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.
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