Trimethylsilyl chloride, quenching

When this type of reaction is quenched with trimethylsilyl chloride, rather than by neutralization, a trimethylsilyl ether of the adduct is isolated. This result shows that the tetrahedral adduct is stable until the reaction mixture is hydrolyzed. 

A study aimed at optimizing yields in this reaction found that carbinol formation was a major competing process if the reaction was not carried out in such a way that all of the lithium compound was consumed prior to hydrolysis.113 Any excess lithium reagent that is present reacts extremely rapidly with the ketone as it is formed by hydrolysis. Another way to avoid the problem of carbinol formation is to quench the reaction mixture with trimethylsilyl chloride.114 This procedure generates the disilyl acetal, which is stable until hydrolysis. 

The solid residue of the preparation from lithium powder, trimethylsilyl chloride, tetrachlorosilane and methyllithium may be highly pyrophoric. Caution in quenching into dilute acid is advised. 

The addition of trimethylsllyl chloride proved crucial to the success of the procedure described here. Use of aqueous ammonium chloride as a quenching reagent (instead of trimethylsilyl chloride) resulted in a reaction mixture that contained up to 30% of the corresponding tertiary alcohbl. 

A study of methods for controlling the grafting sites of polystyrene polymers may serve as an example for the quantitative and structural analysis of the site of lithiation. Trimethylsilyl chloride serves as the quenching agent owing to the low incidence of side reactions besides metal replacement. Thus, on varying the conditions of metallation of low molecular weight polystyrene (409) and poly(4-methylstyrene) (410), aromatic and... 

Other papers of interest in this section report transamination of camphor-3-carbothioamides with secondary cyclic amines, reaction of camphorquinone with dimethyl /S-ketoglutarate, the use of fenchone (212 X=0) in alkene formation from Grignard reagents, bromination of 2-e/itfo-6-endo-dibromobornane to yield 2,3,6-endo-tribromoborn-2-ene, and camphor-enol trimethylsilyl ether formation by quenching the reaction mixture of butyl-lithium and camphor tosyl-hydrazone with trimethylsilyl chloride. ... 

To a solution of isophthalaldehyde (40 g, 0.3 mol.) in chloroform (400 ml) and methyl 3-mercaptopropanoate (68 ml, 0.6 mol) was added dropwise trimethylsilyl chloride (48 ml, 0.38 mol) over 30 min. The reaction mixture was stirred at room temperature for 2 hours. The reaction was quenched with 25% aq. NH4OAc, extracted with ethyl acetate, dried and evaporated. Flash chromatography of the residue afforded 50 g of the title compound. 

The synthesis of 1,5-diketones 521 from 3,4-dihydropyranones 519 has been reported and is shown in Scheme 95 <1999T9333>. Organolithium reagents were used to open the lactone reagents, and best results were achieved when the reactions were quenched with trimethylsilyl chloride prior to hydrolytic workup. 

Silylation at carbon can be achieved via quenching an imidazole anion with a silylating agent such as trimethylsilyl chloride, as discussed in CHEC-II(1996). 

A synthesis of pyrroles and pyridines is possible by addition of dilithium species (5) to carbonyls (Scheme 2). The syn lithiation to give (5) was established by quenching (5) with trimethylsilyl chloride. ... 

Simpkins has also applied the well-documented homochiral lithium amide (HCLA) base chemistry [102] to these substrates, and has found that upon treating franj-4-t-butyl(diphenyl)silyloxythiane oxide with an optically active, camphor-derived base followed by quenching with trimethylsilyl chloride, non-racemic products are isolable in up to 69% enantiomeric excess (Scheme 4.50) [102]. 

The quenching of dihydropyran anion with trimethylsilyl chloride yields only 2-trimethylsilyl A -dihydropyran (45). The reaction takes place at the harder of the two basic centers (C-2, C-4). Carbon-2 is the harder because it is flanked on one side by an oxygen atom. 

Somewhat related to the Madelung and Wender indole syntheses is the method developed by Smith and Visnick, which features the dilithio species from ortho-sXkyl-N-in-methylsilyl anilines reacting with carboxylic acid esters to give 2-substitnted and 2,3-disubstituted indoles [1, 2], The value of this indole synthesis is seen by its numerous applications by Smith and coworkers in the synthesis of indole alkaloids [3-12], The basic reaction and some examples are shown in Scheme 1. The requisite silylated anilines were prepared by lithiation (n-bntyllithinm, -78 °C) of the aniline followed by quenching with trimethylsilyl chloride. For the synthesis of 2,3-disubstituted indoles an inverse quench is preferred (equation 3). To lithiate ort/to-ethyl-A -methylsilyl aniline, n-butyllithium-tetramethylethylene-diamine (TMEDA) was required. Indole 1 is an intermediate in the synthesis of (H-)-cinchonamine. 

SiloxyfuIvenes. Dimethylfulvene added dropwise to a soln. of Li-diisopropylamide in tetrahydrofuran at —78° under N2, benzaldehyde added when the yellow colour had disappeared, stirred for 0.5 h at —78°, treated with trimethylsilyl chloride, and stirred for a further 5 h at the same temp. - product. Y 76%. F.e. and isolation of 8-hydroxyfulvenes by quenching with acid, s. J.-E. Nystrom et al.. Tetrahedron Letters 29, 4997-5000 (1988). 

Addition of lithium dimethyl cuprate to cyclohexenone followed by quenching with trimethylsilyl chloride gave (170), from which enolate (171) could be regenerated with methyl-lithium. Reaction of (171) with a-trimethylsilyl methyl ketone (172) gave a... 

---