Dimethyl sulfonium groups

An intramolecular nucleophilic substitution of the dimethyl sulfide group by a cathodically generated radical anion is postulated in the formation of the in-dane derivative 133 from the sulfonium salt 134 (Eq. (203)). 

The overall strategy is shown in Figure 2. In the first step, nonradio-active cobalt (II) is bound to bleomycin A2 and air-oxidized to form the stable cobalt (III)-bleomycin A2 complex. The dimethyl(y-aminopropyl)-sulfonium group at the right side of the structure is unique to bleomycin A2 the other bleomycins have quite different terminal amine residues. Since the biological transport properties of all of the bleomycins are similar (17), the structure of the terminal amine residue appears to have relatively little influence on transport into cancer cells therefore this residue is a promising site for chemical modification. 

Chloro(dimethyl)sulfonium salts are extremely reactive, usually losing the chlorine as anion and thus able to transfer the dimethylsulfonium group readily to nucleophilic compounds such as alcohols, compounds containing acidic CH groups, organic sulfides, and disulfides.627... 

In the alcohol oxidations, the sulfonium intermediate (2, nucleophile = R2C(OH)) loses a proton and dimethyl sulfide to give the carbonyl compound (42). The most common mechanism for the decomposition of (2) is attack by a mild base to remove a proton from one of the methyl groups. Subsequent cycHc coUapse leads to the carbonyl compound and dimethyl sulfide (eq. 9) ... 

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]. 

Frejd and co-workers utilized a different tactic for aniline cyclization by first employing a Heck-Jeffery protocol under solvent-free conditions to prepare o-amino dehydrophenylalanine derivatives from o-aminoaryl iodides with the former undergoing a spontaneous la cyclization-elimination sequence to afford 2-methoxycarbonyl indoles <06S1183>. Dimethyl(methylthio)sulfonium trifluoromethanesulfonate (DMTST) was used by the Okuma group to promote the cyclization of o-vinyl-A-p-toluenesulfonylanilide to N-tosylindole <06CL1122>. 

The very rapid exchange reaction between dimethyl sulfide and MeSSMe2 (43) is accompanied by a much slower, and irreversible, reaction (47) between the same reagents that involves nucleophilic attack of the sulfide on one of the sulfonium methyl groups and that leads to the formation of trimethylsulfonium ion and dimethyl disulfide (Kim and Caserio, 1974). Other sulfides (RSCH3) react similarly to give RS(CH3)2. When the sulfide is trideuteriomethyl... 

A. Hasegawa, M. Ogawa, H. Ishida, and M. Kiso, a-Predominant glycoside synthesis of Af-acetylneuraminic acid with the primary hydroxyl group in carbohydrates using dimethyl-(methylthio)sulfonium triflate as a glycosyl promoter, J. Carbohydr Chem. 9 393 (1990). 

Aluminum chloride, 15 Arenediazonium tetrafluoroborates, 19 Rhodium(II) carboxylates, 266 Tris(dimethylamino)sulfonium difluoro-trimethylsilicate, 336 Asymmetric reactions Addition reactions to carbonyl groups Bis(2,4-dimethyl-3-pentyl) tartrate, 36 (S)-( + )-2-Methoxymethylpyrrolidine, 180... 

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... 

Examples of 5-exo cyclizations in which the hydroxy group is constrained by a five-membered ring are shown by equation (53). The stereoselectivity in these cyclizations ranges from quite high in iodocy-clization (9 1 in H2O and >20 1 in CH2CI2) to only moderate (2—3 1) with mercury and phenylselenenyl chloride. P This type of cyclization has been widely applied to synthesis of prostacyclins.146 Similar cyclizations with dimethyl(methylthio)sulfonium fluoroborate have been reported recently.35... 

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