Thermal transformation of cyclopropylazoarenes into the five-membered nitrogen-containing heterocycles

Article abstract of DOI:10.1007/s11172-008-0227-0

Cyclopropylazoarenes containing methoxy groups in the aromatic ring give the corresponding N-arylpyrazolines on the reflux in o-dichlorobenzene or on SnCl₂ catalysis at 80 °C in good yields. The products can be smoothly oxidized into the corresponding pyrazoles. Thermolysis of cyclopropylazoarenes containing hydroxy groups in the aromatic ring proceeds more complicated. Thus in the case of resorcin azo derivative, strong resinification of the reaction mixture is observed and the corresponding N-arylpyrazoline is isolated only in -40% yield. Under similar conditions, thermolysis of 1-cyclopropyl- and 1-(1-methylcyclopropyl)azo-2-naphthol proceeds otherwise and unexpectedly leads to naphtho[1,2-d]oxazole derivatives with degradation of the cyclopropane ring.

Full text of DOI:10.1007/s11172-008-0227-0

Russian Chemical Bulletin, International Edition, Vol. 57, No. 8, pp. 1718—1724, August, 2008
1718
Thermal transformation of cyclopropylazoarenes
into the fiveꢀmembered nitrogenꢀcontaining heterocycles
R. A. Novikov, I. P. Klimenko, E. V. Shulishov, V. A. Korolev, and Yu. V. Tomilov
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 6390. Eꢀmail: tom@ioc.ac.ru
Cyclopropylazoarenes containing methoxy groups in the aromatic ring give the correꢀ
sponding Nꢀarylpyrazolines on the reflux in oꢀdichlorobenzene or on SnCl2 catalysis at 80 °C
in good yields. The products can be smoothly oxidized into the corresponding pyrazoles.
Thermolysis of cyclopropylazoarenes containing hydroxy groups in the aromatic ring proceeds
more complicated. Thus in the case of resorcin azo derivative, strong resinification of the
reaction mixture is observed and the corresponding Nꢀarylpyrazoline is isolated only in ∼40%
yield. Under similar conditions, thermolysis of 1ꢀcyclopropylꢀ and 1ꢀ(1ꢀmethylcyclopropyl)azoꢀ
2ꢀnaphthol proceeds otherwise and unexpectedly leads to naphtho[1,2ꢀd]oxazole derivatives
with degradation of the cyclopropane ring.
Key words: cyclopropylazoarenes, thermolysis, Nꢀarylpyrazolines, Nꢀarylpyrazoles,
naphtho[1,2ꢀd]oxazoles, heterocyclization.
Owing to the last years research directed on a developꢀ
ment of methods for the generation and trapping of
cyclopropyldiazonium ion, it was shown that this interꢀ
mediate can afford products of azoꢀcoupling in preparative
yields.1,2 As a rule, NꢀcyclopropylꢀNꢀnitrosourea serves
as the source of cyclopropyldiazonium since its decomꢀ
position under action of bases in the presence of active
azo components, CHꢀacids or hydroxy arenes, leads
to cyclopropylhydrazones1 or cyclopropylazoarenes,2,3
respectively. It should be noted that cyclopropylazo comꢀ
pounds are the structural analogs of vinylcyclopropanes,
the ability of which to give cyclopentenes under therꢀ
molysis is well known.4 Similarly, cyclopropylazo comꢀ
pounds rearrange into Nꢀsubstituted pyrazolines.5—10
However, transformations of functionalized cyclopropylꢀ
azo compounds are practically not studied due to low
availability of these compounds. Development of conveꢀ
nient methods for the preparation of cyclopropylazoarenes
gives a possibility, in particular, to study their thermal
transformations and to use this methodology for the
synthesis of substituted Nꢀarylpyrazolines, pyrazoles, and,
in some cases, fused 1,3ꢀoxazoles.
1ꢀ(1ꢀmethylcyclopropyl)azoꢀ2ꢀnaphthol (2c), as well as
their Oꢀmethylated derivatives, viz., 1ꢀcyclopropylazoꢀ
2,4ꢀdimethoxybenzene (1b) and 1ꢀcyclopropylazoꢀ
2ꢀmethoxynaphthalene (2b), as the subjects of our
research.
Compound 2c was obtained by the reaction of excess
2ꢀnaphthol with methyl NꢀnitrosoꢀNꢀ(1ꢀmethylcycloꢀ
propyl)carbamate12 in the presence of Cs2CO3 as the base
at room temperature (Scheme 1). The reaction is slow
1
(9 days), but rather selective. According to the H NMR
spectra, denitrosation of starting methyl Nꢀnitrosoꢀ
Nꢀ(1ꢀmethylcyclopropyl)carbamate12 and partial methyꢀ
lation of 2ꢀnaphthol at the hydroxy group occured as the
side processes.
Scheme 1
As some literature data show, isomerization of cycloꢀ
propylazo compounds into pyrazolines proceeds under
both the thermolysis5—7 (140–200 °C) and photolysis8,9
(254 or 366 nm). In addition, it was shown10 that addition of
SnCl2 allows one to reduce temperature of the process to
80 °C and to obtain isomerization products in good yields.
We used readily available 4ꢀcyclopropylazoresorꢀ
cinol (1a),11 1ꢀcyclopropylazoꢀ2ꢀnaphthol (2a),2 and
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1686—1692, August, 2008.
1066ꢀ5285/08/5708ꢀ1718 © 2008 Springer Science+Business Media, Inc.

Thermolysis of cyclopropylazoarenes
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 8, August, 2008
1719
In the 1H NMR spectrum of compound 2c, the signal
for the proton of the OH group is observed at δ 13.8,
which is characteristic of the hydroxyl bound to the azo
fragment by a hydrogen bond.2,3 The signal for the methyl
group appears as the singlet at δ 1.69, while the protons of
the cyclopropane ring as two muliplets at δ 1.24 and 1.58,
respectively.
