Dimethyl tetrafluoroborate

In contrast, cleavage of alkyl and also aryl thioglycosides with dimethyl(meth-ylthio)sulfonium tetrafluoroborate takes place with total inversion of configuration [9] (equation 12) The latter reagent is commercially available or easily prepared as a crystalline nonhygroscopic solid [10]. All the three above-mentioned reagents... 

Heating thioacetal 410 in the presence of dimethyl(methylthio)sulfonium tetrafluoroborate (DMTSF) yielded l-methylperhydropyrido[l,2-n]pyrimi-dine-2,6-dione (411) (OOJOC235). 

Notable examples of general synthetic procedures in Volume 47 include the synthesis of aromatic aldehydes (from dichloro-methyl methyl ether), aliphatic aldehydes (from alkyl halides and trimethylamine oxide and by oxidation of alcohols using dimethyl sulfoxide, dicyclohexylcarbodiimide, and pyridinum trifluoro-acetate the latter method is particularly useful since the conditions are so mild), carbethoxycycloalkanones (from sodium hydride, diethyl carbonate, and the cycloalkanone), m-dialkylbenzenes (from the />-isomer by isomerization with hydrogen fluoride and boron trifluoride), and the deamination of amines (by conversion to the nitrosoamide and thermolysis to the ester). Other general methods are represented by the synthesis of 1 J-difluoroolefins (from sodium chlorodifluoroacetate, triphenyl phosphine, and an aldehyde or ketone), the nitration of aromatic rings (with ni-tronium tetrafluoroborate), the reductive methylation of aromatic nitro compounds (with formaldehyde and hydrogen), the synthesis of dialkyl ketones (from carboxylic acids and iron powder), and the preparation of 1-substituted cyclopropanols (from the condensation of a 1,3-dichloro-2-propanol derivative and ethyl-... 

The C6 position of a V,./V-dialkyl-3//-azepin-2-amine, e.g. 1, displays remarkable reactivity towards electrophilic substitution, and with dimethyl(methylsulfanyl)sulfonium tetrafluorobor-ate undergoes methylsulfanylation and quaternization to yield 6-(methylsulfanyl)-3//-azepin-ium tetrafluoroborates, e.g. 2, identical to those obtained by quaternization of the free bases with trityl tetrafluoroborate.64 Basification of the salts with potassium carbonate yields the free bases, e.g. 3, which decompose during distillation or on exposure to air. 

Neutral tertiary and secondary amides react with very reactive alkylating agents, such as triethyloxonium tetrafluoroborate, to give O-alkylation.63 The same reaction occurs, but more slowly, with tosylates and dimethyl sulfate. Neutralization of the resulting salt provides iminoethers. 

Thianthrene cation radical tetrafluoroborate 139 has been found to add to 2,3-dimethyl-2-butene 138 at —15 °C to give adduct 2,3-dimethyl-2,3-(5,10-thianthreniumdiyl)butane ditetrafluoroborate 140, which was isolated and characterized by 111 NMR spectroscopy at —15 °C (see Equation 40) <2006JOC3737>. The adduct 140 was stable in CD3CN solution at —15 °C but decomposed quickly at 23 °C, forming the salt of 2,4,4,5,5-pentamethyl-2-oxazoline with loss of thianthrene. 

The anodic oxidation of the tetrafluoroborate anion occurs at potentials higher than 2.1 V and the remaining hexafluorophosphate and imide anions are oxidised at potentials higher than 2.0 V. Hence, the stability window of the EMImBF4 and BMImBF4 is 4.2 V. Ionic liquids BMImPF6 and EMImN(Tf)2 shows a similar stability window of ca. 4.1 V. However, the window of the BMPyN(Tf)2, is considerably lower ca. 3.0 V. This is consistent with data (ca. 4.1-4.2 V) found for a series of ionic liquids based on EMIm+ and DMPIm+ (l,2-dimethyl-3-propylimidazolium) cations [12],... 

DMTSF = dimethyl(methylthio)sulfonium tetrafluoroborate X = H, C02Me, aryl... 

Padwa et al. <20010L1781, 2004JOG33> succeeded in constructing the saturated pyrrolizinones 125 by photo-chemical-promoted intramolecular cyclization of thiolactams 123 leading to 124. Treatment of the latter with Raney-Ni in ethanol afforded compound 125a, while treatment with dimethyl(methylthio)sulfonium tetrafluoroborate (DMTSF) followed by Raney-Ni leads to bicyclic hexahydropyrrolizin-3-ones 125b (Scheme 21). 

