Asymmetric Boracarboxylation of Styrenes Using Carbon Dioxide

Abstract

The boracarboxylation reaction has potential for the production of natural products and drug candidates, but the development of an asymmetric version of this transformation is challenging. We report an enantioselective boracarboxylation of styrenes, enabled by a copper catalyst containing chiral phosphines. Our experimental conditions provide yields between 31–76% and enantiomeric ratios from 80:20 up to 98:2 for electron-rich styrenes. Oxidation of a boracarboxylation product gives (S)-tropic acid, an intermediate towards several tropane alkaloids. A computational analysis of the mechanistic details shows a complex pattern of competing reaction pathways, highlighting challenges encountered when developing asymmetric reactions using CO₂.