Pyrazoles cyanation

Azoles can form stable compounds in which metallic and metalloid atoms are linked to nitrogen. For example, pyrazoles and imidazoles Af-substituted by B, Si, P and Hg groups are made in this way. Imidazoles with a free NH group can be Af-trimethylsilylated and Af-cyanated (with cyanogen bromide). Imidazoles of low basicity can be Af-nitrated. 

Cyanations of benzimidazolium or benzimidazole N-oxides have been reported (93CHE127). Cyanopyrazoles are formed by irradiation of pyrazoles in the presence of cyanide ions in photosubstitution reactions. 

The isomeric conversions of A-carbamido derivatives are similar, and are described in the above-mentioned papers as well as in other publications76,183,184,469,724-726 the A-carbamido derivatives are obtained by direct acylation brought about by the action of potassium cyanate on the hydrochlorides of pyrazoles.183... 

N-bridging cyanate in low yields (17-23% after heating for 24 h Scheme 11). Conversion was found to proceed at comparable rates in ethanol or acetonitrile, and it was thus concluded that hydrolytic processes by traces of water do not play a role. Cyanate formation also was observed with Af-methylurea or 7/,7/-dimethylurea, but not with Af,A -dimethylurea or tetramethylurea, which shows that at least one NH2 group is essential for the elimination reaction to occur. A possible interpretation is that bridging of urea over the binuclear core through its O atom and one amino N atom is a key step for the conversion (58). This finding is in line with the discovery of urea-to-cyanate transformation for several pyrazolate-based dinickel complexes with urea bound in the N,0-bridging mode (see below). 

In all the above cases, however, subsequent hydrolysis of the formed cyanate could not be achieved, even when the more stable pyrazolate complex with triazacyclononane compartments was used to allow forcing conditions in aqueous solution. Conversions at the bimetallic scaffold of 24 relevant to the urease mechanism are summarized in Scheme 16 (72). 

The cyanide (CN ) is converted to cyanogen chloride (CNCl) at pH < 8, without hydrolyzing to the cyanate, by reaction with the Chloramine-T which acts as a source of hypochlorous acid (HOCl). After the reaction is complete, the CNCl forms a blue dye (pyrazole blue) on the addition of the pyridine-pyrazalone reagent. 

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