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

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 stereoselectivity on the ring size of the substrate using the ligand 1,2:5,6-di-O-cyclohexylidene-3,4-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.

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