posted on 2022-09-15, 18:14authored byP. Veeraraghavan Ramachandran, Abdulkhaliq A. Alawaed, Henry J. Hamann
Investigation of a variety of Lewis acids for the hydroboration-hydrolysis
(reduction) of ketones with amine-boranes has revealed that catalytic
(10 mol %) titanium tetrachloride (TiCl4) in diethyl ether
at room temperature immensely accelerates the reaction of ammonia
borane. The product alcohols are produced in good to excellent yields
within 30 min, even with ketones which typically requires 24 h or
longer to reduce under uncatalyzed conditions. Several potentially
reactive functionalities are tolerated, and substituted cycloalkanones
are reduced diastereoselectively to the thermodynamic product. A deuterium
labeling study and 11B NMR analysis of the reaction have
been performed to verify the proposed hydroboration mechanism.