Trimethylsilyl preparation

The composition of the enol ethers trimethylsilyl prepared from an enolate mixture reflects the enolate composition. If the enolate formation can be done with high regio-selection, the corresponding trimethylsilyl enol ether can be obtained in high purity. If not, the silyl enol ether mixture must be separated. Trimethylsilyl enol ethers can be prepared directly from ketones. One procedure involves reaction with trimethylsilyl... 

Monosubstitution of acetylene itself is not easy. Therefore, trimethylsilyl-acetylene (297)[ 202-206] is used as a protected acetylene. The coupling reaction of trimethylsilylacetylene (297) proceeds most efficiently in piperidine as a solvent[207]. After the coupling, the silyl group is removed by treatment with fluoride anion. Hexabromobenzene undergoes complete hexasubstitution with trimethylsilylacetylene to form hexaethynylbenzene (298) after desilylation in total yield of 28% for the six reactions[208,209]. The product was converted into tris(benzocyclobutadieno)benzene (299). Similarly, hexabutadiynylben-zene was prepared[210j. 

Allylalion of the alkoxymalonitrile 231 followed by hydrolysis affords acyl cyanide, which is converted into the amide 232. Hence the reagent 231 can be used as an acyl anion equivalent[144]. Methoxy(phenylthio)acetonitrile is allylated with allylic carbonates or vinyloxiranes. After allylation. they are converted into esters or lactones. The intramolecular version using 233 has been applied to the synthesis of the macrolide 234[37]. The /i,7-unsaturated nitrile 235 is prepared by the reaction of allylic carbonate with trimethylsilyl cyanide[145]. 

Various S-nucleophiles are allylated. Allylic acetates or carbonates react with thiols or trimethylsilyl sulfide (353) to give the allylic sulfide 354[222], Allyl sulfides are prepared by Pd-catalyzed allylic rearrangement of the dithio-carbonate 355 with elimination of COS under mild conditions. The benzyl alkyl sulfide 357 can be prepared from the dithiocarbonate 356 at 65 C[223,224], The allyl aryl sufide 359 is prepared by the reaction of an allylic carbonate with the aromatic thiol 358 by use of dppb under neutral condi-tions[225]. The O-allyl phosphoro- or phosphonothionate 360 undergoes the thiono thiolo allylic rearrangement (from 0-allyl to S -allyl rearrangement) to afford 361 and 362 at 130 C[226],... 

One type of o-aminobenzyl anion synthon is a mixed Cu/Zn reagent which can be prepared from o-toluidines by / i.s-trimethylsilylation on nitrogen, benzylic bromination and reaction with Zn and CuCN[l]. Reaction of these reagents with acyl halides gives 2-substituted indoles. 

Another o-aminobenzyl anion equivalent is generated by treatment of A-trimethylsilyl-o-toluidinc with 2.2 eq. of n-butyllithium. Acylation of this intermediate with esters gives indoles[2]. This route, for example, was used to prepare 6.2D, a precursor of the alkaloid cinchonamine. 

Similar halogenations have been done on 2-lithio-l-phenylsulfonylindole[2], 2-Lithio-l-phenylsulfonylindole is readily converted to the 2-(trimethylsilyl) derivative[2,3]. 2-Trialkylstannylindoles can also be prepared via 2-lithio-indoles[4,5], 2-Sulfonamido groups can be introduced by reaction of a 2-lithioindole with sulfur dioxide, followed by conversion of the sulfinic acid group to the sulfonyl chloride with A-chlorosuccinimide[6]. 

