New bicyclo[6.1.0]nonyne (BCN) ring-strained alkynes (e.g. endo- 2) are readily ­accessible, stable, and exhibit excellent kinetics in metal-free alkyne-azide and alkyne-nitrone ­cycloadditions. The C _S symmetry of BCN simplifies NMR analysis and produces a single ­regioisomer upon cycloaddition.