synlett. 2015;26:1106; (b) Hu J, Ma J, Zhu Q, et al. Green Chem. 2015;17:1219. 19. In the case of a primary propargylic amine 6, even by employing 5 mol% of TBAF as a catalyst, the carboxylative cyclization of 6 hardly proceeded, as shown below.
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22. 23. .
20. (a) Tran TP, Ellsworth EL, Stier MA, et al. Bioorg Med Chem Lett. 2004;14:4405; (b) Andrus MB, Mettath SN, Song C. J Org Chem. 2002;67:8284; (c) Mounetou E, Legault J, Lacroix J, Gaudreault RC. J Med Chem. 2001;44:694; (d) Russo F, Romeo G, Guccione S, De Blasi A. J Med Chem. 1991;34:1850. 21. (a) Sadeghzadeh SM. Catal Sci Technol. 2016;6:1435; (b) Saptal VB, Bhanage BM. ChemCatChem. 2016;8:244; (c) Zhao Y, Yu B, Yang Z, et al. Angew Chem Int Ed. 2014;53:5922;
24. 25. 26. 27. 28. 29. 30.
(d) Ma J, Han B, Song J, et al. Green Chem. 2013;15:1485; (e) Kimura T, Sunada H, Kamata K, Mizuno N. Inorg Chem. 2012;51:13001. Mizuno T, Ishino Y. Tetrahedron. 2002;58:3155. (a) Zhao Y, Wu Y, Yuan G, et al. Chem Asian J. 2016;11:2735; (b) Nale D-B, Saigaonkar SD, Bhanage BM. J CO2 Util. 2014;8:67; (c) Lu W, Ma J, Hu J, et al. Green Chem. 2014;16:221; (d) Patil YP, Tambade PJ, Deshmukh KM, Bhanage BM. Catal Today. 2009;148: 355. Gao J, He L-N, Miao C-X, Chanfreau S. Tetrahedron. 2010;60:4063. Lu W, Ma J, Hu J, Zhang Z, Wu C, Han B. RSC Adv. 2014;4:50993. Gainer MJ, Bennett NR, Takahashi Y, Looper RE. Angew Chem Int Ed. 2011;50: 684. Molinaro C, Jamison TF. J Am Chem Soc. 2003;125:8076. Kayaki Y, Yamamoto M, Suzuki T, Ikariya T. Green Chem. 2006;8:1019. Xiao Y, Kong X, Xu Z, Cao C, Pang G, Shi Y. RSC Adv. 2015;5:5032. Wang Q, Lu C, Zhao B, Yao Y. Eur J Org Chem. 2016:2555.
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Efficient synthesis of 2-oxazolidinones and quinazoline-2,4(1H,3H)diones from CO2 catalyzed by tetrabutylammonium fluoride Akira Fujii, Hideaki Matsuo, Jun-Chul Choi, Tadahiro Fujitani, Ken-ichi Fujita* National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki, 305-8565, Japan
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 March 2018 Received in revised form 16 April 2018 Accepted 18 April 2018 Available online 21 April 2018
By employing tetrabutylammonium fluoride (TBAF) as a catalyst, the various carboxylative cyclizations of the propargylic amines having internal alkynes with CO2 proceeded to afford the corresponding 2oxazolidinones. In this case, it was also found that the generated 2-oxazolidinones were tautomerized into the corresponding 2-oxazolones due to the basicity of TBAF. In addition, we performed the synthesis of quinazoline-2,4(1H,3H)-dione from 2-aminobenzonitrile and CO2 by using TBAF as a catalyst. © 2018 Elsevier Ltd. All rights reserved.
