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 1a and mesitylacetylene in a sealed glass tube at 160 °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 1a with a 1:1 mixture of mesitylacetylene and tert-butylacetylene at 160 °C for 24 h afforded
3a and 4a in 30% and 44% yields, respectively. No products arising from the reaction of 1a
with tert-butylacetylene were detected. The reaction of 1a with mesitylacetylene in the
presence of a large excess of dimethylphenylsilane at 160 °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 1a 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 1a 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 1a. The results of X-ray crystallographic analysis for 3a and 4a are described.