Synthesis of 3-arylazo-1H-pyridazin-4-ones from difluoroboron chelates of 1,3-diketones

Article abstract of DOI:10.1007/s11172-007-0243-5

A convenient method for the synthesis of 6-R-3-arylazo-1H-pyridazin-4-ones from difluoroboron chelates of acetylacetone and aroylacetones was developed. The method is based on the ability of the methyl group of the chelates to react with two equivalents of a diazonium salt.

Full text of DOI:10.1007/s11172-007-0243-5

Russian Chemical Bulletin, International Edition, Vol. 56, No. 8, pp. 1561—1565, August, 2007
1561
Synthesis of 3ꢀarylazoꢀ1Hꢀpyridazinꢀ4ꢀones
from difluoroboron chelates of 1,3ꢀdiketones*
I. V. Kravtsov, P. A. Belyakov, S. V. Baranin, and V. A. Dorokhovꢀ
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 5328. Eꢀmail: vador@ioc.ac.ru
A convenient method for the synthesis of 6ꢀRꢀ3ꢀarylazoꢀ1Hꢀpyridazinꢀ4ꢀones from
difluoroboron chelates of acetylacetone and aroylacetones was developed. The method is based
on the ability of the methyl group of the chelates to react with two equivalents of a diazoꢀ
nium salt.
Key words: 1,3ꢀdiketones, difluoroboron chelates, diazonium tetrafluoroborate, 3ꢀarylazoꢀ
1Hꢀpyridazinꢀ4ꢀone.
In our previous studies1,2 of using boron chelates of
Scheme 1
1,3ꢀdiketones in the synthesis of nitrogenꢀcontaining
heterocyclic compounds, we have proposed novel routes
to 5ꢀaroylmethylpyrazoles and pyrazolo[1,5ꢀc]pyrimidines
via reactions of amide acetals with βꢀdiketone difluoroꢀ
boron chelates at their exocyclic methyl group followed
by heterocyclization of the condensation products under
the action of binucleophilic reagents (hydrazines, thioꢀ
semicarbazide, and aminoguanidine).
Apparently, electrophilic reagents other than amide
acetals (e.g., diazonium salts) can also be used in reacꢀ
tions with βꢀdiketone difluoroboron chelates (for a preꢀ
liminary communication, see Ref. 3). It is well known
that diazonium salts react with acetylacetone at position 3
to give 3ꢀarylhydrazonopentaneꢀ2,4ꢀdione.4 Azo coupling
with aroylacetones occurs analogously. We found, howꢀ
ever, that condensation of difluoroboron complexes of
the above βꢀdiketones involves two equivalents of a diꢀ
azonium salt.
2
a
b
c
d
R
Me
Ph
Ar
Ph
2
e
f
R
Me
Ph
Ar
4ꢀMeOC6H4
4ꢀClC6H4
4ꢀMeOC6H4
4ꢀMeOC6H4
4ꢀClC6H4
2,4ꢀMe2C6H3 4ꢀMeOC6H4
g
4ꢀClC6H4 4ꢀClC6H4
The reaction proceeds at ~0 °C in methanol—sulfolane
(1 : 1) in the presence of sodium acetate. The resulting
dark red crystalline complexes decompose on reflux in
pyridine—butanol (3 : 1) to give 3ꢀarylazoꢀ1Hꢀpyridazinꢀ
4ꢀone derivatives (2a—g) identified by spectroscopic
methods (Scheme 1). Note that in a reaction with one
equivalent of the aryldiazonium salt, the monocoupling
product cannot be isolated and half the starting chelate 1
remains nonconsumed.
Reagents and conditions: i) NaOAc, H2O, MeOH, sulfolane,
0—2 °C; ii) BuOH, pyridine, ∆.
acetate, and ethanol but insoluble in hexane and diethyl
ether). The mass spectra of the pyridazinones obtained
show molecular ion peaks M+. The azo coupling reaction
is possible in two ways a and b (Scheme 2) leading to the
structural isomers of arylazopyridazinꢀ4ꢀones that differ
in the position of the arylazo group: compounds 2 (reacꢀ
tion with two equivalents of aryldiazonium tetrafluoroꢀ
borate at the methyl group) or 3 (reaction at both the
methyl group and the C atom of the methine group of the
chelate ring) (see Scheme 2).
