1-Methylimidazole as an Organic Catalyst for [3+3]-Cyclodimerization of Acylethynylpyrroles to Bisdipyrrolo[1,2-Ia/I:1′,2′-Id/I]pyrazines

Acylethynylpyrroles, now readily available by the cross-coupling of pyrroles with acylbromoacetylenes in solid Al[sub.2]O[sub.3] media, in the presence of 1-methylimidazole underwent unprecedentedly easy (40-45 °C) cyclodimerization into bis(acylmethylidene)dipyrrolo[1,2-a:1′,2′-d]pyrazines in up to 51% yield. Some other organic and inorganic basic catalysts can also trigger this cyclodimerization, but less efficiently.