Silicon−Carbon Unsaturated Compounds. 72. Thermolysis of Acylpolysilanes with Diphenylketene

The thermolysis of pivaloyl- and adamantoyltris(trimethylsilyl)silane (1 and 2) with diphenylketene in a sealed glass tube at 140 °C for 24 h afforded 2-tert-butyl- and 2-adamantyl-1,1-dimethyl-3-[methylbis(trimethylsiloxy)silyl]-4,4-diphenyl-1-silacyclobut-2-ene (6 and 7) in 44% and 50% isolated yields, respectively. Related thermolysis of mesitoyltris(trimethylsilyl)silane (3) with diphenylketene at 160 °C for 24 h, however, proceeded with high stereospecificity to give cis-3-diphenylmethylene-4-mesityl-2-trimethylsiloxy-2,4-bis(trimethylsilyl)-2-siloxetane (8) in 44% yield. When 8 was heated at 200 °C for 24 h, 1-mesityl-3,3-diphenyl-1-(trimethylsilyl)propadiene was obtained in 43% yield. Computational analyses for the formation of siloxetanes arising from addition of silenes to ketene and succesive isomerization of the siloxetanes thus formed, leading to the products, are described. The results of X-ray crystallographic analysis for the product 6 formed by the co-thermolysis of 1 and diphenylketene are reported.