Compounds 2 are orangeꢀred solids that are poorly
soluble in most organic solvents (except for compounds
2a,e, which are well soluble in chloroform, benzene, ethyl
1
The H and 13C NMR spectra of the pyridazinones
* Dedicated to Academician V. A. Tartakovsky on the occasion
of his 75th birthday.
obtained contain signals that are consistent in number,
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1502—1506, August, 2007.
1066ꢀ5285/07/5608ꢀ1561 © 2007 Springer Science+Business Media, Inc.

1562
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 8, August, 2007
Kravtsov et al.
Scheme 2
integral intensity ratio, and position with the structures of
both isomers 2 and 3. For instance, the singlets for the
protons at δ 6.54—6.80 correspond to the CH proton of
chelate structures 4a—g (see Scheme 2) rather than 5a—g.
These compounds were precipitated from the reaction
mixture by water and washed with hexane. Chelates 4a,b,e
were obtained in the analytically pure state; the other
complexes were used in further transformations without
additional purification. Compounds 4a,b,e are poorly
soluble in all organic solvents and their mass spectra conꢀ
tain molecular ion peaks M+. Their 11B NMR spectra
show a signal at δ ~0 for the tetracoordinate boron atom.
The IR spectra (KBr) of complexes 4a,b,e exhibit no
absorption band of the carbonyl group at 1620—1700 cm–1
(which corresponds to O,Oꢀcoordination of the B atom)
1
the pyridazine ring. The methyl protons in the H NMR
spectra of the compounds obtained from acetylacetone
difluoroboron chelate 1a and 4ꢀmethoxyphenylꢀ and
phenyldiazonium tetrafluoroborates show highꢀfield sigꢀ
nals at δ 2.19 and 2.23, respectively. The IR spectra exꢀ
hibit an absorption band due to the conjugated carbonyl
group at ~1630 (in KBr) or ~1620 cm–1 (in CHCl3).
However, more detailed studies by 2D 1H—1H and
1H—13C correlation spectroscopy showed that the reacꢀ
tion follows pathway a yielding isomers 2a—g. The
NOESY5 spectrum (CDCl3) of the pyridazinone obtained
from chelate 1a and phenyldiazonium tetrafluoroborate
contains two intense crossꢀpeaks due to spatial interacꢀ
tions of the methyl protons at δ 2.19 with the CH proton
of the heterocycle at δ 6.66 and with the orthoꢀprotons of
only one benzene ring at δ 7.39, which corresponds to
structure 2a. The signals in the 13C NMR spectrum were
assigned by the HSQC6 and HMBC methods.7 It should
be noted that the HMBC spectrum shows 1H—13C interꢀ
actions between the methyl protons and the carbon atom
of the CH group of the heterocycle and an interaction of
the CH proton of the heterocycle with the carbon atom of
the methyl group. Such correlations are possible only for
structure 2a.
but contains a wide band at 3300—3600 cm–1
.
The structures of intermediate chelates were examꢀ
1
ined by H and 13C NMR spectroscopy with compound
4e as an example. In the 1H and 13C NMR spectra of this
complex, the signals for the protons at δ 3.90 and for the
C atom at δ 55.7 of two methoxy groups coincide, which
is some evidence for structure 4e. The signals in the
13C NMR spectrum were assigned by the HSQC and
HMBC methods. The HMBC spectrum (CDCl3) shows
crossꢀpeaks due to longꢀrange interactions between the
protons of the exocyclic methyl group at δ 2.37 and the
carbon atom of the CH group of the chelate ring at δ 97.1
and due to interactions of the methyl protons and the
CH proton of the chelate ring with the same carbonyl
C atom at δ 179.2. The CH proton in the chelate ring at
δ 6.83 interacts with two carbonyl C atoms, while the NH
proton at δ 16.57 interacts with two quaternary C atoms,
one of which is the ipsoꢀC
Such compounds can arise only from a double attack
of the aryldiazonium cation on the same exocyclic methyl
group of the chelate. This is indirectly confirmed by the
fact that the dibenzoylmethane difluoroboron chelate does
not enter into an azo coupling reaction with phenylꢀ
diazonium tetrafluoroborate.
