Enantioselective Cu-catalyzed 1,4-additions of organozinc and Grignard reagents to enones: exceptional performance of the hydrido-phosphite-ligand BIFOP-H

Enantioselective Cu-(I),Cu-(II)-(i.e. CuCl, CuCl2, Cu(OTf)(2))-catalyzed 1,4-additions of organozinc, i.e. (Et, Me)(2)Zn, and Grignard reagents, i.e. (Et, Me)MgBr, to chalcone, cyclohexenone and chromone are studied, employing fencholate-based phosphorus ligands, e.g. biphenyl-2,2-bisfenchyl hydrido phosphite = BIFOP-H. The CuCl<bold>BIFOP</bold>-H-catalyzed 1,4-addition of Et2Zn to chalcone yields up to 93% and 99% ee, exceeding established BINOL- and TADDOL-based phosphoramidite ligands. Remarkably, CuCl performs better in 1,4-additions to chalcone (CuCl: 76% ee; Cu(OTf)(2): 49% ee; CuCl2: 42% ee) while Cu(OTf)(2) performs better in 1,4-additions to cyclohexenone (Cu(OTf)(2): 65% ee; CuCl: 20% ee). The computation of the reaction pathway is done for the Cu-I-catalyzed 1,4-addition to chalcone (Cu-II will be in situ reduced to Cu-I by a reagent, TPSS-D3(BJ)/def2-TZVP//B3LYP-D3(BJ)/def2-SVP) for six different model ligands, i.e. (MeO)(2)P-X (X = H, F, Me, OMe, NMe2 and PMe3). Origins of enantioselectivities are analyzed (M06-2X-D3/def2-TZVP//B3LYP-D3(BJ)/def2-SVP) for transition structures of the 1,4-methylation of chalcone with the Cu<bold>BIFOP</bold>-H catalyst and explain the experimentally observed (R)-enantiomer's preference.