Addition to compounds with contiguous double bonds

Addition to compounds with contiguous double bonds 

Compoimds containing functional groups which can be generally represented as X=Y=Z may react by electrophilic addition with suitable species A-B, where A is the electrophilic and B the nucleophilic centre. A general representation is shown in equation (88). This general 

The formation of carbamoyl azides from isocyanates is the best known application of this method of synthesis. The reaction v/as discovered in 1901 by Hantzsch and Vagt who prepared carbamoyl azide itself from isocyanic acid and hydrazoic acid °. Alkyl and aryl carbamoyl azides are usually obtained in good yields from low temperature reactions between hydrazoic acid and the corresponding isocyanate in non-aqueous (equation 89) 

Ketene also appears to react with hydrazoic acid according to the general mechanism outlined in equation (88). Carbamoyl azides are produced and it is thought that the reaction proceeds by initial protonation and subsequent attack by azide ion to afford an acyl azide further reaction of the derived isocyanate would then lead to the observed product (equation 90). 

Additions of hydrazoic acid to carbon-sulphur double bonds may conceivably be of the general type outlined in equation (88) but do not constitute a synthetic route to azides. Recent corrections to the earlier literature relating to this field are, however, noteworthy. It was originally suggested that thiocarbamoyl azides (193) were obtained from organic isothiocyanates and hydrazoic acid. The spectroscopic studies of Lieber and co-workers have now established that the products are in fact thiatriazoles (194). The reactions of sodium azide with isothiocyanates , and carbon disulphide , which were also previously considered to furnish organic azides, have now been shown to produce the heterocyclic compounds 195 and 196 respectively. 

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