Oxazaborolidinone-Catalyzed Enantioselective Diels−Alder Reaction of Acyclic α,β-Unsaturated Ketones

allo-Threonine-derived O-acyl-B-phenyl-oxazaborolidinones are demonstrated to be powerful and highly enantioselective Lewis acid catalysts for the Diels−Alder reaction of simple acyclic enone dienophiles, expanding the scope of ketone dienophiles and dienes. With 10 to 20 mol % of catalyst, the Diels−Alder adducts are obtained in 76−98% ee with high endo-selectivity. The catalyst exhibits high activity for the reaction with the less reactive β-substituted dienophiles and the less reactive 1,3-cycohexadiene and 1,3-butadiene derivatives. The application of the catalysts to the Diels−Alder reaction of furan is also described.