Preparation of Oꢀmethylated derivatives 1b and 2b was
a difficult problem since the hydroxy groups in compounds
1a and 2a, located in orthoꢀposition to the azo fragment,
form stable intramolecular hydrogen bond with the nitrogen
atom2,3 and, owing to this, can be hardly involved into
chemical transformations. We tried several methods for
the methylation of phenols suggested in the literature. It
turned out that the use of MeI in CH2Cl2 in the presence
of K2CO3 or the twoꢀphase system NaOH—H2O/CH2Cl2
in the presence of a phaseꢀtransfer catalyst did not give
the desired methylation products in considerable yields.
An etherial solution of diazomethane in the absence of a
catalyst can not methylate compounds 1a and 2a either,
whereas their interaction with CH2N2 in the presence
of catalytic amount of BF3•Et2O leads to the complex
mixture of compounds.
obtain dimethoxy derivative 1b in no less than 60% yield.
In this case, despite of the use of 3.3 equiv. of MeI per
1 mol of the substrate, the methylation of the OH group
closer to the azo fragment is not yet complete, while the
excess of methyl iodide partially methylates the aromatic
ring in the forming methoxybenzenes 1b and 3 to afford
substituted toluenes 4 and 5 (Scheme 3). The reaction
mixture was separated by column chromatography on SiO2
using a mixture of toluene with methanol in the ratio
100 : 1 as the eluent to isolate compounds 1b and 4 and a
mixture of azophenols 3 and 5, which then was separated
in the system toluene—light petroleum, 1 : 3.
Scheme 3
OMe
1
2
t
1) Bu OK/DME
1a
3
+
+
3
I
2) Me
OMe
4
N
N
Selective methylation of azoresorcinol 1a has been
successfully accomplished under action of diazomethane
in the presence of HBF4. In this case, the hydroxy group
not involved into the formation of intramolecular hydroꢀ
gen bond undergoes the methylation; 2ꢀcyclopropylazoꢀ
5ꢀmethoxyphenol (3) is the reaction product, which was
isolated in 63% yield (Scheme 2).
1b (60%)
OMe
OMe
3
Me
Me
2
+
+
1
OMe
O
H
6
N
N
N
N
Scheme 2
4 (11%)
5 (8%)
1
In the H NMR spectra of compounds 4 and 5, the
signals for the methyl groups resonate as the singlets at
δ 2.19 and 2.09, respectively, whereas the protons of the
aromatic ring as two doublets with the spinꢀspin coupling
constant ca. 9 Hz, which is characteristic of this type
of substitution. The structures of compounds obtained
were also confirmed by the 13C NMR spectra, mass specꢀ
trometry and elemental analysis data.
Methylation of naphthol 2a under similar conditions
proceeds more selectively and gives methoxy derivative
2b in 72% yield (Scheme 4). The 1H NMR spectrum
of the compound obtained differs from that for starting
naphthol in the absence of the upfield signal for the OH
group and appearance of the singlet for the methoxy group
at δ 3.94. The signals for other protons change insignifiꢀ
cantly in comparison with 2a. In the 13C NMR spectrum,
the signals for the C(2) and C(3) atoms undergo the largꢀ
est shift: both are shifted by ∼5 ppm downfield on passing
from 2a to 2b.
In the 1H NMR spectrum of compoundя 3, the signal
for the proton of the OH group is observed at δ 12.2,
which is characteristic of the hydroxyl bound to the azo
fragment by a hydrogen bond. Earlier, we have shown3
that hydroxy groups in orthoꢀ and paraꢀpositions with
respect to cyclopropylazo fragment appear in the 1H NMR
spectra at δ 11.7 and 5.6, respectively.
For the methylation of both hydroxy groups in comꢀ
pound 1a, we developed a procedure according to which
compound 1a was first treated with ButOK in dimethoxyꢀ
ethane and then, methyl iodide was added to the solution
of the phenoxide obtained. This procedure allowed us to

1720
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 8, August, 2008
Novikov et al.
Scheme 4
proceeds in a more complicated way. The reflux of
azophenol 1a in oꢀdichlorobenzene leads to a rather strong
resinification of the reaction mixture, however, when the
reaction was carried out for 1 h and when conversion of
the starting azophenol is incomplete (∼50%), the correꢀ
sponding pyrazoline 6a can be obtained (see Scheme 5),
the yield of which with respect to the converted azophenol
1a is ∼41%. Attempts to obtain for pyrazoline 6a satisfacꢀ
tory elemental analysis data were unsuccessful because of
its low stability, but its structure was reliably confirmed by
the mass spectrometry and 1H and 13C NMR spectroꢀ
scopy data (see Experimental).
Under similar conditions, thermolysis of azonaphthol
2a proceeds differently and, instead of expected pyrazoline,
leads to naphtho[1,2ꢀd]oxazole 8a, its homologs 8b,c,
and 1ꢀ(2ꢀhydroxynaphthyl)ꢀ1Hꢀpyrazole (9a). When
the reaction is carried out under argon their ratio is
∼1 : 1 : 1 : 0.2 (73% total yield, Scheme 6). When the
reaction is carried out in air, they are formed approxiꢀ
mately in equal amounts. It can be noted that the presꢀ
ence of oxygen has insignificant influence on the course
of the reaction and the composition of the products
remains unchanged. When the reaction temperature is
reduced to 160 °C, its rate decreases and naphthoxazoles
8a—c practically are not formed. Compound 9a is
obtained as the only reaction product with partial resinificaꢀ
tion of starting azonaphthol 2a.
N
N
N
N
OMe
OH
t
1) Bu OK
2)MeI
2a
2b (72%)
Thermolysis of cyclopropylazoarenes 1b and 2b in
boiling xylene or oꢀdichlorobenzene showed that their
rearrangement into pyrazolines begins at ∼140 °C,
however, proceeds yet too slow at this temperature,
approximately by 10% for 6 h. Conducting the reaction in
boiling oꢀdichlorobenzene under Ar for 6 h was more
efficient: in this case, pyrazolines 6b and 7b (Scheme 5)
were obtained in 84—86% yield as lowꢀmelting airꢀsensiꢀ
tive crystals.
