Enantioconvergent Copper Catalysis: In Situ Generation of the Chiral Phosphorus Ylide and Its Wittig Reactions.

Abstract

The Wittig reaction, which produces alkenes from phosphorus ylides (P-ylides) and carbonyls, is one of the most powerful tools in chemical synthesis. This Nobel Prize-winning reaction is widely used in natural product synthesis, fine chemical production (i.e., medicines and agricultural agents), and polymer functionalization. Despite these great achievements, the potential of the Wittig reaction, particularly regarding the access of chiral alkene building blocks, has not been fully exploited. The main area that requires additional exploration is the development of general and practical methods to efficiently prepare chiral P-ylides. Here, we show that highly functionalized chiral P-ylides can be easily synthesized through a copper-catalyzed asymmetric propargylic alkylation reaction from phosphonium salts and racemic propargylic esters. The subsequent Wittig reactions enable the synthesis of versatile alkene building blocks, chiral α-propargylic acrylates, and α-propargylic allenoates, with a wide substrate scope and satisfactory functional group compatibility. This transformation features inexpensive transition-metal catalysts, user-friendly conditions, easily available feedstock, and high-valued products.