Boric acid as a precatalyst for BH(3)-catalyzed hydroboration

We report that boric acid, BO(3)H(3), is a good precatalyst for the BH(3)-catalyzed hydroboration of esters using pinacolborane as a borylation agent. Using microwave irradiation as an energy source, we demonstrated that a dozen esters were converted into the corresponding boronate ethers in good yields. It was also possible to use boric acid as a precatalyst to reduce carbonates and alkynes. Considering the hazardous and pyrophoric nature of BH(3) solutions, boric acid proves to be a safe and green precatalyst for the metal-free reduction of unsaturated species.