Enantioselective Catalytic 1,2-Benzoxazolyl Migration for Tertiary α-Hydroxy Ester Synthesis.

Asymmetric catalytic rearrangement, particularly the enantioselective benzilic ester rearrangement of α-diketones, represents a potent synthetic tool for cleaving C─C bonds to generate optically active tertiary α-hydroxy esters. However, enantioselective benzilic ester rearrangement involving a 1,2-heterocycle shift presents significant challenges owing to inadequate enantiomeric differentiation and steric hindrance associated with tertiary alcohols. In this study, we employed chiral Lewis acid and bifunctional squaramide catalysts for enantioconvergent benzilic ester rearrangement, achieving high enantioselectivity in the construction of tertiary alcohols with chemically versatile functional groups and the synthesis of a novel chiral benzoxazole-oxazoline (Boox) ligand for asymmetric electrocatalysis. DFT calculations elucidated a hemiketal-initiated reaction mechanism, pivotal 1,2-heterocycle shift transition states, and catalytic interactions that govern the increased enantioselectivity of the enantioconvergent benzilic ester rearrangement, furnishing crucial insights into the underlying mechanism.