atom of the paraꢀmethoxyꢀ
phenyl substituents. The obꢀ
served correlations allow unꢀ
Based on the structures of the final pyridazinones, one
could assume that intermediate boron complexes have
ambiguous assignment of
structure 4 to the intermeꢀ

Synthesis of 3ꢀarylazoꢀ1Hꢀpyridazinꢀ4ꢀones
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 8, August, 2007
1563
11B and 19F NMR spectra were recorded on a Bruker ACꢀ200
instrument (64 and 188 MHz, respectively). Mass spectra were
recorded on a Kratos MSꢀ30 instrument (EI, 70 eV). ATR studꢀ
ies of compound 4e were performed on a Shimadzu FTIRꢀ8400S
spectrometer (Shimadzu, Japan). Other IR spectra were recorded
on a Specord Mꢀ82 instrument (KBr).
a
The geometries were optimized and the vibrational frequenꢀ
cies and energies in the IR spectra were calculated with
the PRIRODA program system12,13 (PBE functional,14 DFT
method, TZ2P basis set).
Tributyl borate was prepared according to a known proꢀ
cedure.15
b
c
Acetylacetone difluoroboron complex (1a). Boron trifluoride
etherate (12.7 mL, 0.1 mol) was slowly added in an inert atmoꢀ
sphere to a solution of acetylacetone (15.4 mL, 0.15 mol) and
tributyl borate (13.5 mL, 0.05 mol) in diethyl ether (10 mL).
The reaction mixture was kept at room temperature for 16 h.
The solvent was removed and the residue was cooled in a freezꢀ
ing chamber. The precipitate that formed was filtered off and
washed with light petroleum (10 mL). Recrystallization from
diethyl ether gave chelate 1a (18.5 g, 83%) as white crystals,
m.p. 43 °C (cf. Ref. 16: m.p. 43 °C (chloroform—ligroin)).
11B NMR (CH3CN), δ: 0.43.
Aroylacetone difluoroboron chelates 1b—d were prepared acꢀ
cording to a known procedure17 from appropriate aroylacetones
and BF3•Et2O in benzene.
Benzoylacetone difluoroboron chelate (1b). Yield 95%, m.p.
155—156 °C (benzene) (cf. Ref. 16: m.p. 155 °C (benzene)).
4ꢀChlorobenzoylacetone difluoroboron chelate (1c). Yield
89%, m.p. 227—228 °C (ethyl acetate) (cf. Ref. 18: m.p.
226.5—228 °C).
4000
3000
2000
ν/cm–1
Fig. 1. Experimental IR spectrum of compound 4e (a) and the
simulated IR spectra for its cyclic (b) and linear structures (c).
The absorption bands due to the NH stretching vibrations are
hatched.
diate. Thus, the corresponding derivatives of 3ꢀ(1,3ꢀdioxoꢀ
propyl)formazan act as chelating ligands in complexes 4.
The presence of the formazan fragment in chelates 4a—g
allows intramolecular hydrogen bonding (IHB) to be
formed.
Using attenuated total internal reflection (ATR)
IR spectroscopy for chelate 4e, we excluded the water
stretching vibrations. The resulting spectrum contained a
set of absorption bands at 2844—3199 cm–1, including a
band due to the NH stretching vibrations. To verify the
presence of hydrogen bonding, we performed quantumꢀ
chemical calculations of the frequencies and energies of
the bond vibrations in compound 4e (see Fig. 1). For a
linear structure, the calculated frequency of the NH
stretching vibrations is 3255 cm–1, while for a cyclic strucꢀ
ture, its value is 2893 cm–1. Therefore, the formazan fragꢀ
ment of chelate 4e exists in the cyclic form stabilized by
an intramolecular hydrogen bond. The presence of this
bond can also be responsible for a substantial downfield
shift of the signal for the NH proton in the 1H NMR
spectrum.
2,4ꢀDimethylbenzoylacetone difluoroboron chelate (1d).
Yield 84%, m.p. 120—121 °C. Found (%): C, 60.65; H, 5.52.
