Diels-Alder reactions of 1,5-dihydropyrano[3,4-b]pyrrol-5(1H)-ones, pyrrole-2,3-quinodimethane analogues; a new synthesis of indoles

Article abstract of DOI:10.1016/S0040-4020(01)90360-6

The pyrano[3,4-b]pyrrol-5-(1H)-ones 7 are stable cyclic analogues of pyrrole-2,3-quinodimethane, and undergo Diels-Alder reaction with a range of acetylenes (dimethyl acetylenedicarboxylate, ethyl propiolate, ethyl trimethylsilylpropynoate, benzyne and the acetylene equivalent, phenyl vinyl sulfoxide), to give, after loss of carbon dioxide, indoles. The Diels-Alder reaction can be extended to the intramolecular variant to give cycloalka-[e]- and [g]-indoles.