HALOGENATION OF 2-UNSUBSTITUTED AND 2-METHYLIMIDAZO...
453
Table 2. Spectral parameters of compounds IIa–IIc, IIe, IIg, IIIa, IIIc–IIIe, IVa, IVc, IVd, Vb, and Vf–Vh
Comp.
no.
1
a
IR spectrum,
ν(C=O), cm
H NMR spectrum, δ, ppm
–1
IIa
IIb
IIc
IIe
IIg
8.21 d (1H, 7-H, J = 2.0 Hz), 8.37 d (1H, 5-H, J = 2.0 Hz), 8.39 s (1H, 2-H)
2.59 s (3H, 2-CH
3.94 s (3H, 3-CH
2.70 s (3H, 5-CH
2.68 s (3H, 2-CH
3
3
3
3
), 8.02 d (1H, 7-H, J = 1.96 Hz), 8.27 d (1H, 5-H, J = 1.96 Hz)
), 8.07 s (1H, 2-H), 8.24 d (1H, 7-H, J = 2.0 Hz), 8.49 d (1H, 5-H, J = 2.0 Hz)
), 8.16 s (1H, 2-H), 8.28 s (1H, 7-H)
3
), 3.84 s (3H, 3-CH ), 8.03 d (1H, 7-H, J = 1.94 Hz), 8.34 d (1H, 5-H, J = 1.94 Hz)
IIIa 7.50 s (1H, 7-H), 11.19 br.s (1H, 1-H), 11.75 br.s (1H, 3-H)
1695
1695
1700
1705
1700
1695
1700
IIIc 3.30 s (3H, 3-CH
IIId 3.36 s (3H, 1-CH
IIIe 2.61 s (3H, 5-CH
3
3
3
), 7.67 s (1H, 7-H), 11.57 br.s (1H, 1-H)
), 7.80 s (1H, 7-H), 11.70 br.s (1H, 3-H)
), 7.37 s (1H, 7-H), 10.83 br.s (1H, 1-H), 11.32 br.s (1H, 3-H)
IVa 7.48 s (1H, 7-H), 11.21 br.s (1H, 1-H), 11.74 br.s (1H, 3-H)
IVc 3.25 s (3H, 3-CH
3
), 7.47 s (1H, 7-H), 11.40 br.s (1H, 1-H)
), 7.48 s (1H, 7-H), 11.93 br.s (1H, 3-H)
IVd 3.33 s (3H, 1-CH
3
Vb
Vf
8.27 d (1H, 7-H, J = 1.98 Hz), 8.56 d (1H, 5-H, J = 1.98 Hz)
2.63 s (3H, 5-CH
4.29 s (3H, 3-CH
4.25 s (3H, 1-CH
3
3
3
), 8.22 s (1H, 7-H)
b
Vg
Vh
), 8.34 d (1H, 7-H, J = 1.96 Hz), 8.59 d (1H, 5-H, J = 1.96 Hz)
), 8.29 d (1H, 7-H, J = 2.0 Hz), 8.55 d (1H, 5-H, J = 2.0 Hz)
a
1
The H NMR spectra of IIa, IIb, IIe, IIIa, IIIc–IIIe, IVa, IVc, IVd, Vb, Vf, and Vh were recorded in DMSO-d
6
, and of the others,
in CDCl
3
.
b
+
Mass spectrum of Vg, m/z (Irel, %): 462 (6) [M] , 382 (100), 290 (15), 288 (35), 210 (70), 198 (85), 183 (45), 156 (40), 79 (81).
and purified by recrystallization from appropriate
solvent (Table 1).
and the solution was neutralized with 25% aqueous
ammonia. The precipitate was filtered off, washed with
water, dried, and recrystallized from appropriate sol-
vent (Table 1).
5
,6-Dibromo- and 6-bromo-5-methylimidazo-
[
4,5-b]pyridin-2-ones IIIa and IIIc–IIIe (general
6
-Bromo-2-tribromomethylimidazo[4,5-b]pyri-
procedure). A solution of 11 mmol of bromine in 3 ml
of glacial acetic acid was added dropwise under stir-
ring to a solution of 5 mmol of imidazopyridine Ia, Ic–
Ie, or IIe in 20 ml of glacial acetic acid. An abundant
solid precipitated, the suspension was heated for 5 h on
a boiling water bath, and the solvent was distilled off
under reduced pressure to dryness. The residue was
dissolved in 15 ml of water, the solution was neutral-
ized with 25% aqueous ammonia, and the precipitate
was filtered off, dried, and recrystallized from ap-
propriate solvent (Table 1).
dines Vb and Vf–Vh (general procedure). A solution
of 20 mmol of bromine in 5 ml of glacial acetic acid
was added in portions under stirring to a solution of
5
2
mmol of imidazo[4,5-b]pyridine Ib or If–Ih and
0 mmol of sodium acetate in 15 ml of glacial acetic
acid. An abundant solid precipitated, the suspension
was heated for 5 h on a boiling water bath, the solvent
was distilled off under reduced pressure to dryness, the
residue was dissolved in 15 ml of water, and the solu-
tion was neutralized with 25% aqueous ammonia. The
precipitate was filtered off, dried, and recrystallized
from appropriate solvent (Table 1).
5
,6-Dichloroimidazo[4,5-b]pyridin-2-ones IVa,
IVc, and IVd (general procedure). Dry chlorine was
passed over a period of 15 min through a solution of
REFERENCES
2
4
.1 mmol of imidazo[4,5-b]pyridine Ia, Ic, or Id and
.2 mmol of sodium acetate in 7 ml of glacial acetic
1
. US Patent no. 3719683, 1973; Ref. Zh., Khim., 1974,
no. 5N372P; US Patent no. 4152434, 1979; Ref. Zh.,
Khim., 1979, no. 15O195P.
acid. The resulting suspension was heated for 5 h on
a boiling water bath until it turned homogeneous. The
solvent was distilled off under reduced pressure to
dryness, the residue was dissolved in 15 ml of water,
2. US Patent no. 4195088, 1980; Ref. Zh., Khim., 1980,
no. 23O343P.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 41 No. 3 2005