Silicon-carbon unsaturated compounds. 70. Thermolysis and photolysis of acylpolysilanes with mesitylacetylene

The thermolyses of adamantoyl-, pivaloyl-, and mesitoyltris(trimethylsilyl)silane (1a, 1b, and 1c) with mesitylacetylene were investigated. The cothermolysis of la and mesitylacetylene in a sealed glass tube at 160 degrees C for 24 h afforded the 1:3- and 1:4-adduct, (1E,4Z)-5-adamantyl-2,4-dimesityl-1-[(mesitylethynyl)bis(trimethylsilyl)silyl]-5-(trimethylsiloxy)penta-1,4-diene (3a) and (1E,4Z,6Z)-7-adamantyl-2,4,6-trimesityl-1-[(mesitylethynyl)bis(trimethylsilyl)silyl]-7-(trimethylsiloxy)hepta-1,4,6-triene (4a), in 33% and 48% yields. Similarly, the thermolysis of 1b and 1c with mesitylacetylene also gave 1:3- and 1:4-adducts (3b and 3c) in 33% and 32% yields and (4b and 4c) in 46% and 19% yields, respectively. The thermolysis of la with a 1:1 mixture of mesitylacetylene and tert-butylacetylene at 160 degrees C for 24 h afforded 3a and 4a in 30% and 44% yields, respectively. No products arising from the reaction of la with tert-butylacetylene were detected. The reaction of la with mesitylacetylene in the presence of a large excess of dimethylphenylsilane at 160 degrees C for 24 h gave 3a and 4a in 19% and 27% yields, respectively. In the presence of tris(trimethylsilyl)silane, however, the thermolysis of la with mesitylacetylene produced (Z)-2-mesityl-1-[tris(trimethylsilyl)silyl]-ethene in high yield, and the starting compound 1a was recovered. The results of radical addition of tris(trimethylsilyl)silane to mesitylacetylene and tert-butylacetylene have also been reported. Irradiation of la in the presence of 1 equiv of mesitylacetylene in hexane with a high-pressure mercury lamp gave a 1:2-adduct, 2-[(E)-(2-adamantyl-1-mesityl-2-trimethylsiloxy)ethenyl]-3-mesityl-1,1-bis(trimethylsilyl)-1-silacyclobut-3-ene (Ca), 3a, and 4a in 6%, 4%, and 2% yields, respectively, in addition to 67% of the unchanged starting compound la. The results of X-ray crystallographic analysis for 3a and 4a are described.