Tertiary silyl lithium compounds

The synthesis of R R R SiLi compounds under vacuum (Evans, Jones and Rees, 1967) provides a contrast to the previous example, being very simple, and is a useful instance of the adaptation of a conventional method (Gilman and Lichtenwalter, 1958) to h.v.t. The objects of the syntheses were MejPhSiLi, MePhjSiLi and PhgSiLi whose reaction with 1,1-diphenyl-ethylene was to be studied. The preparation of all three organo-Li compounds was very similar, and the reaction is shown in Equation (5.2)  

The disilane was introduced through the side arm into vessel C and the whole apparatus evacuated with heating. The disilane was then sublimed into D which was sealed off at B. A known quantity of TFIF was distilled into D, from the THF supply H, after which the rig was sealed off at E and F. Previous to this, a film of Li had been deposited in A (Garst and Zabotny, 1965). The solution of the disilane in THF was run into A which was then sealed off at G. The reaction was left to continue at 0 °C for one week, and the final, filtered solution was stored in a sealed ampoule at —25 °C. 

The omission of details such as the making of the Li film, the filtering, or the exact manner of using the reagent, shows that Evans et al. assume a certain familiarity with h.v.t. on the part of their readers, in marked contrast to Vairon and Sigwalt. 

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Reductive cleavage of sulphides, selenides, and tellurides on Raney nickeP and cleavage by lithium in THE, leading to secondary or tertiary alkyl-lithium compounds, are useful synthetic operations novel variations are involved in the cleavage of dialkenyl sulphides with EtjSiH (giving low yields of silyl sulphides) and of alkenyl, aryl, and allyl sulphides and selenides with PPhj and... 

The best alkylating agents for silyl enol ethers are tertiary alkyl halides they form stable carbocations in the presence of Lewis acids such as TiCLj or SnCLj. Most fortunately, this is just the type of compounds that is unsuitable for reaction with lithium enolates or enamines, as elimination results rather than alkylation a nice piece of complementary selectivity. 

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