L- sulfonium

Hurtley and Smiles4 had isolated fused-ring derivatives of 2 as early as 1926, but were understandably unable to find a satisfactory explanation for the valence relationships on the basis of the views held at that time. Wizinger and Soder,6 in 1958, were the first to suggest that these aryl-l,3-benzodithiol-l-sulfonium salts were derivatives of the resonance-stabilized benzo-l,3-dithiolium cation. 

Dimethy Ipropyny l-sulfonium bromide Sulfoxides, Dimethyl sulfoxide Thiirane 1-oxide Tosy Imethylisocyanide Dialkoxysulfuranes Me,N-S-NMe, (Bisdimethylamino-sulfane) Thioacetamide Benzothiazole-2-thione, 3-methyl-Thiazolium salts - bromide, N-lauryl-Et,NCSSH Thiourea, Thioureas 1 -A cety l-2-thiourea Thiourea dioxide Selenourea Thiocyanates ArN C S (NCS),... 

The Tolfium values for S,S-dialkyl-S-(phenaq l)sulfonium salts have been measured and found to be -14.5 kcal mol This suggests that these sulfonium salts might be expected to undergo more facile electron transfer photosensitization than... 

K. Angermaier and H. Schmidbaur, The supramolecular structures of complex tri[gold(l)]sulfonium cations, Chem. Ber., 1994, 127, 2387-2391. 

Scheme 5.38 Generation of protonic acid in resist matrix PH containing an tria l sulfonium salt Ar3S X as acid generator [152,153].

Thioglycosides can be activated for gfycosylation reactions with sulfur electrophiles, e.g., with dimethyl(methylthio)sulfonium triflate or with methanesulfenyi bromide and silver(l +) to form reactive sulfonium intermediates (F. Dasgupta, 1988). 

Tetramethyl-l,2-oxathietane (138) was prepared by diazotization of 139, which was prepared from the aziridine (140) (86JA3811).Tlie reaction presumably involves the decomposition of the sulfonium ion intermediate (141).Tire dichloromethane solution of 138 at -20°C is sufficiently stable to permit exploration of the chemical reactions. Tire oxathietane 138 undergoes a formal [[Pg.248]

When bromoacetyl chloride is used instead of bromoacetic acid, the anilide 33 is formed at the first stage. Its subsequent cyclization also leads to 32. This approach to benzotellurazinone is similar to that developed for the synthesis of 2//-l,4-benzothiazin-3(4//)-ones (66CJC1247). Significantly, attempts to isolate the intermediate sulfonium salts analogous to 30 were unsuccessful. 

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). 

Sulfonium ions are themselves useful alkylating agents because a nucleophile can attack one of the groups bonded to the positively charged sulfur, displacing a neutral sulfide as leaving group. We saw an example in Section l 1.6... 

The sulfonium precursor route may also be applied to alkoxy-substituted PPVs, but a dehydrohalogenation-condensation polymerization route, pioneered by Gilch, is favored 37]. The polymerization again proceeds via a quinomethide intermediate, but die syndicsis of the conjugated polymer requires only two steps and proceeds often in improved yields. The synthesis of the much-studied poly 2-methoxy-5-(2-ethylhexyloxy)-l,4-phenylene vinylene], MEH-PPV 15 is outlined in Scheme 1-5 33, 35]. The solubility of MEH-PPV is believed to be enhanced by the branched nature of its side-chain. 

Prolonation of thiepins leads to //-thiepinium ions, for which a homoaromatic character has been discussed.24 The 5//-1 -benzothiepinium ion can be regarded as a benzohomothiopyrylium ion, whereas the 3//-l-benzothiepinium ion is postulated as having a localized sulfonium ion structure.25... 

