Unequivocal determination of isomeric products of reaction between 3- methyl-1-phenyl-2-pyrazoline-4,5-dione and aromatic 1,2-diamines

Article abstract of DOI:10.1016/S0040-4020(99)00433-0

Regioselectivity of condensation of 3-methyl-1-phenyl-2-pyrazoline-4,5- dione with aromatic 1,2-diamines is dependent on substituent present. Isomeric 3-methyl-1-phenyl-1H-pyrazolo-[3,4-b]quinoxaline products are distinguished by comparison of their 2D z-gradient selected ¹H,1⁵N HMBC (Heteronuclear Multiple Bond Correlation) spectra. Multiplicity of H5 signal, which is recognizable by the cross-peak for CH₃(3)-N4 and H5-N4 interactions, indicates substitution in position 6 or 7. The applied method is expected to be useful for structure determinations in other positional isomers.