Ring Contraction Reactions of Methyl Quinoline 1-Oxide 5-Carboxylates via the Corresponding Benz [d]-1, 3-oxazepines. A Facile Synthesis of Methyl Indole 4-Carboxylate and Its Derivatives

Abstract

A new synthetic method of the 4-substituted indoles from 5-substituted quinoline 1-oxides was developed. The method involves a photochemical ring enlargement of the N-oxides to benz [d]-1, 3-oxazepines and subsequent ring contraction to these indoles under thermal or photochemical conditions. An interesting ring contraction of the 6-alkoxycarbonyl-2-cyanobenz [d]-1, 3-oxazepine to 5-aminoisocoumarins and their ring transformation to the 4-alkoxycarbonylindoles were also disclosed.