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.