Copper-Catalyzed Asymmetric Conjugate Addition of Dimethyl-zinc to Acyl-N-methylimidazole Michael Acceptors: Scope,Limitations and Iterative Reactions
Résumé
An efficient copper-catalyzed enantioselective conjugate addition of dimethylzinc to unsaturated 2-acyl-N-methylimidazoles has been achieved using a chiral bidentate hydroxyalkyl-NHC ligand. The reactions proceed with excellent regioselectivity (1,4 vs. 1,6 and 1,8) in extended conjugated systems to afford the 1,4-adducts in high enantioselectivities. This regioselectivity could be ascertained by DFTstudies highlighting the crucial role of the imidazole ring. Thanks to the development of efficient protocols to regenerate the unsaturated 2-acyl-N-methylimidazole moiety, an iterative process has been developed ultimately leading to 3,5,7 all-syn or anti-anti polydeoxypropionate stereodiads.