Addition reactions of heterocyclic compounds. Part 77. Reaction of dimethyl acetylenedicarboxylate with 2- and 3-alkyl substituted indoles and the formation of (1 + 1 DMAD–CH4O) adducts

Abstract

Dimethyl acetylenedicarboxylate (DMAD) adds to 1,3-dimethylindole in moist acetic acid to give 2-substituted adducts. The dienone formulation for a product from 1,2,3-trimethylindole and DMAD has been confirmed by making use of proton-coupled ¹³C n.m.r. spectra. The generality of the formation of this (1 + 1 DMAD-CH₄O) adduct is shown by the preparation of a further five new dienones including two bicyclo[9,3,1]pentadecadienones.