Copper‐Catalyzed Chan‐Lam Reaction and Sequential [2,3]‐Rearrangement to Prepare α‐Benzotriazinium Ketones

A variety of α‐benzotriazinium ketones were prepared in 38%‐89% yields through a copper(II)‐catalyzed Chan‐Lam reaction and [2,3]‐rearrangement in a one pot reaction open to air from N‐hydroxybenzotriazin‐4‐ones and alkenyl boronic acids at room temperature. Experimental results showed that the copper catalyst not only played as cross‐coupling catalyst but also served as Lewis acid catalyst to control the chemoselectivity of [2,3]‐rearrangement. The reaction tolerated various linear and cyclic disubstituted alkenyl boronic acids. Moreover, α‐benzotriazinium ketone could be easily prepared in gram scales. The present method highlights dual roles of copper catalyst and [2,3]‐rearrangement of N,O‐vinyl moiety.