Scheme 5
Thermolysis of azonaphthol 2c proceeds similarly and
leads to oxazoles 8a and 8b and 3ꢀmethylꢀ1ꢀ(2ꢀhydroxyꢀ
naphthyl)ꢀ1Hꢀpyrazole (9b) in the ratio ∼6.5 : 1 : 3.5. Comꢀ
pound 2c thermally is less stable than 2a: ∼3 h at 180 °C
is needed for the complete conversion of 2c, whereas
for azonaphthol 2a ∼12 h is required. The compounds
obtained were isolated in individual states by column chroꢀ
matography on SiO2.
The structures of naphthooxazoles 8a—c were estabꢀ
lished on the bases of the 1H and 13C NMR spectra. It was
found that the spectra of compounds 8a,b completely
agree with those described in the literature,13 whereas the
1H and 13C NMR spectra for oxazole 8c differ from those
for 8b by the absence of the signal for the methyl group at
δH 2.75 or δC 14.7 and by the presence of two groups of
R = H (a), Me (b)
The 1H NMR spectra of pyrazolines obtained are
characterized by the signals for the protons of the heteroꢀ
cyclic fragment appearing as a narrow triplet at δ 6.9 for
proton H(3), doublet of triplets at δ 2.9 for two protons H(4),
and a triplet at δ 3.6 for the methylene protons H(5). In
this case, the chemical shifts and the spinꢀspin coupling
constants for the protons of the aromatic ring changes
insignificantly on passing from the azo compounds to
pyrazolines. To obtain satisfactory data of elemental
analysis, pyrazolines 6b and 7b, because of their rather
low stability, were additionally purified by preparative TLC
directly before the analysis.
1
signals characteristic of the ethyl substituent. In the H
NMR spectra of pyrazoles 9a,b, the signals for the proꢀ
1
tons are in the aromatic region: δH 6.40—7.90. In the H
NMR spectrum of compound 9b, the signal for the meꢀ
thyl group at δH 2.46 is also present, that is characteristic
of the methyl group at the aromatic ring.
At present, we cannot give a reasonable scheme for
the formation of naphthooxazole and its homologs
because of improbability of elimination of the C2H5N,
CH3N, or NH fragments from the starting cyclopropylꢀ
azoarene 2a, which points out either the possibility of its
bimolecular transformations or proceeding of oxidationꢀ
reduction processes.
In contrast to the methoxy derivatives of azoarenes 1b
and 2b, thermolysis of hydroxy derivatives 1a and 2a

Thermolysis of cyclopropylazoarenes
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 8, August, 2008
1721
Scheme 6
of the pyrazolines obtained in THF and addition of cataꢀ
lytic amount of hydrochloric acid, we found that under
these conditions, pyrazoles 10 and 9c are formed with
rather good selectivity in 78 and 61% yield, respectively
(Scheme 7). The atmospheric oxygen can play the role of
oxidant in this reaction. In the absence of HCl, the oxidaꢀ
tion is slower and nonselective.
Scheme 7
1
The H NMR spectra of the products can definitely
indicate aromatization of the heterocyclic ring, in which
the signals for the protons of the pyrazole ring with charꢀ
acteristic chemical shifts and corresponding muliplicity
appear, as well as the chemical shifts for three carbon
atoms of this fragment in the 13C NMR spectra at δ 106
(C(4)), 132 (C(5)), and 140 (C(3)), that corresponds to
the expected chemical shifts for the Nꢀarylꢀsubstituted
pyrazole ring.14
R = H (a), Me (b), Et (c)
In conclusion, we showed that thermolysis of cycloꢀ
propylazoarenes containing OH or OMe groups in
orthoꢀposition to the azo fragment can lead to pyrazolines
in high yield, the subsequent oxidation of which
in a number of cases proceeds selectively and leads to
pyrazoles. Thermolysis in boiling oꢀdichlorobenzene is
preferable; though the use of SnCl2 as the catalyst allows
one to significantly decrease the temperature of the
process, however, leads to a decrease in the yields of
the target products, and can not be applied at all for the
compounds with OH group. Thermolysis of 1ꢀcycloꢀ
propylazonaphthol (2a) proceeds quite unexpectedly: it is
accompanied by the fragmentation of the azocyclopropane
fragment with the formation of naphtho[1,2ꢀd]oxazole
derivatives.
Thermolysis of azo compounds 1a,b and 2a,b in
boiling benzene in the presence of SnCl2 according to the
procedure described earlier10 did not give a considerable
advantage. It turned out that compounds 1a and 2a
rapidly give insoluble precipitate, possibly, owing to the
coordination of the free OH group with the tin atom,
and further heating does not lead to any identifiable
products. Under similar conditions, compounds 1b and
2b methylated at the hydroxyl give expected pyrazolines
6b and 7b in 65 and 63% yield, respectively (see Scheme 5),
however, at 80 °C, the reaction is accompanied by a
considerable resinification.
We supposed that the low yields of pyrazolines 6b
and 7b in the case of catalytic version of the reaction can
be caused by elimination of HCl owing to the partial
hydrolysis of SnCl2 during the reaction. After dissolution
On the whole, the use of methoxyꢀsubstituted cycloꢀ
propylazoarenes is more preferable since their transforꢀ

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Russ.Chem.Bull., Int.Ed., Vol. 57, No. 8, August, 2008
Novikov et al.
was separated by column chromatography on SiO2 (eluent —
toluene—methanol, 100 : 1) to obtain a mixture of compounds 3
and 5 (75 mg) as yellow oil, azo compound 4 (55 mg, 11%)
as yellow oil with the purity of ∼95%, and azo compound 1b
(276 mg, 60%) as yellowish orange needleꢀlike crystals
with m.p. 51—52 °C. The mixture of compounds 3 and 5
was repeatedly separated by column chromatography on SiO2
(eluent — toluene—light petroleum (40—70), 1 : 3) to obtain
azophenol 3 (32 mg, 7%), identical to the sample described
earlier,11 and azo compound 5 (36 mg, 8%) as yellow crystals
with m.p. 55—56 °C.
mations during thermolysis proceed with higher yields,
are more predictable, and the pyrazolines formed are more
stable to air oxygen.
