Unusual temperature dependence of enantioselectivity in asymmetric reductions by chiral NADH models

摘要

Unusual stereoselectivity changes, i.e., enhancement and inversion of enantioselectivity with increasing temperature, were observed in the asymmetric reduction of methyl benzoylformate with chiral 1,4-dihydropyridines possessing amino acid residues as ligating chiral auxiliaries. The differential activation parameters, Delta Delta H double dagger(S-R) and Delta Delta S Sigma double dagger(S-R), obtained from the Eyring plots demonstrate that the entropy term controls the enantiodifferentiating step, accounting for the observed unique temperature dependencies.