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

Thermolysis of pivaloyltris(trimethyisilyl)silane (1a) with tert-butyldimethylsilylacetylene at 120 degrees C gave 2-tert-butyl-3-tertbutyldimethylsilyl-2-trimethylsiloxy-1, 1-bis(trimethylsilyl)-1-silacyclobut-3-ene (2a). Similar treatment of adamantoyltris(trimethylsilyl)silane (1b) at 120 degrees C produced 2-adamantyl-3-tert-butyldimethylsilyl-2-1,1-bis(trimethylsilyl)-1-silacyclobut-3-ene (2b). Thermolysis of la with tert-butyldimethylsilylacetylene at 160 degrees C, however, gave 1-tert-butyl-1-(tertbutyldimethylsilyl)-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 degrees C produced [2 + 2] cycloadducts arising from the reaction of silenes generated thermally from la and Ib with mono(silyl)acetylenes analogous 2a and 2b, along with small amounts of 1:2 adducts. At 160 degrees 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. (C) 2000 Elsevier Science S.A. All rights reserved.