Keywords: Carbon dioxide Catalysis Tetrabutylammonium fluoride
1. Introduction The chemistry of carbon dioxide (CO2) has drawn much attention in the last two decades because CO2 is abundant, nontoxic, non-flammable, and easily available. Moreover, CO2 is one of the most attractive C1 building blocks to displace toxic reagents such as phosgene and carbon monoxide.1 CO2 also has great potential as a renewable resource for the production of value-added chemicals, and thus much effort has been expended to incorporate CO2 in fine chemical synthesis.2 However, because CO2 is thermodynamically stable and kinetically inert due to its high oxidation state, organometallic complexes of noble metals must often be used as catalysts for the chemical fixations of CO2.3 Recently, transformations of CO2 have also been achieved by metal-free organocatalysts through the activation of CO2 or substrates.4 Previously, as an example of organocatalysts, tetrabutylammonium fluoride (TBAF) was reported to catalyze the cyclization reaction of b-alkynyl hydrazines to give the corresponding azaproline derivatives.5 This transformation appeared to be caused by a quaternary ammonium cationep interaction with the triple bond of alkynes.6 In addition, several other TBAF-catalyzed cyclization reactions of alkynyl compounds have been reported.7 Recently, we discovered that the carboxylative cyclization of a propargylic amine having a terminal alkyne with CO2 is catalyzed by the quaternary
* Corresponding author. E-mail address: [email protected] (K. Fujita). https://doi.org/10.1016/j.tet.2018.04.059 0040-4020/© 2018 Elsevier Ltd. All rights reserved.
ammonium salts to provide the corresponding 2-oxazolidinone.8 Among the quaternary ammonium salts applied to the carboxylative cyclization, TBAF was found to be the most effective. We report herein the TBAF-catalyzed carboxylative cyclization of various propargylic amines with CO2 to provide 2-oxazolidinones, and the quaternary ammonium salt-catalyzed tautomerization of a 2-oxazolidinone into the corresponding 2-oxazolone. Moreover, we found that TBAF was the most effective quaternary ammonium salt for the synthesis of quinazoline-2,4(1H,3H)-diones from 2aminobenzonitriles and CO2.9 2. Results and discussion 2.1. Synthesis of 2-oxazolidinones from propargylic amines and CO2 2-Oxazolidinones are important heterocyclic compounds in many applications in organic synthesis and pharmaceutical chemistry. For example, they can be used as cholesteryl ester transfer protein inhibitors and monoamine oxidase inhibitors.10 Syntheses of 2-oxazolidinones by the carboxylative cyclization of propargylic amines with CO2 have been reported to be catalyzed by organometallic complexes of noble metals11 such as silver12 and gold.13 Recently, a number of metal-free catalysts, such as superbases,14 N-heterocyclic carbenes,15 triethanolamine,16 and cyanuric acid,17 which are less expensive and environmentally benign, have been used for the carboxylative cyclization of propargylic amines with CO2 as alternatives to organometallic catalysts. Very recently, we found that 1 mol% of TBAF catalyzes the carboxylative
A. Fujii et al. / Tetrahedron 74 (2018) 2914e2920
Scheme 1. Carboxylative cyclization of a propargylic amine 1a with CO2.
cyclization of propargylic amine 1a, which has a terminal alkyne, to provide the corresponding 2-oxazolidinone 2a under CO2 pressure of 0.5 MPa at 110 C, as shown in Scheme 1. This reaction was considered that the propargylic amine 1a reacted with CO2 to form the corresponding carbamic acid, then the carbamic acid was dually activated by a quaternary ammonium cationep interaction with the triple bond and a fluoride ionehydrogen interaction with OH of the carbamic acid.8
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First, we performed the TBAFecatalyzed carboxylative cyclization of propargylic amine 1b, which has an internal alkyne, with CO2 as shown in Table 1. A t-butanol solution of propargylic amine 1b and 1 mol% of TBAF as a catalyst were stirred for 12e24 h in a sealed autoclave under a CO2 atmosphere of 0.5 MPa at 90e110 C. By carrying out the carboxylative cyclization of 1b at 110 C for 12 h, the corresponding 2-oxazolidinone 2b was obtained in an 83% chemical yield along with a small amount of a 2-oxazolone 3b (3%; Table 1, entry 1). Similarly, in our previous report using an N-heterocyclic carbene as a catalyst, a small amount of 2-oxazolidinone was obtained in the carboxylative cyclization of a propargylic amine.15a Then, by carrying out the carboxylative cyclization of 1b at 90 C for 24 h, the corresponding 2-oxazolidinone 2b was obtained in an 85% chemical yield and the formation of 2-oxazolone 3b was suppressed, probably due to the low reaction temperature (1%; Table 1, entry 3). We subsequently examined the time-course of the carboxylative cyclization of propargylic amine 1b at 90 C (Fig. 1). The results showed that the chemical yield of 2-oxazolidinone 2b increased till
Table 1 Carboxylative cyclization of propargylic amine 1b with CO2.a
Entry
Temp ( C)
Time (h)
Yield of 2b (%)b
Yield of 3b (%)b
Recovery of 1b (%)b
1 2 3
110 90 90
12 12 24
83 55 85
3 1 1
0 44 9
a b
Reaction conditions: 1b (1 equiv.), TBAF (1 mol%), t-BuOH (1 M based on 1b), carried out at 90e110 C for 12e24 h in a sealed autoclave under a CO2 atmosphere of 0.5 MPa. Determined by the integration of 1H NMR with reference to an internal standard.
