Sulfonium salts alkylation with

Resin-bound benzylic thioethers can be converted to sulfonium salts by S-alkylation with triethyloxonium tetrafluoroborate. These sulfonium salts react with palladium(O) complexes to yield benzylpalladium complexes, which undergo Suzuki coupling with arylboronic acids (Entry 7, Table 4). 

A modification of this general procedure was used in the synthesis of (prop-2-enylidene)cyclo-propane (allylidenecyclopropane, 12).Allyl bromide was first alkylated in 81 -90% yield with l-lithio-l-(phenylsulfanyl)cyclopropane (10) in the presence of copper(I) iodide or cop-per(I) iodide-dimethyl sulfide. The adduct was then methylated with methyl fluorosulfonate or with dimethyl sulfate, and the sulfonium salt cleaved with powdered potassium hydroxide in dimethyl sulfoxide, to give the product in 50-70% overall yield for the second step. 

Sulfur IS more nucleophilic than oxygen (Section 8 7) and sulfides react with alkyl halides much faster than do ethers The products of these reactions called sulfonium salts, are also more stable than the corresponding oxygen analogs... 

Section 16 17 Sulfides react with alkyl halides to give sulfonium salts... 

It is well known that aziridination with allylic ylides is difficult, due to the low reactivity of imines - relative to carbonyl compounds - towards ylide attack, although imines do react with highly reactive sulfur ylides such as Me2S+-CH2-. Dai and coworkers found aziridination with allylic ylides to be possible when the activated imines 22 were treated with allylic sulfonium salts 23 under phase-transfer conditions (Scheme 2.8) [15]. Although the stereoselectivities of the reaction were low, this was the first example of efficient preparation of vinylaziridines by an ylide route. Similar results were obtained with use of arsonium or telluronium salts [16]. The stereoselectivity of aziridination was improved by use of imines activated by a phosphinoyl group [17]. The same group also reported a catalytic sulfonium ylide-mediated aziridination to produce (2-phenylvinyl)aziridines, by treatment of arylsulfonylimines with cinnamyl bromide in the presence of solid K2C03 and catalytic dimethyl sulfide in MeCN [18]. Recently, the synthesis of 3-alkyl-2-vinyl-aziridines by extension of Dai s work was reported [19]. 

Alkyl halides, treated with thioethers, give sulfonium salts. Other leaving groups have also been used for this purpose. ... 

Thia-[2,3]-Wittig sigmatropic rearrangement of lithiated carbanions 47, obtained by deprotonation of the S-allylic sulfides 46, affords the thiols 48 or their alkylated derivatives 49. The corresponding sulfonium ylides 51, prepared by deprotonation of the sulfonium salts 50 also undergoes a [2,3]-sigmatropic shift leading to the same sulfides 49 [36,38] (Scheme 13). As far as stereochemistry is concerned, with crotyl (R R =H,R =Me) and cinnamyl (R, R =H,R =Ph) derivatives, it has been shown that the diastereoselectivity depends on the nature of the R substituent and on the use of a carbanion or an ylide as intermediate. 

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. 

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). 

The Cu(I)-catalyzed cyclization for the formation of ethyl ( )-tetrahydro-4-methylene-2-phenyl-3-(phenylsulfonyl)furan-3-carboxylate 82 has been accomplished starting from propargyl alcohol and ethyl 2-phenylsulfonyl cinnamate. Upon treatment with Pd(0) and phenylvinyl zinc chloride as shown in the following scheme, the methylenetetrahydrofuran 82 can be converted to a 2,3,4-trisubstituted 2,5-dihydrofuran. In this manner, a number of substituents (aryl, vinyl and alkyl) can be introduced to C4 <00EJO1711>. Moderate yields of 2-(a-substituted N-tosyIaminomethyl)-2,5-dihydrofurans can be realized when N-tosylimines are treated with a 4-hydroxy-cis-butenyl arsonium salt or a sulfonium salt in the presence of KOH in acetonitrile. The mechanism is believed to involve a new ylide cyclization process <00T2967>. 

In addition to routes involving resolution and asymmetric synthesis, optically active sulfonium salts have been prepared in a stereospecific way by Andersen (158,159). Thus, synthesis of the optically active dialkyl-p-tolylsulfonium salts 114 from the optically active ethoxy-sulfonium salt 115 was accomplished by the addition of alkyl Grig-nard or dialkylcadmium reagents. This reaction occurs with inversion... 

Another aspect of the reactivity of the sulfur atom is illustrated by a reaction done on thianthrene. Indeed, 8 is not sufficiently nucleophilic to be alkylated by methods that work well with dialkyl and alkyl aryl sulfides, although Saeva was able to alkylate it by reaction with -cyanobenzyl bromide and silver triflate <1986T6123>. The sulfonium salt 52 bearing a methyl group can be obtain by an acid-promoted reaction with methyl formate (Equation 4) <1998JCX37522>. 

Alkylation of Etiolates with Chiral Selenonium Salts, Sulfonium Salts and Mixed Sulfates... 

The selenonium and sulfonium salts act as chiral alkylating agents for carbon nucleophiles under weakly basic conditions which avoid any ylide formation from the salt. When 2-methoxycarbonyl-l-oxoindane is treated with an (.S )-etliyl(methyl)phenylselenoniurn perchlorate, the (S)-2-methyl and (i )-2-ethyl derivatives are obtained with a low enantiomeric excess (Table 1). Reac-... 

Table 1. Enantioselective 2-Alkylation of 1,3-Dicarbonyl Compounds with Chiral Selenonium or Sulfonium Salts...

The 2-methyl and the 2-ethyl derivatives have opposite configurations. Moreover, their configurations are associated with the configuration of the alkylating sulfonium salt (l )-sul-fonium salts always lead to (R)-2-methyl and (5 )-2-ethyl derivatives, whereas the reverse is observed with (S)-sulfonium salts. No change in the absolute configuration of the products is detected when the counterion is changed from -10-camphorsulfonate to perchlorate (Table 1). 

Alkylation of 2-methoxycarbonyl-l-oxoindane with these sugar-substituted sulfonium salts gives the (/f)-2-alkyl derivatives with enantiomeric excesses up to 12%, while alkylation of ethyl 2-methyl-3-oxobutanoate with allyl or benzyl(aryl)sulfonium perchlorates gives 2-allyl-(or benzyl)-substituted ethyl 2-methyl-3-oxobutanoates 5 with enantiomeric excess up to 25%12. 

Alkyl halides, treated with thioethers, give sulfonium salts.776... 

Isothiochroman undergoes simple alkylation at the sulfur to form sulfonium salts,237 is ring-opened and desulfurized with Raney nickel,244 and is ring-opened to 2-(o-tolyl)ethyl mercaptan with Ca(NH3)6.258... 

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