In the title compound, C11H9N5O, the pyrazolo­pyrimidin-4-one ring system is almost planar, with a maximum deviation of 0.0546 (13) Å for the O atom. The crystal packing is stabilized by inter­molecular N—H⋯N, C—H⋯O and C—H⋯N hydrogen bonds. In addition, π–π stacking is found between the pyridine ring and the pyrazolo­pyrimidin-4-one ring systems, with centroid–centroid distances in the range 3.9627 (12)–4.6781 (12) Å.

The asymmetric unit of the title compound, C9H10N4O, comprises three independent molecules, two pairs of which differ significantly in the rotational orientation of the azido group and one pair having very similar conformations; the N—N—C—C torsion angles are −173.9 (2), −102.7 (2) and −173.6 (2)°. In the crystal, each independent molecule forms N—H...O hydrogen bonds with its glide-plane-related counterparts, forming zigzag chains extending along the c-axis direction.

In the title molecule, C17H16N2OS, the dihydroimidazolone ring is slightly puckered and the methylsulfanyl group is nearly coplanar with it. In the crystal, two sets of C—H...O hydrogen bonds form corrugated layers of molecules parallel to the ac plane. The layers pack with normal van der Waals contacts between them.

In the title molecule, C17H20N2O4, the inner part of the ester substituent is nearly perpendicular to the dihydropyridazine ring, forming a dihedral angle of 83.21 (7)°. In the crystal, inversion dimers are formed by pairwise C—H...O interactions with the dimers connected into chains extending along the b-axis direction by C—H...π(ring) interactions. The chains are connected by π-stacking interactions to give corrugated layers parallel to the ab plane. The terminal ethyl group is disordered over two two sets of sites with the major component having a site occupancy factor of 0.715 (10)

The quinoxaline portion of the title molecule, C21H19N5O3, is not quite planar as indicated by a dihedral angle of 3.38 (7)° between the constituent rings. The molecule is `U-shaped', which is consolidated by an intramolecular antiparallel carbonyl electrostatic interaction with C··O distances of 2.8905 (16) and 3.0221 (15) Å, in the crystal forms corrugated layers through C—H...O and C—H...N hydrogen bonds and C—H...π(ring) and π-stacking interactions.