Cycloaddition Reactions of in situ Generated C2D2 in Dioxane: Efficient Synthetic Approach to D2‐Labeled Nitrogen Heterocycles

Abstract In this work, an universal synthetic approach for the synthesis of D 2 ‐labeled nitrogen heterocycles based on cycloaddition reactions of in situ generated dideuteroacetylene is reported. A key feature of this method is the use of 1,4‐dioxane as a deuterium‐exchange‐proof solvent, which allowed the access to dideuterosubstituted heterocycles in up to 99 % deuteration degree. The method was demonstrated to be suitable for the synthesis of D 2 ‐labeled triazoles, isoxazoles, pyrazoles and pyridazines.