Rhodium-catalyzed deoxygenation and boronization of ketones

  The versatility of ketones makes them valuable in medicine, agrochemistry, and materials science, and the carbonyl group can also be converted into a variety of useful functional groups, an important one being the conversion to a C=C double bond. The classical methods for the synthesis of C=C double bonds from ketones include Wittig, HWE-, Tebbe-, Peterson-, and Julia-Lythgoe olefination reactions, but the α-carbon of the ketone is not involved. Deoxyalkenylation involving the α-carbon of the ketone is less well studied.The Shapiro reaction, as well as enolates and alcohols derived from ketones can give deoxyalkenylated products by reduction or dehydration, but in general, there are many steps, organometallic reagents are required, or strong bases or acids are used. Therefore, the strategy of direct deoxygenation from ketones to olefins remains an important challenge.


       In a domestic work, a rhodium-catalyzed deoxygenation and boronization reaction of ketones with B2pin2 was reported to efficiently generate olefins, vinyl boronic esters, and vinyl ester bis-boronic esters. The reaction conditions are mild, with a wide range of substrates and good functional group compatibility. Mechanistic studies show that the ketone initially undergoes a rhodium-catalyzed deoxygenation reaction to generate olefin via the intermediate of enolization of boron, followed by a rhodium-catalyzed dehydroboration of the olefin to generate vinyl borate and vinyl bis(borate), and the mechanism of the reaction is also supported by DFT calculations.