Experimental
1H and 13C spectra were recorded on a Bruker AMꢀ300
spectrometer (300 and 75.5 MHz, respectively) for solutions in
CDCl3 containing 0.05% Me4Si as the internal standard. Mass
spectra were recorded on a Finnigan MAT INCOSꢀ50 instruꢀ
ment (EI, 70 eV, direct inlet). Silica gel 60 (0.040—0.063 mm,
Merck) was used for chromatography. Azo compounds 1a and
2a and methyl Nꢀ(1ꢀmethylcyclopropyl)Nꢀnitrosocarbamate
were synthesized according to the procedures described
earlier.11,2,12 Solutions of CH2N2 and HBF4 were prepared
according to the known procedure.15
2ꢀCyclopropylꢀ1ꢀ(2,4ꢀdimethoxyphenyl)diazene (1b). Found
(%): C, 64.27; H, 7.04; N, 13.51. C11H14N2O2. Calculated (%):
C, 64.06; H, 6.84; N, 13.58. Partial MS, m/z (Irel (%)): 206 (80)
[M]+, 191 (41) [M – Me]+, 164 (43), 150 (23), 136 (42), 122
(53), 107 (45), 39 (100). 1H NMR (CDCl3), δ: 1.21 and 1.47
(both m, 2 H each, CH2CH2); 3.75 (tt, 1 H, CH, Jtrans = 3.4 Hz,
Jcis = 7.1 Hz); 3.82 and 3.96 (both s, 3 H each, 2 OMe); 6.44
4ꢀCyclopropylazoꢀ1ꢀmethoxybenzene. A solution of HBF4 in
Et2O (0.1 mL, 0.008 mmol) and a solution of CH2N2 in CH2Cl2
(15 mL, 4.5 mmol) were added to a solution of 4ꢀcyclopropylꢀ
azophenol (50 mg, 0.3 mmol) in CH2Cl2 (10 mL). The reaction
mixture was stirred for 3 h at room temperature, then, another
portion of the HBF4 solution (0.1 mL) was added followed by a
portionwise addition of the CH2N2 solution in CH2Cl2 (40 mL,
12 mmol) for 1 h. After 2 h, the reaction was stopped, a few
drops of acetic acid was added into the reaction mixture to
decompose the excess CH2N2. The solution obtained was washed
with saturated aqueous NaHCO3 (2×20 mL) and NaCl (2×20 mL),
dried with MgSO4, and concentrated in vacuo. The residue was
purified by preparative TLC (SiO2, eluent — benzene) collectꢀ
ing the yellow band with Rf = 0.45 to obtain 4ꢀcyclopropylazoꢀ
1ꢀmethoxybenzene (18 mg, 36%) as yellow oil. Partial MS,
m/z (Irel (%)): 176 (81) [M]+, 161 (100) [M – Me]+, 121 (37)
4
3
(dd, 1 H, H(5), J = 2.5 Hz, J = 8.9 Hz); 6.54 (d, 1 H, H(3),
4J = 2.5 Hz); 7.37 (d, 1 H, H(6), 3J = 8.9 Hz). 13C NMR, δ:
9.5 (CH2CH2); 51.1 (CH); 55.5 and 56.0 (2 OMe); 98.7
(C(3)); 104.9 (C(5)); 118.1 (C(6)); 135.7 (C(1)); 156.7 and
162.3 (C(2) + C(4)).
2ꢀCyclopropylꢀ1ꢀ(2,4ꢀdimethoxyꢀ3ꢀmethylphenyl)diazene (4).
Partial MS, m/z (Irel (%)): 220 (81) [M]+, 205 (73) [M – Me]+,
190 (25) [M – C2H6]+, 178 (58) [M – C3H6]+, 39 (100). 1H
NMR (CDCl3), δ: 1.21 and 1.47 (both m, 2 H each, CH2CH2);
2.19 (s, 3 H, Me); 3.77 (tt, 1 H, CH, Jtrans = 3.4 Hz, Jcis = 7.1 Hz);
3.83 and 3.93 (both s, 3 H each, 2 OMe); 6.59 (d, 1 H, H(5),
3J = 9.0 Hz); 7.24 (d, 1 H, H(6), 3J = 9.0 Hz). 13C NMR, δ: 8.8
(Me); 9.5 (CH2CH2); 50.8 (CH)); 55.7 and 62.8 (2 OMe); 105.7
(C(5)); 114.8 (C(6)); 120.1 (C(3)); 139.6 (C(1)); 156.0 and
159.9 (C(2) + C(4)).
1
[M – C3H5N]+, 107 (35) [M – C3H5N2]+. H NMR (CDCl3),
6ꢀCyclopropylazoꢀ3ꢀmethoxyꢀ2ꢀmethylphenol (5). Found
(%): C, 64.19; H, 6.74; N, 13.77. C11H14N2O2. Calculated
(%): C, 64.06; H, 6.84; N, 13.58. Partial MS, m/z (Irel (%)):
206 (98) [M]+, 164 (100) [M – C3H6]+, 108 (72), 39 (88). 1H
NMR (CDCl3), δ: 1.25 and 1.36 (both m, 2 H each, CH2CH2);
2.09 (s, 3 H, Me); 3.77 (tt, 1 H, CH, Jtrans = 3.9 Hz, Jcis = 6.7 Hz);
3.88 (s, 3 H, OMe); 6.55 (d, 1 H, H(5), 3J = 8.8 Hz); 7.55 (d, 1 H,
H(6), 3J = 8.8 Hz); 12.43 (br.s, 1 H, OH). 13C NMR, δ: 7.6 (Me);
10.0 (CH2CH2); 48.3 (CH); 55.8 (OMe); 102.0 (C(4)); 113.5
(C(2)); 130.0 (C(5)); 131.8 (C(6)); 152.2 (C(3)); 160.2 (C(1)).
1ꢀ(2,4ꢀDihydroxyphenyl)ꢀ4,5ꢀdihydroꢀ1Hꢀpyrazole (6a).
