Asymmetric conjugate additions of dialkylzinc reagents to enones promoted by new purely atropisomeric phosphoramidite ligands

Abstract

Enantiopure 1,1′-binaphthylazepine was employed in the preparation of two new phosphoramidites by reaction of the corresponding dichlorophosphoramidite with (R)- or (S)-BINOL. In such compounds the chirality of both diol and amine moieties is only due to atropisomerism. Their catalytic efficiency was tested in the enantioselective copper-catalyzed conjugate addition of dialkylzinc reagents to acyclic, cyclic and macrocyclic α,β-unsaturated ketones. Interestingly, the diastereoisomeric ligands provided the same enantioselectivity in the addition to chalcone, but worked differently with cyclic and macrocyclic enones. The best result, as far as enantiomeric excess is concerned, was observed in the conjugate addition of Me2Zn to 2-cyclopentadecenone, affording the valuable fragrance (-) muscone in 84%ee. ©ARKAT USA, Inc.