Enantioselective organo-SOMO catalysis: The α-vinylation of aldehydes

Carbon-carbon bond formation using enolates is one of the most studied areas in synthetic transformations. The enantioselective α-vinylation of aldehydes via enolates is an important organic reaction that still needs to be developed because of constraints brought about by unwanted epimerization and isomerization side reactions. In this report, the investigators describe a new protocol for the enantioselective catalytic α-vinylation of aldehydes in the presence of boron salts, an amine catalyst and an oxidant. The key to the enantio- and regioselectivity of this protocol is the formation of an activated 3π-electron SOMO transition state initially formed by the coupling of the amine catalyst to the aldehyde (Scheme 1). Screening tests using optimized conditions on a series of α-substituted aldehydes and various trifluoroborate salts with the oxidant, CAN, consistently delivered enantioenriched α-vinyl aldehydes with preference to an α-(E)-conformation. (Chemical Equation Presented).