Catalytic Access to Diastereometrically Pure Four‐ and Five‐Membered Silyl‐Heterocycles Using Transborylation

Silyl‐heterocycles offer a unique handle to expand and explore chemical space, reactivity, and functionality. The shortage of catalytic methods for the preparation of diverse and functionalized silyl‐heterocycles however limits widespread exploration and exploitation. Herein the borane‐catalyzed intramolecular 1,1‐carboboration of silyl‐alkynes has been developed for the synthesis of 2,3‐dihydrosilolyl and silylcyclobut‐2‐enyl boronic esters. Successful, catalytic carboboration has been achieved on a variety of functionally diverse silyl‐alkynes, using a borane catalyst and transborylation enabled turnover. Mechanistic studies, including 13C‐labelling, computational studies, and single‐turnover experiments, suggest a reaction pathway proceeding by 1,2‐hydroboration, 1,1‐carboboration, and transborylation to release the alkenyl boronic ester product and regenerate the borane catalyst.