DACN(Tos2) is a a click chemistry reagent containing an cycloalkynes group. The alkyne moiety within the ring has a unique bent structure and high reactivity toward cycloaddition reactions. DACN(Tos2) through such strain-promoted azide-alkyne cycloadditions (SPAAC) using cycloalkynes. DACN(Tos2) can be used for the research of molecular conjugation.