Oxidative coupling of phenols. Part 10. The role of steric effects in the formation of C–O coupled products

Abstract

The formation of C–O coupled products in the oxidative coupling of phenols is hindered by bulky ortho-substituents in the aryloxyl radical intermediates as shown by the predominant formation of the ortho-ortho-C–C coupling products in the oxidation of o-t-butyl- and 2,4-di-t-butyl-phenol. 3,5-Di-t-butyl-phenol gives exclusively the ortho-O-dimeric product as steric effects prevent the sandwich approach of two aryloxyl radicals necessary for C–C coupling.