Simple synthesis of γ-carbolines

Abstract

indoles, γ-carbolines, Bischler-Napieralski reaction, Leuckart-Wallach reaction. γ-Carboline derivatives and their hydrogenated analogs are less popular than the structurally isomeric β-carbolines [1]. None the less, γ-carbolines are of interest pharmacologically since compounds having various forms of biological activity are found in this class [2-5] and so the development of novel routes of synthesizing the γ-carboline framework is timely. Thanks to the availability of tryptamine derivatives, electrophilic cyclizations of the Pictet-Spengler, Bischler-Napieralski and related type processes are widely used for the synthesis of β-carbolines [1]. Analogous reactions amongst methods for preparing γ-carbolines [2, 6-9] occupy a modest placement [10, 11] and this is likely related to the lesser availability of the corresponding amines. In this work we report preliminary data regarding a novel synthesis of γ-carbolines in which the key stage is a Bischler-Napieralski reaction. As a result of a Leuckart-Wallach type reductive amination the indole