Single electron transfer in the phototransformations of β-ionone in the presence of electron acceptors

Abstract

Single electron transfer (SET) in the photoreaction of (E)-β-ionone (I) and its derivatives with electron acceptors (quinones) has been detected in acetonitrile by CIDNP techniques. Analysis of CIDNP data has shown that the radical cation of I is formed during its photolysis in the presence of chloranil (CA), 2,5-dichlorobenzoquinone, and 2,3-dichloro-5,6-dicyanobenzoquinone. In the presence of benzo- and duroquinones (DQ), the radical cation is generated from the isomer of I, α-pyran (II). Consideration of combined CIDNP, EPR and electrochemical data, and quantum chemical analysis has demonstrated that the radical cations of I and II do not undergo cis–trans isomerization. It was suggested that in the reaction under study, adducts of I and II with quinones are possible precursors of the isomerized (Z)-β-ionone. Data favoring formation of two types of adducts, 2+2 cycloadditions of CA to I, and ethers resulting from I and II and quinones (CA, DQ), have been obtained.