Fig. 1. Time-course curves of the carboxylative cyclization of propargylic amine 1b.
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48 h, then mildly decreased thereafter. On the other hand, the formation of 2-oxazolone 3b was observed with a decrease in the yield of 2-oxazolidinone 2b. Fig. 1 suggests that the carboxylative cyclization of propargylic amine 1b with CO2 proceeds to initially provide 2-oxazolidinone 2b, and that the generated 2oxazolidinone 2b is tautomerized into the corresponding 2oxazolone 3b, the tautomerization into which was also reported in a case using an N-heterocyclic carbene as a catalyst.15a Next, we examined the tautomerization of 2-oxazolidinone 2b into 2-oxazolone 3b through the use of various tetrabutylammonium salts as catalysts, as shown in Table 2.18 First, by the stirring of a t-butanol solution of 2-oxazolidinone 2b at 80 C for 6 h under an argon atmosphere through the use of 5 mol% of TBAF, 2b was tautomerized to afford 2-oxazolone 3b in a 55% chemical yield (Table 2, entry 1). In contrast, when tetrabutylammonium chloride, bromide, or acetate was used as a catalyst, no 2-oxazolone 3b was obtained (Table 2, entries 2e4). On the other hand, when tetrabutylammonium hydroxide was employed as a catalyst, 2-oxazolone 3b was obtained in a 67% chemical yield (Table 2, entry 5), which was higher than the yield in the case using TBAF. From these results, it is assumed that the tautomerization of 2-oxazolidinone 2b into 2oxazolone 3b was caused by the deprotonation of CH2N in 2b due to the basicity of the catalyst.
Table 2 Tautomerization of 2-oxazolidinone 2b using various tetrabutylammonium salts as catalysts.a.
In order to prevent the tautomerization of 2-oxazolidinone 2b into 2-oxazolone 3b under the carboxylative cyclization of propargylic amine 1b with CO2, we carried out the carboxylative cyclization of 1b catalyzed by tetrabutylammonium acetate (Table 3). However, the formation of 2-oxazolone 3b was detected under the reaction conditions for the carboxylative cyclization of 1b (1%; Table 3, entry 4). In addition, for the purpose of catalyzing the carboxylative cyclization of 1b, TBAF was more effective than tetrabutylammonium acetate (Table 3, entries 1 and 2). Finally, we performed the carboxylative cyclizations of various propargylic amines 1 to provide the corresponding 2-oxazolidinone 2 by employing TBAF as a catalyst under controlled reaction conditions, as shown in Table 4. The introduction of a methoxy or a methyl group at the phenyl group in R1 decreased the reactivity of the triple bond, as in our previous report.15 In these cases, by carrying out the reaction for 48 h, the corresponding 2-oxazolidinone 2 was mainly obtained (Table 4, entries 2 and 4). In contrast, when a trifluoromethyl or a cyano group was introduced at the phenyl group in R1, the initial carboxylative cyclization of 1 appeared to proceed smoothly due to the high reactivity of the triple bond, and the generated 2-oxazolidinone 2 appeared to be tautomerized into the corresponding 2-oxazolone 3 at 110 C. As a result, 2-oxazolone 3 was mainly obtained by carrying out the reaction at 110 C for 24 h (Table 4, entries 5 and 7). In these cases, by carrying out the reaction at 70 C, the corresponding 2-oxazolidinone 2 was mainly obtained (Table 4, entries 6 and 8). In the case of the methyl group in R1, even by employing 5 mol% of TBAF as a catalyst, the corresponding 2-oxazolidinone 2h was obtained in an only 8% chemical yield (Table 4, entry 12).19
2.2. Synthesis of quinazoline-2,4(1H,3H)-diones from 2-aminobenzonitriles and CO2 Entry
Catalyst
Yield of 3b (%)b
1 2 3 4 5
Bu4NF Bu4NCl Bu4NBr Bu4NOAc Bu4NOH
55 0 0 0 67
a Reaction conditions: catalyst (5 mol%), 2b (1 equiv.), t-BuOH (0.2 M based on 2b), carried out at 80 C for 6 h in glassware. b Determined by the integration of 1H NMR with reference to an internal standard.
