Copper-Catalyzed Protoboration of 1,3-Diynes as a Platform for Iterative Functionalization

This paper presents the protoboration of 1,3-diynes as a platform for the iterative functionalization of various groups on enynes and dienes. Synthetic approaches to targets with high complexity are directed toward using small, modular building blocks similar to a “Lego” construction using iterative chemistry and automated synthesis. Organoboron compounds are currently in the spotlight for achieving these goals. Here, we report an operationally simple, regioselective protoboration of 1,3-diynes using a mixed diboron reagent and Cu(I)/phosphine catalyst to provide enynylboronates in good yields. Under similar conditions, diprotoboration of 1,3-diynes was also achieved to access bench-stable 1,4-diboryl-1,3-dienes in good yields and regioselectivities. The iterative coupling capabilities of the products have been demonstrated along with other downstream transformations offering a range of value-added skeletons.