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

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.