SEMICONDUCTOR-CATALYZED PHOTOADDITION - GAMMA,DELTA-UNSATURATED AMINES FROM CYCLOPENTENE AND SCHIFF-BASES

Irradiation of methanolic cadmium sulfide suspensions in the presence of Schiff bases and cyclopentene opens an easy access to new gamma,del ta-unsaturated amines. Their formation can be described as a kind of p aired photoelectrolysis induced by the photogenerated electron-hole pa ir trapped at reactive surface sites of CdS. At the reductive site the imine is converted to an alpha-aminobenzyl radical by a proton-couple d electron transfer, while at the oxidative site cyclopentene is trans formed to the cyclopentenyl radical through deprotonation of the inter mediate radical cation. C-C coupling of these radicals affords the add ition products. Competitive dimerisation of the radicals produces hydr odimers of the imines and dehydrodimers of the olefin, as demonstrated in the case of 1-phenylcyclohexene. Using optical active imines, we f ound no significant diastereoselectivity. In the absence of an olefin the alcoholic solvent was added to the imine. The molecular structure of one hydrodimer was resolved by X-ray analysis. When CdS/Pt was used as photocatalyst, hydrolysis products of the imine were formed, sugge sting involvement of an intermediate OH radical.