Application of Zinc(II)-Binol for the Formal Aza-Diels-Alder Reaction of N-Arylimines with Danishefsky's Diene: CD-Based Absolute Stereochemistry Determination, Origin of Asymmetric Induction and Mechanistic Considerations

Abstract

Zinc(II)–binol has been employed as an efficient Lewis acid catalyst (10 or 100 mol-% loading) for the formal aza-Diels–Alder reaction of ester, furyl and dimethyl acetal-substituted N-aryl imines. Asymmetric induction varies from poor to good, with the major enantiomer obtained being (S) when the (S)-binol complex has been employed. The absolute stereochemistry of the dimethyl acetal-substituted cycloaduct was determined by CD, and both efficient aza-Diels–Alder reaction and asymmetric induction are proposed to be dependent upon the formation of bidentate zinc-imine complexes. These complexes have been modelled using semiempirical methods