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

A new Ti(IV) complex obtained from the C2-symmetric amino diol (1R,5R)-3-aza-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 Evans' oxazolidinones as dienophiles and cyclopentadiene as the diene high yields of the adducts with moderate enantioselectivity, under different reaction conditions are achieved. The effects of solvent, temperature and ligand on the enantioselectivity of the Diels-Alder products are reported. Molecular modelling studies provide an understanding of the diastereofacial selectivity of the Diels-Alder reactions. Asymmetric carbonyl-ene reactions between various glyoxylate esters and α-methyl styrene are also described.