The thermolysis of pivaloyl- and adamantoyltris(trimethylsilyl)silane (1a and 1b) with bis(trimethylsilyl)butadiyne and bis(dimethylphenylsilyl)butadiyne at 120°C gave regiospecifically 2-trimethylsiloxy-3-silylethynyl-1-silacyclobut-3-ene derivatives (2a, 2b and 3a, 3b), arising from the reaction of silenes generated thermally from 1a and 1b with the butadiynes. Similar treatment of 1a and 1b in the presence of bis(trimethylsilyl)butadiyne and bis-(dimethylphenylsilyl)butadiyne at 160 °C gave 2,5-dihydro-1,2-oxasilole derivatives (4a, 4b and 5a, 5b). When 2a and 2b were heated in the presence of methanol at 160 °C, methanol adducts 6a and 6b were obtained, respectively, as the sole product. The ring-opening processes of 2a and the regiochemistry of [2 + 2] cycloaddition of the silene with bis(silyl)-butadiyne and bis(silyl)but-1-en-3-yne are discussed on the basis of theoretical treatment, The thermolysis of 1a and 1b with bis(tert-butyldimethylsilyl)butadiyne at 160 °C produced [2 + 2] cycloadducts (7a and 7b). With bis(tert-butyldimethylsilyl)butadiyne at 220 °C, 1a and 1b gave 2,5-dihydro-1,2-oxasilole derivatives (8a and 8b). The reaction of 1a and 1b with (E)-1,4-bis(dimethylpnenylsilyl)but-1-en-3-yne and (E)-1,4-bis(pentamethyldisilanyl)-but-1-en-3-yne at 120 °C produced regiospecifically 2trimethylsiloxy-3-[trans-(silyl)ethenyl] -1-silacyclobut-3-ene derivatives (9a, 9b and 10a, 10b). At 200 °C, similar treatment of 1a and 1b with silyl-substituted but-1-en-3-ynes afforded 2,5-dihydro-1,2-oxasilole derivatives (11a, 11b and 12a, 12b, respectively). UV-vis absorption and fluorescence spectra have been reported.
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