The title compound, C20H19N5O2, exhibits whole-mol­ecule disorder the refined ratios of the two components being 0.57 (2):0.43 (2). In the major component, the essentially planar [maximum deviation 0.033 (17) Å] fused pyrimidine and triazole ring system forms a dihedral angle of 10.5 (3)° with the phenyl ring, while in the minor component of disorder this angle is 27.5 (5)°. The crystal structure is stabilized by π–π stacking inter­actions between symmetry-related triazole and pyrimidine rings, with centroid–centroid distances of 3.594 (10) Å.

In the title compound, C18H23N5O2, the triazolopyrimidine ring system is essentially planar, with a maximum displacement of 0.032 (2) Å, and forms a dihedral angle of 87.59 (15)° with the phenyl ring. In the crystal, mol­ecules are linked by inter­molecular C—H⋯O hydrogen bonds and C—H⋯π inter­actions into chains parallel to the c axis.

In the title compound, C22H17N3O5, synthesized via the aza-Wittig reaction of ethyl 3-(phenyl­imino­methyl­ene­amino)­benzofuran-2-carboxyl­ate, benzene isocyanate and diethyl 2-amino­succinate, the imidazo[1,2-a]benzo[4,5]furo[2,3-d]pyrim­idine ring system is essentially planar (r.m.s. deviation for all 16 non-H atoms = 0.020 Å). The phenyl ring is twisted with respect to this ring system, making a dihedral angle of 54.23 (4)°. The crystal packing is stabilized by weak inter­molecular C—H⋯O inter­actions.

In the title compound, C19H16ClN5O2, the triazolopyrimidine ring system is essentially planar, with a maximum displacement of 0.021 (4) Å, and forms dihedral angles of 1.09 (9) and 87.74 (9)° with the phenyl and benzene rings, respectively. Short intra­molecular C—H⋯O and C—H⋯N hydrogen-bonding inter­actions occur within the molecule. In the crystal structure, mol­ecules are linked by inter­molecular C—H⋯O hydrogen bonds into chains parallel to the b axis. In addition, π–π stacking inter­actions involving the triazole and pyrimidine rings of adjacent mol­ecules are observed, with centroid–centroid distances of 3.600 (3) Å.

In the title compound, C14H15N5O2, the whole mol­ecule apart from the terminal C atoms of the isopropyl group is located on a crystallographic mirror plane. An intra­molecular C—H⋯N hydrogen-bonding inter­action may stabilize the mol­ecular conformation. The crystal packing features weak slipped π–π inter­actions between the pyrimidine and the phenyl rings of symmetry-related mol­ecules [centroid–centroid distance = 3.746 (1)Å, slippage of 1.574 Å].