Trimethylsilylation, electrochemical reactions

S-Trimethylsilyl sulphones, reactions of 629 Trisulphones, electrochemical reactions of 1028-1030... 

Mercaptoethanol reacts with trimethylsilyl enol ethers to give oxathiolans of the parent ketones. The anodic dimerization of enol ethers to give ketals of 1,4-dicar-bonyl compounds, has been studied. The electrochemical reaction is first order with respect to enol ether, and zero order with respect to the solvent, methanol. These data, together with the observed tail-to-tail coupling, indicate a reaction via radical intermediates. ... 

Electrochemical oxidation of l-(trimethylsilyl)dienes in MeOH affords 129 in moderate to satisfactory yield. It is worth noting that the reaction shows some diastereoselectivity (equation 109)1". 

Polymeric sulfur lutride (or polythiazyl) (2) was first reported in 1910. It is prepared by the solid-state polymerization of S2N2 at 0°C over several days (see Section 5.1.3). The polymer is also obtained in high yield from the reaction of (NSC1)3 with trimethylsilyl azide in acetoiufrile or by the electrochemical reduction of S5N5+ salts. 

Reduction of an aryl halide at a cadmium-modified nickel cathode in DMF containing TBABF4 leads to a formylation reaction between aryl carbanions and the solvent [186]. Two papers [187,188] have appeared in which reduction of aryl halides gives an aryl carbanion, which, by acting as a base to deprotonate a suitable nitrile, can cause coupling of the nitrile with esters, aldehydes, and ketones. Electrochemical trimethylsilylation of aryl halides can be effected at a stainless-steel or carbon-cloth cathode in THF-HMPA containing TEABF4 and trimethylchlorosilane [189]. 

A unique acceptor, 5,6-difluoro-2-alkyl-4,7-di(thiophen-2-yl)-2H-benzo-[d][l,2,3]triazole, i.e., FTAZ, structurally similar to the DTflBT, has distinctly different electrochemical properties from those of DTifBT. The alkylation of the central nitrogen in fluorinated benzotriazole is suggested to be carried out in polar aprotic solvents such as DMF to promote the Sn2 reaction. However, typical brominations of the alkylated FTAZ with bromine ended with low yields and a new route was thus developed. The 4 and 7 positions of fluorinated benzotriazole are first deprotonated by a non-nucleophilic base, LDA, and then quenched by trimethylsilyl chloride (TMSCl). The as-formed C Si bonds are more activated than the original C-H bonds so that the alkyl FTAZ benzotriazole can then be successfully brominated (Scheme 15.6). ... 

Under electrochemical reduction conditions allyl acetates undergo Pd-catalyzed reduction to give alkenes in good yield (Scheme 1). The reaction may proceed via two-electron (2 e) reduction of the rr-allylpalladium intermediate. The allyl anion thus formed is protonated selectively at the terminal position to provide an internal alkene predominantly. In the presence of an excess of chlorotrimethylsilane (ca. 13 equiv), trimethylsilylation takes place at the less substituted allylic termini to provide allylsi-lanes in moderate to good yield (Scheme 1). The same products are obtained in similar yield by the protonation and silylation of a-phenylallyl acetate. The reaction may be... 

Recently, (phenylthiomethyl)trimethylsilane (1), or the anion (2) thereof, has been used to synthesize vinylsilanes from a-trimethylsUyloxiranes, in Peterson-type olefination reactions to generate vinyl sulfides, and also as a radical precursor under electrochemical conditions. Addition reactions of (phenylth-iomethyl)trimethylsilyl carbene (10), prepared via two independent methods, to olefins have also heen disclosed. ... 

A route to aryltrimethylsilanes was also described by this process [3]. In THF-HMPA, the carbanions Ar generated by cathodic reduction are trapped by MejSiCl to form ArSiMoj. This reaction is possible because MejSiCl is reduced at a more negative potential than aryl halides. In THF-DMPU instead of THF-HMPA the electrochemical reductive silylation of trifluoromethylbenzene led to the corresponding mono-, bis- or tris-trimethylsilyl derivatives, respectively, PhCFjSiMej, PhCF(SiMe3)2 and PhC(SiMe3)3 [4]. 

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