Chiral Guanidine Catalyzed Direct Aldol Reaction

Significance

The authors disclose a direct ­asymmetric aldol reaction of 5H-oxazol-4-ones 2 and aldehydes 3 catalyzed by chiral guanidines 1 with high stereoselectivities. Guanidine catalysts 1 might act as bifunctional catalysts generating an enolate anion from 2 and directing 3 into a chiral environment via additional hydrogen bond with the OH group. The obtained aldol adduct 4 can be transformed to an α,β-dihydroxycarboxylic acid derivative possessing a quaternary α-carbon atom without loss of enantiopurity.