Copper‐Catalyzed Borylative Dearomatization of Internal Alkynes With Pyrimidinium Salts and Diborons

A three‐component borylative dearomatization reaction of alkynes with B 2 pin 2 and pyrimidinium salts is herein reported. The reaction features broad substrate scope (up to 40 examples) using CuCl/AmPhos as the precatalyst, yielding a series of boryl alkenyl 1,2‐dihydropyrimidines as the products in moderate‐to‐high yields. Scale‐up reactions and further transformations of the products are also demonstrated.