Quinazoline-2,4(1H,3H)-diones and their derivatives have attracted much attention due to their wide range of biological and pharmacological activities.20 The reaction of CO2 with 2aminobenzonitriles is an environmentally benign process with 100% atom efficiency, and it has been widely investigated by use of various catalysts21 including DBU,22 imidazolium salt,23 and guanidine.24 Very recently, Dyson et al. reported that 10 mol% of TBAF or tetramethylphosphonium salts catalyzed the formation of quinazoline-2,4(1H,3H)-dione from 2-aminobenzonitrile under atmospheric pressure of CO2 at 90 C and proposed its
Table 3 Carboxylative cyclization of propargylic amine 1b with CO2.a
Entry c
1 2 3c 4 a b c
Catalyst
Time (h)
Yield of 2b (%)b
Yield of 3b (%)b
Bu4NF Bu4NOAc Bu4NF Bu4NOAc
12 12 48 48
55 36 89 86
1 0 2 1
The reaction conditions were identical to those in Table 1. Determined by the integration of 1H NMR with reference to an internal standard. Cited from Fig. 1.
A. Fujii et al. / Tetrahedron 74 (2018) 2914e2920
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Table 4 Carboxylative cyclizations of various propargylic amines 1 for the synthesis of 2-oxazolidinones 2.a
Entry
1 2 3 4 5 6 7 8 9 10 11 12 a b
1 R1
R2
4-CH3OC6H4 4-CH3OC6H4 4-CH3C6H4 4-CH3C6H4 4-CF3C6H4 4-CF3C6H4 4-CNC6H4 4-CNC6H4 C6H5 C6H5 CH3 CH3
CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH2C6H5 CH2C6H5 CH2C6H5 CH2C6H5
1c 1c 1d 1d 1e 1e 1f 1f 1g 1g 1h 1h
Yield (%)b
Bu4NF
Temp.
Time
(mol%)
(ºC)
(h)
2c-h
3c-h
1 2 1 1 1 1 1 1 1 1 1 5
110 110 110 110 110 70 110 70 110 110 110 110
24 48 24 48 24 24 24 3 24 18 24 24
22 78 77 89 12 84 2 88 84 91 1 8
0 5 1 3 57 6 64 12 9 3 0 0
The reaction conditions were identical to those in Table 1. Determined by the integration of 1H NMR with reference to an internal standard.
catalytic cycle.9 On the other hand, in this paper, by employing 1 mol% of various quaternary ammonium salts, which is similar to the amount of catalysts used for the synthesis of 2oxazolidinones 2, we examined the synthesis of quinazoline2,4(1H,3H)-diones from 2-aminobenzonitriles under a pressurized CO2 atmosphere. In order to optimize the catalyst, we examined the synthesis of quinazoline-2,4(1H,3H)-dione 5a from 2-aminobenzonitrile 4a with CO2 through the use of 1 mol% of various catalysts, such as quaternary ammonium salts and organic bases, as shown in Table 5. First, we confirmed that stirring of a DMSO solution of 2aminobenzonitrile 4a at 110 C for 3 h under a CO2 atmosphere of 2 MPa in the absence of catalysts yielded none of the corresponding quinazoline-2,4(1H,3H)-dione 5a (Table 5, entry 1). Next, by a screening of the catalytic activity of various tetraalkylammonium halides (Table 5, entries 2e7), TBAF was found to afford the highest chemical yield among them (55%; Table 5, entry 4). This result suggests that the higher basicity of the counter anion of the tetraalkylammonium salt facilitates the carboxylative cyclization of 4a with CO2. It was also found that a tetraalkylammonium fluoride with longer alkyl groups afforded a higher chemical yield (Table 5, entries 2e4). In addition, tetrabutylammonium acetate afforded a 40% chemical yield (Table 5, entry 8). On the other hand, by employing quaternary ammonium hydroxides with various structures, the chemical yields of 5a were low in all cases (1e6%; Table 5, entries 9e12). This may have been due to the formation of bicarbonate ion from the hydroxide ion in the presence of CO2.25 Although cesium fluoride moderately catalyzed the reaction to afford 5a in a 45% chemical yield (Table 5, entry 13), organic bases such as 1,1,3,3tetramethylguanidine (TMG) and triethanolamine did not catalyze the reaction effectively (11% and 0%; Table 5, entries 14 and 15, respectively).
