Science of Synthesis

MacMillan, D. W. C.; Beeson, T. D., Science of Synthesis: Asymmetric Organocatalysis, (2012) 1, 273.

The validity of SOMO catalysis as a new mode of activation was first demonstrated with the direct enantioselective α-allylation of aldehydes.[‌9‌] The alkene moiety of an allyl π-nucleophile ‌3‌ acts as a SOMOphile to the transiently formed radical cation ‌2‌, generating a secondary radical ‌4‌, which after oxidation can undergo an E1 elimination to furnish an allylated species ‌5‌. Hydrolysis subsequently regenerates the imidazolidinone catalyst ‌1‌ and provides the α-allylated aldehyde ‌6‌ (‌Scheme 4‌). Enantioselectivity is achieved by facial shielding of the 3π-electron system by the benzyl substituent of the catalyst after being forced into the geometry away from the large tert-butyl substituent.

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References