Main Group Acetylides in Copper(I)‐Catalyzed Azide–Alkyne Cycloaddition (CuAAC)

We report a systematic evaluation of 23 main group (MG) acetylides (Groups 13–17) in CuAAC, confirming prior MG acetylide reports and identifying tin acetylides as novel competent substrates in CuAAC. Optimized protocols for the corresponding triazolides were developed, and 1,4‐regioselectivity was confirmed by single‐crystal X‐ray crystallography. Infrared spectroscopic analysis revealed that alkyne C≡C stretching frequencies decrease systematically upon descending any group, consistent with back‐donation from the heteroatom into the alkyne π*‐orbital and increased electron density at the β‐carbon—features we propose are prerequisites for productive CuAAC. Acetylides of lighter elements (Si, Ge, B) undergo protonolysis under the reaction conditions rather than cycloaddition. Collectively, these results identify metal‐like polarizability as the key criterion governing MG acetylide reactivity in CuAAC and provide a spectroscopic handle for predicting the behavior of heteroatom‐substituted alkynes in this reaction.