Influence of the Position of tert-Butyl Substituents on Reactivity of Quinone Dimers Yielding Dibenzofuran-1,4-diones

Abstract

Reactivity of two isomeric quinone dimers, 5,5'-di-tert-butyl-2,2'-bisbenzoquinone (2) and 6,6'-di-tert-butyl-2,2'-bisbenzoquinone (3) have been compared. Both quinone dimers underwent thermal cyclization in ethanol to give dibenzofuran-1,4-diones exclusively, the reaction proceeding faster for 3 than for 2. Molecular modeling analysis indicates that the different reactivity should be explained in terms of the steric hindrance of tert-butyl group in 2, which prevents approaching of solvent molecules to C=O moiety so that the solvent-assisted proton transfer occurs more slowly.