Electrophilic silylating reagents

The addition of the electrophilic silyl reagent strongly activates the enone. It has also been found that Lewis acids, such as AICI3, accelerate the reaction of dialkylzincs with... 

The introduction of TMSOTf as a highly electrophilic silylating reagent led to its widespread use and there are a very large number of reactions which employ the reagent in either stoichiometric or catalytic amounts. 

Although the introduction of silyl moieties is usually accomplished by electrophilic silyl reagents, recently their anionic congeners began to enjoy more and more popularity, as they are readily available by metal-halogen exchange or by cleavage reactions. 

Electrophilic Silylation Reagent. l,2-Bis(chlorodimethyl-silyl)ethane is not only an effective amine silylating reagent, but can also be employed in reactions with other anions. For example, when treated with the silver sulfonate salt as in eq 11, the nonafluorobutanesulfonic acid silyl ester (27), an extremely powerful silylating reagent, results.Carbanions are also effectively trapped by (1) A series of rigid butadiene Diels-Alder precursors such as (28) have been prepared in this fashion as outlined in eq 12.12... 

Recent advances include the use of new chiral bases, extention to substrates other than ketones, and trapping with electrophiles other than silylating reagents and aldehydes. Regarding alternate substrates and electrophiles, the Simpkins group reported alkylation of a prochiral diester with common alkyl halides with >98% ee [46]. Simpkins and coworkers have also demonstrated desym-metrization of cyclic imides, in this case with trapping by silyl groups [47]. 

Iodonium salts 49 and 50 are efficient electrophilic alkylating reagents towards a variety of organic nucleophiles, including silyl enol ethers. The reaction with silyl enol ether 51 proceeds under mild conditions and selectively affords the appropriate product of alkylation 52 along with iodobenzene as the by-product (Scheme 24) [41]. 

Benzenediazonium tetrafluoroborate has also been investigated as an electrophilic aminating reagent in the reaction with the ketene silyl acetal 2 derived from the /1-hydroxy ester 119. 

At first, we considered the transformation of the carbamate moiety into more reactive functions. It was shown that Z-O-enecarbamate can be transformed into Z-silyl enol ether 10 by treatment of 8 with methyllithium and quenching of this intermediate lithium enolate 9 by electrophilic silicon reagents. Assuming this lithium enolate intermediate 9 would be able to react with other electrophile reagents, the preparation of more reactive functions including Z-vinyl phosphate and Z-vinyl triflate was considered. The remaining and important question was whether the Z-stereochemistry of this double bond would be preserved. 

Electrophilic trifluoromethylation reagents can be generated from the treatment of trifluoromethyl biphenyl sulfoxides with Tf20. These reagents will react with a wide range of nucleophiles including carbanions, aromatics, silyl enol ethers, thiolates, and phosphines (eq 90). ... 

HMIS Health 3, Flammability 3, Reactivity 1 Uses Electrophilic reagent silylation reagent Manuf./Distrib. AP Resources http //www.apr.co.kr. Advanced Synthesis Tech. http //www. advancedsynthesis. com, Aldrich http //www.sigma-aidrich.com, Fluka http //www.sigma-aidrich. com, Gelest http //www.geiest. com Sigma... 

In addition to organozinc, -silyl, -magnesium, and -borane reagents employed respectively in Negishi, Hiyama, Kumada, and Suzuki cross-coupling reactions with various electrophiles, organozirconium reagents were... 

The chiral silyllithium reagent methyl(naphthyl)(phenyl)silyl-lithium is configurationally stable at and below room temperature, and reacts with methyl(naphthyl)(phenyl)silyl chloride with retention at the nucleophilic silyl group and inversion at the electrophilic silyl group... 

Related Electrophilic Silyl Ketene Acetal Reagents. A... 

Only few procedures for enantioselective animation of enoiates have been developed [256]. The stoichiometric use of several chiral electrophilic animation reagents was plagued by low enantioselectivity [257]. Evans and Johnson developed a first efficient catalytic approach that is based on the reaction of sihcon enoiates with azodicarboxylate derivatives [258]. Thus, silyl enol ethers 526 were reacted with azoimide 527 under catalysis of the copper f-butyl-PHOX complex 216a. The presence of 1 equiv. of trifluoroethanol was crucial for high conversion. 

Alkyl silyl ethers are cleaved by a variety of reagents Whether the silicon-oxygen or the carbon-oxygen bond is cleaved depends on the nature of the reagent used Treatment of alkoxysilanes with electrophilic reagents like antimony tri-fluonde, 40% hydrofluonc acid, or a boron tnfluonde-ether complex results in the cleavage of the silicon-oxygen bond to form mono-, di-, and tnfluorosiloxanes or silanes [19, 20, 21) (equations 18-20)... 

Another useful application of these Reformatsky reagents is their conversion to difluaraketene silyl acetals and subsequent reaction of these ketene silyl acetals with electrophiles [86, 89, 90] (equation 59)... 

Lcad(rV) trifluoroacetate is a strong electrophilic and oxidizing reagent It IS a valuable reagent for the hydroxylatton of aromatic compounds [5S, 59] Lead(IV) trifluoroacetate also reacts with silylated benzenes with the exclusive formation of the corresponding trifluoroacetate esters [59] (equation 28)... 

Scheme 2.12 shows some representative Mannich reactions. Entries 1 and 2 show the preparation of typical Mannich bases from a ketone, formaldehyde, and a dialkylamine following the classical procedure. Alternatively, formaldehyde equivalents may be used, such as l>is-(di methyl ami no)methane in Entry 3. On treatment with trifluoroacetic acid, this aminal generates the iminium trifluoroacetate as a reactive electrophile. lV,A-(Dimethyl)methylene ammonium iodide is commercially available and is known as Eschenmoser s salt.192 This compound is sufficiently electrophilic to react directly with silyl enol ethers in neutral solution.183 The reagent can be added to a solution of an enolate or enolate precursor, which permits the reaction to be carried out under nonacidic conditions. Entries 4 and 5 illustrate the preparation of Mannich bases using Eschenmoser s salt in reactions with preformed enolates. 

Epoxides can also be converted to allylic alcohols using electrophilic reagents. The treatment of epoxides with trialkyl silyl iodides and an organic base gives the silyl ether of the corresponding allylic alcohols.154... 

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