Asymmetric Diels–Alder Reactions of an Acrylic Acid Derivative Using a Chiral Titanium Catalyst

Asymmetric Diels–Alder reactions of an acrylic acid derivative using a catalytic amount of a chiral titanium reagent were performed with several dienes. The titanium catalyst was prepared by the alkoxy exchange between dichlorodiisopropoxytitanium(IV) and a chiral 1,4-diol derived from (2R,3R)-tartrate. By the use of the titanium catalyst, the reaction between 3-acryloyl-1,3-oxazolidin-2-one and dienes proceeded in a toluene–petroleum ether mixture in the presence of Molecular Sieves 4A to afford the Diels–Alder adducts in 72–100% yields and 88–>96% enantioselectivity. This reaction can be applied to a diene containing a hetero atom such as 2-ethylthio-1,3-butadiene, which affords the Diels–Alder adduct in a high optical purity. In this paper are also described the methods for determining the optical purities of the obtained 4-substituted 3-cyclohexenecarboxylic acid derivatives.