Development of Decarboxylative Cyanation Reactions for C‑13/C-14 Carboxylic Acid Labeling Using an Electrophilic Cyanating Reagent

Degradation-reconstruction approaches for isotope labeling synthesis have been known for their remarkable efficiency, but applications are scarce due to some fundamental limitations of the chemistries developed to date. The decarboxylative cyanation reaction, as a degradation-reconstruction approach, is especially useful in rapid carboxylic acid carbon isotope labeling, however development toward its application as a widespread technique has stalled at the early stages due to numerous limitations which include somewhat narrow applicability. Employing the electrophilic cyanating reagent <i>N</i>-cyano-<i>N</i>-phenyl-<i>p</i>-toluenesulfonamide (NCTS) as the cyano source, efficient decarboxylative cyanation chemistry has been developed for aryl and alkyl carboxylic acids respectively with two rationally designed reaction pathways. The reactions provided good yields of nitrile products from carboxylic acids, with complete retention of isotopic purity from the [¹³CN]-NCTS used. The reaction conditions are relatively mild requiring no oxidant and no excess toxic heavy metal and the reagent [^13/14CN]-NCTS is a stable, easy-to-handle crystalline solid that can be prepared quickly and effectively from the readily available [^13/14C]-KCN. The following work describes this novel and efficient method for alkyl and aryl carboxylic acid isotopic labeling using a single reagent