Silacyclopropenes 1,2-hydrogen shifts

The photolysis of tris(trimethylsilyl)phenylsilane in the presence of a series of alkynes alforded the silacyclopropene through silylene addition to the triple bond. Those obtained from monosubstituted alkynes underwent photochemical isomerization to the disilanyl-alkyne through a 1,2-hydrogen shift (Scheme 48) (80JOM(190)117). Disubstituted alkynes form silirenes that can be isolated by preparative GLC. 

Similar photolysis of 20 in the presence of 1-trimethylsilylpropyne produces a silacyclopropene in 33% yield. In this case, small amounts of two other compounds, l-trimethylsilyl-l-(r-phenyl-2, 2, 2 -trimethyldi-silanyl)propadiene (2% yield) arising from a 1,3-hydrogen shift of the initially formed silacyclopropene and l-bis(trimethylsilyl)phenylsilylpro-pyne (2% yield), are also obtained. Formation of the latter compound can be best explained in terms of another type of photochemical migration in-... 

Photolytic generation of phenyl(trimethylsilyl)silylene in the presence of terminal alkynes gave silacyclopropenes, which upon further irradiation, rearranged to disilylethyne derivatives (79) via a [l,2]-hydrogen shift (three examples, 14-40% yield), (Scheme 23) <77JOM(l3l)Cl5, 79JOM(i79)377, 80JOM( 190)117 >. 

However, when the silacyclopropene was derived from a silylalkyne, 1,3-hydrogen shifts, 1,2-hydrogen shifts and 1,2-trimethylsilyl shifts were photochemically induced leading to silylallenes and silylalkynes, respectively23 (equation 13). 

Irradiation of tris(trimethylsilyl)phenylsilane in the presence of hex-l-yne and other alkynes affords the corresponding silacyclopropenes. Those silacyclopropenes formed from monosubstituted acetylenes undergo further photoisomerization to disilanylacetylenes via a 1,2-hydrogen shift. Two competing pathways have been observed on irradiation of the disilabicyclo[2.2.2]octa-2,5-diene... 

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