In an extensive ab initio MO study the structures, energies and vibrational spectra of the sulfonium ions H3S with n=l-4 were studied at the MP2/6-311(2df,2pd) level of theory [70]. It was confirmed that HsS is of Csv symmetry with dsH= 134.6 pm and bond angles of 94.2° This cation had previously been isolated as a component of the salt [H3S][SbF6] [71] and had been observed spectroscopically [72]. The experimental gas phase re geometry is dsH= 135.02 pm and 0 hsh=94.189° [72] which agrees well with the ab initio calculated values by Botschwina et ah dsH=135.0 pm, aHsn=94.2° [73]. 

FIGURE 6.18 Oxidation of ortAo-methylphenols to the corresponding ortho-quinone methide via transient zwitterionic intermediates that are stabilized by forming a complex 19 with the 2,5-dihydroxy[l,4]benzoquinone-derived bis(sulfonium ylide). 

Patel, A. Netscher, T. Rosenau, T. Stabilization of ortho-quinone methides by a bis (sulfonium ylide) derived from 2,5-dihydroxy-[l,4]benzoquinone. Tetrahedron Lett. 2008, 49, 2442-2445. 

The dansyl derivative 9-azidononyl-5-(dimethylamino)naphthalene-l-sulfonate 35 was used by Yi and collaborators [91] as an azido-fluorescent label in a tandem method of sulfonium alkylation and click chemistry for the modification of biomolecules. Fluorescent labeling of a protein was successfully carried out after simple incubation of BSA with sulfonium salt 36 followed by azido-containing fluorophore 35, at room temperature. 

Yi L, Shi J, Gao S et al (2009) Sulfonium alkylation followed by click chemistry for facile surface modification of proteins and tobacco mosaic virus. Tetrahedron Lett 50 759-762... 

Shimizu and co-workers reported that thermal decomposition of A4-thiabenzenes ylides afforded both thienofuran and thiophene derivatives in addition to the expected alkyl-rearranged products. A plausible mechanism was proposed with a [3.1.0] bicyclic sulfonium salt 9 as the key reactive intermediate <2001J(P1)2269>. Warren and co-workers, in their study of stereospecific phenysulfanyl migrations, found that [l,4]-sulfanyl participation could compete with the usual [l,2]-sulfanyl participation <1999SL1211>. Rearrangement of alcohol 18 with TsCl in pyridine gave an inseparable mixture of isomeric chlorides, 19 and 20, in a ratio of 52 48, as shown in Equation (3). 

They proposed that [l,4]-sulfanyl participation gave a [2.2.1] bicyclic sulfonium salt intermediate 10a. This could be captured by the chloride anion to give either 19 (by path a) or 20 (by path b) as outlined in Scheme 3. It should be noted that the usual [l,2]-sulfanyl participation, via spirocyclic sulfonium ion 21, would only give the unrearranged chloride 19. 

Thiopyrylium ions have been shown to behave as effective dienophiles. Shimizu and co-workers demonstrated that 2-benzothiopyrylium salts undergo [4+2+]-type cationic polar cycloadditions with various 1,3-dienes yield benzo-fused bicyclic sulfonium salts <1994J(P1)3129> (see Section 8.32.2.1.2 of CHEC-II(1996)). However, in this study the authors observed that cycloaddition of 2-benzothiopyrylium salt 40 with 2,3-dimethylbuta-l,3-diene 41a with prolonged reaction times caused a decrease in yield of the cycloadduct 22a (see entries 1 and 2 in Table 5 and Equation 10). In fact, stirring of the reaction mixture for 30 h did not afford the cycloadduct at all, see entry 3, but gave an undetermined complex mixture. 

Benzothiopyrylium salts have also been shown to undergo [4+2+]-polar cycloadditions with 1,3-dienes in dry 1,2-dichloroethane at room temperature <1996J(P1)2227>. Treatment of 43 with 2,3-dimethylbuta-l,3-diene 41a afforded benzo-fused bicyclic sulfonium salts 22, as shown in Equation (12) and Table 6. The 4-cyano-substituted benzothiopyrylium salt 43d proved to be the most reactive of these substrates (see entry 4). 

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