2-azabicyclo[2.2.1]hept-5-en-3-one;7-bromo-6-(difluoromethylidene)-2-azabicyclo[2.2.1]heptan-3-one;7-bromo-6-(difluoromethylidene)-2-[(4-methoxyphenyl)methyl]-2-azabicyclo[2.2.1]heptan-3-one;7-bromo-6-(difluoromethylidene)-2-methyl-2-azabicyclo[2.2.1]heptan-3-one;7-bromo-2-[(4-methoxyphenyl)methyl]-2-azabicyclo[2.2.1]heptane-3,6-dione;7-bromo-2-[(4-methoxyphenyl)methyl]-6-methyl-2-azabicyclo[2.2.1]heptan-3-one;(3S)-4-(difluoromethylidene)-3-(imino-lambda3-chloranyl)cyclopentene-1-carboxylic acid;methyl (3S)-4-(difluoromethylidene)-3-methylcyclopentene-1-carboxylate