NH Me MeO OMe CHO NH NH OMe OMe Me Me NH Me O2N CHO NH NH NO2 Me Me NH Me O NH O O O NH NH NH Ph O NH NH NH Ph O Me Me Me 1b 1c 2b 2c 3b 3c 1a 1a 1a 4b 4c 2a 4b 5c 1a Products Substrates 424 J. CHEM. RESEARCH (S), 1997 J. Chem. Research (S), 1997, 424–425† Montmorillonite Clay-catalysed Synthesis of Bis(indol-3-yl)- methanes and 1,2-Bis(indol-3-yl)ethanes† Amiya Krishna Maiti and Prantosh Bhattacharyya* Department of Chemistry, Bose Institute, 93/1, A.P.C. Road, Calcutta 700009, India Condensation of indoles with carbonyl compounds in the presence of montmorillonite clay produces bis(indol- 3-yl)methanes in good yield; an extension of this procedure, involving nucleophilic ring opening of oxiranes, produces 1,2-bis(indol-3-yl)ethanes.During the past few years a large number of natural products containing bis(indolyl)methanes,1 and bis(indolyl)ethanes2 have been isolated from marine sources. Some of these have been found to have biological activity. We are, therefore, interested in developing a new and efficient method for the preparation of these moieties by condensation of carbonyl compounds and nucleophilic ring opening of oxiranes with indole respectively, in the presence of montmorillonite clay K-10.Many applications of montmorillonite clay K-10 in organic synthesis are found in the literature.3 Traditionally, condensation reactions of indoles with carbonyl compounds involve use of BF3–Et2O, AcOH, heat, etc.4,5 However, acidic clay is inexpensive, stable and noncorrosive, and moreover work-up procedures are very simple: just by filtering, the clay can be separated from the reaction mixtures.Thus we become interested in exploring the use of clays in the synthesis of the bis(indolyl)methane and bis(indolyl)ethane moieties. We have found that the condensation and ring opening proceed smoothly in the presence of montmorillonite clay under mild conditions. Montmorillonite clay has a high specific area and its Lewis acidity is as efficient as that of AlCl3.6 This increases the electrophilicity of the carbonyl carbon as well as of the oxirane carbon and welcomes the participation of indole in the cleavage.The results are reported in Table 1. Experimental Melting points are uncorrected and were determined on a Toshniwal apparatus. IR spectra were recorded on a Shimadzu model IR-408 spectrometer. 1H NMR spectra were recorded on a JEOL 100 MHz instrument using [2H6]DMSO as solvent and Me4Si as internal standard.Column chromatography was performed on silica gel (60–120 mesh, Merck). Montmorillonite clay K-10 was purchased from Aldrich. General Procedure.·To a solution of indole (0.02 mol) and the carbonyl compound/oxirane (0.01 mol) in chloroform (254 ml) *To receive any correspondence. †This is a Short Paper as defined in the Instructions for Authors, Section 5.0 [see J. Chem. Research (S), 1997, Issue 1]; there is therefore no corresponding material in J.Chem. Research (M).J. CHEM. RESEARCH (S), 1997 425 montmorillonite K-10 clay (1 g) was added and the mixture stirred at room temperature. After completion of the reaction, the whole mixture was filtered and the clay-free material, after chromatography over silica gel, gave the pure bis(indol-3-yl)methane and 1,2-bis(indol-3-yl)ethane. Received, 26th February 1997; Accepted, 31st July 1997 Paper E/7/01355H References 1 S. A. Morris and R. J. Anderson, Tetrahedron, 1990, 46, 715. 2 G. Bifulco, I. Bruno, R. Riccio, J. Lavayre and G. Bourdy, J. Nat. Prod., 1995, 58, 1254. 3 P. Laszlo, Science, 1987, 235, 1472 and references cited therein. 4 R. J. Sundberg, The Chemistry of Indoles, Academic Press, New York, London, 1970. 5 E. Leete, J. Am. Chem. Soc., 1959, 6023. Table 1 Condensations on clay surface Reaction Found (required) (%) time Yield Mp Molecular Substrate (t/min) Product (%)a (T/°C) formula C H dH b 1a, 1b 30 1c 70 150 C27H26N2O2 79.00 (79.02) 6.30 (6.34) 2.0 (6 H, s), 3.64 (3 H, s), 3.84 (3 H, s), 5.96 (1 H, s), 6.72 (1 H, s), 6.84–7.20 (10 H, m), 7.68 (2 H, s, D2O exch.) 1a, 2b 25 2c 85 254 C25H21N3O2 75.92 (75.95) 5.29 (5.31) 2.0 (6 H, s), 6.0 (1 H, s), 6.68–7.64 (10 H, m), 8.04 (2 H, d), 9.96 (2 H, s, D2O exch.) 1a, 3b 30 3c 80 116 C19H13NO2 79.38 (79.44) 4.45 (4.53) 2.42 (3 H, s), 7.10–8.28 (9 H, m), 8.44 (2 H, br s, D2O exch.) 2a, 4b 135 4c 55 140 C24H20N2 85.65 (85.71) 5.82 (5.95) 3.50 (2 H, d), 4.76 (1 H, t), 6.82–7.32 (13 H, m), 7.56 (2 H, d), 7.70 (2 H, br s, D2O exch.) 1a, 4b 120 5c 60 232 C26H24N2 85.24 (85.31) 6.55 (6.59) 2.06 (6 H, s), 3.72 (2 H, d), 4.52 (1 H, t), 6.80–7.40 (11 h, m), 7.58 (2 H, d), 8.82 (2 H, br s, D2O exch.) aYields refer to pure isolated products. bIn [2H6]DMSO at 100 MHz.