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Synlett 2005(10): 1551-1554  
DOI: 10.1055/s-2005-869849
LETTER
© Georg Thieme Verlag Stuttgart · New York

Microwave-Accelerated Samarium Triiodide Catalyzed Conjugate Addition of Indoles with Electron-Deficient Olefins

Zhuang-Ping Zhan*, Kai Lang
Department of Chemistry and The Key Laboratory for Chemical Biology of Fujian Province, College of Chemistry and Chemical ­Engineering, Xiamen University, Xiamen 361005, P. R. China
Fax: +86(592)2185780; e-Mail: zpzhan@xmu.edu.cn;
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Publication History

Received 4 April 2005
Publication Date:
12 May 2005 (online)

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Abstract

A fast, efficient, environmentally benign, solvent-free procedure under microwave irradiation, using silica gel supported reagents, for the samarium triiodide catalyzed conjugated addition of indoles with electron-deficient olefins has been developed.

Key words

microwave irradiation - samarium triiodide - indoles - α,β-unsaturated compounds - Michael reaction

11

Typical Experimental Procedure.
To a solution of SmI3 (0.1 mmol) in MeCN (1 mL) was added indole (1 mmol) or 2-methylindole (1 mmol) or 2-phenylindole (1 mmol), electron-deficient olefin (1 mmol) and silica gel (0.25 g). Then the mixture was mixed thoroughly and dried under reduced pressure. The contents were taken in a 5-mL conical flask and was placed in a microwave oven (cooking type, Galanz WP 700P 21-6) and irradiated for 2 min or 15 min at 680 W. After completion of the reaction indicated by TLC, the reaction mixture was allowed to cool, diluted with CH2Cl2 and passed through a short silica gel column using CH2Cl2 as eluent. The solvent was evaporated under reduced pressure and the residue was purified by column chromatography to afford the corresponding 3-alkylated indole.
Procedure for the Reactions with Methyl Vinyl Ketone. To a solution of SmI3 (0.1 mmol) in MeCN (1 mL) was added indole (1 mmol) or 2-methylindole (1 mmol) or 2-phenylindole (1 mmol), and silica gel (0.25 g). Then the mixture was mixed thoroughly and dried under reduced pressure, followed by the addition of methyl vinyl ketone (1 mmol) in CH2Cl2 (0.5 mL) while stirring. The following work up was the same to typical experimental procedure. All new compounds were fully characterized by 1H NMR, 13C NMR, MS, IR and elemental analysis.
3-(1-Benzyl-1 H -indol-3-yl)-1,3-diphenylpropan-1-one (e): Yield: 332 mg (80%). IR (film): νmax = 3034, 1680, 1598, 1493 cm-1. 1H NMR (500 MHz, CDCl3): δ = 3.72 (dd, J = 7, 16.5 Hz, 1 H), 3.81 (dd, J = 7, 16.5 Hz, 1 H), 5.09 (t, J = 7 Hz, 1 H), 5.26 (s, 2 H), 6.90-7.07 (m, 4 H), 7.10-7.21 (m, 3 H), 7.23-7.30 (m, 5 H), 7.33-7.47 (m, 5 H), 7.50-7.55 (m, 1 H), 7.88-7.93 (m, 2 H). 13C NMR (125 MHz, CDCl3): δ = 38.3, 45.3, 49.9, 109.7, 118.4, 119.1, 119.8, 121.9, 125.6, 126.3, 126.6, 127.3, 127.5, 127.8, 128.1, 128.4, 128.5, 128.7, 132.9, 137.0, 137.2, 137.6, 144.3, 198.6. ESI-MS: m/z (%) = 416 (88)[M + H+], 438 (100) [M + Na+]. Anal. Calcd for C30H25NO: C, 86.72; H, 6.06; N, 3.37. Found: C, 86.84; H, 6.05; N, 3.43.
3-[1-(4-methoxyphenyl)-2-nitroethyl]-1 H -indole (m): Yield: 278 mg (94%). IR (film): νmax = 3412, 3058, 1610, 1548, 1509, 1373 cm-1. 1H NMR (500 MHz, CDCl3): δ = 3.79 (s, 3 H), 4.91 (dd, J = 7.5, 12.5 Hz, 1 H), 5.06 (dd, J = 7.5, 12.5 Hz, 1 H), 5.15 (t, J = 7.5 Hz, 1 H), 6.86 (d, J = 8.5 Hz, 2 H), 7.03 (s, 1 H), 7.09 (t, J = 7.5 Hz, 1 H), 7.21 (t, J = 7.5 Hz, 1 H), 7.26 (d, J = 8.5 Hz, 2 H), 7.36 (d, J = 7.5 Hz, 1 H), 7.45 (d, J = 7.5 Hz, 1 H), 8.10 (s, 1 H). 13C NMR (125 MHz, CDCl3): δ = 40.9, 55.2, 79.7, 111.3, 114.3, 114.8, 119.0, 119.9, 121.4, 122.7, 126.1, 128.8, 131.2, 136.5, 158.9. ESI-MS: m/z (%) = 297 (15) [M + H+], 319 (100) [M + Na+]. Anal. Calcd for C17H16N2O3: C, 68.91; H, 5.44; N, 9.45. Found: C, 68.80; H, 5.32; N, 9.46.
1-Benzyl-3-[1-(4-methoxyphenyl)-2-nitroethyl]-1 H -indole (n): Yield: 367 mg (95%). IR (film): νmax = 3027, 1606, 1548, 1501, 1373 cm-1. 1H NMR (500 MHz, CDCl3): δ = 3.53 (s, 3 H), 4.66 (dd, J = 7, 11 Hz, 1 H), 4.79 (dd, J = 7, 11 Hz, 1 H), 4.93 (t, J = 7 Hz, 1 H), 5.00 (s, 2 H), 6.64-6.71 (m, 2 H), 6.76-6.80 (m, 1 H), 6.86-6.93 (m, 3 H), 6.96-7.02 (m, 1 H), 7.04-7.16 (m, 6 H), 7.26-7.34 (m, 1 H). 13C NMR (125 MHz, CDCl3): δ = 40.6, 49.6, 54.8, 79.5, 109.8, 113.6, 114.0, 119.0, 119.4, 122.2, 125.4, 126.4, 126.6, 127.4, 128.5, 128.6, 131.2, 136.7, 137.1, 158.6. ESI-MS: m/z (%) = 387 (100) [M + H+], 409 (91) [M + Na+]. Anal. Calcd for C24H22N2O3: C, 74.59; H, 5.74; N, 7.25. Found: C, 74.46; H, 5.73; N, 7.13.