Asymmetric Diels-Alder and ene reactions promoted by a Ti(IV) complex bearing a C-2-symmetric tridentate ligand

A new Ti(IV) complex obtained from the Ct-symmetric amino diol (1R,5R)-3-az a-3-benzyl-1,5-diphenyl pentan-1,5-diol, (1R,5R)-1, is used effectively as a Lewis acid promoter in asymmetric Diels-Alder reactions. Using various Ev ans' oxazolidinones as dienophiles and cyclopentadiene as the diene high yi elds of the adducts with moderate enantioselectivity, under different react ion conditions are achieved. The effects of solvent, temperature and ligand on the enantioselectivity of the Diels-Alder products are reported. Molecu lar modelling studies provide an understanding of the diastereofacial selec tivity of the Diels-Alder reactions. Asymmetric carbonyl-ene reactions betw een various glyoxylate esters and cc-methyl styrene are also described. (C) 1999 Elsevier Science Ltd. All rights reserved.