Synthetic Studies of Indoles and Related Compounds. XXVIII. Intramolecular Vinylation of Pyrrole Derivatives Using Palladium : a New Synthetic Method for Substituted Indoles

Abstract

The cyclization of methyl (E)-6-oxo-6-[1-(phenylsulfonyl)-1H-pyrrol-3-yl]-2-hexenoate (8a) using an equimolar amount of palladium chloride gave methyl 4-hydroxy-1-(phenylsulfonyl)-1H-indole-7-acetate (11a) in 33% yield. The similar cyclization of methyl (E)-6-acetoxy-6-[1-(phenylsulfonyl)-1H-pyrrol-3-yl]-2-hexenoate (8c) proceeded smoothly to give methyl 1-(phenylsulfonyl)-1H-indole-7-acetate (11c) and 4-acetoxy-7-methyoxycarbonylmethylidene-1-phenylsulfonyl-4, 5, 6, 7-tetrahydro-1H-indole (10c) in 41% and 22% yields, respectively. Conversion of the tetrahydroindole (10c) to the indole (11c) was accomplished in 44% yield by treatment with p-toluenesulfonic acid in benzene. Methyl (E)-6-[1-(phenylsulfonyl)-1H-pyrrol-3-yl]-2-hexenoate (8d) gave 11c and 7-methoxycarbonylmethylidene-1-phenylsulfonyl-4, 5, 6, 7-tetrahydro-1H-indole (10d) in 27% and 40% yields, respectively. The cyclization of ethyl (E)-4-(5-methoxycarbonyl-4-pentenyl)-1H-pyrrole-2-carboxylate (18) also gave the corresponding indole-7-acetate (20) and 7-methoxycarbonylmethylidene-4, 5, 6, 7-tetrahydro-1H-indole (21) in 16% and 49% yields, respectively.