Thioethers thiocyanates

Pyrrolethiols, readily obtained from the corresponding thiocyanates by reduction or treatment with alkali, rapidly oxidize to the corresponding disulfides. They are converted into thioethers by reaction with alkyl halides in the presence of base. Both furan- and thiophene-thiols exist predominantly as such rather than in tautomeric thione forms. 

Experiments with cyclic thioethers (80JCS(P1)1693), thiourea, thiocyanate and ethyl xan-thate always led to destruction of oxaziridines (73AJC2159). Products of complicated consecutive reactions could be isolated but only with some difficulty, e.g. (92) from a reaction with carbon disulfide (74JOC957), and (93), obtained by trapping with butadiene a product of a reaction between an oxaziridine and a thiirane (80JOC1691). 

Treatment of 3,4-dinitrofurazan with potassium thiocyanate in acetic acid at 10-20°C led to the corresponding thiocyanate 214 in 83% yield along with a small amount of 3-mercapto-4-nitrofurazan, whereas at 70-75°C the precursor was converted into a mixture of the disulfide 215 (38%) and tricycle 216 (27%). Thioether 217 was prepared in 78% yield by reaction of 3,4-dinitrofurazan and sodium sulfide (95MC25) (Scheme 145). 

Gut I, Nerudova J, Stiborova A, et al. 1985. Acrylonitrile inhalation in rats II. Excretion of thioethers and thiocyanate in urine. J Hyg Epidemiol Microbiol Immunol 29 9-13. 

Trifluoromethyl thioethers are produced in a fluoride-catalysed one-pot reaction of alkyl or aryl thiocyanates with trifluoromethyl silanes [37]. The reaction is initiated by fluoride ion displacement of the trifluoromethyl anion from the silane the thioether is formed from the thiocyanate by displacement by the trifluoromethyl anion of the cyanide ion, which then perpetuates the reaction. Trifluoromethyl selenoethers are obtained by an analogous route. In a similar manner, disulphides can be converted into trifluoromethyl thio- or selenoethers [38],... 

In the unconventional synthesis of thioethers (Scheme 4.11), cyanide ion is displaced from thiocyanates by carbanions [52, 53], which have been generated under phase-transfer catalytic conditions (cf. 4.1.12). Thiocyanates are readily obtained by a standard catalysed nucleophilic substitution reaction [4, 54-58] (see Table 4.19). Aryl thiocyanates are obtained from activated aryl halides [4, 57] (see Chapter 2). 

In the reaction of the phenylacetonitrile carbanion with thiocyanates, a major side reaction leads to the formation of the dialkyl disulphides, as a result of the base-catalysed decomposition of the thiocyanate. This side reaction is reported to be insignificant in the reactions of the other carbanions. Phenylacetonitrile reacts with 1,2-ethanyl bisthiocyanate to produce 2-cyano-2-phenyl-1,3-thiolanes [52] under conditions analogous to those used for the synthesis of the thioethers (Scheme 4.12). 

Synthesis of thioethers from alkyl thiocyanates (Table 4.18)... 

Selected examples of the conversion of thiocyanates into thioethers... 

Thiols react directly with non-activated alkynes [15] and with 1-alkynyl thioethers [16] to yield alkenyl thioethers in good yield (>76%), whereas thiocyanate anions only add to non-activated alkynes under acidic phase-transfer catalytic conditions on the addition of mercury(II) thiocyanate. Terminal alkynes are converted into vinyl thiocyanates, but disubstituted alkynes also form vinyl isothiocyanates [17]. Major by-products are the ketones formed by solvolysis of the alkynes. 

The amino and bromo substituents in the 3//-azepine (111 X = Br) are susceptible to nucleophilic displacement and are hydrolyzed surprisingly easily by aqueous methanol or DMF to the azepine-2,7-dione. Sodium thiocyanate in DMF yields the aminothiocyanate (111 R = SCN) (67JOC2367). It has been noted that amidine formation with the lactim thioether (112) is much slower than with isomer (113) (77JHC933). 

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