Trimethylsilyl bromide

Fig. 3. Synthesis of diacidic and monoacidic N-1 a2etidinone phosphonates and phosphinates where TMSBr is trimethylsilyl bromide BSA is...

Me3SiCH2CH=CH2i TsOH, CH3CN, 70-80°, 1-2 h, 90-95% yield. This silylating reagent is stable to moisture. Allylsilanes can be used to protect alcohols, phenols, and carboxylic acids there is no reaction with thiophenol except when CF3S03H is used as a catalyst. The method is also applicable to the formation of r-butyldimethylsilyl derivatives the silyl ether of cyclohexanol was prepared in 95% yield from allyl-/-butyldi-methylsilane. Iodine, bromine, trimethylsilyl bromide, and trimethylsilyl iodide have also been used as catalysts. Nafion-H has been shown to be an effective catalyst. 

The related planar pyrrole analog 118 has also been prepared (2) from either ethyl or benzyl pyrrole-2-carboxylate 116. Direct alkylation with diethyl phosphonomethyl triflate (70) and base produced the N-phosphonomethylpyrrole 2-carboxylate 117, which was deprotected with trimethylsilyl bromide and saponified to the corresponding phosphonic acid 118. 

The synthesis of S-phosphonothiazolin-2-one 133 started with 2-bromothiazole 129. Nucleophilic displacement of the 2-bromide proceeded cleanly with hot anhydrous sodium methoxide to give 2-methoxythiazole 130. Low-temperature metalation of 130 with n-butyl lithium occurred selectively at the 5-position (76), and subsequent electrophilic trapping with diethyl chlorophosphate produced the 5-phosphonate 131. Deprotection of 131 was accomplished either stepwise with mild acid to pn uce the thiazolin-2-one intermediate 132, or directly with trimethylsilyl bromide to give the free phosphonic acid 133, which was isolated as its cyclohexylammonium salt. 

Trimethylsilyl iodide 17, which can be generated in situ by reaction of trimethyl-silyl chloride (TCS) 14 with Nal in acetonitrile [1], converts alcohols 11, in high yields at room temperature, into their iodides 773a, HI, and hexamethyldisiloxane (HMDSO) 7 [1-8, 12]. Likewise esters such as benzyl benzoate are cleaved by Me3SiCl 14/NaI in acetonitrile under reflux [Ij. Reactions of alcohols 11 with trimethylsilyl bromide 16 in chloroform or, for in situ synthesis of 16 from liBr and TCS 14 in acetonitrile and with HMDS 2 and pyridinium bromide perbromide, proceed only on heating in acetonitrile or chloroform to give the bromides 773 b in nearly quantitative yield [3, 8, 12] (Scheme 6.1). 

In general, cyclization can be expected in compounds having the potential for formation of five- or six-membered rings. In addition to the more typical bromination reagents, such as those listed in Table 4.2, the combination of trimethylsilyl bromide, a tertiary amine, and DMSO can effect bromolactonization. 

Sekine, M., Tetsuaki, T., Yamada, K. and Hata, T., A facile synthesis of phos-phoenolpyruvate and its analogue utilizing in situ generated trimethylsilyl bromide, /. Chem. Soc., Perkin I, 2509, 1982. 

W Beck, G Jung. Convenient reduction of S-oxides in synthetic peptides, lipopeptides and peptide libraries, (trimethylsilyl bromide) Lett Pept Sci 1,31, 1994. 

Hydrogen bromide, trimethylsilyl bromide and acetyl bromide have all been proven to be suitable bromide transfer agents [e.g. 12, 13]. Tetra-n-butylammonium salts catalyse the interconversion of dichloroalkanes into bromochloroalkanes and chloroiodoalkanes upon reaction with an excess of bromo- and iodobutane, respectively [14]. Similarly, mixed bromochloromethanes are obtained from the reaction of dibromochloromethane with benzyltriethylammonium chloride under basic conditions [15]. 

Toluene-(4-sulfomethyl)phosphonic acid diethyl ester Hydrogen chloride Trimethylsilyl bromide Ammonium hydroxide... 

