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Molecular Transformation to Pyrroles, Pentafulvenes, and Pyrrolopyridines via [2 + 2] Cycloaddition of Propargylamines with Tetracyanoethylene.

In this paper, we describe an efficient and atom-economical synthesis of highly functionalized pyrroles, pentafulvenes, and pyrrolopyridines by [2 + 2] cycloaddition-retroelectrocyclization of N -substituted propargylamines with tetracyanoethylene, followed by the treatment of the intermediately obtained tetracyanobutadiene derivatives with silica gel. In this reaction, silica gel plays an important role to promote the intramolecular cyclization to afford the heterocyclic products from the tetracyanobutadiene intermediates. The products were obtained selectively depending on the substituent on the nitrogen atom of the starting propargylamines.