Order versus disorder in two isomorphous pyrazolone-substituted di­ethyl propane­dioates prepared using a three-component one-pot reaction under solvent-free conditions

Two new substituted propane­dioate esters have been synthesized using a three-component solvent-free thermal reaction between diethyl propane­dioate (diethyl malonate), 5-chloro-3-methyl-1-phenyl-1H-pyrazole-4-carbaldehyde and an aryl azide, forming two new C—C bonds in a single step. The products diethyl (RS)-2-[(4-bromo­phen­yl)(5-methyl-3-oxo-2-phenyl-2,3-di­hydro-1H-pyrazol-4-yl)meth­yl]propane­dioate, C₂₄H₂₅BrN₂O₅ (I), and diethyl (RS)-2-[(4-chloro­phen­yl)(5-methyl-3-oxo-2-phenyl-2,3-di­hydro-1H-pyrazol-4-yl)meth­yl]propane­dioate, C₂₄H₂₅ClN₂O₅ (II), are isomorphous, with Z′ = 2 in space group P2₁/n. The two independent mol­ecules in compound (I) are both fully ordered, while each of the independent mol­ecules in compound (II) is disordered, but in different ways. In one mol­ecule of (II), the N-phenyl ring is disordered over two sets of atomic sites having occupancies 0.635 (10) and 0.365 (10), and in the other mol­ecule the ester function is disordered over two sets of atomic sites having occupancies 0.690 (5) and 0.310 (5). In both structures, the two independent mol­ecules adopt different conformations and, in each structure, the mol­ecules are linked into complex sheets by a combination of N—H⋯O, C—H⋯O and C—H⋯π(arene) hydrogen bonds. Comparisons are made with some related structures.