Enantioselective copper catalysed 1,4-conjugate addition reactions using chiral N-heterocyclic carbenes

The preparation of a variety of chiral N-heterocyclic carbene (NHC) precursors is described. The relative merits of imidazolinium salts and silver carbenes as NHC precursors are discussed with respect to their synthesis, stability and performance in the copper catalysed conjugate addition of dialkyl zinc reagents to a variety of Michael acceptors. Enantioselectivities of up to 93% were achieved using as little as 4% of chiral ligand.

Graphical abstractChiral N-heterocyclic carbenes have been shown to be excellent ligands for the copper catalysed conjugate addition of dialkyl zinc reagents to various Michael acceptors. Up to 93% enantiomeric excess has been achieved for the addition of diethyl zinc to cycloheptenone using as little as 4 mol% of catalyst.Figure optionsDownload full-size imageDownload as PowerPoint slide