A photochemical organocatalytic strategy for the direct enantioselective β-benzylation of α,β-unsaturated aldehydes is reported. The chemistry capitalizes upon the light-triggered enolization of 2-alkyl-benzophenones to afford hydroxy-o-quinodinomethanes. These fleeting intermediates are stereoselectively intercepted by chiral iminium ions, transiently formed upon condensation of a secondary amine catalyst with enals. Density functional theory (DFT) studies provided an explanation for why the reaction proceeds through an unconventional Michael-type addition manifold, instead of a classical cycloaddition mechanism and subsequent ring-opening.
Light-Driven Enantioselective Organocatalytic β-Benzylation of Enals
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Angew. Chem., Intl. Ed. 2017, 56, 3304-3308, DOI: 10.1002/anie.201612159.
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