Trimethylsilyl fluoride

Related Reagents. Acrylonitrile boron trifluoride etherate ceric(rV) ammonium nitrate 2,3-dichloro-5,6-dicyano-/7-benzo-quinone drrhodium(II) tetrakis[methyl 4(/J)-2-oxazolidinone-4-carboxylate] drrhodium(II) tetrakis[(5)-Ai-phthaloyl-r-leucinate] DMSO epichlorohydrin lithium aluminum hydride methyl acrylate methyl lithium methyl triflate tetrabuty-lammonium fluoride trimethylsilyl chloride rhodium(II) tetraacetate. 

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. 

Trimethylsilyl ethers are readily cleaved by fluoride ion, mild acids, and bases. If the TMS derivative is somewhat hindered, it also becomes less susceptible to cleavage. A phenolic TMS ether can be cleaved in the presence of an alkyl TMS ether [Dowex lX8(IfO ), EtOH, rt, 6 h, 78% yield]. ... 

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],... 

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

Trimethylsilyl ethers are quite susceptible to acid hydrolysis, but acid stability is quite dependent on the local steric environment. For example, the 17o -TMS ether of a steroid is quite difficult to hydrolyze. TMS ethers are readily cleaved with the numerous HF-based reagents. A polymer-bound ammonium fluoride is advantageous for isolation of small polar molecules. ... 

Aryl and alkyl trimethylsilyl ethers can often be cleaved by refluxing in aqueous methanol, an advantage for acid- or base-sensitive substrates. The ethers are stable to Grignard and Wittig reactions and to reduction with lithium aluminum hydride at —15°. Aryl -butyldimethylsilyl ethers and other sterically more demanding silyl ethers require acid- or fluoride ion-catalyzed hydrolysis for removal. Increased steric bulk also improves their stability to a much harsher set of conditions. An excellent review of the selective deprotection of alkyl silyl ethers and aryl silyl ethers has been published. ... 

The Boekelheide reaction has found utility in other synthetic methodology. An approach to 2,3-pyridynes made use of this chemistry in the preparation of the key intermediate 30. Treatment of 28 with acetic anhydride produced the desired pyridone 29. Lithiation was followed by trapping with trimethylsilyl chloride and exposure to triflic anhydride gave the pyridyne precursor 30. Fluoride initiated the cascade of reactions that resulted in the formation of 2,3-pyridyne 31 that could be trapped with appropriate dienes in Diels-Alder reactions. 

Trimethylsilylethynylpyrazole was deprotected by treatment with tetrabutyl-ammonium fluoride (TBAF) to give monosubstituted acetylene in 90% yield. (96ADD193). The same conditions were used to cleave the trimethylsilyl group in l-tetrahydropyranyl-3-carboxyethyl-4-[2-(trimethylsilyl)ethynyl]pyrazole (96INP 9640704). 

A useful route to 2,1,3-benzothiadiazoles is the F -catalyzed cyclization of l-(4-X-C6F4)-3-trimethylsilyl-l, 3-diaza-2-thiallenes [90JFC(50)359]. Fluoride ion catalysis is also used in the formation of heterocycles from pentafluorobenzoyl and -phenoxy compounds (81BCJ3447). Pentafluoro-phenylcarbonimidoyl dichloride with primary amines gave guanidines,... 

The trimethylsilyl protecting group can be removed by routine deprotection with triethylamine -hydrogen fluoride complex. 

Sulfones with a trimethylsilyl or trialkylstannyl group at the -position or at the -position are readily converted to olefins upon treatment with tetra-n-butylammonium fluoride in THF (equations 39-41). The method is compatible with the presence of a variety of functionalities. 

A similar elimination in which the tin is attacked by fluoride anions (cf. the reaction of silanes with F ) has been used179 to synthesize terminal methylene compounds as in equation (75). An analogous reaction sequence using a trimethylsilyl group in place of the trialkyltin group has been published by Hsiao and Shechter180 as part of a synthesis of substituted 1,3-butadienes. 

Thus removal of water from classical rather inactive fluoride reagents such as tetrabutylammonium fluoride di- or trihydrate by silylation, e.g. in THF, is a prerequisite to the generation of such reactive benzyl, allyl, or trimethylsilyl anions. The complete or partial dehydration of tetrabutylammonium fluoride di- or trihydrate is especially simple in silylation-amination, silylation-cyanation, or analogous reactions in the presence of HMDS 2 or trimethylsilyl cyanide 18, which effect the simultaneous dehydration and activation of the employed hydrated fluoride reagent (cf, also, discussion of the dehydration of such fluoride salts in Section 13.1). For discussion and preparative applications of these and other anhydrous fluoride reagents, for example tetrabutylammonium triphenyldifluorosilicate or Zn(Bp4)2, see Section 12.4. Finally, the volatile trimethylsilyl fluoride 71 (b.p. 17 °C) will react with nucleophiles such as aqueous alkali to give trimethylsilanol 4, HMDSO 7, and alkali fluoride or with alkaline methanol to afford methoxytri-methylsilane 13 a and alkali fluoride. 

Fluoride-catalyzed condensations of aldehydes and ketones such as benzaldehyde with N,N-bis(trimethylsilyl)sulfenamide 529 furnish sulfenimides such as 530 in 82-96% yield [103] (Scheme 5.34). 

Because allyltrimethylsilane 82 or benzyltrimethylsilane 83 can be regarded as combinations of the hard trimethylsilyl cation and the soff allyl or benzyl anions, pyridine N-oxide 860 reacts with excess 82 or 83 in the presence of catalytic amounts of tetrabutylammonium fluoride di- or trihydrate in THF to give 2-allyl-or 2-benzylpyridines 948 and 950 [60]. The general reaction of silicon reagents such as 82 and 83 or of trimethylsilyl cyanide 18 with fluoride to generate allyl or... 

O-Trimethylsilyl nitronates 1036 have been used in fluoride-catalyzed aldol-type condensations with aldehydes and ketones to give a-trimethylsilyloxy-nitro com-... 

Heating perfluorbutylsulfonyl fluoride 1316 with HMDS 2 and CsF in DMF affords the N-nonaflylamidine 1317 in 62% yield, trimethylsilyl fluoride 71, and HMDSO 7 [90]. Di(fluorosulfonyl)phenoxysulfonylmethane 1318 reacts with excess lithium trimethylsilanolate 98 to give, via 1319, vvdth elimination of HMDSO 7, the lithium salt 1320 in 95% yield [91] (Scheme 8.35). 

Carbon-phosphorus double bonds are also formed in addition reactions of tris(trimethylsilyl)phosphine 1692 (which can be readily prepared from white phosphorus, sodium, and TCS 14 [13a,b,c]) to give oxazohum fluorides 1691 which then give the azaphospholes 1694, via 1693 [3, 14]. On addition of 1692 to 1695, the diazaphosphole 1696 [3, 15] is prepared, whereas l,3-azaphospholo[l,2a]pyridines 1698 [16] are formed from 1692 and 1697, and 1,3-thiaphospholes 1700 are formed from the dithiohum fluorides 1699 [17]. l,3-Benzodiphospholyl anions 1703 are generated by reaction of acid chlorides with the dihthium salts 1701, via 1702 [18] (Scheme 11.3). 

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