Table 5 Optimization of the catalyst for the synthesis of quinazoline-2,4(1H,3H)-dione 5a.a
Entry
Catalyst
Yield of 5 (%)b
Recovery of 4 (%)b
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
none Me4NF Et4NF Bu4NF Bu4NCl Bu4NBr Bu4NI Bu4NOAc Me4NOH Bu4NOH (C6H13)4NOH (C16H33)Me3NOH CsF TMG triethanolamine
0 38 41 55 0 0 0 40 3 5 6 1 45 11 0
99 61 59 45 >99 >99 99 60 90 91 93 98 54 88 >99
a Reaction conditions: 4a (1 equiv.), catalyst (1 mol%), DMSO (1 M based on 4a), carried out at 110 C for 3 h in a sealed autoclave under a CO2 atmosphere of 2 MPa. b Determined by the integration of 1H NMR with reference to an internal standard.
Finally, we performed the synthesis of various quinazoline2,4(1H,3H)-diones 5 at 110 C for 24 h under a CO2 atmosphere of
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2 MPa by employing 1 mol% of TBAF as a catalyst, as shown in Table 6. 2-Aminobenzonitrile derivatives with electronwithdrawing or electron-donating groups at benzene 4b-f could react with CO2 to provide the corresponding quinazoline2,4(1H,3H)-diones 5b-f in excellent chemical yields in all cases (96e99%; Table 6, entries 2e6). On the other hand, 2-amino-3cyanopyridine 4g with CO2 provided 5g in a moderate chemical yield under the present reaction conditions (59%; Table 6, entry 7).
Table 6 Syntheses of various quinazoline-2,4(1H,3H)-diones 5.a
3. Conclusion In the case of the TBAFecatalyzed carboxylative cyclization of a propargylic amine having an internal alkyne with CO2, it was found that a 2-oxazolone is obtained by the tautomerization of the generated 2-oxazolidinone, which was similar to the result obtained using an N-heterocyclic carbene as a catalyst. By optimization of the reaction conditions, including the reaction temperature and the reaction time, we could perform the TBAFecatalyzed carboxylative cyclization of a propargylic amine to provide the corresponding 2-oxazolidinone selectively. Further, it was found that TBAF is the most effective quaternary ammonium salt for catalyzing the carboxylative cyclization of 2-aminobenzonitriles when using a catalyst concentration of 1 mol% under a pressurized CO2 atmosphere. 4. Experimental 4.1. General
Entry
Substrate
Yield (%)b
Product
1
4a
5a
97
2
4b
5b
98
3
4c
5c
96
Kieselgel 60 F254 (Merck) was used for TLC, and Wakogel C-300 (Wako) was used for silica gel column chromatography. Degassed solvent was prepared by freeze-pump-thaw cycling of commercially available dry solvents for the carboxylative cyclization of propargylic amines 1, the tautomerization of 2-oxazolidinone 2b, and the synthesis of quinazoline-2,4(1H,3H)-diones 5. Propargylic amines 1b-h and 2-oxazolidinone 2b were prepared by the methods reported in the literature (1b,13e 1c, e,26 1d,13a 1f,15b 1g,27 1h,12e 2b15b). The other reagents, and the dry solvents were commercially available and were used as received. Carbon dioxide (Showa Denko Gas Products Co., Ltd., purity > 99.99%) was used without further purification. 1 H and 13C NMR spectra were measured with a Bruker Avance III 400 spectrometer (1H: 400 MHz; 13C: 100 MHz). Chemical shifts were reported as ppm downfield from TMS as an internal standard in d units. Coupling constants (J) were given in hertz (Hz). 4.2. Carboxylative cyclization of a propargylic amine 1 with CO2: general procedure
