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TiCl4-Catalyzed Hydroboration of Ketones with Ammonia Borane
P Veeraraghavan Ramachandran1, Abdulkhaliq A Alawaed1, Henry J Hamann1
1Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States.
Abstract:
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.
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