Quantum chemical calculation on catalytic epoxidation by vanadium complexes

Abstract

The epoxidation of three stereolabeled methyl-substituted chiral allylic alcohols with an allylic strain, namely 3-methylbut-3-en-2-ol (r1), trans-pent-3-en-2-ol (r2) and cis-pent-3-en-2-ol (r3), has been studied by the density functional theory method, B3LYP/6-31G(d). For the VO(OH)[subscript 3]/H[subscript 2]O[subscript 2] oxidant, the vanadium (V) metal rapidly exchanges its ligands for the hydrogen peroxide and allylic alcohol (step 1 and 2). The latter is coordinative activated for oxygen transfer through its enhanced electrophilic character (step 3). And final step is the ligand-substitution to give products and release catalysts. For each substrate, the free energies of intermediate complexes, their threo and erytho transition state, and the corresponding product complexes were calculated. The threo:erytho product ratios have been estimated from the computed free-energies for the competing threo and erytho transition states to be 99.7:0.3 (r1),80.9:19.1 (r2) and 72.2:27.8 (r3)