Generation of oxodiazonium ions 1. Synthesis of [1,2,5]oxadiazolo[3,4-c] cinnoline 5-oxides

Article abstract of DOI:10.1007/s11172-011-0084-0

Methods for the synthesis of [1,2,5]oxadiazolo[3,4-c]cinnoline 5-oxides, which include the reaction of 3-nitramino-4-(R-phenyl)furazans or their O-methyl derivatives with electrophilic agents, have been developed. Unsubstituted [1,2,5]oxadiazolo[3,4-c]cin

Full text of DOI:10.1007/s11172-011-0084-0

Russian Chemical Bulletin, International Edition, Vol. 60, No. 3, pp. 536—547, March, 2011
536
Generation of oxodiazonium ions
1. Synthesis of [1,2,5]oxadiazolo[3,4ꢀc]cinnoline 5ꢀoxides
M. S. Klenov, M. O. Ratnikov, A. M. Churakov, V. N. Solkan, Yu. A. Strelenko, and V. A. Tartakovsky
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 5328. Eꢀmail: churakov@ioc.ac.ru
Methods for the synthesis of [1,2,5]oxadiazolo[3,4ꢀc]cinnoline 5ꢀoxides, which include the
reaction of 3ꢀnitraminoꢀ4ꢀ(Rꢀphenyl)furazans or their Oꢀmethyl derivatives with electrophilic
agents, have been developed. Unsubstituted [1,2,5]oxadiazolo[3,4ꢀc]cinnoline 5ꢀoxide was
synthesized from 3ꢀnitraminoꢀ4ꢀphenylfurazan upon the action of phosphorus anhydride or
oleum, as well as from Oꢀmethyl derivative of 3ꢀnitraminoꢀ4ꢀphenylfurazan upon the action of
H2SO4, MeSO3H, CF3CO2H and BF3•Et2O, while 6ꢀ, 7ꢀ, 8ꢀ, and 9ꢀnitroꢀsubstituted
[1,2,5]oxadiazolo[3,4ꢀc]cinnoline 5ꢀoxides — from the corresponding 3ꢀnitraminoꢀ4ꢀ(nitroꢀ
phenyl)furazans upon the action of the H2SO4ꢀHNO3 nitrating mixture. A suggestion has been
made that an oxodiazonium ion is formed in these reactions from nitramines or their Oꢀmethyl
derivatives upon the action of electrophilic agents, which is further involved into the intraꢀ
molecular reaction of electrophilic aromatic substitution (SEAr) with the aryl group. The strucꢀ
ture of [1,2,5]oxadiazolo[3,4ꢀc]cinnoline 5ꢀNꢀoxides was confirmed by 1H, 13C, and 14N NMR
spectra. Theoretical studies by the B3LYP/6ꢀ311G(d,p) method of combined molecular system
(Oꢀmethylated 3ꢀnitraminoꢀ4ꢀphenylfurazan + [H3SO4]+) resulted in calculation of thermoꢀ
dynamic parameters of the sequence of cascade elementary reactions leading to the formation
of [1,2,5]oxadiazolo[3,4ꢀc]cinnoline 5ꢀoxide.
Key words: cinnolines, furazans, azoxy compounds, nitramines, oxodiazonium ion, electroꢀ
philic aromatic substitution, quantum chemical calculations, 1H, 13C, 14N NMR spectroscopy.
Oxodiazonium ions [Ar—N=N=O]+ have structures
Scheme 1
isoelectronic to a nitronium ion, however, unlike for the
latter, method for the generation of oxodiazonium ions
bound to an aryl group have been discovered only recently.
Two independent groups of researchers1,2 suggested that
the mechanism of formation of annulated 1,2,3ꢀtriazinꢀ4ꢀ
one 2ꢀoxides from nitramines containing an orthoꢀcyano
group includes intermediate formation of an oxodiazoniꢀ
um ion (Scheme 1), and this was confirmed by its intraꢀ
molecular trapping with the phenyl substituent.
We have considered a possibility of the intermediate
formation of an oxodiazonium ion in the synthesis of anꢀ
nulated 1,2,3,4ꢀtetrazine 1,3ꢀdioxides (see Review 3 and
references cited therein). It was suggested that this ion was
formed by the intermolecular reaction of nitramines
Ar—NHNO2 with some electrophilic agents. At the same
time, other mechanisms for the formation of 1,2,3,4ꢀtetrꢀ
azine 1,3ꢀdioxides can be suggested, which do not involve
oxodiazonium cation as a kinetically independent species.
The main purpose of the present work is to confirm
formation of the oxodiazonium cation in the reactions of
primary aromatic nitramines with electrophilic agents by
its trapping with the phenyl ring. 3ꢀNitraminoꢀ4ꢀphenylꢀ
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 523—534, March, 2011.
1066ꢀ5285/11/6003ꢀ536 © 2011 Springer Science+Business Media, Inc.

