Newly designed buckle units for copper-free click chemistry: 4,8-diazacyclononynes (DACNs) were efficiently synthesized with a one-potprocedure from commercially available 2-butyne-1,4-diol. The synthesized DACNs possess versatile connectors for the introduction of functional units and exhibit high click reactivity.
A variety of medium‐sized cycloalkynes were efficiently synthesized by the double Nicholas reaction of cobalt complex and bis(hetero)substituted acyclic compound. The alkyne moiety within the ring has a unique bent structure and high reactivity toward cycloaddition reactions. Furthermore, preparation of multifunctionalized alkynes was achieved by embedding the cycloalkyne within a peptide chain.