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

Regioselectivity of condensation of 3-methyl-1-phenyl-2-pyrazoline-4,5-dion e with aromatic 1,2-diamines is dependent on substituent present. Isomeric 3-methyl-1-phenyl-1H-pyrazolo-[3,4-b]-quinoxaline products are distinguishe d by comparison of their 2D z-gradient selected H-1,N-15 HMBC (Heteronuclea r Multiple Bond Correlation) spectra. Multiplicity of H5 signal, which is r ecognizable by the cross-peak for CH3(3)-N4 and H5-N4 interactions, indicat es substitution in position 6 or 7. The applied method is expected to be us eful for structure determinations in other positional isomers. (C) 1999 Els evier Science Ltd. All nights reserved.