Selective Catalytic Cross-Cyclotrimerization En Route to 1,4-Diborylated Benzenes and Their Synthetic Transformations

A synthesis of 1,4-diborylated benzenes was achieved by the Ru-catalyzed regioselective co-cyclotrimerization of alkynes with a commercially available ethynyl boronate. The reaction is applicable to a wide array of alkynes with metal-coordinating groups, providing synthetically useful diborylated benzenes in 23-68% isolated yields. DFT calculations shed light on the reaction course and the origin of its remarkable regioselectivity. Selected diborylated benzenes were converted into various products, such as quinones and hydroquinones, including three natural bioactive small molecules.