Treatment of the a-acetoxy ether 322 with trimethylsilyl bromide affords the axial 4-bromotetrahydropyran 323 (Equation 137). This axial selective Prins cyclization can also be conducted in the presence of acetyl bromide, but use of SnBr4 affords equatorial 4-bromotetrahydropyrans and hence the all ry -product <2004JA9904>. 

In the examples of electrophilic substitution of vinylsilanes described rove, collapse of the carbon-silicon bond to form a carbon-carbon 7t bond faster than nucleophilic attack on the carbocation by the anionic counterion l the electrophile. This is not always the case. For example, on treatment of -l-trimethylsilylpropene with bromine followed by aqueous ethanol, (Z)--bromopropene is formed almost exclusively (Figure Si5.10). This is pnsistent with anti addition of bromine to the double bond followed by anti limination of trimethylsilyl bromide. 

X-Ray studies of crystals of pyridine complexes with trimethylsilyl bromide and iodide (264) and of N-methylimidazole adducts to trimethyl-chlorosilane (265) were performed. The tetracoordinate silicon structure of these complexes was proved. The distances between the halogen and silicon atoms in pyridine adducts are 4.359 and 4.559 A for bromine and iodine, respectively, which is approximately 2 A greater than the sum of the covalent radii and significantly longer (0.5 A) than the sum of the van der Waals radii. This result is consistent with the ionic structures of the complexes in the solid state. The distance from silicon to nitrogen (1.86 A) is evidently larger than the length of typical Si—N bonds (1.75 A), which... 

Since the excess trimethylsilyl bromide was difficult to remove, an alternative sequence was investigated (Scheme 10). After bromination of the silyl enol ether, the reaction mixture was poured into water to hydrolyze both the trimethylsilyl bromide and the anhydride. On heating this bromoacid as before, an unexpected compound was formed. This can be rationalized as follows The reaction proceeds from the enol form, and the mechanism is formally 1,5 elimination of hydrogen bromide with concomitant loss of carbon dioxide. The second decarboxylation is analogous to the one seen earlier, and would be expected of the a,8-unsaturated ketone. 

Chiral di- and tripropyl ethers, 59b and 60b for example, have been synthesized as shown in Figure 14.121 Complete O-alkylation of the monobenzyl ether was possible with n-propyl iodide in THF/DMF with NaH as base. The cone and the partial-cone conformers were formed in a 1 1 ratio and could be separated chroma-tographically. Alkylation with n-propyl bromide in the presence of Cs2C03 in acetone gave the di-O-propylated compound 59a, in which both propoxy groups in anti orientation, in good yield. The cleavage of the benzyl ether with trimethylsilyl bromide led to the final products 59b and 60b. 

Reduction of this intermediate by hydrogen transfer from 1,4-cyclohexa-diene in the presence of platinum leads to loss of the carbobenzoxy group and formation of the transient primary amine 119. The terminal primary amino group in that product then participates in a second addition-elimination sequence to form an eight-membered ring (120). Treatment of this intermediate with trimethylsilyl bromide then cleaves the ethyl ethers on phosphorus to give the free phosphonic acid and thus perzinfotel (121). ... 

The reaction is not particularly useful for preparation of enolizable a-diketones. The main complication is that the liberated trimethylsilyl bromide reacts with the newly formed enolic function, thus giving rise to a new double bond to which bromine can be added. Thus several bromination products of the a-diketones together with decomposition products are formed. 

Low Cleavage with Trimethylsilyl Bromide in Trifluoroacetic Acid... 

Epoxides 159 were converted to allylic alcohols 161 in high yields in acetonitrile in a one-pot procedure. The reaction involved triphenylphos-phine-catalyzed epoxide opening with trimethylsilyl bromide, followed by elimination of the trimethylsilyl bromohydrin from 160 with DBU at reflux temperature (84JA7854). 

Morishima, N, Koto, S, Kusuhara, C, Zen, S, One-stage a-glucosylation using tetra-O-benzyl-a-D-glucose and mixture of trimethylsilyl bromide, cobalt(ll) bromide, tetrabutylammonium bromide, and molecular sieve, Chem. Lett., 427-428, 1981. 

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