1600-5368 5-Chloro-3-methyl-1-phenyl-1 H-pyrazole-4-carbaldehyde : sheets built from C — H O and C — H p ( arene ) hydrogen bonds

The aldehydic fragment is almost coplanar with the adjacent pyrazole ring, but the two ring planes are inclined at 71.3 (2) (Table 1). Within the pyrazolecarbaldehyde portion of the molecule, the bonds N1—C5 and C4—C41 are both short for their types (Allen et al., 1987), while bonds C4—C5 and C41— O4 are both long for their types, suggesting some contribution to the overall molecular–electronic structure from the chargeseparated form (Ia) (see scheme). The molecules of (I) are linked into sheets by a combination of one C—H O hydrogen bond and one C—H (arene) hydrogen bond (Table 2); each of these hydrogen bonds Received 11 March 2005 Accepted 14 March 2005 Online 25 March 2005


Comment
The title compound, (I), was prepared under Vilsmeyer conditions in which chlorination of C5 occurs in addition to the expected formylation, giving a versatile intermediate for the synthesis of fused pyrazolo heterocycles via cyclocondensation reactions (Paul et al., 2001).
The aldehydic fragment is almost coplanar with the adjacent pyrazole ring, but the two ring planes are inclined at 71.3 (2) ( Table 1). Within the pyrazolecarbaldehyde portion of the molecule, the bonds N1-C5 and C4-C41 are both short for their types (Allen et al., 1987), while bonds C4-C5 and C41-O4 are both long for their types, suggesting some contribution to the overall molecular-electronic structure from the chargeseparated form (Ia) (see scheme).

Experimental
For the preparation of (I), phosphoryl chloride (0.35 mol, 32 ml) was added dropwise to ice-cold dimethylformamide (0.16 mol, 12 ml). To this mixture was added 3-methyl-1-phenyl-5-pyrazolone (0.05 mol) and the reaction mixture was then heated under reflux for 1 h. After cooling, the reaction mixture was poured into ice-cold water (300 ml). The solid which precipitated was collected by filtration, washed with water, dried and recrystallized from ethanol to give pale-yellow crystals (m.p. 417 K) suitable for single-crystal X-ray diffraction   Part of the crystal structure of compound (I), showing the formation of an R 2 2 (16) ring centred at ( 1 2 , 1 2 , 1 2 ). For the sake of clarity, H atoms not involved in this motif have been omitted. Atoms marked with an asterisk (*) are at the symmetry position (1 À x, 1 À y, 1 À z).

Figure 4
Stereoview of part of the crystal structure of compound (I), showing the formation of a (102) sheet. For the sake of clarity, H atoms not involved in these motifs have been omitted.   Hydrogen-bonding geometry (Å , ).
Two very low angle reflections (202) and (01 ) were omitted from the final refinement because of partial attenuation and/or extinction.All H atoms were located in difference maps and then treated as riding atoms, with C-H = 0.95 Å and U iso (H) = 1.2U eq (C) for aromatic and aldehyde H atoms or C-H = 0.98 Å and U iso (H) = 1.5U eq (C) for methyl H atoms. The methyl group was modelled using six H-atom sites, all with occupancy 0.5.