Sulfur—silicon bonds reactions with

The silicon-halogen, silicon-oxygen, and silicon-sulfur bonds of the haiogenosil-anes, siiyl ethers, and siiyi thioethers are cleaved by reaction with LAH, AIH3, or DIBAH, and the corresponding siiyl hydrides are obtained [CGI, CG2]. Ultrasound activation can be applied [LG2] (Figure 5.9), Anionic pentacoordinated silicon compounds are reduced to hydrogenosilanes by LAH or DIBAH [BC6]. 

You have now seen how enols and enolates react with electrophiles based on hydrogen (deuterium), carbon, halogens, silicon, sulfur, and nitrogen. What remains to be seen is how new carbon-carbon bonds can be formed with alkyl halides and carbonyl compounds in their normal electrophilic mode. These reactions are the subject of Chapters 26-29. We must first look at the ways aromatic compounds react with electrophiles. You will see similarities with the behaviour of enols. 

While organometallic reagents condense with N-substituted imines (Schiff bases) to afford, after hydrolysis, good yields of substituted amines, the reaction with N-unsubstituted imines (203) derived from ammonia (which are easily hydrolyzed and self condense) is not synthetically useful. As a result, the use of masked imines containing labile silicon- or sulfur-Hiitrogen bonds, such as N-trimethylsilyl-imines (204) or N-sulfenimines (205), has been explored. 

In the reaction with thiophene 32, the disilathiirane 38 was unexpectedly formed in about 50 % yield by way of sulfur extraction. The X-ray structure analysis of the disilathiirane 38 revealed a very short Si-Si bond length of 230.5 pm and an almost planar environment at the silicon atoms (angular sum C-Si-C + C-Si-Si + Si-Si-C = 358 7°) [10]. These features are typical for related three-membered rings of this type and were also observed for other disilathiiranes [13]. As illustrated by the isolation of the 1,2-disilacyclohexadiene 39, sulfur abstraction from 32 seems to be initiated by [2+4]-cycloaddition of disilene 3. The bicyclic compound 40 is most likely formed by photoisomerization of 39 [14]. 

Reaction with ei,fi-Unsaturated Sulfoxides. The reaction of TMSI with a, -unsaturated sulfoxides in chloroform at ambient temperature is a mild, efficient, and general method for the preparation of carbonyl compounds (eq 63). The proposed reaction mechanism is shown in eq 63. Formation of a strong oxygen-silicon bond is followed by reduction of the sulfur function and oxidation of iodide to iodine, the latter precipitating in chloroform. The trimethylsiloxy anion attacks the unsaturated carbon linked to the sulfur function, which leaves the substrate, allowing the formation of the sUyl enol ether species. Finally, hydrolysis converts the silyl enol ether into the carbonyl compound. ... 

None of these rubbers has carbon-carbon double bonds. Consequently, they have relatively good aging properties, but, on the other hand, they cannot be vulcanized by the classical sulfur process. For this reason, some of these rubbers are cross-linked with the aid of peroxides, and, in this case, by polymerization of vinyl groups in the case of some silicone rubbers or by free radical transfer reactions in the case of ethylene/vinyl acetate or acrylic rubbers. Other speciality elastomers are cross-linked by reaction with diamines, for example, in the cases of acrylic, epichlorohydrin and fluorine rubbers. 

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