Synthesis of C-Bridged Spiro Carbosilanes

The comparably convenient access to compound 228 opens a way to the synthesis of spiro carbosilanes [78]  

Similarly, reaction of compound 2 with (BrMe Si—CH2)2SiMc2 yielded the spiro compound 237 [78]  

C-metallation of compound 230 is of interest in subsequent syntheses. The lithiated intermediate 238 reacts by abstraction of lithium bromide, forming a reactive intermediate 239 which then dimerizes to produce compound 240 [78]  

The formation of compound 240 occurs as a result of a very selective reaction path, resulting in an 85% yield. 

The four-membered ring in compound 240 displays an unusual stability. It is cleaved neither by HBr nor Br2, whereas the same ring in (Me2Si—CH2)2 readily undergoes such cleavage at —78 °C. This unsual stability is also displayed by 1,1,3,3-tetramethyl-2,2,4,4-tetrakis(trimethylsilyl)-l, 3-disilacyclobutane [79]. 

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