Reaction of 1-tert-butyl-3,4-diphenyl-1,2,4-triazol-5-ylidenes with a malonic ester

Four stable carbenes, 1-tert-butyl-3,4-diaryl-1,2,4-triazol-5-ylidenes 1a-d, including new fluorine-containing compounds 1c,d, react with a malonic ester to afford heterocyclic zwitterionic compounds 5a-d. The reactions with more acidic compounds (ethyl acetoacetate, malononitrile and 1,3-dimethylbarbituric acid) proceed with substrate deprotonation to form the respective azolium salts 6a-c. The X-ray crystal structure of 5a was also determined.