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Synlett 2002(11): 1783-1786
DOI: 10.1055/s-2002-34889
LETTER
© Georg Thieme Verlag Stuttgart · New York

Rh2(OAc)4-Catalyzed Regioselective Intermolecular C-H Insertion Reactions: Novel Synthesis of 2-Pyrrol-3′-yloxindoles

Sengodagounder Muthusamy*, Chidambaram Gunanathan
Central Salt and Marine Chemicals Research Institute, Bhavnagar 364 002, India
Fax: +91(278)567562; e-Mail: salt@csir.res.in;
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Publication History

Received 27 August 2002
Publication Date:
21 October 2002 (online)

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Abstract

Regioselective synthesis of 2-pyrrol-3′-yloxindoles has been achieved by the reactions of cyclic diazo carbonyl compounds 1a-e with pyrrole and substituted pyrroles (2a-d) in the presence of rhodium(II) acetate catalyst via intermolecular C-H insertion reaction.

Key words

C-H insertion reaction - oxindole - pyrrole - rhodium(II) acetate

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General Procedure for the Synthesis of 2-Pyrrol-3′-yloxindoles: In an oven-dried flask, a solution containing 1.2 equiv of pyrrole and 1 mol% of rhodium(II) acetate dimer in 10 mL of dry dichloromethane (dried over phosphorous pentoxide) was degasified under an argon atmosphere. To this reaction mixture, a solution of 1 equiv of appropriate cyclic diazoamide in dry dichloromethane was added dropwise slowly for 1 h period under an argon atmosphere at r.t. The reaction mixture was allowed to stir and followed by TLC till the disappearance of the starting material. The solvent was removed under reduced pressure and the residue purified by flash silica gel column chromatography to afford the respective C-H insertion products.

