Asymmetric Synthesis of Axially Chiral Biaryls by Nickel-Catalyzed Grignard Cross-Coupling of Dibenzothiophenes

摘要

Catalytic asymmetric Grignard cross-coupling of 1,9-disubstituted dibenzothiophenes (6a―c) and dinaphthothiophene (6d) with aryl- and alkyl-Grignard reagents (7) proceeded with high enantio-selectivity (up to 95% ee) in the presence of a nickel catalyst (3―6 mol %) coordinated with 2-diphenylphosphino-1, 1'-binaphthyl (H-MOP) or oxazoline-phosphine ligand (i-Pr-phox) in THF to give 2-mercapto-2'-substituted-1, 1'-biphenyls (8a―c) and 2-mercapto-2'-substituted-1, 1'-binaph-thyls (8d) in high yields. The mercapto group in the axially chiral cross-coupling products was converted into several functional groups by way of the methylsulfinyl group. The rate of flipping in dinaphthothiophene was measured by variable-temperature ~(31)P NMR analysis of methyl-phenylphosphinyldinaphthothiophene derivative (21).