Anion trapping, chlorotrimethylsilane

Grobe and Hegge demonstrated that aluminum powder in fV-methylpyrrolidinone (NMP) can also be used for the reduction of bromotrifluoromethane in the presence ofchlorotrimethyl-silane to produce trimethyl(trifluoromethyl)silane, a method more convenient than the modified Ruppert procedure. The C Br bond of bromochlorodifluoromethane is selectively reduced by aluminum powder in. V-methylpyrrolidinone in the presence of ehlorotrimethylsilane giving (chlorodifluoromethyl)trimethylsilane in 80% isolated yield. The process appears to involve a two-electron reduction of the C Br bond of bromochlorodifluoromethane followed by trapping of the resulting CFjCU" anion by chlorotrimethylsilane. Aluminum powder, corresponding to a net consumption of two electrons per mole of bromochlorodifluoromethane. is needed for the reduction. 

The vinylcyclopropane rearrangement is an important part of Trost s seco-alkylation sequence (see sec. 8.8.B.ii). In this protocol, trimethylsilyloxyvinylcyclopropanes such as 524 are generated by reaction with diphenylcyclopropyl sulfide and subsequent reaction with lithium diisopropyl amide (LDA), to open the oxaspiro-pentane) and trapping the resulting alkoxide anion with chlorotrimethylsilane. Thermal... 

Commonly employed anion-stabilizing groups are those containing silicon (Table 5.4, Entries 1-5). Magnus et al. reported that epoxysilane 147 could be deproto-nated with t-BuLi, and that the lithiated epoxide 148 thus generated could be trapped with allyl bromide to give epoxysilane 149 in a synthetically useful yield (Scheme 5.34) [55], Iodomethane (88%) and chlorotrimethylsilane (60%) could also be trapped. 

The use of an ester as an anion-stabilizing group for a lithiated epoxide was demonstrated by Eisch and Galle (Table 5.5, Entry 11). This strategy has been extended to a,P-epoxy-y-butyrolactone 191, which could be deprotonated with LDA and trapped in situ with chlorotrimethylsilane to give 192, which was used in a total synthesis of epolactaene (Scheme 5.45) [69], The use of a lactone rather than a... 

Alkyl alkanoates are reduced only at very negative potentials so that preparative scale experiments at mercury or lead cathodes are not successful. Phenyl alkanoates afford 30-36% yields of the alkan-l-ol under acid conditions [148]. Preparative scale reduction of methyl alkanoates is best achieved at a magnesium cathode in tetrahydrofuran containing tm-butanol as proton donor. The reaction is carried out in an undivided cell with a sacrificial magnesium anode and affords the alkan-l-ol in good yields [151]. In the absence of a proton donor and in the presence of chlorotrimethylsilane, acyloin derivatives 30 arc formed in a process related to the acyloin condensation of esters using sodium in xylene [152], Radical-anions formed initially can be trapped by intramolecular addition to an alkene function in substrates such as 31 to give aiicyclic products [151]. 

The isomeric 4-phenyl-1,2,3-thiadiazole underwent fragmentation under the same conditions, although successful reaction could be achieved using LDA, provided that chlorotrimethylsilane was present m situ to trap the 5-anion as it was formed (Scheme 102)(85S945). 

Unsuccessful direct means of detecting the hypothesized intermediates we have been unable to trap the hypothesized oxime anion intermediate with either methyl iodide or chlorotrimethylsilane in the presence of base. We did not observe any characteristic infrared signals using IR probes. 

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