Silicon–carbon unsaturated compounds. 68. Reactions of silenes produced thermally and photochemically from acylpolysilanes with diketones

The reactions of the silenes produced thermally from (Me3Si)3SiCOR (1a–1d; R=t-Bu, Ad, Ph, and Mes) with benzil in a sealed glass tube at 140 °C gave the respective five-membered cyclic compounds, 2,5-dioxa-1-silacyclopent-3-enes (2a–2d) in high yields. The silenes from 1a–d also reacted with 4,4′-dimethylbenzil to give the 2,5-dioxa-1-silacyclopent-3-ene derivatives. The photolysis of 1a and 1b in the presence of benzil in a benzene solution gave the respective products, 3,6-dioxa-1-silacyclohex-4-enes (3a and 3b) arising from [2+4] cycloaddition in high yields. The thermolysis of 3a and 3b in a sealed tube at 140 °C afforded 2a and 2b, respectively, in quantitative yields.