Difunctionalization of Aldehydes via Electrophilic Acylation: Access to α-Acyloxyphosphonium Salts and Subsequent Diversely Substituted Enol Esters

The synthesis of sterically hindered α-functionalized phosphonium salts is of significant interest yet remains challenging. This work presents a difunctionalization of aldehydes with electrophilic acylphosphonium salts to access α-acyloxyphosphonium salts. The reaction was scoped across 43 examples with varied aldehyde and acylphosphonium salt structures, affording α-acyloxyphosphonium salts in yields ranging from 17% to 95%. These products can engage with aldehydes in Wittig reactions to generate diverse substituted enol esters. Mechanism studies indicate that the additive acts as a nucleophile, facilitating the dissociation of trivalent phosphine from an intermediate acyl group. This study enhances our understanding of acylphosphonium salts as a novel class of electrophilic reagents and provides valuable insights for their future application in organic synthesis.