Enantioselective Addition of Diethylzinc to Benzaldehyde Catalyzed by an Organometallic Ti(IV) Compound and a Xylose Derivative

A derivative of D-xylose, 1,2-O-isopropylidene-alpha-D-xylofuranose (1), with Ti((OPr)-Pr-i)(4) was used as a chiral catalyst in the asymmetric alkylation of benzaldehyde with diethylzinc (Et2Zn) for the high-yield production (90% conversion) and moderate enantioselectivity (45% ee (S)) of 1-phenyl-1-propanol. Optimum conditions (conversion and enantioselectivity) for the catalytic system formed by 1 and Ti(IV) were 10.0 mol % of 1 and 1 equivalent of Ti(IV) with respect to benzaldehyde in CH2Cl2 as a solvent, at room temperature. In the asymmetric alkylation of benzaldehyde with Et2Zn compound 1 in substoichiometric amount with Ti((OPr)-Pr-i)(4) forms a chiral catalyst of the Ti(IV)-sugar type that ensures the good-yield conversion and the enantioselectivity of the reaction