Surface photochemistry. A symmetry forbidden [1,3] sigmatropic hydrogen shift mediated by CdS

Abstract Excitation of CdS in the absence of oxygen in the presence of cyclic derivatives of diphenylcyclobutene gave the cation radical of the latter which underwent a reversible double bond migration. The structures of the products were established on the basis of spectral data ( 1 H, 13 C NMR, MS, UV). Tests were performed to show that the reaction proceeds, at least in part, intramolecularly, and, therefore, represents the first example of a suprafacial [1,3] sigmatropic hydrogen shift via a radical cation. This suprafacial pathway is symmetry forbidden in closed shell systems. Oxidation products were isolated when the irradiation was performed in an aerated system. The use of excited 9,10-dicyanoanthracene as an electron acceptor did not lead to the expected products; instead the sensitizer was consumed and two thermally unstable adducts were isolated. Their formation could be quenched by 1,2,4-trimethoxybenzene.