Synthesis and nitration of dimethyl-(3-thienyl)sulfonium salts

Conclusions A method was developed for the synthesis of the difficultly accessible methyl (5-nitro-3-thienyl) sulfide, which consisted in the conversion of methyl 3-thienyl sulfide to the sulfonium salt, with subsequent nitration and demethylation.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1161–1163, May, 1973.     

Synthesis of some sulfonium salts and ylides containing the isoxazole nucleus

Some dimethylisoxazolylmethylsulfonium salts and the corresponding ylides were synthetized and their chemical behaviour studied. Dimethylsullonium-5-isoxazolyl methylides (XIa,b) give 5-isoxazolyloxiranes (XIIa,d) and XIII when allowed to react with carbonyl compounds. Ring opening products from these oxiranes are also reported.     

Synthesis and reactions of the optically active selenols derived from monoterpenes

A convenient methodology for the synthesis of optically active selenols, derived from p-menthane, carane, and pinane, is described. The selenols were oxidized with air to give the optically active diselenides, and were also converted into the corresponding allylic selenides via reaction with Z- and E-cinnamyl, geranyl, and neryl chlorides. Oxidation of the allylic selenides with mCPBA gave the optically active alcohols via [2,3]-sigmatropic rearrangement of the in situ generated allylic selenoxides.     

An efficient synthesis of imidazolinium salts using vinyl sulfonium salts

The synthesis of imidazolinium salts from the reaction of formamidines and (2-bromoethyl)diphenylsulfonium triflate is described. A variety of symmetrical and unsymmetrical imidazolinium triflate salts were synthesized in high yield in short reaction times under mild conditions. Aromatic and aliphatic N-substituents work well. The reaction is proposed to proceed via generation of a vinyl sulfonium salt intermediate from the bromoethylsulfonium triflate.     

Photoinitiated polymerization of aryl cyclic sulfonium salts

Polymers are produced by direct photolysis of substituted aryl cyclic sulfonium Zwitterionic salts in solution or film. Analysis of zwitterionic monomers via ¹³C NMR, UV, and IR spectroscopy as well as X‐ray diffraction clearly identifies the structures taking part in the photoinduced polymerization in the solid crystalline films. The protonated form of the zwitterionic monomers, however, fails to produce detectable amounts of polymer upon photolysis under any conditions. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 571–584, 2001     

Stereoselectivity in the alkylation of sulfonium salts

The stereoselectivity in the alkylation of sulfonium salts is attributed to the formation of an intermediate lithio-sulfonium salt rather than a free ylid.     

Synthesis of thiols from isobornylphenols

4-(3-Sulfanylpropyl)-2-isobornyl-6-methylphenol and 4-(sulfanylmethyl)-2,6-diisobornylphenol were synthesized from the corresponding 4-(bromoalkyl)phenols according to known procedures. Isobornylphenol with a trimethylene linker was converted into thiol by alkaline hydrolysis of thiouronium salt. The methylene-bridged analog was obtained by reduction of S-benzyl thioacetate with LiAlH₄.     

C-prenylation of isopentenyl derivatives with sulfonium salts

Reaction of isopentenyl acetate (or n-butyl ether) with oil soluble prenyl sulfonium salts in the presence of a hindered amine leads to prenylation on the terminal carbon atom.     

Stabilization of p-block organoelement terminal hydroxides, thiols, and selenols requires newer synthetic strategies

Metal hydroxides represent a very interesting and highly useful class of compounds that have been known to chemists for a very long time. While alkali and alkaline earth metal hydroxides (s‐block) are commonplace chemicals in terms of their abundance and their use in a chemical laboratory as bases, the interest in Brønsted acidic molecular terminal hydroxides of p‐block elements, such as aluminum and silicon, has been of recent origin, with respect to the variety of applications these compounds can offer both in materials science and catalysis. Moreover, these systems are environmentally friendly, relative to the metal halides, owing to their ‐OH functionality (resembling that of water). Design and conceptualization of the corresponding terminal thiols, selenols, and tellurols (M? SH, M? SeH, and M? TeH) offer even more challenging problems to synthetic inorganic chemists. This concept summarizes some of the recent strategies developed to stabilize these otherwise very unstable species. The successful preparation of a number of silicon trihydroxides a few years back resulted in the generation of several model compounds for metal–silicates. The recent synthesis of unusual aluminum compounds such as RAl(OH)₂, RAl(SH)₂, and RAl(SeH)₂ with terminal EH (E=O, Se, or Se) groups is likely to change the ways in which some of the well‐known catalytic conversions are being carried out. The need for very flexible and innovative synthetic strategies to achieve these unusual compounds is emphasized in this concept.     

