Synthetic Studies on Indoles and Related COmpounds. XXIX. Attempted Syntheses of Benz[f]indoles by Cyclization Reactions

Abstract

Syntheses of benz[f]indoles from 1, 2-disubstituted naphthalene derivatives by means of cyclization reactions were attempted. The Fischer indolization of 1-methyl-(5a), 1-chloro-(5b), or 1-nitro-(5c)-2-naphthylhydrazones gave only benz[e]indole derivative or decomposed products, and the desired 9-substituted benz[f]indole (3) was not produced. On the other hand, the Fischer indolization of 2-methoxy-1-naphthylhydrazone (17) gave ethyl 5-chlorobenz[g]indole-2-carboxylate (19). The hemetsberger reaction of 1-methyoxy-2-naphthylazido acrylate (26a) gave an azirine (28a) and a nitrile (29a), whereas the same reaction of 1-chloro-2-naphthylazido acrylate (26b) gave the desired 4-chlorobenz[f]indole in a poor yield together with large amounts of by-products, the azirine (28b), the nitrile (29b) and the benz[g]indole (20). These results show that cyclization reactions of a 2-substituent toward the 3-position in naphthalene derivative are not suitable for preparing benz[f]indoles.