Synthesis of 1-Cyanoalkynes and Their Ruthenium(II)-Catalyzed Cycloaddition with Organic Azides to Afford 4-Cyano-1,2,3-triazoles.

A new method to convert terminal alkynes under relatively mild conditions to 1-cyanoalkynes using in situ formed cyanogen is described. 1-Cyanoalkynes have a higher reactivity than terminal alkynes in the ruthenium(II)-catalyzed regiospecific azide-alkyne cycloaddition to afford 4-cyano-1,2,3-triazoles. A mechanistic proposal different from the one that terminal alkynes adopt under the same reaction conditions is proposed. This work provides a new and convenient two-step sequence to prepare 4-cyano-1,2,3-triazoles from terminal alkynes and organic azides.