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All new compounds exhibited spectral data consistent with their structures. Selected spectral data: 3-(1-Benzyl-1 H -pyrrol-2-yl)-1-methyl-1,3-dihydro-indol-2-one (3a): Colorless solid. Mp 115-117 °C (hexane/EtOAc). IR (KBr): 2932, 1716, 1609, 1490, 1464, 1368, 1345, 1302, 1253, 1180, 1085, 714 cm-1. 1H NMR (200 MHz, CDCl3): δ = 3.09 (s, 3 H, N-CH3), 4.55 (s, 1 H), 5.14 (d, 1 H, J = 16.3 Hz), 5.51 (d, 1 H, J = 16.3 Hz), 5.78-5.80 (m, 1 H), 6.09 (t, 1 H, J = 2.5 Hz), 6.69 (t, 1 H, J = 2.5 Hz), 6.79 (d, 1 H, J = 7.7 Hz), 6.97-7.04 (m, 3 H), 7.12-7.33 (m, 5 H). 13C NMR (50.3 MHz, CDCl3): δ = 26.9 (N-CH3) 45.1 (CH), 51.7 (N-CH2), 108.0 (CH), 108.7 (CH), 109.3 (CH), 123.2 (CH), 124.0 (CH), 125.7 (CH), 126.1 (quat-C), 127.2 (CH), 127.7 (CH), 128.0 (quat-C), 128.1 (CH), 128.9 (CH), 129.3 (CH), 138.9 (quat-C), 144.9 (quat-C), 175.4 (quat-C). MS: m/z = 302 (38.5) [M+], 212 (23.7), 211(100), 168 (14.3), 157 (17.6), 156 (94.5), 154(13), 91(84). Anal. Calcd for C20H18N2O: C, 79.44; H, 6.00; N, 9.26. Found: C, 79.26; H, 5.98; N, 9.23. 3-(1-Benzyl-1 H -pyrrol-3-yl)-1-methyl-1,3-dihydro-indol-2- one (4a): Colorless solid. Mp 96-98 °C (hexane/EtOAc). IR (KBr): 2928, 1718, 1627, 1469, 1463, 1368, 1355, 1309, 1263, 1187, 1066, 720 cm-1. 1H NMR (200 MHz, CDCl3): δ = 3.18 (s, 3 H, N-CH3), 4.56 (s, 1 H), 4.99 (s, 2 H, N-CH2), 6.11 (t, 1 H, J = 2.2 Hz), 6.61-6.73 (m, 2 H), 6.93 (d, 1 H, J = 7.1 Hz), 7.05-7.36 (m, 8 H). MS:
m/z = 212 [M+]. Anal. Calcd for C20H18N2O: C, 79.44; H, 6.00; N, 9.26. Found: C, 79.19; H, 6.02; N, 9.29. 1-Methyl-3-[1-(4-methyl-benzyl)-1 H -pyrrol-2-yl]-1,3-dihydro-indol-2-one (3f): Colorless oil. IR (neat): 2983, 1713, 1613, 1493, 1470, 1421, 1372, 1349, 1305, 1265, 1125, 1086, 740 cm-1. 1H NMR (200 MHz, CDCl3): δ = 2.29 (s, 3 H, ArCH3), 3.09 (s, 3 H, N-CH3), 4.55 (s, 1 H), 5.10 (d, 1 H, J = 16.1 Hz), 5.46 (d, 1 H, J = 16.1 Hz), 5.77 (t, 1 H, J = 1.7 Hz), 6.07 (t, 1 H, J = 2.9 Hz), 6.67 (t, 1 H, J = 1.7 Hz), 6.77 (d, 1 H, J = 7.8 Hz), 6.99-7.29 (m, 7 H). 13C NMR (50.3 MHz, CDCl3): δ = 21.8 (CH3), 27.0 (CH3,) 45.2 (CH), 51.6 (N-CH2), 107.9 (CH), 108.7 (CH), 109.3 (CH), 123.2 (CH), 124.0 (CH), 125.7 (CH), 127.3 (CH), 128.3 (quat-C), 129.0 (CH), 130.0 (CH), 135.8 (quat-C), 137.7 (quat-C), 145.0 (quat-C), 175.4 (quat-C). MS: m/z = 316 [M+]. Anal. Calcd for C21H20N2O: C, 79.72; H, 6.37; N, 8.85. Found: C, 79.92; H, 6.35; N, 8.82. 1-Methyl-3-[1-(4-methyl-benzyl)-1 H -pyrrol-3-yl]-1,3-dihydro-indol-2-one (4f): Colorless oil. IR (neat): 2965, 1715, 1612, 1486, 1467, 1451, 1363, 1347, 1320, 1280, 1116, 1085, 735 cm-1. 1H NMR (200 MHz, CDCl3): δ = 2.26 (s, 3 H, ArCH3), 3.19 (s, 3 H, N-CH3), 4.55 (s, 1 H), 4.94 (s, 2 H, N-CH2), 6.10 (t, 1 H, J = 2.4 Hz), 6.59-6.64 (m, 2 H), 6.83 (d, 1 H, J = 7.4Hz), 7.01-7.17 (m, 5 H), 7.26-7.32 (m, 2 H). MS: m/z = 316 [M+]. Anal. Calcd for C21H20N2O: C, 79.72; H, 6.37; N, 8.85. Found: C, 79.89; H, 6.39; N, 8.87. 3-[1-(3,5-Dimethyl-benzyl)-1 H -pyrrol-2-yl]-1-methyl-1,3-dihydro-indol-2-one (3k): Gray color solid. Mp 156-158 °C (hexane/EtOAc). IR (KBr): 2920, 1717, 1609, 1492, 1467, 1372, 1343, 1304, 1127, 1086, 843, 750 cm-1. 1H NMR (200 MHz, CDCl3): δ = 2.25 (s, 6 H, ArCH3), 3.13 (s, 3 H, N-CH3), 4.59 (s, 1 H), 5.07 (d, 1 H, J = 16.2 Hz), 5.45 (d, 1 H, J = 16.2 Hz), 5.79 (t, 1 H, J = 1.8 Hz), 6.09 (t, 1 H, J = 2.9 Hz), 6.64 (s, 2 H), 6.69 (t, 1 H, J = 1.8 Hz), 6.75-6.86 (m, 2 H), 7.01 (t, 1 H, J = 7.45 Hz), 7.14 (d, 1 H, J = 7.18 Hz), 7.28 (t, 1 H, J = 7.59 Hz). 13C NMR (50.3 MHz, CDCl3): δ = 21.9 (CH3), 26.9 (CH3,) 45.2 (CH), 51.7 (N-CH2), 107.8 (CH), 108.6 (CH), 109.2 (CH), 123.1 (CH), 124.0 (CH), 125.1 (CH), 125.6 (CH), 127.2 (quat-C), 127.3 (quat-C), 128.3 (quat-C), 129.0 (CH), 129.7 (CH), 138.7 (quat-C), 138.9 (quat-C), 144.9 (quat-C), 175.5 (quat-C). MS: m/z = 330 [M+]. Anal. Calcd for C22H22N2O: C, 79.97; H, 6.71; N, 8.48. Found: C, 79.74; H, 6.69; N, 8.51.