Silicon–carbon unsaturated compounds. 77. Thermal behavior of cis- and trans-1-silacyclobut-3-ene formed from pivaloyl[tert-butylbis(trimethylsilyl)]silane and tert-butylacetylene

The reaction of tert-butylbis(trimethylsilyl)silyl potassium with pivaloyl chloride gave pivaloyl[tert-butylbis(trimethylsilyl)]silane (1) in 89% yield. The cothermolysis of 1 with tert-butylacetylene at 140 °C for 24 h produced the mixture consisting of cis- and trans-1,2,3-tri(tert-butyl)-2-(trimethylsiloxy)-1-(trimethylsilyl)-1-silacyclobut-3-ene (cis-2 and trans-2) in a ratio of 0.7: 1, in 88% combined yield. The thermolysis of the mixture, cis-2 and trans-2, at 250 °C for 24 h proceeded to give trans-1,2,4-tri(tert-butyl)-1-(trimethylsiloxy)-2-(trimethylsilyl)-1-silacyclobut-3-ene (4) as a single product in 96% yield. Similar treatment of cis- and trans-2 at 190 °C for 15 h afforded silylcyclopropene 3 quantitatively, which underwent further isomerization at 250 °C to give trans-1-silacyclobut-3-ene 4 in quantitative yield.

The thermolysis of the mixture consisting of cis-2 and trans-2 at 190 °C produced silylcyclopropene 3 as the sole product. Similar thermolysis of 3 at 250 °C proceeded with high stereospecificity to give trans-1-silacyclobut-3-ene 4 in quantitative yield.Figure optionsDownload as PowerPoint slideHighlights
► New cis- and trans-1-silacyclobut-3-enes were synthesized.
► The thermolysis of them at 190 °C produced silylcyclopropene.
► At 250 °C, it underwent isomerization to give trans-1-silacyclobut-3-ene.