4
4d
5d
>99
5
4e
5e
>99
6
4f
5f
98
7
4g
5g
59
To a t-butanol solution (0.6 mL) of a propargylic amine 1 (0.6 mmol) in a stainless steel autoclave was added a quaternary ammonium salt (0.006e0.03 mmol) under an argon atmosphere. The autoclave was sealed, heated at 70e110 C and then pressurized with CO2 of 0.5 MPa. The carboxylative cyclization of 1 proceeded by the magnetic stirring of the resulting mixture at 70e110 C for the indicated time. After the reaction the autoclave was cooled in an ice bath and depressurized. The chemical yields of the 2-oxazolidinone 2 and the 2-oxazolone 3 were determined by integrating 1H NMR with reference to an internal standard (3hydroxybenzyl alcohol except in the case of 1b, when benzoin methyl ether was used instead), a dichloromethane solution (2 mL) of which was added to the reaction mixture. 2-Oxazolidinones 2b-h are known compounds, and their NMR spectra were found to agree with the values reported in the literature (2b-d, f, g,15b 2e,28 2h14). 2-Oxazolones 3b-g are known compounds, and their NMR spectra also agreed with the values reported in the literature.18a 4.3. Tautomerization of 2-oxazolidinone 2b into 2-oxazolone 3b: general procedure
a b
The reaction conditions were identical to those in Table 5. Isolated yield.
To a t-butanol solution (0.8 mL) of 2-oxazolidinone 2b (0.16 mmol) in glassware was added tetrabutylammonium salt (0.008 mmol) under an argon atmosphere. Tautomerization of 2b
A. Fujii et al. / Tetrahedron 74 (2018) 2914e2920
proceeded by the stirring of the resulting mixture at 80 C for 6 h. After the filtration of the reaction mixture through a silica gel pad, the chemical yield of 2-oxazolone 3b was determined by integrating 1H NMR with reference to an internal standard (3hydroxybenzyl alcohol), a dichloromethane solution (2 mL) of which was added to the filtrate. 4.4. Synthesis of quinazoline-2,4(1H,3H)-diones 5 from 2-aminobenzonitriles 4 and CO2: general procedure
2919
8.7 Hz, 1H, ArH), 7.13 (d, J ¼ 8.7 Hz, 1H, ArH); 13C NMR (100 MHz; DMSO‑d6) d 161.7, 150.0, 140.1, 137.5, 128.9, 117.8, 116.2, 113.8. 4.4.7. Pyrido[2,3-d]pyrimidine-2,4(1H,3H)-dione (5g)30 Pale yellow solid; 1H NMR (400 MHz; DMSO‑d6) d 11.68 (s, 1H, NH), 11.47 (s, 1H, NH), 8.60 (dd, J ¼ 1.8, 4.8 Hz, 1H, ArH), 8.26 (dd, J ¼ 1.8, 7.8 Hz, 1H, ArH), 7.25 (dd, J ¼ 4.8, 7.7 Hz, 1H, ArH); 13C NMR (100 MHz; DMSO‑d6) d 162.4, 154.6, 152.4, 150.4, 136.4, 118.9, 109.9. Acknowledgment
