Syntheses via Metallation of CH2 or CH Groups

The underlying principle in this method is the metallation of a skeletal C atom in carbosilanes by organolithium compounds. As examples, (Me2Si— 112)3 and the Si-methylated 1,3,5,7-tetrasilaadamantane were investigated (Chapt. I1I.4). 

In this way, (Me2Si — 112)3 is caused to react with BuLi to produce the mono-lithiated compound  

The reaction is so fast that it is practically complete at the end of the addition of the lithiating reagent. Trapping the Li-intermediate by means of suitable Si-functional compounds enabled the isolation of skeletal -silylated compounds in approximately 70-80% yield. The use of KO Me3 in THF has the advantage of short reaction times and relatively simple work-up. However, the application remains limited to Me Ad and Si-methylated carbosilanes because of competing side reactions. For example, Me3BrAd reacts to form Me3(Mc3 —0)Ad. 

The principal metallation reactions proceed without difficulty to the formation of the successive compounds 

Compound 178, an oily colourless liquid can also be obtained in a 73 % yield in an alternative way  

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