C
12H13BF2O2. Calculated (%): C, 60.55; H, 5.50. MS,
1
m/z (Irel (%)): 238 [M]+ (45), 223 (100). H NMR (CDCl3), δ:
2.39, 2.40 (both s, 6 H, Me2C6H3); 2.59 (s, 3 H, Me); 6.35 (s,
1 H, CH=); 7.14 (m, 2 H, Ar); 7.60 (d, 1 H, Ar, J = 8.3 Hz).
11B NMR (THF), δ: 0.89. IR, ν/cm–1: 3136, 2984, 1616,
1540 (br).
Difluoroboron chelate of 3ꢀ(1,3ꢀdioxobutyl)ꢀ1,5ꢀdiphenylꢀ
formazan (4a). A solution of NaOAc (82 mg, 5 mmol) in water
(2 mL) was added dropwise at 0 °C to a solution of chelate 1a
(0.30 g, 2 mmol) and phenyldiazonium tetrafluoroborate (0.96 g,
5 mmol) in a mixture of sulfolane (5 mL) and methanol (5 mL).
Immediately after the first drops of the solution were added, the
reaction mixture turned bright red. The solution was stirred at
20 °C for 4 h, kept for 16 h, and then poured into water (100 mL).
The precipitate that formed was filtered off, washed with water
(50 mL) and hexane, and recrystallized from acetonitrile. The
yield of chelate 4a was 82%, m.p. 188—189 °C. Found (%):
C, 57.13; H, 4.22; N, 16.06. C17H15BF2N4O2. Calculated (%):
C, 57.30; H, 4.21; N, 15.73. MS, m/z (Irel (%)): 356 [M]+ (17),
In contrast to pyridazinꢀ3ꢀone derivatives, isomeric
pyridazinꢀ4ꢀones are probably less accessible and, accordꢀ
ingly, less studied.8,9 Using the "methodology of chelate
organic synthesis",10,11 we developed a simple and effiꢀ
cient method for the synthesis of novel 3ꢀarylazoꢀ1Hꢀ
pyridazinꢀ4ꢀones.
1
315 (6). H NMR (CDCl3), δ: 2.38 (s, 3 H, Me); 6.86 (s, 1 H,
CH=); 7.40—7.80 (m, 10 H, Ar); 16.39 (s, 1 H, NH). 11B NMR
(CHCl3), δ: 0.85. IR, ν/cm–1: 3076, 1552, 1500.
Difluoroboron chelate of 3ꢀ(1,3ꢀdioxoꢀ3ꢀphenylpropyl)ꢀ1,5ꢀ
bis(4ꢀmethoxyphenyl)formazan (4b) was obtained analogously
from chelate 1b (0.42 g, 2 mmol) and 4ꢀmethoxyphenyldiꢀ
azonium tetrafluoroborate (1.11 g, 5 mmol). The yield of cheꢀ
late 4b was 73%. Found (%): C, 59.99; H, 4.36; N, 11.52.
C24H21BF2N4O4. Calculated (%): C, 60.27; H, 4.43; N, 11.71.
Experimental
1
H and 13C NMR spectra were recorded on a Bruker
WMꢀ250 instrument (250 and 63 MHz, respectively) at 25 °C.

1564
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 8, August, 2007
Kravtsov et al.
MS, m/z (Irel (%)): 478 [M]+ (8), 343 (63). 1H NMR
(DMSOꢀd6), δ: 3.86 (s, 6 H, 2 OMe); 7.12, 7.68, 7.98, 8.22 (all
m, 14 H, Ar and CH=); 16.08 (s, 1 H, NH). 11B NMR (CH3CN),
δ: 0—5 (br.s). IR, ν/cm–1: 3048, 2948, 2840, 1600, 1556, 1512.
