New C2-Symmetric optically active salen Ligands and their Cobalt(II) complexes.: Hydridoborate reduction of prochiral C=O and C=C bonds

Novel optically active salen ligands and their cobalt(II) complexes were synthesized on the basis of 1.3-dioxolane. Spectral parameters of the complexes and their catalytic activity in enantioselective reduction of carbonyl and unsaturated compounds with sodium tetrahydridoborate were studied. The catalytic reduction of acetophenone is characterized by quantitative yield. the optical yields ranging from 0 to 42%. Benzil and ethyl benzoylformate undergo noncatalytic reduction. The catalytic activity and enantioselectivity in the reduction prochiral C = C bond strongly depend on the solvent and change from low to moderate values in the reduction of methyl 2-acetylamino-3-phenylprop-2-enoate. Dimethyl 2-methylidenebutane-1,4-dioate is reduced in DNIF and its mixtures with ethanol and toluene in quantitative yield; in chloroform, the optical yield reaches 89%, but the chemical yield sharply decreases.