Semiconductor-catalysed photoaddition:

Article abstract of DOI:10.1002/cber.19961290808

Irradiation of methanolic cadmium sulfide suspensions in the presence of Schiff bases and cyclopentene opens an easy access to new γ,δ-unsaturated amines. Their formation can be described as a kind of paired photoelectrofysis induced by the photogenerated electron-hole pair trapped at reactive surface sites of CdS. At the reductive site the imine is converted to an a-arninobenzyl radical by a proton-coupled electron transfer, while at the oxidative site cyclopentene is transformed to the cyclopentenyl radical through deprotonation of the intermediate radical cation. C-C coupling of these radicals affords the addition products. Competitive dimerisation of the radicals produces hydrodimers of the imines and dehydrodimers of the olefin, as demonstrated in the case of l-phenylcyclohexene. Using optical active imines, we found no significant diastereoselectivity. In the absence of an olefin the alcoholic solvent was added to the inline. 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, suggesting involvement of an intermediate OH radical. VCH Veagsgcsellschaft mbH, 1996.