Silicon–carbon unsaturated compounds. 62. Reactions of silenes produced thermally from pivaloyl- and adamantoyltris(trimethylsilyl)silane with mono(silyl)acetylenes

Thermolysis of pivaloyltris(trimethylsilyl)silane (1a) with tert-butyldimethylsilylacetylene at 120°C gave 2-tert-butyl-3-tert-butyldimethylsilyl-2-trimethylsiloxy-1,1-bis(trimethylsilyl)-1-silacyclobut-3-ene (2a). Similar treatment of adamantoyltris(trimethylsilyl)silane (1b) at 120°C produced 2-adamantyl-3-tert-butyldimethylsilyl-2-trimethylsiloxy-1,1-bis(trimethylsilyl)-1-silacyclobut-3-ene (2b). Thermolysis of 1a with tert-butyldimethylsilylacetylene at 160°C, however, gave 1-tert-butyl-1-(tert-butyldimethylsilyl)-3-[(trimethylsiloxy)bis(trimethylsilyl)silyl]-1,2-propadiene (3a), along with 1:2 adduct (4a). Similar reaction of 1b gave 1-adamantyl-1-(tert-butyldimethylsilyl)-3-[(trimethylsiloxy)bis(trimethylsilyl)silyl]-1,2-propadiene (3b) similar to 3a, together with 1:2 adduct (4b). Thermolysis of 1a and 1b in the presence of dimethylphenylsilylacetylene or triphenylsilylacetylene at 120°C produced [2+2] cycloadducts arising from the reaction of silenes generated thermally from 1a and 1b with mono(silyl)acetylenes analogous 2a and 2b, along with small amounts of 1:2 adducts. At 160°C, the similar treatment of 1a and 1b afforded propadiene derivatives arising from the ring opening reactions of [2+2] cycloadducts, in addition to 1:2 adducts.