Reactivity of Methyl Mandelate−Ti(IV)-enediolate:  Oxidative Homocoupling versus Aldol and Direct Mannich-Type Syn-Diastereoselective Condensation

Methyl mandelate undergoes quantitative oxidative homocoupling on treatment with TiCl₄/amine at room temperature. In the presence of ArCHO, quantitative syn-diastereoselective aldol condensation takes over the dimerization, whereas exclusive Mannich-type syn-diastereoselective reaction is observed in the presence of both ArCHO and PhNH₂. The subsequent reactions of the title intermediate do not depend on how it is generated.