Silylcarbenes 1,2-methyl shifts

Photolysis of l-methyl-2,3,4,5-tetraphenylsilacyclopentadienyldiazomethane (55) with an excess of methanol gave the diazirine 56 and the methanol adducts 59, 60 and 61 (equation 14)38. Products 59 and 60 appear to be derived from the methanolysis of silabenzene (46b), which could arise by a ring expansion of silacyclopentadienylmethyl-carbene (49b). On the other hand, compound 61 is the evident product of methanolysis of 5-silafulvene (57) formed by a methyl shift in 49b. Diazirine 56 was also found to produce silylcarbene under photochemical and thermal conditions and led to the same products 59,60 and 61. 

The complex reaction sequence shown in equation 34 might provide some rationalization. The formation of the silylcarbene 141 is suggested, based on experimental results from related reactions , but there is no evidence for the formation of 141 nor for a silylene intermediate. Thus, the transformation 137 142 might proceed via a dyotropic rearrangement as well. The facile 1,3-methyl shift in 2-trimethylsilylsilenes which interconverts 142 139 is well known from Wiberg -type silenes . 139 (R = i-Bu) is stable in solution at room temperature over days and isomerizes only slowly to 140 (R = t-Bu) which rapidly dimerizes giving a 1,3-disilacyclobutane . 

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