Isothiourea-catalyzed functionalization of pyrrolyl- and indolylacetic acid : enantioselective synthesis of dihydropyridinones and one-pot synthesis of pyridinones

Abstract

A protocol for the isothiourea‐catalyzed enantioselective functionalization of pyrrolyl‐ and indolylacetic acids has been developed. Stereodefined dihydropyridinones are accessed through formal [4+2] cycloaddition of an in situ generated isothiouronium enolate with α,β‐unsaturated ketimines. The dihydropyridinones are obtained in moderate to excellent yield (26–97%), excellent diastereocontrol (all >95 : 5 dr) and moderate to excellent enantiocontrol (75 : 25–99 : 1 er). An unusual elimination of pyrrole or indole from the dihydropyridinone to access achiral pyridinones was observed and could be selectively promoted. A further one‐pot synthesis using an acyl imidazole was developed to give pyridinones in good to excellent yields (67–91%).