Enantioselective intramolecular cyclopropanation via a cationic sulfoxonium-Rh-carbene.

Abstract

The synthesis of heavily substituted chiral cyclopropanes presents a significant challenge in organic chemistry due to the inherent strain and steric congestion of these three-membered rings. In this work, we report a highly enantioselective intramolecular cyclopropanation of tri-substituted alkenes via a sulfoxonium-Rh-carbene intermediate, resulting in the formation of highly congested penta-substituted chiral cyclopropanes. The cationic sulfur-substituted Rh-carbene was produced by reacting an I,S-ylide with a paddlewheel Rh catalyst, which undergoes highly enantioselective cyclopropanation. Notably, the incorporation of a sulfoxonium group at one of the bridgehead carbons enhances the chemical versatility of the products, enabling diverse transformations through multiple mechanistic pathways. This work expands the toolkit for synthesizing penta-substituted chiral cyclopropanes and demonstrates the viability of using cationic carbenes in enantioselective transformations. Density functional theory (DFT) calculations reveal that chalcogen bonding play a critical role in differentiating the diastereomeric pathways, providing insights into the enantioselectivity.