The photochemistry of trans-1,4,4,4-tetraphenyl-but-2-en-1-one: A highly efficient aryl migration (type B) enone photorearrangement

Abstract

Photolysis of trans-1,4,4,4-tetraphenylbut-2-en-1-one (3) in acetonitrile or benzene leads to trans–cis isomerization (7) along with rearrangement to trans-1-benzoyl-2,2,3-triphenylcyclopropane (8). Formation of the latter product represents a new example of the aryl migration (type B) enone photorearrangement reaction first reported by Zimmerman and co-workers for 4,4-diphenylcyclohex-2-en-1-one (1). The quantum yield in the case of enone 3 (0.4) is approximately 10 times greater than that for 4,4,-diphenylcyclohex-2-en-1-one, a result that is ascribed to steric acceleration of phenyl migration from the triphenylmethyl group plus greater resonance stabilization of the intermediate biradical.Key words: photochemistry, mechanism, rearrangement, aryl migration, enone, di-π-methane.