2,2'-Bis(diarylstibano)-1,1'-binaphthyls (BINASbs); a useful chiral ligand for palladium-catalyzed asymmetric allylic alkylation, and the structure of a BINASb-PdCl_2 complex

摘要

The first attempt to use enantiopure antimony ligands 1-4 as a chiral auxiliary was successfully accomplished in a palladium-catalyzed asymmetric alkylation of 1,3-diphenylprop-2-ene-1-yl acetate with dimethyl malonate. Under the optimized conditions, the allylation product can be obtained with up to 96% ee in 84% chemical yield by use of enantiopure C_2-symmetric 2,2'-bis[di(p-tolyl)stibano]-1,1'-binaphthyl [BINASb(p-Tol)] 4a as a chiral ligand with O-bis(trimethylsilyl)acetamide (BSA) and potassium acetate. The structure of the intermediary BINASb-PdCl_2 complex was elucidated by single crystal X-ray analysis, implying that the BINASb should work as a bidentate chiral ligand in the reaction.