Bromotrimethylsilane

Fensta-bank, L. Joumet, M. Lacote, E. Malacria, M., Recent Res. DeveL In Organic Chem. 1997, i, 385. 

Hasegawa, 1. Niwa, T. Takayama, T., biorg. Chem. Commun. 2005, 8, 159. 

Solubility sol CCI4, CHCI3, CH2CI2, CICH2CH2CI, MeCN, toluene, hexanes reactive with THF (ethers), alcohols, and somewhat reactive with EtOAc (esters). 

Form Supplied in colorless liquid, packaged in ampules. Analysis of Reagent Purity well characterized by H, C, and Si NMR spectroscopy. 

Handling, Storage, and Precaution extremely sensitive to light, air, and moisture fumes in air due to hydrolysis (HBr), and becomes discolored upon prolonged storage (free Br2). 

Submitted by CLAUDIO PALOMO and JESUS M. AIZPURUA Checked by JOYCE Y. COREY1 and JANET BRADDOClC 

The methods for the preparation of bromotrimethylsilane include the treatment of hexamethyldisiloxane with bromine reagents such as phosphorus tribromide,1,2 2,2,2-tribromo-l, 3,2 /5-benzodioxaphosphole (catechyl phosphorus tribromide),2 and aluminium tribromide,3 the yields being in the range from 73 to 87%. A further method4 shows that bromotrimethylsilane can be obtained from aminosilanes and hydrobromic acid, but the yield (55%) is lower than in the former methods. Other methods involve the use of expensive reagents, such as hexamethyldisilane, l,4-bis(trimethylsilyl)-2, 5-cyclohexadiene, and 1,4-dihydro-l, 4-bis(trimethylsilyl)naphthalene.5 Finally, some alternative procedures have been developed for its in situ preparation.5 

The following procedure is an operatively simple route for the synthesis of bromotrimethylsilane on a preparative laboratory scale from reagents that are readily accessible and inexpensive. This could be a method of choice in some laboratories despite the fact that bromotrimethylsilane is now commercially available (Petrach Systems, Aldrich, or Alpha). Moreover, the procedure also serves as a suitable method for the synthesis of azidotrimethylsilane and isocyanatotrimethylsilane, and is specially useful for the preparation of cyanotrimethylsilane. Thus a mixture of triphenylphosphine dibromide, hexamethyldisiloxane, and a catalytic amount of powdered metal zinc in 1,2-dichlorobenzene is heated under reflux to produce bromotrimethylsilane in nearly quantitative yield, which is simultaneously distilled over a suspension of the corresponding pseudohalogenoacid salt in N, /V-dimethylformamide as solvent.6 

Under an atmosphere of dry nitrogen gas, the dropping funnel is replaced by a fractional distillation apparatus provided with a 10-cm Vigreux column and a 5-cm water-cooled condenser. The system is heat-dried under a flow of nitrogen gas with an electric heat gun or may be assembled from oven-dried glassware. The mixture is then heated over a period of 20-30 min until the silicone oil bath reaches 130-140 °C. During this time, the initial yellow precipitate is partially dissolved and the mixture refluxes smoothly. The silicone oil bath is maintained at this temperature for an additional 30 min. Heating is then increased over the period of 1 h to achieve distillation of the product the final oil temperature reaches 200 to 215 °C. 

Bromotrimethylsilane has proven to be useful for a wide variety of applications most of them being reviewed.5 8 Other recent applications are mild cleavage of oxiranes,9 the synthesis of glycosyl bromides,10 the selective cleavage of tetrahydro-2,5-dimethoxyfuran and tetrahydro-2,6-dimethoxy-pyran,11 the cleavage of esters and ethers,12 and the synthesis of benzyl bromides.13 

Miscellaneous Reactions. Bromodimethylborane can also be used to convert dialkyl, aryl alkyl, and diaryl sulfoxides to the corresponding sulfides (eq 15). Typically, the sulfoxides are treated with 2.5 equiv of Me2BBr in dichloromethane at —23 °C for 30 min and at 0°C for 10 min. Bromine is produced in the reaction and must be removed in order to avoid possible side reactions. This is accomplished by saturating the solution with propene prior to introducing the reagent or by adding cyclohexene. Phosphine oxides and sulfones failed to react under the conditions used to deoxygenate sulfoxides. 

Bromodimethylborane has also been used as a catalyst for the Pictet-Spengler reaction (eq 16) and to catalyze the 1,3-transposition of an ally lie lactone.  

Related Reagents. Boron Tribromide Boron Trichloride Bromobis(isopropylthio)borane 9-Bromo-9-borabicyclo-[3.3.l]borane B-Bromocatechalborane. 

Yvan Guindon Paul C. Anderson Bio-Mega/Boehringer Ingelheim Research, Laval, Quebec, 

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The completion of the synthesis of gilvocarcin V (2) only requires a few functional group manipulations. Hydrogenolysis of the four benzyl groups, followed by acetylation of the liberated hydroxyl groups, provides 30 in 68 % overall yield. After cleavage of the MOM ether in 30 with bromotrimethylsilane, application... 

Rearrangement reactions are also catalyzed by silicon Lewis acids the example in Scheme 77 uses Me3SiOTf 331 iodo- and bromotrimethylsilanes are also effective. 

Direct electrophilic silylation of thiadiazole 321 with bromotrimethylsilane (TMSBr) under basic conditions provides easy access to C-silyl thiadiazole 322, which can serve as a synthetic equivalent of an organometallic intermediate or a silyl-protected azole <06S 1279>. 

Acid bromides.1 Acid chlorides can be converted to acid hromidcs by, reaction with bromotrimethylsilane (75 -95% yield). Acid iodides can be obtained by use of lodotrimethylsilane. 

Glycosyl bromides.1 Glycosyl bromides can be prepared conveniently and in High yield by reaction of bromotrimethylsilane with anomcric glycosyl acetates. Ulter groups at other positions are stable under the mild conditions (25°, HCC13, 4II min) employed. Methyl glycosides can also be used, but 1,2-O-isopropylidenes rend very slowly. 

For the synthesis of simple peptides in which the phosphorus-containing amino acid analogue is at the C-terminal end of the peptide, acid-catalyzed cleavage of the diester has been used to produce the phosphonic diacid.153,6X1 However, the strong acid needed to effect this transformation makes the strategy unattractive for more complex molecules and it has largely been superceded by the use of bromotrimethylsilane (see Section 10.10.3.2.1). 

Scheme 27 Cleavage of Phosphonate Diesters with Bromotrimethylsilane 119"121 ...

Scheme 28 Selective Cleavage of a Phosphonate Methyl Ester with Bromotrimethylsilane 66 ...

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