Episulphonium intermediates

The latter reaction sequence was of importance since addition of the thiol glutathione to arene-oxide intermediates under control of hepatic glutathione-S-epoxide transferase enzyme(s) is a very important metabolic transformation. It would appear probable that most of the structures of the arene oxide-glutathione adducts (premercapturic acids) reported in the literature before 1975 are incorrect with respect to the position of the hydroxy and thioether substituents (they should now be reversed). Addition of thiomethoxide anion to arene oxide 70 may occur via 1,6- and 1,4-addition, although one of these thioether adducts could also be accounted for by the alternative arene-oxide intermediate obtained from an oxygen-walk. Styrene 3,4-oxide (S3) has been observed to react with ethanethiol to yield three adducts which appear to aromatize to three isomeric ethylthiostyrenes without the formation of episulphonium intermediates. ... 

The intervention of episulphonium ion intermediates in the synthesis of azidosugars has been postulated by Christensen and Goodman in order to rationalize the product (140), formed on interaction of azide ion with the furanoside (141). Direct replacement with inversion at C(2) did not occur rather, a mixture of the diazides 140 2ind 142 was obtained by nucleophilic attack of azide ion on the episulphonium ion (143). A similar episulphonium intermediate (144) has been invoked to rationalize the conversion of methyl 4,6-0-benzylidene-... 

We perceive that this solvent effect is due to the competition between the equatorial phenylthio moiety and the solvent for the active sites of the promoter, tin(II) chloride. When ether is employed as the solvent, it may form a complex with the active sites of the promoter (62 and 63), thereby allowing the participation of the sulfur and the formation of the episulphonium intermediate (64). Reaction of the glycosyl acceptor with this transient intermediate selectively forms the p-glycoside (65). We found that when the reaction was carried out in dichloromethane, in the presence of dimethyl sulfide, the p-glycoside was obtained, presumably due to the complexation of the additive to the active sites of the promoter. When dichloromethane is used as the solvent with no dimethyl sulfide... 

This reaction is employed in the ring closure, as in Eq. (55) [228], where XXI is anodically oxidized in methanol. It might be surprising that a five-membered ring is formed in preference to a six-membered ring an episulphonium ion is probably formed as an intermediate. 

The addition of sulphenyl or selenenyl chlorides to dialkyl alkatrienylphosphonates has led to the claim that heterocyclic phosphonic derivatives may be formed (equations 35 and 36) admixed with, but inseparable from, the l,2-oxaphosph(V)ol-3-ene co-products, and also thought to be derived through the 2,3-episulphonium (or analogous selenonium) intermediates . ... 

Thio-substituted j8-lactams are conveniently prepared by a [3 + 1] cyclization involving the 1,3 -dianion of a phenylthio-acetamide and methylene iodide. It is thought that an episulphonium salt is an intermediate (Scheme 121). 

In the synthesis of a p-Iactam, the construction of the N-C(4) bond requires P-halo-amides, which are not readily available. A new method employs the addition of sulphenyl halides to ap-unsaturated amides, e.g. (84), followed by intramolecular substitution. The method provides a stereoselective route to the P-lactam (86) via the episulphonium-type intermediate (85). 

In aqueous solution the p-chloroethyl functional group of SM forms a reactive cyclic intermediate, an episulphonium ion (ESI), that subsequently reacts with a nucleophile to form an alkylated product. This is a nucleophilic substitution (SN) reaction. If the rate determining step in the reaction is unimolecu-lar these reactions are denoted as SNl, if bimolecular, SN2 (Scheme 2.1). 

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