Mechanistic Insights on a Metal‐Free Borylative Cyclization of Alkynes Using BCl3: A Theoretical Investigation

Abstract The metal‐free reactions between alkynes and BCl 3 were investigated by means of DFT calculations, focusing on elucidating the detailed cyclization mechanism and the different chemoselectivity between internal and terminal alkynes. The results showed that borylative cyclization of internal alkynes proceeded via kinetically favorable stepwise complexation, electrophilic dearomatization, hydrogen migration and rearomatization. In contrast, for terminal alkynes, the competitive chloroboration step, which followed the complexation step, was more feasible than electrophilic dearomatization, affording the thermodynamically stable addition products irreversibly.