Synthesis and Reactions of Homoditopic Stable Nitrile N‐Oxide as a Powerful Tool for Catalyst‐Free Constructions of Macromolecular Architectures

Abstract Nitrile N ‐oxide is a highly reactive 1,3‐dipole that undergoes 1,3‐dipolar cycloaddition reactions to various dipolarophiles. However, the high reactivity of nitrile N ‐oxide leads to side reactions with nucleophiles and self‐reactions, resulting in a decrease in the cycloadduct yield. The bulky substituent around nitrile N ‐oxide kinetically suppresses such undesirable side reactions, stabilizing nitrile N ‐oxide, and improving 1,3‐dipolar cycloaddition efficiency. Homoditopic stable nitrile N ‐oxides as a ligation tool between unsaturated bonds are developed, although the challenge of the large‐scale synthesis remains. Herein, the practical synthesis of a homoditopic stable nitrile N ‐oxide from bismaleimide is reported. Three simple steps, namely, Michael addition, oximation, and oxidation, produce the homoditopic nitrile N ‐oxide in 87% overall yield without purification process using column chromatography. The ligation capacity of nitrile N ‐oxide is discussed through polycycloadditions with several bisdipolarophiles and the cross‐linking reaction of polyacrylonitrile.