Dimethyl sulfonium 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). 

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. 

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). 

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... 

To methylenecyclohexane (0.96 g. 10 mmol) in CH2C12 (20 mL) was added at 0 C with stirring dimethyl(methylsulfanyl)sulfonium tetrafluoroborate (2.16 g, 11 mmol) and stirring was continued for 20 min. Afterwards, a slight excess of Et3N 3HF (2.4 g, 15 mmol) dissolved in CH2C12 (10 mL) was added dropwise at 0 "C and the mixture was stirred for a further 3 h at rt. The mixture was then poured onto ice water, neutralized, extracted, dried, and the solvents evaporated to give the crude title compound yield 1.54 g (95%) bp 72-73 C/l 5 Torr. 

Bromopentacarbonylmanganese, 49 tom -Bromotetracarbonyl(methyl-methylidyne)chromium, 50 frmethylidyne)tungsten, 49 Carbonylhydridotris(triphenylphosphine)-rhodium(I), 329 Chromium carbonyl, 51 Decacarbonyldimanganese, 49 Dicarbonylcyclopentadienylcobalt, 96 Dicarbonyl(cyclopentadienyl)[(dimethyl-sulfonium)methyl]iron(II) tetrafluoroborate, 98... 

Addition of a sulfenyl chloride to an alkene in the presence of silver fluoride affords (3-fluoro sulfides, as shown in equation (2).18 The same trans adducts can also be prepared from the sulfenyl chloride adducts and silver fluoride. An alternative procedure for the formal addition of methanesulfenyl fluoride to alkenes involves the use of dimethyl(methylthio)sulfonium tetrafluoroborate and triethylamine tris(hy-drofluoride) as in equation (3).19... 

An alternative route from alkenes to 2-azasulfides reported by the groups of Caserio and Trost involves addition of a thiosulfonium salt, e.g. dimethyl(methylthio)sulfonium tetrafluoroborate (MeSS-Me2+ BF4-), followed by treatment of the resultant thiosulfenylated adduct with an amine or other nitrogen nucleophiles (Schemes 2320 and 24).35 Trost reports that the addition of the thiosulfonium salt can be followed by addition of an oxygen nucleophile, such as acetate, or a carbon nucleophile, such as cyanide, effecting oxosulfenylation and cyanosulfenylation, respectively (Scheme 25).36... 

Azasulfenylation of alkenesf s The adducts of dimethyl(methylthio)-sulfonium tetrafluoroborate (1) with alkenes react slowly but smoothly with various nitrogen nucleophiles to give products of overall rrarw-addition to the alkene. Regioselectivity depends on the substitution pattern of the alkene and on the nucleophilicity of the attacking reagent, and is subject to some control. The mechanism of this azasulfenylation is not certain it may involve an episulfonium ion. 

Dimethyl methylphosphonate, 203 Dimethyl(methylthio)sulfonium tetrafluoroborate, 204-206 Dimethyl 2-oxoglutaconate, 206-207 Dimethyl 3-oxoglutarate, 193-194... 

The ring-opening reaction on 4-methyl-2-thia-7-aza-tricyclo[5.3.0.01,4]decan-8-one 39 was carried out by treatment with dimethyl(methylthio)sulfonium tetrafluoroborate (DMTSF) <20010L1781, 2004JOG33>. Methylthiolation of the thietane sulfur produces a transient alkylthiosulfonium salt which easily dissociates to the iV-acyliminium ion 40. Once formed, 40 readily undergoes loss of a proton to give the product 40 (Equation 11). 

A convenient method for the synthesis of annulated 2-alkylthio-5-aminofurans has been described by Padwa et al. The reaction sequence involves the formation of a thionium group from readily available dithioacetals upon treatment with dimethyl(methylthio)sulfonium tetrafluoroborate (DMTSF). The thionium ion undergoes cyclization with the 7-carbonyl group followed by an elimination step to yield the 2,3,5-trisubstituted furans in good to excellent yields (Equation 29) <2002JOC1595>. The alkylthioaminofuran reaction products can be utilized to constmct polyclic frameworks of natural products in a subsequent Diels-Alder reaction. 

