B/Pd-Catalyzed Asymmetric Propargylic Substitution for Vicinal Quaternary/Tertiary Stereocenters

Abstract

All-carbon quaternary stereogenic centers are pivotal motifs in bioactive molecules, yet their enantioselective construction in acyclic systems remains a formidable challenge due to severe steric hindrance and conformational flexibility. Although the alkynyl group is a versatile synthetic handle for diverse functionalizations, the catalytic asymmetric synthesis of alkynyl-substituted all-carbon quaternary centers is significantly underdeveloped. Herein, we report an unprecedented asymmetric propargylic substitution of tertiary propargylic carbonates with α-hydroxy ketones, enabled by a synergistic B/Pd dual-catalytic system. Unlike traditional Pd-catalyzed pathways that typically favor allene formation, this protocol uniquely preserves the alkyne moiety to deliver alkynyl-substituted all-carbon quaternary stereocenters bearing a vicinal tertiary stereocenter with excellent diastereo- and enantiocontrol. Notably, the catalytic system effectively overcomes the inherent steric congestion of coupling two bulky partners and achieves the precise discrimination between two sterically and electronically similar alkyl groups (e.g., methyl vs ethyl) on the propargylic carbon. Chiral phosphoramidite-palladium catalysts play a critical role in creating a differentiated chiral environment to achieve exceptional levels of enantioselectivity.