Introduction: Unexpected series of N,N-disubstituted formamidines were obtained upon
the reaction of 2-amino-3-cyano-4.6-diarylpyridines with triflouroroacetic anhydride (TFAA) in
dimethyl formamide (DMF).
Methods: The syn/anti ratio of N,N-disubstituted formamidines was calculated by applying the
1H-NMR additivy increment rule. The mechanism of formamidine formation is suggested using
the experimental results, 1H NMR and 13C NMR spectroscopy and successfully computed with
DFT calculations using the B3LYP functional and 6-311G (p,d) basis set.
Results: The reaction mechanism classified as unexpected nucleophilic attack reaction of the
solvent (DMF) on the carbonyl group leaving a positively charged intermediate which was
attacked with nitrogen atom of the amine form N,N-disubstituted formamidines. Bond lengths and
Mulliken atomic charges were calculated to support the reliability of the predicted reaction
mechanism. The activation energy of each species appears in the reaction pathway was calculated.
Conclusion: HOMO-LUMO analysis showed that the reaction pathway is preferred to proceed
through the suggested mechanism. It is clear that DMF is not the appropriate solvent in the case of
preparation of triflouroacetamide.