Table 5: To a DMSO‑d6 solution (1 mL) of 2-aminobenzonitrile 4a (1 mmol) in a stainless steel autoclave was added a catalyst (0.01 mmol) under an argon atmosphere. The autoclave was sealed, heated at 110 C and then pressurized with CO2 of 2 MPa. The cyclization reaction of 4a proceeded by the magnetic stirring of the resulting mixture at 110 C for 3 h. After the reaction the autoclave was cooled in an ice bath and depressurized. The chemical yield of quinazoline-2,4(1H,3H)-dione 5a was determined by integrating 1H NMR with reference to an internal standard (3,5-dimethoxybenzyl alcohol), which was added to the reaction mixture. Table 6: DMSO solution (6 mL) of 4 (6 mmol) was treated for the carboxylative cyclization of 4 with CO2 according to the procedure of Table 5. After the reaction, the autoclave was cooled in an ice bath and depressurized, and the reaction mixture was added to water (60 mL). The precipitation was collected by filtration, washed with water and diethyl ether, and then dried in vacuo at 35 C for 15 h to give the pure product 5. Quinazoline-2,4(1H,3H)-diones 5a-g are known compounds, and their NMR spectra were found to agree with the values reported in the literature. 4.4.1. Quinazoline-2,4(1H,3H)-dione (5a)29 White solid; 1H NMR (400 MHz; DMSO‑d6) d 11.28 (s, 1H, NH), 11.14 (s, 1H, NH), 7.89 (d, J ¼ 7.4 Hz, 1H, ArH), 7.64 (t, J ¼ 7.6 Hz, 1H, ArH), 7.20e7.16 (m, 2H, ArH); 13C NMR (100 MHz; DMSO‑d6) d 162.9, 150.4, 140.9, 135.0, 127.0, 122.3, 115.4, 114.4. 4.4.2. 6,7-Dimethoxyquinazoline-2,4(1H,3H)-dione (5b)29 White solid; 1H NMR (400 MHz; DMSO‑d6) d 11.09 (s, 1H, NH), 10.91 (s, 1H, NH), 7.26 (s, 1H, ArH), 6.68 (s, 1H, ArH), 3.83 (s, 3H, CH3), 3.79 (s, 3H, CH3); 13C NMR (100 MHz; DMSO‑d6) d 162.4, 154.9, 150.4, 145.0, 136.5, 107.2, 106.2, 97.8. 55.8, 55.7. 4.4.3. 6-Methylquinazoline-2,4(1H,3H)-dione (5c)24 White solid; 1H NMR (400 MHz; DMSO‑d6) d 11.20 (s, 1H, NH), 11.04 (s, 1H, NH), 7.69 (s, 1H, ArH), 7.46 (dd, J ¼ 1.7, 8.3 Hz, 1H, ArH), 7.07 (d, J ¼ 8.3 Hz, 1H, ArH) 2.32 (s, 3H, CH3); 13C NMR (100 MHz; DMSO‑d6) d 162.8, 150.3, 138.7, 135.9, 131.5, 126.5, 115.3, 114.2, 20.2. 4.4.4. 6-Fluoroquinazoline-2,4(1H,3H)-dione (5d)24 Pale yellow solid; 1H NMR (400 MHz; DMSO‑d6) d 11.43 (s, 1H, NH), 11.21 (s, 1H, NH), 7.61e7.53 (m, 2H, ArH), 7.22e7.19 (m, 1H, ArH); 13C NMR (100 MHz; DMSO‑d6) d 162.2 (4JC-F ¼ 2.8 Hz), 157.3 (1JC-F ¼ 238.2 Hz), 150.1, 137.6, 122.9 (2JC-F ¼ 24.1 Hz), 117.6 (3JC3 2 F ¼ 7.8 Hz), 115.4 ( JC-F ¼ 7.5 Hz), 112.0 ( JC-F ¼ 23.7 Hz). 4.4.5. 6-Chloroquinazoline-2,4(1H,3H)-dione (5e)24 Pale yellow solid; 1H NMR (400 MHz; DMSO‑d6) d 11.36 (brs, 2H, NH), 7.82 (d, J ¼ 2.3 Hz, 1H, ArH), 7.69 (dd, J ¼ 2.5, 8.7 Hz, 1H, ArH), 7.18 (d, J ¼ 8.8 Hz, 1H, ArH); 13C NMR (100 MHz; DMSO‑d6) d 161.8, 150.1, 139.7, 134.8, 126.3, 125.9, 117.5, 115.8. 4.4.6. 6-Bromoquinazoline-2,4(1H,3H)-dione (5f)24 Pale yellow solid; 1H NMR (400 MHz; DMSO‑d6) d 11.44 (s, 1H, NH), 11.27 (s, 1H, NH), 7.94 (d, J ¼ 2.3 Hz, 1H, ArH), 7.80 (dd, J ¼ 2.4,
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