Thermal rearrangements of unsaturated and strained organosilanes and their hydrocarbon counterparts
The flash vacuum pyrolysis (FVP) of 2-[superscript]2H-dimethyl-silylacetylene afforded ([superscript]2H-dimethylsilyl)acetylene. FVP of dimethylsilylphenylacetylene yielded mainly phenylacetylene. These results are consistent with the formation of silacyclopropene intermediates;The FVP of 1-phenylpropyne yielded phenylallene, indene, and phenylacetylene. 3-[superscript]13C-1-Phenylpropyne yielded indene which contained the [superscript]13C label at every position. The FVP 3-[superscript]13C-indene showed that the carbon label was not appreciably scrambled at carbons other than the 1 and 3 positions;1-[superscript]2H-Indene produces mainly 2-[superscript]2H- and 3-[superscript]2H-indene upon pyrolysis at low temperatures. At higher temperatures, 4-[superscript]2H, 5-[superscript]2H, 6-[superscript]2H-, and 7-[superscript]2H-indene are also formed by intramolecular rearrangements. The FVPs of [alpha],[beta],[beta]-trideuterostyrene, [alpha]-[superscript]2H-toluene, and 4-[superscript]2H-toluene show them to be thermally stable towards intramolecular rearrangements at both low and high temperatures. These results suggest that 1-[superscript]2H-indene undergoes the first reported thermally allowed 1,9-sigmatropic migration;Addition of thermally generated dimethylsilylene to 1,2-butadiene and 3-methyl-1,2-butadiene did not yield silacyclobutene but instead to 2-dimethylsilyl-1,3-butadiene and 2-dimethylsilyl-3-methyl-1,3-butadiene, respectively. However, the pyrolysis of thermal dimethylsilylene generator 1-methoxy-1,1,2,2,2-pentamethyldisilane in the presence of 1,2-propadiene did not yield any silicon containing adducts;The flash vacuum pyrolysis of 1-[superscript]2H-1-trimethylsilylcyclopropane resulted in the formation of 95% 2-[superscript]2H-3-trimethylsilylpropene and 5% 3-[superscript]2H-3-trimethylsilylpropene. This result is consistent with cleavage of the shorter C2-C3 cyclopropane bond being the major isomerization pathway.