Direct synthesis of diastereomerically pure glycosyl sulfonium salts

It is reported that stable glycosyl sulfonium salts can be generated via direct anomeric S-methylation of ethylthioglycosides. Mechanistically, this pathway represents the first step in the activation of thioglycosides for glycosidation; however, it can further allow for the synthesis and isolation of quasi-stable sulfonium ions, representing a new approach for studying these key intermediates.     

Synthesis and conformational analysis of bicyclic sulfonium salts. Structures related to the glycosidase inhibitor australine

The syntheses of eight sulfonium compounds with structures related to the naturally occurring pyrrolizidine alkaloid, australine, in which the bridgehead nitrogen atom is replaced by a sulfonium ion, are described. The synthetic strategy relies on the intramolecular attack of a cyclic thioether across a terminal double bond in the presence of a suitable electrophile. We postulate that these compounds, having a permanent positive charge on the sulfur atom, will mimic the highly unstable oxacarbenium ion transition state in a glycosidase-catalyzed hydrolysis reaction. The conformational preferences of these compounds, based on analysis of 1H-1H vicinal coupling constants and 1D-NOESY data, are attributed to both steric and electrostatic interactions. These compounds will be used in the study of structure-activity relationships with glycosidase enzymes.     

Synthesis of pyrrolidin-2-ones via tandem reactions of vinyl sulfonium salts under mild conditions

A novel and efficient synthesis of pyrrolidin-2-ones through the tandem reactions of vinyl sulfonium salts with malonyl amides under very mild conditions is reported. The reaction demonstrates a wide tolerance toward various aryls, acyl, sulfonyl, and benzyl while aliphatic groups delivering the tetrahydro-2-oxofuran product.     

Electroorganic chemistry—XV : Electroreduction of sulfonium and ammonium salts. Formation of sulfonium ylids

In the electroreduction of sulfonium and ammonium salts, sulfonium ylid was generated from the sulfonium salt, whereas in the case of the ammonium salt, nitrogen ylid was not formed but the N+C bond was reductively cleaved. On the basis of the controlled potential electrolysis, it seems acceptable that the mechanism of formation of sulfonium ylid involves the direct electron transfer to the sulfonium salt as the initiation step.     

Synthesis and applications of chiral organoboranes generated from sulfonium ylides

The reactions of aryl-stabilized sulfonium ylides with trialkyl/triarylboranes have been investigated. Clean monohomologation of the boranes with only a small amount of the higher homologation products (<10%) was observed. The homologation products were isolated as the alcohols (treatment with H2O2/NaOH) and amines (treatment with NH2OSO3H). Although the reactions were conveniently conducted at 5 degrees C, the ylide reaction with tributylborane was very fast even at -78 degrees C (complete after 15 min). Use of chiral sulfides rendered the reactions asymmetric, and high enantioselectivity (>95% ee) was observed in all cases. The ylide-borane reaction was applied to short syntheses of the anti-inflammatory agents neobenodine and cetirizine, both of which contain a chiral diarylmethylalkoxy and diarylmethylamino moiety, respectively.     

Crystal structure of the sulfonium salts of natural azulenes

The molecular and crystal structure of dimethyl-(1,4-dimethyl-7-ethylazulyl)-sulfonium perchlorate and dimethyl-(1,4-dimethyl-7-isopropylazulyl)-sulfonium perchlorate was determined by X-ray diffraction analysis. Their crystal structure is mainly determined by C-H...π intermolecular interactions.     

Synthesis of d- and l-erythro 1,5-dithiopent-1-enopyranoside sulfonium salts and their evaluation as glycosidase inhibitors

A series of sulfonium salts derived from 1,5-dithiopent-1-enopyranosides was prepared in a three-step sequence from protected d- and l-erythrofuranoses. The key step is the nucleophilic displacement of a leaving group by a sulfur atom of carbohydrate-derived ketene dithioacetals. Such compounds were assayed for their properties as glycosidase inhibitors.