Difluoroboron chelate of 3ꢀ(1,3ꢀdioxobutyl)ꢀ1,5ꢀbis(4ꢀ
methoxyphenyl)formazan (4e) was obtained analogously from
chelate 1a (0.30 g, 2 mmol) and 4ꢀmethoxyphenyldiazonium
tetrafluoroborate (1.11 g, 5 mmol). The yield of chelate 4e
was 85%, m.p. 194—195 °C. Found (%): C, 54.60; H, 4.52;
N, 13.29. C19H19BF2N4O4. Calculated (%): C, 54.81; H, 4.57;
N, 13.46. MS, m/z (Irel (%)): 416 [M]+ (42), 350 (16). 1H NMR
(CDCl3), δ: 2.37 (s, 3 H, Me); 3.90 (s, 6 H, 2 OMe); 6.83 (s,
1 H, CH=); 7.02, 7.67 (both d, 2 H each, Ar, J = 9.2 Hz); 16.57
(s, 1 H, NH). 13C NMR (CDCl3), δ: 24.4 (Me); 55.6 (OMe);
97.1 (C(3)); 115.0 (mꢀCAr); 121.5 (oꢀCAr); 135.4 (C(1)); 140.0
(ipsoꢀCAr); 161.0 (pꢀCAr); 179.2 (C(2)); 188.4 (C(4)). 11B NMR
m/z (Irel (%)): 440 [M]+ (30). 1H NMR (DMSOꢀd6), δ: 2.12 and
2.20 (both s, 3 H each, 2 Me); 3.67 and 3.87 (both s, 3 H each,
2 OMe); 6.54 (s, 1 H, H(5)); 6.81, 7.14, 7.89 (all d, 2 H each,
Ar, J = 8.9 Hz); 6.97 (br.s, 2 H, Ar); 7.26 (m, 3 H, Ar). IR,
ν/cm–1: 2972, 2832, 1628, 1600, 1508.
1ꢀ(4ꢀMethoxyphenyl)ꢀ3ꢀ(4ꢀmethoxyphenylazo)ꢀ6ꢀmethylꢀ
pyridazinꢀ4(1H )ꢀone (2e). Yield 60%, m.p. 160—161 °C.
Found (%): C, 64.91; H, 5.13; N, 16.11. C19H18N4O3. Calcuꢀ
lated (%): C, 65.13; H, 5.18; N, 15.99. MS, m/z (Irel (%)):
350 [M]+ (18), 231 (25), 216 (22). 1H NMR (CDCl3), δ: 2.20 (s,
3 H, Me); 3.86, 3.88 (both s, 6 H, 2 OMe); 6.67 (s, 1 H, H(5));
6.98 (m, 4 H, Ar); 7.30 (m, 2 H, Ar); 7.98 (d, 2 H, Ar, J =
8.9 Hz). IR, ν/cm–1: 3060, 3012, 2924, 2836, 1632, 1604,
1580, 1512.
1ꢀ(4ꢀChlorophenyl)ꢀ3ꢀ(4ꢀchlorophenylazo)ꢀ6ꢀphenylpyridꢀ
azinꢀ4(1H )ꢀone (2f). Yield 63%, m.p. 210—211 °C (from ethyl
acetate). Found (%): C, 62.82; H, 3.61; N, 12.98.
C22H14Cl2N4O. Calculated (%): C, 62.72; H, 3.35; N, 13.30.
MS, m/z (Irel (%)): 420 [M – H]+ (16). 1H NMR (DMSOꢀd6),
δ: 6.76 (s, 1 H, H(5)); 7.36 and 7.41 (both s, 9 H total, Ar); 7.69
and 7.92 (both d, 2 H each, Ar, J = 8.9 Hz). IR, ν/cm–1: 2974,
1636, 1588, 1508.
1,6ꢀBis(4ꢀchlorophenyl)ꢀ3ꢀ(4ꢀchlorophenylazo)pyridazinꢀ
4(1H )ꢀone (2g). Yield 59%, m.p. 233—234°C. Found (%):
C, 58.11; H, 2.86; N, 12.27. C22H13Cl3N4O. Calculated (%):
C, 57.98; H, 2.88; N, 12.29. MS, m/z (Irel (%)): 454
[M – H]+ (7). 1H NMR (DMSOꢀd6), δ: 6.80 (s, 1 H, H(5));
7.44 (br.s, 8 H, Ar); 7.70 and 7.91 (both d, 2 H each, Ar, J =
8.5 Hz). IR, ν/cm–1: 3048, 1632, 1492.
(CHCl3), δ: 0.76. 19F NMR (CDCl3), δ: –140.60. IR, ν/cm–1
:
2968, 1604, 1580, 1512.