Etherification. The reaction of alkyl haUdes with sugar polyols in the presence of aqueous alkaline reagents generally results in partial etherification. Thus, a tetraaHyl ether is formed on reaction of D-mannitol with aHyl bromide in the presence of 20% sodium hydroxide at 75°C (124). Treatment of this partial ether with metallic sodium to form an alcoholate, followed by reaction with additional aHyl bromide, leads to hexaaHyl D-mannitol (125). Complete methylation of D-mannitol occurs, however, by the action of dimethyl sulfate and sodium hydroxide (126). A mixture of tetra- and pentabutyloxymethyl ethers of D-mannitol results from the action of butyl chloromethyl ether (127). Completely substituted trimethylsilyl derivatives of polyols, distillable in vacuo, are prepared by interaction with trim ethyl chi oro s il an e in the presence of pyridine (128). Hexavinylmannitol is obtained from D-mannitol and acetylene at 25.31 MPa (250 atm) and 160°C (129). 

Gas Chromatography Analysis. From a sensitivity standpoint, a comparable technique is a gas chromatographic (gc) technique using flame ioni2ation detection. This method has been used to quantify the trimethylsilyl ester derivative of biotin in agricultural premixes and pharmaceutical injectable preparations at detection limits of approximately 0.3 pg (94,95). 

Phenylstibine [58266-50-5] C H Sb, has been obtained by the reduction of phenyldiio do stihine [68972-61-2] CgH3l2Sb, (73) or phenyldichlorostibine [5035-52-9] 031130.2, (74) with lithium borohydride. It has also been prepared by the hydrolysis or methanolysis of phenylbis(trimethylsilyl)stibine [82363-95-9] C22H23Si2Sb (75). Diphenylstibine [5865-81-6] C22H22Sb, can be prepared by the interaction of diphenylchlorostibine [2629-47-2] C22H2QClSb, with either Hthium borohydride (76) or lithium aluminum hydride (77). It is also formed by hydrolysis or methanolysis of diphenyl (trimethylsilyl)stibine [69561-88-2] C H SbSi (75). Dimesitylstibine [121810-02-4] h.3.s been obtained by the protonation of lithium dimesityl stibide with trimethyl ammonium chloride (78). The x-ray crystal stmcture of this secondary stibine has also been reported. 

Methylthiophene is metallated in the 5-position whereas 3-methoxy-, 3-methylthio-, 3-carboxy- and 3-bromo-thiophenes are metallated in the 2-position (80TL5051). Lithiation of tricarbonyl(i7 -N-protected indole)chromium complexes occurs initially at C-2. If this position is trimethylsilylated, subsequent lithiation is at C-7 with minor amounts at C-4 (81CC1260). Tricarbonyl(Tj -l-triisopropylsilylindole)chromium(0) is selectively lithiated at C-4 by n-butyllithium-TMEDA. This offers an attractive intermediate for the preparation of 4-substituted indoles by reaction with electrophiles and deprotection by irradiation (82CC467). 

The trimethylsilyl group has been used to prepare stable aci-nitro esters and these react with alkenes to produce intermediate isoxazolidines which were readily converted into 2-isoxazolines (Scheme 119) (73ZOB1715, 74DOK109, 78ACS(B)ll8>. 

A newer method for the preparation of nitronic esters, namely utilizing the (9-trimethyl-silyl ester, has been reported and these are prepared by the reaction of alkylnitro compounds and (V,(V-bis(trimethylsilyl)acetamide. These nitronic esters also undergo cycloaddition with alkenes to produce isoxazolidines (equation 54) (74MIP41601, 74DOK109, 78ACS(B)ll8). 

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. 

When potassium fluoride is combined with a variety of quaternary ammonium salts its reaction rate is accelerated and the overall yields of a vanety of halogen displacements are improved [57, p 112ff. Variables like catalyst type and moisture content of the alkali metal fluoride need to be optimized. In addition, the maximum yield is a function of two parallel reactions direct fluorination and catalyst decomposition due to its low thermal stability in the presence of fluoride ion [5,8, 59, 60] One example is trimethylsilyl fluoride, which can be prepared from the chloride by using either 18-crown-6 (Procedure 3, p 192) or Aliquot 336 in wet chlorobenzene, as illustrated in equation 35 [61],... 