Dimethyl(methylsulfanyl)sulfonium tetrafluoroborate and triethylamine trishydrofluoride react with alkenes by a stereospecific formal, 2-addition of methancsulfenyl fluoride across the C =C bond. 524,693 example, cyclohexene undergoes addition of the elements of methancsulfenyl fluoride to form t -fl x-l-fluoro-2-(methylsulfanyl)cyclohexane (9) in 90% yield. 

Sulfenylation with simultaneous nucleophilic addition to alkenes can be efficiently achieved using dimethyl(methylthio)sulfonium tetrafluoroborate (DMTSF) in the presence of an appropriate nucleophile. This approach has recently been applied to the synthesis of a variety of a-function-alized thio derivatives39 41. 

Table 3. Formation of a-Amino, a-Nitro. ot-Azido and ot-Pyrrolidino Methylsulfenylated Compounds by Treatment of Alkenes with Dimethyl(methylthio)sulfonium Tetrafluoroborate and a Nitrogen Nucleophile39...

Nucleophilic attack on alkenes initiated by dimethyl(methylthio)sulfonium tetrafluoroborate is also a very efficient method for the addition of carbon nucleophiles to unsaturated systems40,41. The results of cyanosulfenylation of alkenes are collected in Table 440. 

Treatment of cycloalkenes 15 with dimethyl(methylthio)sulfonium tetrafluoroborate (DMTSF) in acetonitrile210,211, followed by evaporation of the solvent, addition of dimethylformamide to the residue and further addition of the sodium anion of 6-amino-4-chloropurine provides owu-2-methylthio nucleoside analogs 16 in moderate yield with total diastereoselectivity212. 

Abbreviations Ac acetyl Bn benzyl BSP 1-benzenesulfinyl piperidine BTIB bis(trifluoroacetoxy)iodobenzene DAST (diethylamino)sulfur trifluoride DDQ 2,3-dichloro-5,6-dicyano-/)-benzoquinone DMDO dimethyldioxirane DMTSF dimethyl(methylthio)sulfonium tetrafluoroborate DMTST dimethyl(methylthio)sulfonium triflate DTBMP 2,6-Ai-tert-butyl-4-methylpyridine DTBP 2,6-di-tert-butylpyridine DTBPl 2,6-di-tert-butylpyridinium iodide FDCPT l-fluoro-2,6-dichloropyridinium triflate FTMPT l-fluoro-2,4,6-trimethylpyridinium triflate IDCP iodonium dicollidine perchlorate IDCT idonium dicollidine triflate LPTS 2,6-lutidinium p-toluenesulfonate LTMP lithium tetramethylpiperidide Me methyl MPBT S-(4-methoxyphenyl) benzenethiosulflnate NBS A-bromosuccinimide NIS A-iodosuccinimide NlSac A-iodosaccharin PPTS pyridinium p-toluenesulfonate TBPA tris(4-bromophenyl)ammoniumyl hexachloroantimonate Tf trifluoromethanesulfonyl TMTSB methyl-bis(methylthio)sulfonium hexachloroantimonate TMU tetramethylurea Tr trityl TTBP 2,4,6-tri-tert-butylpyrimidine. 

Trost has reported the use of dithioacetals as initiators in vinylsilane-terminated cyclizations (Scheme 11). Reaction of the dimethyl thioketal (26) with dimethyl(methylthio)sulfonium tetrafluoroborate (DMTSF) led to the formation of the allylic sulfide (28) via a 2,3-sigmatropic rearrangement of the initially formed sulfonium salt (27a), which may have been catalyzed by complexation with excess DMTSF. 

The tris(methylsulfanyl)cyclopropenylium salt 19 was also prepared from tetrachlorocyclo-propene (3) by the reaction with dirnethyl(methylsulfanyl)sulfonium tetrafluoroborate and dimethyl disulfide." ... 

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