Cu-catalyzed enantioselective conjugate addition of diethylzinc to cyclic enones with chiral phosphite ligands derived from 1,2 : 5,6-di-O-cyclohexylidene-D-mannitol

摘要

A new and readily in situ prepared catalytic system of copper salts with chiral P,N-ligands or aryl diphosphite ligand, which derived from 1,2:5,6-di-O-cyclohexylidene-D-mannitol, 1,1'-binaphthol, and phenyl isocyanate derivatives, were successfully employed in the enantioselective conjugate additions of diethylzinc to cyclic enones with up to 71% ee. Two notable cooperative effects of the stereochemistry of the ligands on the enantioselectivity were observed in the reactions: one between the phenylcarbamate substituent and the axially chiral binaphthyl moiety; another between the stereogenic centers of mannitol and the chiral binaphthol substituents. A significant dependence of the product yield and stereo selectivity on the ring size of the substrate using the ligand 1,2:5,6-di-O-cyclohexylidene3,4-bis [(S)-1,1'-binaphthyl-2,2'-diyl]phosphite-D-mannitol was also observed: 71% ee for 2-cyclopentenone, 62% ee for 2-cyclohexenone, and 40% ee for 2-cycloheptenone.