Handhng of this volatile and toxic matenal may be avoided by the clever use of the trimethylsilylated perfluorinated resinsulfonic acid [97] This solid reagent is prepared by treatment of the acid form of NAFTON 511 with chloro-tnmethylsilane This reagent exhibits sigmficant stabdity in air (equation 78)... 

Ketene acetals prepared from fluorinated esters by trimethylsilylation undergo Lewis acid-promoted aldol condensations giving satisfactory yields but low diastereoselectivity [27] (equation 22). 

The Cunius degradation of acyl azides prepared either by treatment of acyl halides with sodium azide or trimethylsilyl azide [47] or by treatment of acyl hydrazides with nitrous acid [f J yields pnmarily alkyl isocyanates, which can be isolated when the reaction is earned out in aptotic solvents If alcohols are used as solvents, urethanes are formed Hydrolysis of the isocyanates and the urethanes yields primary amines. 

Trimethylsilyl trifluoromethanesulfonate (trimethylsilyl triflate) is the most synthetically useful representative of the family of trialkylsilyl perfluoroalkane-sulfonates (for a review, see reference 101) This reagent is commercially available or can be prepared easily by the reaction of chlorotrimethylsilane and triflic acid [101] It has wide application in organic synthesis as an excellent silylating reagent... 

Another useful reagent for the preparation of alkynyl lodonium Inflates is [cyano(trifluoromethylsulfonyloxy)(phenyl)]iodine [/i7, 138, 139, 140] prepared from iodosobenzene, trimethylsilyl tnflate, and trimethylsilyl cyanide (equation 71). This reagent reacts with various stannylacetylenes under very mild conditions to form the corresponding alkynyl iodonium salts in high yields [139] (equation 72)... 

Tetraphenylphosphonium Hydrogen Dilluoride Preparation, 193 Trimethylsilyl Fluoride Preparation, 193... 

N,N - Bis(trimethylsilyl)sulfur(rV) diimide Me3SiN=S=NSiMc3 is an especially versatile source of the N=S=N functionality in the formation of both acyclic and cyclic S-N compounds. It is conveniently prepared by the reaction of NaN(SiMc3)2 and thionyl chloride (Eq. 2.5). 

MesSiNs yields (SN)x as a black solid. By contrast, the explosive and insoluble black compound SesNaCla, which probably contains the [SesNaCl]" cation, is prepared by the treatment of SeaCla with trimethylsilyl azide in CH2CI2 (Eq. 2.13). ... 

Tellurium nitride was first obtained by the reaction of TeBt4 with liquid ammonia more than 100 years ago. The empirical formula TeN was assigned to this yellow, highly insoluble and explosive substance. However, subsequent analytical data indicated the composition is Tc3N4 which, in contrast to 5.6a and 5.6b, would involve tetravalent tellurium. This conclusion is supported by the recent preparation and structural determination of Te6N8(TeCl4)4 from tellurium tetrachloride and tris(trimethylsilyl)amine (Eq. 5.5). The TceNs molecule (5.12), which is a dimer of Tc3N4, forms a rhombic dodecahedron in which the... 

Me4N]N3, lose SO2 to give the corresponding [SO2N3] salts.The [SO3N3] anion is prepared by the reaction of Cs[S03Cl] with trimethylsilyl azide (Eq. 9.4). 

The important reagent Mc3SiNSO is obtained by the reaction of thionyl chloride with tris(trimethylsilyl)amine at 70°C in the presence of AICI3 (Eq. 9.9). " It may also be prepared by the interaction of sulfur dioxide with HN(SiMc3)2. ... 

In order to prepare thin fdms of (SN) on plastic or metal surfaces, several processing techniques have been investigated, e.g., the electroreduction of [SsNs]" salts. Powdered (SN) is prepared by the reaction of (NSC1)3 with trimethylsilyl azide in acetonitrile/ The sublimation of (SN) at 135°C and at pressure of 3 x 10 Torr. produces a gas-phase species, probably the cyclic [SsNs] radical, that reforms the polymer as epitaxial fibres upon condensation/... 

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