A solution of azo compound 1a (50 mg, 0.3 mmol) in anhydrous
oꢀdichlorobenzene (4 mL) was refluxed for 1 h under Ar with
stirring, a precipitate formed was filtered off. The filtrate was
concentrated in vacuo at 0.1 Torr. The residue, containing
according to the 1H NMR spectra compounds 1a and 6a, was
separated by preparative TLC on SiO2 (eluent — toluene—ethyl
acetate, 5 : 1) collecting the yellow band with Rf = 0.5 for 1a
and Rf = 0.3 for 6a. The starting azo compound 1a (18 mg) and
pyrazoline 6a (13 mg, 41%) as yellow powder, rapidly liquifying
in air were isolated. Partial MS, m/z (Irel (%)): 178 (67) [M]+,
150 (15) [M – N2]+, 136 (73) [M – C3H6]+, 41 (56), 38 (100).
1H NMR (CDCl3), δ: 2.86 (dt, 2 H, H(4), 3J = 1.9 Hz, 3J = 10.2 Hz);
3.63 (t, 2 H, H(5), 3J = 10.2 Hz); 5.40 (br.s, 1 H, OH); 6.32
(dd, 1 H, H(5´), 4J = 2.7 Hz, 3J = 8.6 Hz); 6.41 (d, 1 H, H(6´),
3J = 8.6 Hz); 6.49 (d, 1 H, H(3´), 4J = 2.7 Hz); 6.81 (t, 1 H,
H(3), 3J = 1.9 Hz); 9.92 (br.s, 1 H, OH). 13C NMR, δ: 32.1
(C(4)); 48.9 (C(5)); 104.8 (C(3´)); 106.1 (C(5´)); 114.1 (C(6´));
127.3 (C(1´)); 139.8 (C(3)); 147.9 and 150.9 (C(2´) + C(4´)).
δ: 1.21 and 1.46 (both m, 2 H each, CH2CH2); 3.66 (tt, 1 H,
CH, Jtrans = 3.6 Hz, Jcis = 7.1 Hz); 3.83 (s, 3 H, OMe); 6.92 (m,
2 H, H(2) + H(6)), 7.60 (m, 2 H, H(3) + H(5)). 13C NMR, δ:
9.4 (CH2CH2); 50.4 (CH); 55.6 (OMe); 114.0 (C(2) + C(6));
123.5 (C(3) + C(5)); 146.4 (C(4)); 161.0 (C(1)).
2ꢀCyclopropylazoꢀ5ꢀmethoxyphenol (3). A solution of HBF4
(0.3 mL, 0.025 mmol) was added to a solution of 4ꢀcycloꢀ
propylazoꢀ1,3ꢀdihydroxybenzene (1a) (100 mg, 0.6 mmol) in
CH2Cl2 (30 mL) with stirring followed by a portionwise addition
of a CH2N2 solution (30 mL, 9 mmol) for 20 min. The reaction
mixture was stirred for 1.5 h at room temperature, a few drops of
acetic acid was added into the reaction mixture to decompose
the excess CH2N2, the solution obtained was washed with satuꢀ
rated aq. NaHCO3 (2×20 mL) and NaCl (2×20 mL), dried with
MgSO4, and concentrated in vacuo. The residue was separated
by column chromatography on SiO2 (eluent — toluene) to
obtain azo compound 3 (68 mg, 63%) as bright yellow crystals
with m.p. 5—6 °C. The 1H and 13C NMR spectra correspond to
those described earlier.11
Methylation of phenol 1a upon treatment with MeI. A soluꢀ
tion of 4ꢀ(cyclopropylazo)resorcinol (1) (400 mg, 2.3 mmol)
in DME (15 mL) was added to a solution of ButOK (780 mg,
7.0 mmol) in DME (25 mL) with stirring. The suspension formed
was stirred for 2 h at room temperature, then MeI (1.08 g,
7.6 mmol) was added and this was stirred for 3 days at 20 °C.
After that, the reaction mixture was diluted with CH2Cl2,
(40 mL), a precipitate formed was filtered off and washed with
CH2Cl2 (10 mL). The filtrate was concentrated and the residue

Thermolysis of cyclopropylazoarenes
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 8, August, 2008
1723
1
1ꢀ(2,4ꢀDimethoxyphenyl)ꢀ4,5ꢀdihydroꢀ1Hꢀpyrazole (6b).
A. Anhydrous SnCl2 (11 mg, 0.06 mmol) was added to a solution
of azo compound 1b (83 mg, 0.4 mmol) in benzene (20 mL)
and the mixture was refluxed for 6 h with stirring under argon.
A black precipitate formed was filtered off, the filtrate was conꢀ
centrated, the residue was purified by preparative TLC on SiO2
(eluent — toluene—methanol, 20 : 1) collecting the band with
Rf = 0.5 to obtain pyrazoline 6b (54 mg, 65%) as colorless
crystals with m.p. 28—30 °C.
[M – Me]+, 142 (54), 115 (45). H NMR (CDCl3), δ: 1.33 and
1.64 (both m, 2 H each, CH2CH2); 3.89 (s, 3 H, OMe); 3.95
(tt, 1 H, CH, Jtrans = 3.3 Hz, Jcis = 7.1 Hz); 7.28 (d, 1 H, H(3),
3J = 9.1 Hz); 7.33 (ddd, 1 H, H(6), 4J = 1.3 Hz, 3J = 6.8 Hz,
3J = 8.1 Hz); 7.43 (ddd, 1 H, H(7), 4J = 1.4 Hz, 3J = 6.8 Hz,
3J = 8.4 Hz); 7.73 (br.d, 1 H, H(4), 3J = 9.1 Hz); 7.75 (br.d,
1 H, H(5), 3J = 8.1 Hz); 7.96 (br.d, 1 H, H(8), 3J = 8.4 Hz).
13C NMR (CDCl3), δ: 10.0 (CH2CH2); 52.1 (CH); 57.1 (OMe);
114.3 (C(3)); 122.3 (C(8)); 124.0 (C(6)); 127.1 (C(7)); 127.2
(C(9)); 127.8 (C(5)); 129.0 (C(4)); 129.1 (C(10)); 136.2 (C(1));
147.5 (C(2)).
