Enantio- and diastereoselective conjugate addition of pyridyl alkyl ketones to enones by Cu(ii)-Lewis acid/Brønsted base catalysis

Abstract

We report herein a chiral Cu(II)-Lewis acid (LA)/Brønsted base-catalyzed process for the enantio- and diastereoselective conjugate addition of various 2-pyridyl alkyl ketones to β-substituted enones under mild conditions. Acid and base catalysts cooperatively deprotonate an α-proton of pyridyl ketones containing diverse alkyl chains, facilitating the generation of α-pyridyl enolates bound to Cu(II)-LA involving carboxylate ligands. The carboxylate ligands which contain extended alkyl chains such as cyclohexanebutyrates, along with a chiral bisphosphine ligand, play a significant role in stereocontrol, supported by experimental and DFT studies. Cu(II) (Z)-enolate complexes, of which one face is effectively blocked by a carboxylate, react with enones to create the stereogenic carbon–carbon bond in the rate-determining step.