Addition reactions of heterocyclic compounds. Part 79. Reaction of dimethyl acetylenedicarboxylate with some cyclohept[b]indoles and cyclo-oct[b]indoles

Abstract

The reactions of dimethyl acetylenedicarboxylate with N-methyl- and pyrido[3,2,1-hi]indoles which have either a penta- or hexa-methylene chain linking positions 2 and 3, have been found to give rise to a very similar array of products. Nineteen new adducts were isolated and their structures established by ¹H and ¹³C n.m.r. spectral comparisons, and in some cases also by chemical transformations. The structures include five new classes of adducts not previously encountered: two types of (1 + 1 DMAD) adducts, one of which is a cyclobutene and the other a 3-maleate; two types of (1 + 2 DMAD) adducts, one with two side chains, and the other having a ring-expanded nine- or ten-membered ring and one side chain; and a (1 + 2 DMAD - CH₄O) adduct, all examples of which exhibit fragmentation on heating to give a carbazole and a spiro-cycloalkyl-keten dimer. The isolation of the two (1 + 1 DMAD) adducts is important as both adduct types have been postulated as intermediates in the formation of more complex adducts.