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

Two new substituted propane-dioate esters have been synthesized using a three-component solvent-free thermal reaction between diethyl propane-dioate (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-bromo-phen-yl)(5-methyl-3-oxo-2-phenyl-2,3-di-hydro-1H-pyrazol-4-yl)meth-yl]propane-dioate, C24H25BrN2O5 (I), and diethyl (RS)-2-[(4-chloro-phen-yl)(5-methyl-3-oxo-2-phenyl-2,3-di-hydro-1H-pyrazol-4-yl)meth-yl]propane-dioate, C24H25ClN2O5 (II), are isomorphous, with Z' = 2 in space group P21/n. The two independent mol-ecules in compound (I) are both fully ordered, while each of the independent mol-ecules in compound (II) is disordered, but in different ways. In one mol-ecule 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 mol-ecule 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 mol-ecules adopt different conformations and, in each structure, the mol-ecules 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.