Precise Cross-Coupling Control during Oxidative Reaction and Polymerization with a Lewis Acid Catalyst

Abstract

The oxidative coupling between 2-naphthol and 3-hydroxy-2-naphthoic acid derivatives with a copper catalyst in an O₂ atmosphere in the presence of a catalytic amount of a Lewis acid was carried out. Both the copper and Lewis acid catalysts significantly affected the cross-coupling and stereo-selectivities, and the cross-coupling specific reaction proceeded to effectively afford a C₁ symmetrical 1,1′-bi-2-naphthol derivative, when using ytterbium trifluoromethanesulfonate [Yb(OTf)₃] as a Lewis acid. This novel binary catalyst system was used for the oxidative cross-coupling polymerization producing poly(binaphthol)s. For example, the polymerization of methyl 3,7-dihydroxynaphthalene-2-carboxylate using Di-μ-hydoxo-bis[(N,N,N′,N′-tetramethylethyienediamine) copper(II)] chloride at room temperature in an O₂ atmosphere in the presence of Yb(OTf)₃ proceeded to give a polymer with a cross-coupling selectivity of 92%, while the polymerization in the absence of the Lewis acid gave a low molecular weight oligomer having a cross-coupling unit ratio of 80%.