Preparation of Alkyl-Substituted Indoles in the Benzene Portion. Part 10. Synthesis of 4- and/or 5-Alkylated 1, 6, 7, 8-Tetrahydrocyclopent[g]indoles, Model Compounds for Herbindole and Trikentrin Syntheses

Abstract

Synthetic pathways leading to model compounds 25, 27, 33, 20d, 32b, 37, and 42 for the marine alkaloids, herbindoles and trikentrins (1b-i), are presented. p-Toluenesulfonic acid-mediated indole cyclization reactions, 19→20 and 38→39, assisted with thiols such as benzylthiol or thiophenol, are key steps for preparation of the compounds having the 1, 6, 7, 8-tetrahydrocyclopent[g]indole structure. Novel reactions of the phenylsulfone group in 20c and 20e with allyltrimethylsilane in the presence of dichloroethylaluminum as well as with trimethylaluminum, are explained in terms of participation of an intermediary reactive species 29.