Geometric Isomerism and DFT Theoretical Explanation of the Unexpected Formation of N, N-disubstituted Formamidines from 2-amino-3-cyano-4.6- diarylpyridines

Abstract

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.