B. A solution of azo compound 1b (120 mg, 0.6 mmol)
in anhydrous oꢀdichlorobenzene (15 mL) was refluxed for 6 h
under Ar with stirring, then the solvent was evaporated in vacuo
at 0.1 Torr. The residue was dissolved in benzene (1 mL), light
petroleum (10 mL) was added, a precipitate formed was
removed, the filtrate was concentrated, and the residue
was purified by column chromatography on SiO2 (eluent —
toluene—methanol, 25 : 1) to obtain pyrazoline 6b (101 mg,
84%). Found (%): C, 64.32; H, 7.07; N, 13.98. C11H14N2O2.
Calculated (%): C, 64.06; H, 6.84; N, 13.58. Partial MS, m/z
(Irel (%)): 206 (100) [M]+, 191 (45) [M – Me]+, 164 (40).
1H NMR (CDCl3), δ: 2.86 (dt, 2 H, C(4)H2, 3J = 1.7 Hz,
1ꢀ(2ꢀMethoxyꢀ1ꢀnaphthyl)ꢀ4,5ꢀdihydroꢀ1Hꢀpyrazole (7b)
was obtained similarly to pyrazoline 6b (method B) from azo
compound 2b (90 mg, 0.4 mmol). After purification of the
product by column chromatography on SiO2 (eluent — toluene—
methanol, 80 : 1) pyrazoline 7b (77 mg, 86%) was obtained as
colorless crystals rapidly oxidizing in air, m.p. 57—59 °C. Partial
MS, m/z (Irel (%)): 226 (100) [M]+, 211 (52) [M – Me]+, 115
(64). 1H NMR (CDCl3), δ: 2.93 (dt, 2 H, H(4), 3J = 1.7 Hz,
3J = 10.2 Hz); 3.66 (t, 2 H, H(5), 3J = 10.2 Hz); 3.89 (s, 3 H,
OMe); 6.87 (t, 1 H, H(3), 3J = 1.7 Hz); 7.26 (d, 1 H, H(3´),
3J = 9.8 Hz); 3.56 (t, 2 H, C(5)H2, J = 9.8 Hz); 3.80 and 3.87
3J = 9.1 Hz); 7.33 (ddd, 1 H, H(6´), J = 1.2 Hz, J = 6.9 Hz,
3
4
3
4
4
3
(both s, 3 H each, 2 OMe); 6.45 (dd, 1 H, H(5´), J = 2.6 Hz,
3J = 8.0 Hz); 7.45 (ddd, 1 H, H(7´), J = 1.3 Hz, J = 6.9 Hz,
3J = 8.5 Hz); 7.74 (br.d, 1 H, H(4´), 3J = 9.1 Hz); 7.76 (br.d,
1 H, H(5´), J = 8.0 Hz); 8.27 (br.d, 1 H, H(8´), J = 8.5 Hz).
13C NMR (CDCl3), δ: 34.5 (C(4)); 51.5 (C(5)); 56.6 (OMe);
113.5 (C(9´)); 114.6 (C(3´)); 123.2 (C(8´)); 123.8 (C(6´)); 126.4
(C(7´)); 127.7 (C(5´)); 128.2 (C(4´)); 129.4 and 133.2 (C(1´)
and C(10´)); 140.3 (C(3)); 154.1 (C(2´)).
3J = 8.6 Hz); 6.51 (d, 1 H, H(3´), 4J = 2.6 Hz); 6.92 (t, 1 H,
H(3), 3J = 1.7 Hz); 7.20 (d, 1 H, H(6´), 3J = 8.6 Hz). 13C NMR,
δ: 34.5 (C(4)); 52.6 (C(5)); 55.6 (2 OMe); 99.6 (C(3´)); 103.9
(C(5´)); 120.4 (C(6´)); 132.3 (C(1´)); 143.2 (C(3)); 152.0 and
156.9 (C(2´) + C(4´)).
1ꢀ(2,4ꢀDimethoxyphenyl)ꢀ1Hꢀpyrazole (10). A solution of
HCl in tetrahydrofuran ((1 mL, 0.4 mmol) prepared by mixing
36% aq. HCl (1.25 g) with tetrahydrofuran (30 mL)) was
added to a solution of pyrazoline 6b (40 mg, 0.2 mmol) in THF
(10 mL) and this was stirred for 4 h at room temperature in
air. After that, anhydrous K2CO3 (200 mg) was added to the
reaction mixture, which was stirred for another 30 min. A preꢀ
cipitate of salts formed was filtered off and the solvent was
removed in vacuo. The residue was separated by column chroꢀ
matography on SiO2 (eluent — toluene—methanol, 40 : 1) to
obtain pyrazole 10 (31 mg, 78%) as colorless oil with the purity
of ∼95%. Partial MS, m/z (Irel (%)): 204 (100) [M]+, 175 (28)
1ꢀ(2ꢀMethoxyꢀ1ꢀnaphthyl)ꢀ1Hꢀpyrazole (9c) was obtained
similarly to pyrazole 10 from pyrazoline 7b (33 mg, 0.15 mmol).
After purification of the product by column chromatography on
SiO2 (eluent — benzene—ethyl acetate, 20 : 1) pyrazole 9c
(20 mg, 61%) was obtained as colorless crystals, m.p. 75—76 °C.
Found (%): C, 74.59; H, 5.76; N, 12.75. C14H12N2O. Calculated
(%): C, 74.98; H, 5.39; N, 12.49. Partial MS, m/z (Irel (%)): 224
(42) [M]+, 97 (73) [M – C3H5N2 – C2H4]+, 57 (100). 1H NMR
(CDCl3), δ: 3.87 (s, 3 H, OMe); 6.55 (dd, 1 H, H(4), 3J = 1.9 Hz,
3J = 2.3 Hz); 7.23 (m, 1 H, H(8´)); 7.36 (ddd, 1 H, H(6´),
4J = 1.5 Hz, 3J = 6.8 Hz, 3J = 8.3 Hz); 7.37 (d, 1 H, H(3´),
[M – H – N2]+, 159 (42). H NMR (CDCl3), δ: 3.83 and 3.85
3J = 9.1 Hz); 7.43 (ddd, 1 H, H(7´), J = 1.5 Hz, J = 6.8 Hz,
3J = 8.3 Hz); 7.66 (dd, 1 H, H(5), 4J = 0.7 Hz, 3J = 2.3 Hz); 7.82
(m, 1 H, H(5´)); 7.87 (dd, 1 H, H(3), 4J = 0.7 Hz, 3J = 1.9 Hz);
7.94 (br.d, 1 H, H(4´), 3J = 9.1 Hz). 13C NMR (CDCl3), δ: 56.9
(OMe); 106.0 (C(4)); 110.0 (C(9´)); 113.6 (C(3´)); 122.1
(C(8´)); 124.4 (C(6´)); 127.7 (C(5´)); 127.8 (C(7´)); 128.8 and
132.3 (C(1´) and C(10´)); 130.7 (C(4´)); 133.0 (C(5)); 140.6
(C(3)); 152.6 (C(2´)).
