PHOTOCHEMICAL 1,3-STANNYL REARRANGEMENT OF ALLYLIC STANNANES

The photochemical 1,3-stannyl rearrangement of allylic stannanes has b een investigated. The photorearrangement of (E)-cinnamyl(triphenyl)sta nnane is not observed in benzene under anaerobic conditions, while the photoinduced 1,3-stannyl migration takes place in the same solvent un der aerobic conditions, or in the presence of organic halides or a rad ical-trapping agent to give a photoequilibrium mixture of the cinnamyl stannane and its branched regioisomer, 1-phenylprop-2-enyl(triphenyl)s tannane, with the latter predominating. Cinnamyl(trialkyl)stannanes an d their homologues also afford the corresponding branched allylstannan es under similar photochemical conditions. These 1,3-stannyl migration s proceed intramolecularly via cinnamyl pi-pi excitation in competiti on with homolytic (cinnamyl)C-Sn bond fission. In contrast, the 1,3-st annyl migration of crotyl-and prenyl-(tributyl)stannanes is not effici ent, but their triphenyl or dibutylphenyl derivatives undergo the 1,3- rearrangement via excitation of the phenyl group(s) on the tin atom to give a regioisomeric mixture of the starting linear tin compounds and the branched ones with the former predominating.