Thiiranium ion

L abbe, J.-P. Dekerk, S. Toppet, J.-P. Declercq, G. Germain, and M. Van Meerssche, Tetrahedron 

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S-Substituted thiiranium ions react with water and alcohols to give trans ring opening (Scheme 72). A report that oxygen nucleophiles attack sulfur as well as carbon has been shown to be incorrect (79ACR282). The intermediate thiiranium ion (57) in the presence of lithium perchlorate readily yields the carbenium ion which undergoes a transannular hydride... 

S-Substituted thiiranium ions react with secondary amines to give ring-opened products. Nitriles also react with thiiranium ions, probably via an open carbenium ion whose formation is favored by increasing the polarity of the medium by the addition of lithium perchlorate (Scheme 79) (79ACR282). An intramolecular displacement by an amide nitrogen atom on an intermediate thiiranium ion has been invoked (80JA1954). 

Thiirane 1-oxide undergoes acid-catalyzed ring opening by ethanethiol to give ethyl 2-ethylthioethyl disulfide. Treatment of thiirane 1,1-dioxide with thiolate anions, sodium sulfide or thiourea gives /3-mercaptosulfinic acid derivatives (75S55). Thiiranium ions are attacked at carbon by most sulfur nucleophiles (79ACR282), but see Section 5.06.3.4.3 for exceptions. 

Halide ions may attack 5-substituted thiiranium ions at three sites the sulfur atom (Section 5.06.3.4.5), a ring carbon atom or an 5-alkyl carbon atom. In the highly sterically hindered salt (46) attack occurs only on sulfur (Scheme 62) or the S-methyl group (Scheme 89). The demethylation of (46) by bromide and chloride ion is the only example of attack on the carbon atom of the sulfur substituent in any thiiranium salt (78CC630). Iodide and fluoride ion (the latter in the presence of a crown ether) prefer to attack the sulfur atom of (46). cis-l-Methyl-2,3-di-t-butylthiiranium fluorosulfonate, despite being somewhat hindered, nevertheless is attacked at a ring carbon atom by chloride and bromide ions. The trans isomer could not be prepared its behavior to nucleophiles is therefore unknown (74JA3146). 

Sometimes, a direct ion-pairing of the chiral cations and anions 8 or 15 is necessary to maximize the NMR separation of the signals [115,116]. Cationic species as different as quaternary ammonium, phosphonium, [4]heterohelice-nium, thiiranium ions, (rj -arene)manganese, ruthenium tris(diimine) have been analyzed with success (Fig. 23). 

Alkenes and alkynes react with sulfur dichloride (SC12), giving 2-chloroethyl(or vinyl)sulfenyl chlorides. The reaction is an electrophilic addition to the multiple bond, and consequently the possible intermediacy of thiiranes, or thiiranium ions analogous to bromonium ions, has been... 

Neighboring group participation effects appear to play a crucial role in the nucleophilic substitution of chlorine in Michael adducts of 1-R, 2-R, 3-X. Thus, this substitution proceeds very easily in any of the adducts formed with an electron rich nitrogen, sulfur and oxygen Michael donor. For the adducts of nitrogen nucleophiles, the facile substitution of the chlorine has been suggested to occur via formation of intermediate aziridinium ions 103 [8] (Scheme 32), and this postulate was later supported by isolation of azaspiropentane derivatives under appropriate conditions in several reactions (see Sect. 3.2.2) [11b, 53,56]. It is most likely that alkylthio substituents in adducts of type 85 participate in the same way to first form spirocyclopropane-annelated thiiranium ion intermediates which are subsequently opened by attack of the incoming nucleophile. 

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