Asymmetric reduction of α,β-unsaturated iminium salts with 1,4-dihydronicotinamide sugar pyranosides

Abstract

3,3,5-Trimethyl-2-cyclohexylidene iminium salts were reduced with 1,4-dihydronicotinamide sugar pyranosides to give optically active 3,3,5-trimethylcyclohexanone in enantiomeric excess ranging over 3–31%. The product stereochemistry changed sensitively with structural variation (including anomers, epimers, and deacetylation) of sugar residues. The reduction by more simplified chiral models, N1-(1′S,2′S)-2′-hydroxy- or acetoxycyclohexyl-1,4-dihydronicotinamide revealed that operation of the functional groups on the sugar moiety is not merely steric in nature for induction of chirality in the product.