Thiocyanates, thioether synthesis

Thiocyanation of aniline, 280 Thioether synthesis from alkyl bromide and NajS, 271... 

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)... 

Miscellaneous Transformations. Cyanotrimethylsilane effects the transformation of acyl chlorides to acyl cyanides, a-chloro ethers and a-chloro thioethers to a-cyano ethers and a-cyano thioethers (eq 19), t-butyl chlorides to nitriles (eqs 20 and 21), 1,3,5-trisubstituted hexahydro-l,3,5-triazines to amino-acetonitriles, the cyanation of allylic carbonates and acetates (eqs 22 and 23), and the formation of aryl thiocyanates from aryl sulfonyl chlorides and sulfinates. The reagent has been used effectively in peptide synthesis and in a range of other synthetic applications. " ... 

Alkyl thiocyanates react with a variety of nucleophiles to yield thioethers (see Sect. 13.4). A particularly clever and useful application of this reaction is the dialkylation of phenylacetonitrile with 1,2-dithiocyanatoethane. The product of this formal oxidation is the ethylenedithioketal of benzoyl cyanide (see Eq. 10.18) [30]. The phase transfer synthesis of the starting material from thiocyanate ion and ethylene bromide... 

Nitro displacement by 3-mercaptopropionitrile anion provides a new synthesis of 2-cyanophenyl thiocyanates (84). The intermediate cyanoethyl thioethers (83) are rapidly converted into the thiol anion via loss of acrylonitrile under the basic reaction conditions. Addition of cyanogen chloride then yields (84) (Scheme 47). 

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