Synthesis of Acetals via α-Diazo Sulfonium Triflate-Mediated Alcohol Functionalization

Conventional acetal syntheses typically rely on stoichiometric amounts of strong Brønsted or Lewis acids, which often lead to harsh reaction conditions, operational complexity, and limited functional-group tolerance. Herein, we report an acid-free Rh(II)-catalyzed tandem O-H insertion/nucleophilic substitution of alcohols with α-diazo sulfonium triflates, enabling the formation of two C-O bonds under mild conditions. In this transformation, alcohols act as bifunctional nucleophiles, allowing efficient access to a diverse array of acetal frameworks. Furthermore, incorporation of a subsequent transesterification step enables the formation of a third C-O bond, providing a modular and flexible strategy for the synthesis of structurally unique acetals and further expanding the synthetic utility of diazo sulfonium salts.