Copper-catalyzed interrupted click reaction: The synthesis of 3-difluoromethyl-substituted 1,2,4-triazinones

A copper-catalyzed interrupted click reaction for the preparation of 3-difluoromethyl-substituted 1,2,4-triazinones is developed. The reaction of terminal alkyne with azide and difluoroacetic anhydride affords the desired products in moderate to good yields. This method provides ready access to 3-difluoromethyl 1,2,4-triazinones, notable synthetic targets, from simple, readily available starting materials. Additionally, the reaction with chlorodifluoroacetic anhydride affords the corresponding 3-chlorodifluoromethyl-substituted 1,2,4-triazinones.