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. H. C. Brown meets diborenes: The few existing strategies for the construction of electron‐precise boron chains involve either strongly reducing reagents or transition‐metal catalysts; both have distinct disadvantages. Thus, the direct hydroboration of diborenes to form new BB bonds and B3 chains is presented. The reaction is diastereoselective and proceeds under mild conditions without the use of strong reducing agents or transition‐metal catalysts. IMe=1,3‐dimethylimidazol‐2‐ylidene; E=O, S.