Photocatalytic oxidative cleavage of alkenes followed by carbonyl stereoselective bioreduction for the synthesis of enantioenriched secondary alcohols

Abstract

Oxidative alkene cleavage of a series of (hetero)aryl alkyl styrenes in aqueous medium has been developed using either 9-mesityl-10-methylacridinium perchlorate ([AcrMes]ClO4) and sodium anthraquinone2-sulfonate (SAS) as photosensitizers under blue LED irradiation. Reaction conditions were studied to find a suitable media for the development of a linear cascade after subsequent stereoselective reduction of the corresponding ketone intermediate. The use of cesium carbonate provided an adequate pH to the reaction medium for the alcohol dehydrogenase action. [AcrMes]ClO4 was found to be the best photocatalyst, allowing the development of concurrent or sequential cascades depending on the ability of the photosensitizer to oxidize back the chiral alcohol to the ketone. Overall, the photobiocatalytic approach has allowed the synthesis of a wide number of alcohol compounds, the formation of (S)- or (R)-enantiomers being attained with excellent stereoselectivity and moderate to good yields