Single electron transfer in the phototransformations of beta-ionone in thepresence of electron acceptors

Single electron transfer (SET) in the photoreaction of (E)-beta-ionone (I) and its derivatives with electron accepters (quinones) has been detected in acetonitrile by CIDNP techniques. Analysis of CIDNP data has shown that th e radical cation of I is formed during its photolysis in the presence of ch loranil (CA), 2,5-dichlorobenzoquinone, and 2,3-dichloro-5,6-dicyanobenzoqu inone. In the presence of benzo- and duroquinones (DQ), the radical cation is generated from the isomer of I, alpha-pyran (II). Consideration of combi ned 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 o f I and II with quinones are possible precursors of the isomerized (Z)-beta -ionone. Data favoring formation of two types of adducts, 2 + 2 cycloadditi ons of CA to I, and ethers resulting from I and II and quinones (CA, DQ), h ave been obtained. (C) 1999 Elsevier Science S.A. All rights reserved.