[GRAPHICS]O-(2-Naphthoyl)-N-tosyl-L-allo-threonine B-phenyloxazaborolidinone catalyzes the asymmetric Mukaiyama-Michael addition of simple acyclic enones to give adducts of 54-85% ee, 2,6-Diisopropylphenal as an additive is demonstrated to effectively retard the undesirable Si+-catalyzed racemic pathway.
Oxazaborolidinone-Catalyzed Enantioselective Diels−Alder Reaction of Acyclic α,β-Unsaturated Ketones
[GRAPHICS]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 beta-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.