Diastereofacial selection in the conjugate reduction of γ-alkyl-α,β-unsaturated carbonyl derivatives. Stereocontrol dictated by aromatic ring–Pd interaction

Abstract

Conjugate reduction of the ethylidene-malonate (1a) and -malonitrile (1b) bearing the chiral centre at the γ-position with hydride reagents or with Li–NH₃ gives the anti-isomer (2) preferentially, while the hydrogenation with Pd–C produces the syn-isomer (3) predominantly: the syn-preference is due to a strong interaction between the aromatic π-system and palladium metal.