Cyano thioethers

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. " ... 

This method for introduction of the thioether functional group tolerates the presence of a broad range of functional groups, such as alkene, ester, carbonyl, and cyano groups. 

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). 

The kinetics of the reaction of diazonium ions XCgH4Nj with benzene-thiolate anions show that initially the syn- azo thioether is formed rapidly, which is followed by the slower syn-anti isomerism. Only in the cases of p-nitro- and p-cyano-benzenediazonium ions is it possible to distinguish between the first and second reactions. Using benzenediazonium ion and the p-Me- and p-OCHj-substituted ions with benzenethiolate, first-order kinetics were observed over the entire range of the reaction. It is postulated that there the rate-determining step is formation of the spn-diazothioether, followed by its rapid isomerization to the ant/ -diazothioether . 

Except for amines (Experiment 52G), which are easily detected by their solubility behavior, all compoimds issued in this experiment will contain heteroelements (N, S, Cl, Br, or I) only as secondary functional groups. These will be subsidiary to some other important functional group. Thus, no alkyl or aryl halides, nitro compounds, thiols, or thioethers will be issued. However, some of the unknowns may contain a halogen or a nitro group. Less frequently, they may contain a sulfur atom or a cyano group. 

This fact can be used to replace the chlorine in a chlorinated molecule via a nucleophilic substitution reaction by an other atom or functional group, for example by other halogens like iodine, by alkyl groups, ethers, thioethers, cyano groups, amines etc. (see Fig. 9). 

An alternative to the synthesis of thioethers in which sulfur is a nucleophile, is a synthesis in which sulfur bears a leaving group. The reaction of a carbanion with a sul-fenyl halide should, in principle, constitute a synthesis of thioethers. Such a reaction of sulfenyl halides has not yet been reported but the case in which sulfur is rendered electrophilic by attached cyano, has been [10]. Thus, benzylthiocyanate reacts with trichloromethide ion (generated from chloroform under phase transfer conditions) according to equation 13.6 to yield (80%) of benzyl trichloromethyl thioether [10]. 

---