[Chemistry of indoles: new reactivities of indole nucleus and its synthetic application].

This review summarizes our studies on the development of new reactivities of the indole nucleus and on its application for the synthesis. These studies involve the following five main subjects: 1) The Vilsmeier-Haack reaction was applied to 1,2,3,4-tetrahydrocarbazole and its N-alkyl compounds. The conditions and the mechanisms of the formation of three kinds of products obtained from the latter compound were clarified, and among the three products, 1,9-dimethylcarbazole-3-aldehyde was found to be useful for the syntheses of olivacine and ellipticine. 2) The Fischer indole synthesis of various 2-substituted phenylhydrazones was examined in detail and it was found that the Fischer indole synthesis of 2-sulfonyloxyphenylhydrazones served a new and convenient method for the synthesis of 7-oxygenated indoles. This reaction was applied to the synthesis of eudistomidin-A. 3) The reactivities of ethyl indole-2-carboxylate for acylation and bromination were also studied, and the use of this compound as a starting material for the synthesis of 4-methoxy-beta-carbolines was successfully investigated. 4) Acylation of ethyl pyrrole-2-carboxylate was concisely studied and this reaction was applied to the syntheses of benzene ring-substituted indoles and benz[f]indoles involving eupolauramine. 5) Two kinds of method for the debenzylation of N-benzylindoles were developed using either AlCl3-benzene or methyl lithium, and they are complementary with each other.