1
4
3
(both s, 3 H each, 2 OMe); 6.40 (br.t, 1 H, H(4), 3J = 2.1 Hz);
6.56 (dd, 1 H, H(5´), 4J = 2.6 Hz, 3J = 8.3 Hz); 6.58 (d, 1 H,
3
3
H(5), J = 2.2 Hz); 7.53 (d, 1 H, H(6´), J = 8.3 Hz); 7.69 (d,
1 H, H(3), 3J = 1.9 Hz); 7.86 (d, 1 H, H(3´), 4J = 2.6 Hz).
13C NMR, δ: 55.7 and 56.0 (2 OMe); 99.7 (C(3´)); 104.6 and
105.9 (C(4) + C(5´)); 123.6 (C(1´)); 126.5 (C(6´)); 131.5 (C(5));
139.8 (C(3)); 153.0 and 159.9 (C(2´) + C(4´)).
1ꢀCyclopropylazoꢀ2ꢀmethoxynaphthalene (2b). A solution
of 1ꢀ(cyclopropylazo)ꢀ2ꢀnaphthol (2a) (300 mg, 1.4 mmol)
in DME (5 mL) was added to a solution of ButOK (225 mg,
2.0 mmol) in DME (10 mL) with stirring. A suspension formed
was stirred for 1 h at 20 °C, then MeI (355 mg, 2.5 mmol)
was added and this was stirred for 3 days. After that, CH2Cl2
(20 mL) was added to the reaction mixture, a precipitate formed
was filtered off and washed with CH2Cl2 (5 mL). The filtrate
was concentrated in vacuo and the residue was purified by
column chromatography on SiO2 (eluent — benzene—methaꢀ
nol, 60 : 1) to obtain 1ꢀ(cyclopropylazo)ꢀ2ꢀmethoxynaphthalene
(2b) (230 mg, 72%) as yellow oil. Found (%): C, 74.53; H, 6.55;
N, 12.29. C14H14N2O. Calculated (%): C, 74.31; H, 6.24;
N, 12.38. Partial MS, m/z (Irel (%)): 226 (100) [M]+, 211 (68)
Compounds 8a, 8b, and 8c. A solution of azo compound 2a
(200 mg, 0.9 mmol) in anhydrous oꢀdichlorobenzene (15 mL)
was refluxed for 12 h under Ar, then the solvent was evaporated
in vacuo at 0.1 Torr and the residue was separated by column
chromatography on SiO2 (eluent — toluene—AcOEt, 50 : 1) to
obtain naphtho[1,2ꢀd]oxazole (8a) (40 mg, 25%) as colorless
crystals with m.p. 60—61 °C (data in Ref. 13: m.p. 61—63 °C),
2ꢀmethylnaphtho[1,2ꢀd]oxazole (8b) (40 mg, 23%), and
2ꢀethylnaphtho[1,2ꢀd]oxazole (8c) (45 mg, 25%) as colorless
oils. 1H and 13C spectra of oxazoles 8a,b agree with those
described earlier.13
2ꢀEthylnaphtho[1,2ꢀd]oxazole (8c). Partial MS, m/z
(Irel (%)): 197 (100) [M]+, 182 (74) [M – Me]+. 1H NMR
3
(CDCl3), δ: 1.51 (t, 3 H, Me, J = 7.6 Hz); 3.09 (q, 2 H, CH2,

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Russ.Chem.Bull., Int.Ed., Vol. 57, No. 8, August, 2008
Novikov et al.
3J = 7.6 Hz); 7.52 (ddd, 1 H, H(8), 4J = 1.3 Hz, 3J = 6.9 Hz,
3J = 8.2 Hz); 7.64 (ddd, 1 H, H(7), 4J = 1.4 Hz, 3J = 6.9 Hz,
the solvent was evaporated in vacuo at 0.1 Torr. The residue was
separated by preparative TLC on SiO2 (eluent — benzene—
AcOEt, 10 : 1) collecting colorless bands with Rf = 0.41 (8b),
Rf = 0.49 (8a), and a red band with Rf = 0.36 (9b) to obtain
naphtho[1,2ꢀd]oxazole (8a) (11 mg, 33%) as colorless crystals,
m.p. 60—61 °C, 2ꢀmethylnaphtho[1,2ꢀd]oxazole (8b) (4 mg,
11%) as colorless oil, and pyrazole 9b (11 mg, 25%) as red oil.
The 1H and 13C NMR spectra of oxazoles 8a,b agree with those
described earlier.13 Compound 9b. Partial MS, m/z (Irel (%)):
224 (100) [M]+, 207 (10) [M–OH]+, 195 (97), 154 (31), 128
(29), 77 (53), 42 (65). 1H NMR (CDCl3), δ: 2.46 (s, 3 H, Me);
6.40 (d, 1 H, H(4), J = 2.3 Hz); 7.30 (d, 1 H, H(3´), J = 8.9 Hz);
7.37 (ddd, 1 H, H(6´), J1 = 8.1 Hz, J2 = 6.8 Hz, J3 = 1.3 Hz);
7.48 (ddd, 1 H, H(7´), J1 = 8.6 Hz, J2 = 6.8 Hz, J3 = 1.4 Hz);
7.77 (dd, 1 H, H(8´), J1 = 8.6 Hz, J2 = 1.3 Hz); 7.81 (br.d, 1 H,
H(4´), J = 8.9 Hz); 7.82 (d, 1 H, H(5), J = 2.3 Hz); 7.83 (br.dd,
3
3J = 8.2 Hz); 7.66 (d, 1 H, H(4), J = 9.0 Hz); 7.76 (br.d, 1 H,
H(5), 3J = 9.0 Hz); 7.96 (br.d, 1 H, H(6), 3J = 8.2 Hz); 8.48
(br.d, 1 H, H(9), 3J = 8.2 Hz). 13C NMR (CDCl3), δ: 11.5
(Me); 22.5 (CH2); 110.7 (C(4)); 122.0 (C(9)); 125.1 (C(8));
125.3 (C(5)); 126.3 (C(13)); 126.9 (C(7)); 128.5 (C(6)); 131.0
(C(10)); 136.4 (C(11)); 148.0 (C(12)); 167.3 (C(2)).
