Carbon-carbon bond formation and pyrrole synthesis via the [3,3] sigmatropic rearrangement of O-vinyl oxime ethers.

A new method for the synthesis of 2,4- and 2,3,4-substituted pyrroles in two or three steps from commercially available ketones and allyl hydroxylamine is described. An iridium-catalyzed isomerization reaction has been developed to convert O-allyl oximes to O-vinyl oximes, which undergo a facile [3,3] rearrangement to form 1,4-imino aldehyde Paal−Knorr intermediates that cyclize to afford the corresponding pyrroles. Optimization and examples of the isomerization and pyrrole formation are discussed.