Enantioselective Diels–Alder Reaction of Acyclic Enones Catalyzed byallo‐Threonine‐Derived Chiral Oxazaborolidinone

An allo‐threonine‐derived O‐(p‐biphenylcarbonyloxy)‐B‐phenyl‐oxazaborolidinone is demonstrated to be a powerful and highly enantioselective Lewis acid catalyst for the enantioselective Diels–Alder reaction of simple acyclic enone dienophiles, expanding the scope of ketone dienophiles and dienes. With 10–20 mol % of the catalyst, the Diels–Alder adducts are obtained with up to 94 % ee and high endo selectivity. The catalyst exhibits a high activity in the reaction with the less reactive β‐substituted dienophiles and the less reactive 1,3‐cycohexadiene and 1,3‐butadiene derivatives. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)