1ꢀ(2ꢀHydroxyꢀ1ꢀnaphthyl)ꢀ1Hꢀpyrazole (9a). A solution of
azo compound 2a (45 mg, 0.22 mmol) in anhydrous oꢀdichloꢀ
robenzene (4 mL) was stirred for 10 h under Ar at 160 °C, then
the solvent was evaporated in vacuo at 0.1 Torr and the residue
was separated by preparative TLC on SiO2 (eluent — ether —
benzene, 1 : 1.5) collecting the yellow band with Rf = 0.90 (the
starting compound 2a) and colorless band with Rf = 0.53 (
the product) to obtain azo compound 2a (20 mg, 45%) and
1
pyrazole 9a (10 mg, 40%) as reddish oil. H NMR (CDCl3), δ:
1 H, H(5´), J1 = 8.1 Hz, J2 = 1.4 Hz); 9.00 (br.s, 1 H. OH). 13
C
6.63 (dd, 1 H, H(4), J1 = 2.4 Hz, J2 = 1.9 Hz); 7.29 (d, 1 H,
H(3´), J = 8.9 Hz); 7.37 (ddd, 1 H, H(7´), J1 = 8.0 Hz,
J2 = 6.8 Hz, J3 = 1.2 Hz); 7.47 (ddd, 1 H, H(6´), J1 = 8.4 Hz,
J2 = 6.8 Hz, J3 = 1.4 Hz); 7.72 (br.dd, 1 H, H(5´), J1 = 8.4 Hz.
J2 = 1.2 Hz); 7.78 (br.d, 1 H, H(4´), J = 8.9 Hz); 7.83 (dd, 1 H,
H(8´), J1 = 8.0 Hz, J2 = 1.4 Hz); 7.89 (d, 1 H, J = 1.8 Hz)
and 7.91 (d, 1 H, J = 2.4 Hz) (H(3) and H(5)); 8.70 (br.s, 1 H,
OH). 13C NMR (CDCl3), δ: 107.1 (C(4)); 119.0 (C(3´)); 119.5
(C(9´)); 120.9 (C(8´)); 123.9 (C(6´)); 127.6 (C(5´)); 128.5
(C(7´)); 127.9 and 129.0 (C(1´) and C(10´)); 139.9 (C(4´));
132.9 (C(5)); 141.2 (C(3)); 149.0 (C(2´)).
NMR (CDCl3), δ: 13.8 (Me); 106.9 (C(4)); 119.0 (C(3´)); 121.0
(C(4´)); 123.8 (C(6´)); 127.2, 128.3, 129.1 and 129.2 (C(3),
C(1´), C(9´) and C(10´)); 127.4 (C(7´)); 128.5 (C(5´)); 129.4
(C(8´)); 133.6 (C(5)); 148.8 (C(2´)).
This work was financially supported by the Russian
Foundation for Basic Research (Project No. 06ꢀ03ꢀ33149).
References
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1ꢀ[(1ꢀMethylcyclopropyl)azo]ꢀ2ꢀnaphthol (2c). 2ꢀNaphthol
(64 mg, 0.32 mmol) and Cs2CO3 (521 mg, 1.6 mmol) were
added to a solution of methyl NꢀnitrosoꢀNꢀ(1ꢀmethylcycloꢀ
propyl)carbamate (50 mg, 0.32 mmol) in CH2Cl2 (5 mL) and this
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benzene—light petroleum (40—70), 1 : 2) collecting a bright
yellow band to obtain azonaphthol 2c (65 mg, 90%) as bright
yellow needleꢀlike crystals with m.p. 60—61 °C. Found (%): C,
74.35; H, 6.53; N, 12.22. C14H14N2O. Calculated (%): C, 74.31;
H, 6.24; N, 12.38. Partial MS, m/z (Irel (%)): 226 (27) [M]+,
211 (2) [M – Me]+, 184 (23), 170 (30), 156 (52), 143 (24), 129
(98), 115 (77), 57 (100). 1H NMR (CDCl3), δ: 1.24 and 1.58
(both m, 2 H each, CH2CH2); 1.69 (s, 3 H, Me); 7.10 (br.d, 1 H,
H(3), J = 9.0 Hz); 7.38 (ddd, 1 H, H(6), J1 = 8.1 Hz, J2 = 6.9 Hz,
J3 = 1.2 Hz); 7.55 (ddd, 1 H, H(7), J1 = 8.3 Hz, J2 = 6.9 Hz,
J3 = 1.3 Hz); 7.73 (br.d, 1 H, H(5), J = 8.1 Hz); 7.74 (br.d, 1 H,
H(4), J = 9.0 Hz); 8.71 (br.d, 1 H, H(8), J = 8.3 Hz); 13.79
(br.s, 1 H, OH). 13C NMR (CDCl3), δ: 18.8 (CH2); 19.2 (Me);
51.4 (C); 120.2 (C(3)); 121.7 (C(8)); 124.1 (C(6)); 127.6 (C(7));
128.0 (C(5)); 127.8 and 128.2 (C(9) and C(10)); 132.8 (C(1));
133.5 (C(4)); 152.7 (C(2)).
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3ꢀMethylꢀ1ꢀ(2ꢀhydroxyꢀ1ꢀnaphthyl)ꢀ1Hꢀpyrazole (9b).
A solution of azo compound 2c (45 mg, 0.20 mmol) in anhydrous
oꢀdichlorobenzene (5 mL) was refluxed for 3.5 h under Ar, then
Received February 11, 2008