organic compounds
Within this chain of rings, pairs of pyrazolopyridine rings
1
bond, its role is to reinforce the chain along [100]. The second
contact, involving atom C6, is between molecules related by
translation along [101]; if this contact is regarded as a weak
hydrogen bond, then its role is to link the chains along [100]
into a sheet parallel to (010).
The structure of the 4-chlorophenyl analogue of (I),
compound (IV) (see scheme) was reported some years ago on
a proof of constitution basis, without discussion [Cambridge
Structural Database (CSD; Allen, 2002) refcode LABDAT
(Quiroga et al., 1998)]. It is clear from the unit-cell dimensions
related by inversion across (n + , 0, 1) have an interplanar
2
˚
spacing of 3.663 (2) A between the pyridine rings, whose ring-
˚
centroid separation is 3.827 (2) A, corresponding to a ring-
centroid offset of 1.106 (2)ꢀ. The interplanar spacing and the
ring-centroid separation are both quite large, and it is possible
that this contact is an adventitious consequence of the
hydrogen bonding, rather than being of structural significance
in itself. Nonetheless, any attractive interaction associated
with this contact will reinforce, albeit weakly, the formation of
the chain of rings parallel to [100].
˚
˚
˚
for (IV) [a = 8.113 (1) A, b = 17.315 (1) A, c = 11.789 (1) A, ꢂ=
104.77 (1)ꢀ in space group P21/n (incorrectly reported as
P21/c)] that (I) and (IV) are by no means isomorphous, as
might possibly have been expected. However, since no H-
atom coordinates for (IV) have been deposited, very little can
be deduced about any supramolecular aggregation in the
structure of (IV). Somewhat similar to (II), and obtained in a
somewhat similar way, is compound (V), which was also
reported on a proof of constitution basis without discussion
(CSD refcode DEZQII; Quiroga et al., 1999), although this
appears to be the only previously reported example of a 1H-
pyrazolo[3,4-b]pyridine carrying two aryl substituents at the 3-
and 4-positions. Examination of the crystal structure of (V)
using the deposited atomic coordinates shows the presence of
two hydrogen bonds, one each of N—HÁ Á ÁN and C—HÁ Á ÁN
types, where the acceptors are, respectively, the pyridine ring
N atom and the nitrile N atom. Inversion-related pairs of
molecules are linked by pairs of N—HÁ Á ÁN hydrogen bonds to
form centrosymmetric R22(8) dimers, just as in (II). However,
in (V) these dimers are linked by the C—HÁ Á ÁN hydrogen
bond to form a sheet lying parallel to (101) and built from
centrosymmetric R22(8) and centrosymmetric R66(44) rings
arranged in a chessboard fashion (Fig. 5). Unlike the structure
of (II), that of (V) contains no C—HÁ Á Áꢀ(arene) hydrogen
bonds.
There are also two short intermolecular C—HÁ Á ÁO contacts
in the crystal structure of (II), both involving nitro atom O2
(Table 2). One of these contacts, involving atom C32, is
between molecules related by translation along the [100]
direction so that, if this contact is regarded as a weak hydrogen
Figure 4
A stereoview of part of the crystal structure of (II), showing the
formation of a chain of hydrogen-bonded rings along [100] built from
N—HÁ Á ÁN and C—HÁ Á Áꢀ(pyridine) interactions. For the sake of clarity, H
atoms not involved in the motif shown have been omitted.
Experimental
For the synthesis of (I), a solution of 5-amino-1-phenyl-3-methyl-
pyrazole (0.5 mmol) and 1-(4-bromophenyl)-3-(dimethylamino)pro-
pan-1-one hydrochloride (0.5 mmol) in pyridine (2 ml) was heated
under reflux for 20 min. The mixture was cooled to ambient
temperature and the product was isolated by filtration, washed with
ethanol and dried prior to purification by column chromatography on
silica gel using chloroform as eluant (yield 75%, m.p. 420–422 K). MS
(70 eV) m/z (%): 365 (M+, 100), 364 (41), 183 (31), 143 (18), 102 (50),
77 (79), 51 (48); HRMS found 365.0535, C19H16BrN3 requires
365.0528. Yellow crystals suitable for single-crystal X-ray diffraction
were obtained by slow evaporation, at ambient temperature and in
air, of a solution in dimethylformamide.
For the synthesis of (II), a solution of 5-amino-3-(4-nitrophenyl)-
1H-pyrazole (1.9 mmol) and 3-(dimethylamino)propiophenone
(1.9 mmol) in pyridine (0.5 ml) was heated under reflux for 20 min.
The solution was cooled to ambient temperature and the product
mixture was collected by filtration, washed with ethanol and dried in
air. The two components were separated by column chromatography
on alumina using chloroform as the eluant. The main product 2-(4-
nitrophenyl)-5-phenyl-6,7-dihydropyrazolo[1,5-a]pyrimidine, (III),
Figure 5
A stereoview of part of the crystal structure of (V), showing the
formation of a hydrogen-bonded sheet parallel to (101). The original
atomic coordinates (Quiroga et al., 1999) have been used and, for the sake
of clarity, H atoms not involved in the motifs shown have been omitted.
ꢁ
Acta Cryst. (2010). C66, o163–o167
Quiroga et al. C19H16BrN3 and C18H12N4O2 o165
Quiroga, Jairo
