Primary Vinyl Ethers as Acetylene Surrogate: A Flexible Tool for Deuterium‐Labeled Pyrazole Synthesis

A novel synthetic path to 1,3‐disubstituted pyrazoles and their deuterated derivatives was developed. It is based on the reaction of vinyl ethers with hydrazonoyl chlorides in the presence of triethylamine. The reaction mechanism, clarified by the joint experimental and computational study, involves 1,3‐dipolar cycloaddition of the in situ generated nitrile imines to vinyl ethers and subsequent cleavage of alcohol from the formed alkoxypyrazoline. The results highlight the possibility of using vinyl ethers as acetylene surrogate and provide a novel access to pyrazoles, 4,5‐dideuteropyrazoles and their regioselectively labeled derivatives, 5‐deuteropyrazoles. A novel synthetic path to 1,3‐disubstituted pyrazoles, 4,5‐dideuteropyrazoles and 5‐deuteropyrazoles based on the interaction of the readily available vinyl ethers and in situ generated nitrile imines was developed. The joint experimental and computational study clarified the mechanism of the process and allowed us to propose a convenient access to regioselectively deuterated pyrazoles.