Dynamic kinetic resolution of phosphines with chiral supporting electrolytes.

Abstract

The synthesis of enantiopure compounds is a central focus in organic chemistry owing to the prevalence of chiral centres in biological systems and the impact of homochirality on molecular properties. With growing recognition of electrochemistry as a powerful tool to improve the scope and sustainability of organic synthesis¹, increasing efforts have been directed towards developing asymmetric electrocatalytic reactions to access challenging chiral molecules^2-4. However, many useful electrochemical reactions rely on direct electrolysis without a catalyst, making them inherently difficult to render enantioselective. Supporting electrolytes are integral to electrochemical systems and, in addition to ensuring sufficient solution conductivity, they can influence the rate and selectivity of electrochemical transformations⁵. Chiral supporting electrolytes can mediate asymmetric reactions via direct electrolysis, but their use in organic electrosynthesis remains largely unexplored^6,7. Here we describe the use of substoichiometric chiral phosphate salts as supporting electrolytes to facilitate the oxidation of racemic trivalent phosphines to afford enantioenriched phosphine oxides. Our approach relies on a dynamic-kinetic-resolution strategy that exploits the rapid pyramidal inversion of an anodically generated phosphoniumyl radical cation⁸, while a high concentration of chiral phosphate at the electrode-electrolyte interface^9,10 enhances enantioselective control during rate-limiting nucleophilic addition. Our results highlight the promise of chiral supporting electrolytes for promoting radical-ion-mediated asymmetric transformations.