Access to 2′-substituted binaphthyl monoalcohols via complementary nickel-catalyzed kumada coupling reactions under mild conditions: Key role of a P,O ligand

摘要

Two complementary Kumada coupling methods for the conversion of monotriflated 1,1′-binaphthalene-2,2′-diol (BINOL) into 2′-substituted binaphthyl monoalcohols under mild conditions are reported. A protocol using NiCl_2(dppe), in combination with an improved preparation of the monotriflate, is effective for 1,1′-binaphthalene-2-ols containing unsubstituted or electron-poor aryl or benzyl 2′-substituents. An alternative procedure, using a potentially hemilabile-bidentate phosphinan-4-ol ligand, is superior for products containing neopentyl or electron-rich aryl 2′-substituents. The obtained binaphthyl alcohols represent potentially useful synthons for chiral ligands and auxiliaries.