Decarboxylative cyanation

Related free-radical alkylation reactions include the trapping of isocyanides and the decarboxylative cyanation reaction. Both methods allow entry to the preparation of labeled carboxylic acids. 

Recently, the solvolyses of l-chloro-l,3,3-triarylallenes 10 (andof 1-butyl-3,3-diphenyl-allenyl chloride) were carried out in the presence of thiocyanate and o-ethyl dithiocar-bonate anions as nucleophiles and found to give the corresponding allenyl derivatives 11 and 12 in good yield (equation 3)18. However, when potassium cyanate was used as a nucleophile, the cyanate ion attacked at the /-position to give the propargyl amines 14 after decarboxylation of the unstable intermediate 13 (equation 4). 

Similarly, reaction of hydrazidoyl halides with sodium cyanate ( ), potassium selenocyanate and sodium azide has been reported. For example, decarboxylation occurs when the carboxylic acid derivative XLIV is treated with sodium azide, and the tetrazole derivative XLVI is isolated... 

In addition to the several early examples cited by Brown [4], Scheme 2 illustrates some applications of the Reissert indole synthesis. Attempts by Beer and colleagues to improve the decarboxylation step in their synthesis of 5-hydroxyindole (equation 2) were unsuccessful, but these workers were able to synthesize 6- and 7-hydroxyindole via a Reissert method [5]. Uhle described an excellent preparation of 4-chloroindole (equation 2) [6], and Singer and Shive synthesized 7-indolecarboxylic acid (equation 3) [7] and 5-indolecarboxylic acid (equation 4) [8] via a Reissert strategy. As seen, both cyanation steps resulted in decarboxylation and cyanide replacement prior to nitrile... 

Aromatic diazonium salts need no further transformations but can be directly cyanated with Cu " CN, as demonstrated in the preparation of 1 " C1105". Alternatively, the use of diphenylphosphoryl azide permits a one-step amino-decarboxylation, without isolation of the intermediately formed acyl azides". ... 

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