Synthesis of Difluoromethyl Chromono[3,2-c]pyrazolines/pyrazoles by [3+2] Cycloaddition Reaction of Difluoroacetohydrazonoyl Bromides with 3-EWG-Chromones

A highly convenient and straightforward strategy for the synthesis of difluoromethyl substituted tricyclic fused chromono[3,2-c]pyrazolines/pyrazoles is developed via [3+2]-cycloaddition of difluoroacetohydrazonoyl bromides to chromene derivatives bearing an electron-withdrawing group at the 3-position. The reaction has the advantages of mild conditions, good tolerance of functional groups, and simple operation.