Difluoroboron chelates 4c,d,g were obtained analogously
from compounds 1b,c,d and used immediately in subsequent
heterocyclization.
1ꢀArylꢀ6ꢀRꢀ3ꢀarylazopyridazinꢀ4(1H )ꢀones (2a—g) (general
procedure). Chelates 4a—g were refluxed in a mixture of pyriꢀ
dine (15 mL) and butanol (5 mL) for 4 h. The pyridine was
removed and the residue was dissolved in chloroform and passed
through a short column with silica gel. The solvent was evapoꢀ
rated and the residue was purified by flash chromatography on
Silpearl silica gel with chloroform as an eluent (for pyridazinoꢀ
nes 2a,e); in the other cases, the reaction product was recrystalꢀ
lized from acetonitrile.
This work was financially supported by the Russian
Academy of Sciences (Basic Research Program of the
Presidium of the Russian Academy of Sciences "Developꢀ
ment of the Methodology of Organic Synthesis and
Creation of Compounds with Valuable Practical Propꢀ
erties").
6ꢀMethylꢀ1ꢀphenylꢀ3ꢀphenylazopyridazinꢀ4(1H )ꢀone (2a).
Yield 51%, m.p. 225—226 °C. Found (%): C, 70.14; H, 4.85;
N, 19.13. C17H14N4O. Calculated (%): C, 70.33; H, 4.86;
1
N, 19.30. MS, m/z (Irel (%)): 290 [M]+ (15), 261 (9). H NMR
(CDCl3), δ: 2.19 (s, 3 H, Me); 6.66 (s, 1 H, H(5)); 7.39 (d, 2 H,
Ar); 7.53 (m, 6 H, Ar); 7.95 (d, 2 H, Ar). 13C NMR (CDCl3), δ:
20.8 (Me); 120.6 (C(5)); 123.7 (oꢀCN=NPh); 126.4 (oꢀCNPh);
128.8 (mꢀCN=NPh); 129.6 (mꢀCNPh); 129.7 (pꢀCNPh);
132.4 (pꢀCN=NPh); 141.8 (ipsoꢀCNPh); 151.5(C(6)); 152.7
(ipsoꢀCN=NPh); 159.0 (C(4)); 167.1 (C(3)). IR, ν/cm–1: 3056,
3012, 1636, 1596, 1496; CHCl3: 3072, 3000, 1620, 1596, 1496.
1ꢀ(4ꢀMethoxyphenyl)ꢀ3ꢀ(4ꢀmethoxyphenylazo)ꢀ6ꢀphenylꢀ
pyridazinꢀ4(1H )ꢀone (2b). Yield 71%, m.p. 220—221 °C.
Found (%): C, 69.68; H, 5.00; N, 13.85. C24H20N4O3. Calcuꢀ
lated (%): C, 69.89; H, 4.89; N, 13.58. MS, m/z (Irel (%)):
412 [M]+ (15). 1H NMR (DMSOꢀd6), δ: 3.68 and 3.87 (both s,
3 H each, 2 OMe); 6.66 (s, 1 H, H(5)); 6.83, 7.14, 7.89 (all d,
2 H each, Ar, J = 8.5 Hz); 7.30 (m, 7 H, Ar). IR, ν/cm–1: 2976,
2840, 1632, 1604, 1580, 1508.
References
1. V. A. Dorokhov, I. V. Kravtsov, P. A. Belyakov, and S. V.
Baranin, Izv. Akad. Nauk, Ser. Khim., 2006, 867 [Russ. Chem.
Bull., Int. Ed., 2006, 55, 898].
2. V. A. Dorokhov, I. V. Kravtsov, P. A. Belyakov, and S. V.
Baranin, Izv. Akad. Nauk, Ser. Khim., 2007, 992 [Russ. Chem.
Bull., Int. Ed., 2007, 56, 5].
3. M. F. Gordeev and V. A. Dorokhov, Izv. Akad. Nauk SSSR,
Ser. Khim., 1988, 1690 [Bull. Acad. Sci. USSR, Div. Chem.
Sci., 1988, 37, 1505 (Engl. Transl.)].
