Ni(II) Tol-BINAP-Catalyzed Enantioselective Michael Reactions of β-Ketoesters and Unsaturated N-Acylthiazolidinethiones
摘要:
The enantioselective addition of beta-ketoesters to unsaturated N-acylthiazolidinethiones catalyzed by Ni(II) Tol-BINAP Lewis acid complexes is reported. Notable features of this reaction are its operation simplicity, the obviated need for the addition of an external base, and the ease with which the adducts are converted into a range of potentially useful derivatives. In particular, the dihydropyrone adducts are versatile scaffolds for further stereoselective elaboration.
Ni(II) Tol-BINAP-Catalyzed Enantioselective Michael Reactions of β-Ketoesters and Unsaturated N-Acylthiazolidinethiones
摘要:
The enantioselective addition of beta-ketoesters to unsaturated N-acylthiazolidinethiones catalyzed by Ni(II) Tol-BINAP Lewis acid complexes is reported. Notable features of this reaction are its operation simplicity, the obviated need for the addition of an external base, and the ease with which the adducts are converted into a range of potentially useful derivatives. In particular, the dihydropyrone adducts are versatile scaffolds for further stereoselective elaboration.
Significant levels of exo-selectivity (exo:endo = > 99:1 to 86:14) and enantioselectivity (95-82% ee) were obtained in the 1,3-dipolar cycloadditions of a number of nitrones with 3-(2-alkenoyl)-2-thiazolidinethiones, using the chiral binaphthyidiimine-Ni(II) complex (5-20 mol %), which was easily prepared form N,N'-bis(3,5-dichrolo-2-hydroxybenzylidene)-1,1'-binaphthyl-2,2'-diamine and Ni(ClO4)2(.)6H(2)O in CHCl3 in the presence of 4 angstrom molecular sieves, as a chiral Lewis acid catalyst.