Study of the oxidative degradation of 2,2,3,4,5-pentaphenyl-3- cyclopentenone by various oxidants ; and, [1,5]-sigmatropic phenyl rearrangements in 2- and/or 5-(p- or m-substituted phenyl)-1,3,4-triphenyl-2,4- cyclopentadien-1-ols: electronic effects at the migration terminus

Abstract

A Harmnett series comprised of seven 2- and/or 5-(p- or m-substituted phenyl)-1,3,4-triphenyl-2,4-cyclopentadien-l-ols was prepared and the ratio of the two-product mixture resulting from their thermal [1,5]- sigmatropic phenyl rearrangements was determined. In this system phenyl could migrate toward either of two positions, and the effect of the substituents upon the direction of migration was investigated to determine the extent of electronic effects in this neutral sigmatropic rearrangement. The results of these rearrangements are used to discuss the proposed transition state for phenyl rearrangements in the pentaphenylcyclopentadienol system. A strictly neutral transition state is proposed.

In addition, the oxidative degradation of 2,2,3,4,5-pentaphenyl-3-cyclopenten-l-one by various oxidants was investigated. This substrate was found to be inert to all the reagents examined, with the exception of diacetyl chromate. The action of this oxidant upon the substrate produced an equimolar mixture of benzil, benzophenone, and benzoic acid in an overall yield of 40 to 42 percent.