6ꢀ(4ꢀChlorophenyl)ꢀ1ꢀ(4ꢀmethoxyphenyl)ꢀ3ꢀ(4ꢀmethoxyꢀ
phenylazo)pyridazinꢀ4(1H )ꢀone (2c). Yield 58%, m.p.
212—213 °C. Found (%): C, 64.45; H, 4.45; N, 12.58.
4. S. M. Pamerter, in Organic Reactions, Ed. R. Adams, Wiley,
New York, 1959, Vol. 10, 576 p.
5. A. Bax and S. Subramanian, J. Magn. Reson., 1986, 67, 565.
6. A. Bax and M. F. Summers, J. Am. Chem. Soc., 1986,
108, 2093.
7. J. Jeener, B. H. Meier, P. Bachmann, and R. R. Ernst,
J. Chem. Phys., 1979, 69, 4546.
8. M. Tisler and P. Kolar, in Adv. Heterocycl. Chem., Ed. A. R.
Katritzky, Academic Press, 2000, 75, 157.
C
24H19ClN4O3. Calculated (%): C, 64.50; H, 4.29; N, 12.54.
MS, m/z (Irel (%)): 446 [M]+ (10). 1H NMR (DMSOꢀd6), δ:
3.70 and 3.87 (both s, 3 H each, 2 OMe); 6.69 (s, 1 H, H(5));
6.86, 7.14, 7.31, 7.89 (all d, 2 H each, Ar, J = 8.9 Hz); 7.39 (br.s,
4 H, Ar). IR, ν/cm–1: 2974, 2836, 1628, 1604, 1584, 1508.
6ꢀ(2,4ꢀDimethylphenyl)ꢀ1ꢀ(4ꢀmethoxyphenyl)ꢀ3ꢀ(4ꢀmethꢀ
oxyphenylazo)pyridazinꢀ4(1H )ꢀone (2d). Yield 60%, m.p.
204—205 °C. Found (%): C, 70.66; H, 5.46; N, 12.73.
9. M. Tisler and B. Stanovnik, in Comprehensive Heterocyclic
Chemistry, Ed. A. R. Katritzky, Pergamon Press, Oxford,
1997, 3, 1.
C
26H24N4O3. Calculated (%): C, 70.89; H, 5.49; N, 12.72. MS,

Synthesis of 3ꢀarylazoꢀ1Hꢀpyridazinꢀ4ꢀones
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 8, August, 2007
1565
10. V. A. Dorokhov, A. V. Vasil´ev, S. V. Baranin, and A. S.
Vorushilov, Izv. Akad. Nauk, Ser. Khim., 2003, 1947 [Russ.
Chem. Bull., Int. Ed., 2003, 52, 2057].
11. V. A. Dorokhov, M. A. Prezent, and V. S. Bogdanov, Izv.
Akad. Nauk, Ser. Khim., 1995, 1118 [Russ. Chem. Bull., 1995,
44, 1080 (Engl. Transl.)].
12. D. N. Laikov, Chem. Phys. Lett., 1997, 281, 151.
13. D. N. Laikov and Yu. A. Ustynyuk, Izv. Akad. Nauk, Ser.
Khim., 2005, 804 [Russ. Chem. Bull., Int. Ed., 2005, 54, 820
(Engl. Transl.)].
15. A. Pelter, K. Smith, and H. C. Brown, Boron Reagents, in
Best Synthetic Methods, Eds A. R. Katritzky, O. MethꢀCohn,
and C. W. Rees, Academic Press, London, 1988, p. 435.
16. G. T. Morgan and R. B. Tunstall, J. Chem. Soc., 1924,
54, 1963.
17. V. M. Neplyuev and T. A. Sinenko, Zh. Org. Khim., 1980,
16, 2558 [J. Org. Chem. USSR, 1980, 16 (Engl. Transl.)].
18. V. A. Reutov and E. V. Gukhman, Zh. Obshch. Khim., 1999,
69, 1672 [J. Org. Chem. USSR, 1999, 69 (Engl. Transl.)].
14. J. P. Perdew, K. Burke, and M. Ernzerhof, Phys. Rev. Lett.,
1996, 77, 3865.
Received July 20, 2007