Synthesis of ethyl 1,2-dihydro-3H-pyrrolo[1,2-a]pyrrole-1-carboxylate by an intramolecular carbenoid reaction

Cupric ion (or copper) or boron trifluoride promoted decomposition of ethyl 2-diazo-4-(pyrrol-1-yl)butanoate 6 produced mixtures of the title compound 7 and cis and trans ethyl 4-(pyrrol-1-yl)buten-2-oates 9 and 10. The formation of 7 by these processes represents the first reported instances of the intramolecular attack of an α-oxocarbenoid or a Lewis acid complexed α-diazoalkylcarboalkoxy function on the pyrrole nucleus.