Epichlorohydrin, 54, 20 with boron trifluoride diethyl etherate and dimethyl ether to give trimethylox-onium tetrafluoroborate, 51, 142... 

Boron trifluoride, with dimethyl ether and epichloro-hydrin to give trimethyl-oxonium tetrafluoroborate,... 

Irradiation of the sodium salt 517 in a solution of maleonitrile in THF gave a 30% yield of the as-spiro[2.6]nonatrienedicarbonitrile 524 (Scheme 6.106). Analogously, fumaronitrile led to the trans-diastereomer 525 exclusively in 29% yield [193b], which was also obtained from (trimethylsilyl)tropylium tetrafluoroborate (519) as precursor of 5 [208]. The interception of 5 by dimethyl fumarate succeeded by generating 5 from 517 by either photolysis [193] or thermolysis [193, 194] and from 519 [208] and afforded the dimethyl trans-dicarboxylate 526 in yields of 50, 40 and 42%, respectively. Liberation of 5 in the presence of dimethyl maleate led also to 526 [194, 214], In this reaction, the isomerization of dimethyl maleate to fumarate could have interfered and hence pretended the loss of the stereochemical information, since... 

Volume 75 concludes with six procedures for the preparation of valuable building blocks. The first, 6,7-DIHYDROCYCLOPENTA-l,3-DIOXIN-5(4H)-ONE, serves as an effective /3-keto vinyl cation equivalent when subjected to reductive and alkylative 1,3-carbonyl transpositions. 3-CYCLOPENTENE-l-CARBOXYLIC ACID, the second procedure in this series, is prepared via the reaction of dimethyl malonate and cis-l,4-dichloro-2-butene, followed by hydrolysis and decarboxylation. The use of tetrahaloarenes as diaryne equivalents for the potential construction of molecular belts, collars, and strips is demonstrated with the preparation of anti- and syn-l,4,5,8-TETRAHYDROANTHRACENE 1,4 5,8-DIEPOXIDES. Also of potential interest to the organic materials community is 8,8-DICYANOHEPTAFULVENE, prepared by the condensation of cycloheptatrienylium tetrafluoroborate with bromomalononitrile. The preparation of 2-PHENYL-l-PYRROLINE, an important heterocycle for the synthesis of a variety of alkaloids and pyrroloisoquinoline antidepressants, illustrates the utility of the inexpensive N-vinylpyrrolidin-2-one as an effective 3-aminopropyl carbanion equivalent. The final preparation in Volume 75, cis-4a(S), 8a(R)-PERHYDRO-6(2H)-ISOQUINOLINONES, il lustrates the conversion of quinine via oxidative degradation to meroquinene esters that are subsequently cyclized to N-acylated cis-perhydroisoquinolones and as such represent attractive building blocks now readily available in the pool of chiral substrates. 

Perhaps the most effective synthesis, albeit an expensive one, involves the direct methylation of alkylimidazoles using trimethyloxonium tetrafluoroborate with concomitant formation of the tetrafluoroborate anion as shown in Scheme 4.3 [12]. This is a single step reaction in which no chloride is present at any stage of the synthesis. The only by-product from this reaction is dimethyl ether which is a volatile and inert gas and it is easily removed. 

Sulfenyl fluorides are extremely unstable and therefore only few perhalosulfenyl fluorides have so far been reported122. The formal addition of the elements of methanesulfenyl fluoride to carbon-carbon double bonds has been obtained123 by a one-pot reaction with dimethyl(methylthio)sulfonium tetrafluoroborate and triethylammonium tris(hydrofluo-ride). With this system also the addition to double bonds is highly stereoselective, at least... 

Methylation of pyrido[l,2-6]cinnolinium-ll-olate (17, R = H) with the soft dimethyl sulfate gave only the A -methyl derivative 43 (74JHC125), whereas the harder trimethyloxonium tetrafluoroborate yielded the 11-methoxy derivative 77 (92CB929). Methylation of pyrido[2,l-a]phthal-azinium-7-olate (20) with methyl iodide afforded a 1 9 mixture of the... 

A cyclized version, xilobam (S), is synthesized from ji-methylpyrrolidone by conversion to the imine (]) by sequential reaction with triethyloxonium tetrafluoroborate and then anhydrous ammonia. When this is reacted with 2,6-dimethyl-phenyl i socyanate, the centrally acting muscle relaxant xilobam (8) is formed. ... 

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