Isothiourea‐Catalyzed Functionalization of Pyrrolyl‐ and Indolylacetic Acid: Enantioselective Synthesis of Dihydropyridinones and One‐pot Synthesis of Pyridinones
Shuyue Zhang, Lucas Bacheley, Claire M. Young, Daniel G. Stark, Timothy J. C. O’Riordan, Alexandra M. Z. Slawin, Andrew D. Smith
Abstract
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%).