Direct hydroboration of B=B bonds: a mild strategy for the proliferation of B-B bonds.

Synthetic access to electron-precise boron chains is hampered by the preferential formation of nonclassical structures. The few existing strategies for this involve either strongly reducing reagents or transition-metal catalysts, both with distinct disadvantages. The synthesis of new furyl- and thienyl-substituted diborenes is presented, along with their direct hydroboration with catecholborane (CatBH) to form a new electron-precise B-B bond and a B3 chain. The reaction is diastereoselective and proceeds under mild conditions without the use of strong reducing agents or transition-metal catalysts commonly used in B-B coupling reactions.