New bidentate chiral phosphoramidites in copper-catalyzed asymmetric 1,4-addition of diethylzinc to cyclic alpha,beta-enones: enantioselective tandem1,4-addition-aldol reactions with 2-cyclopentenone

New bidentate phosphoramidites were prepared starting from alpha,alpha,alph a ',alpha ' -tetraphenyl-2,2-dimethyl-1,3-dioxolane-4,5-dimethanol (TADDOL) or 1,1 ' -bi-2-naphthol (BINOL) and either 1,2-ethylene- or 1,3-propylened iamine N,N ' -disubstituted with achiral or chiral groups. The use of these ligands in the copper-catalyzed enantioselective conjugate addition of die thylzinc to 2-cyclohexenone and 2-cyclopentenone afforded products with e.e .s of up to 89 and 83%. respectively. (C) 2001 Elsevier Science Ltd. All ri ghts reserved.