Thermal cycloaddition of N-arylmaleimides to phenols: the convenient synthesis of bicyclo[2.2.2]oct-2-en-5-one and tricyclo[3.3.0.02,8]octan-2-one derivatives from phenols

Abstract

Monohydric phenols undergo 2,5-thermal cycloaddition of N-substituted maleimides to give bicyclo[2.2.2]oct-2-en-5-ones. Homopolymers of the maleimides are also concurrently formed, except in the case of N-(2,6-dimethylphenyl)maleimide: this is the preferred addend and gave a 63% yield of the 2,5-adduct as a mixture of exo and endo isomers. U.v. irradiation in acetone of the diester (16) derived from the endo adduct of phenol and N-phenylmaleimide gave the tricyclo[3.3.0.0^2,8]octan-3-one (17) in quantitative yield.