Bis(iminophosphoranes) as Useful Building Blocks for the Preparation of Complex Polyaza Ring Systems

Several methodologies based on the aza Wittig-type reaction of bis(iminophosphoranes) have been used for the preparation of a wide variety of nitrogen-containing heterocyclic ring systems. The resulting aza Wittig products, functionalized heterocumulenes, undergo cyclization either by electrocyclic ring-closure, intramolecular amination, [2+2] cycloaddition or intramolecular Diels-Alder cycloaddition. The synthetic utility of bis(iminophosphoranes) when the two iminophosphoranes groups show different reactivity (N-iminophosphorane > C-vinyliminophosphorane > C-aryliminophosphorane) toward the same functionality is also reported.