Synthesis of Difluoromethyl Pyrazolines and Pyrazoles by [3+2] Cycloaddition Reaction of Difluoroacetohydrazonoyl Bromides with Electron‐deficient Olefins.

Difluoroacetohydrazonoyl bromides, which are stable in air at room temperature, are demonstrated to be good difluoromethyl building blocks for construction of CF2H‐substituted pyrazoline and pyrazole compounds via [3+2] cycloaddition with electron‐deficient olefins under mild conditions. A series of CF2H‐substituted pyrazolines and pyrazoles were obtained in good yields. The method has the advantages of mild reaction conditions, good regioselectivity, broad substrate scopes and easy operation. [ABSTRACT FROM AUTHOR]