[1,2,5]Oxadiazolo[3,4ꢀc]cinnoline 5ꢀoxides
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 3, March, 2011
537
furazan and its nitrophenyl derivatives have been chosen
as model compounds.
isomer. Similarly to the Oꢀmethylated nitramines,4 the
Eꢀconfiguration can be assigned to the azoxy fragment of
this compound.
Results and Discussion
Generation of oxodiazonium ions from Nꢀnitramines and
their Oꢀmethyl derivatives upon the action of protic acids or
BF3•Et2O. Nitration of primary amines (direct reaction)
and the corresponding to this process denitration of priꢀ
mary Nꢀnitramines (reverse reaction) have been studied
well enough (see Review 5). Protonation at the N atom
with the formation of the intermediate A (Scheme 4,
Eq. (1)) takes place during the denitration of nitramines,
which decomposes with regeneration of the amine.
At the same time, protonation at the O atom with the
formation of the intermediate B can be also suggested
during the reaction of nitramine with acids, which could
have eliminated H2O to lead to the oxodiazonium ion C
(see Scheme 4, Eq. (2)). Such a direction of protonation
in the aliphatic compounds is considered as probable durꢀ
ing decomposition of primary nitramines in acidic mediꢀ
um.6 While studying heterocyclic compounds, we made
a suggestion that similar reactions take place to exꢀ
plain the transformation of a primary Nꢀnitramine group
to a nitroso group7 (—NHNO2 → —N=O). In addiꢀ
tion, we studied a possibility of the —O—NH—NO2 →
→ [—O—N=N=O]+ transformation in the acidꢀcatalyzed
decomposition of Nꢀnitrohydroxylamines.8
Synthesis of starting compounds. The reaction of amiꢀ
nofurazan 1a with 1 equiv. of KNO3 in H2SO4 (Scheme 2)
results in nitration of the phenyl ring to form all three
possible isomers 1b, 1c, and 1d in 34, 28, and 27% yields,
respectively, which were separated by preparative TLC.
Nitration of aminofurazans 1a and 1b with nitronium
tetrafluoroborate at low temperature in MeCN leads to
Nꢀnitramines 2a and 2b, respectively (Scheme 3). Nitrꢀ
amine 2b in the pure form (m.p. 104—109 °C, decomp.) is
more stable than 2a (m.p. 69—71 °C, decomp.). Methylaꢀ
tion of nitramine 2a with diazomethane in diethyl ether
leads to a mixture of Oꢀ and Nꢀmethyl derivatives 3a and
4a in the ratio 1.8 : 1 (see Scheme 3) in quantitative yield,
which were separated by preparative TLC.
The structures of amines 1b—d, nitramines 2a,b, and
methylated nitramines 3a and 4a were confirmed by the
1H, 13C, and 14N NMR spectra. Full assignment of the
signals in the 13C NMR spectra of these compounds was
made using the 1H—13C (HMBC and HSQC) twoꢀdiꢀ
mensional correlations. According to the 1H and 13C NMR
spectroscopy, Oꢀmethyl compound 3a is a single stereoꢀ
Scheme 2
i. KNO3 (1 equiv.)/H2SO4, 20 °C, 10 min, 89%.
Scheme 3
i. NO2BF4, MeCN, –30 → –10 °C; ii. CH2N2, Et2O, 20°C.
R = H (1a, 2a), NO2 (1b, 2b)

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Klenov et al.
Scheme 4
The reaction of nitramine 2a with an excess of sulfuric
ple, 3a (see Scheme 4, Eq. (3)). The protonated form D
could have eliminated MeOH with the formation of oxoꢀ
diazonium ion C, which can react with the phenyl ring to
give furazano[3,4ꢀc]cinnoline 5ꢀoxides (FCO) 5 (see
Scheme 4, Eq. (4)). Note that the detailed quantum chemꢀ
ical studies of the reaction (3) (see Scheme 4) showed that
protonation of Oꢀmethyl compound 3a with [H3SO4]+
acid or trifluoromethanesulfonic acid for 5 min leads to
a mixture of aminofurazans 1a—d (Scheme 5, Table 1).
Obviously, the reaction proceeds as a denitration process
according to Eq. (1) (see Scheme 4) with subsequent nitraꢀ
tion of amine 1a at the phenyl ring with the liberated nitric
acid. It is obvious that no formation of oxodiazonium ion
by Eq. (2) occurs (see Scheme 4).
Table 1. Reactions of nitramine 2a with acids
Scheme 5
Acid
(concentꢀ
ration (%))
Ratio
acid : H2O
(mol)
Molar ratio of
products (%)*
1a
1b
1c 1d
H2SO4 (100)
H2SO4 (93)
СF3SO3H (100)
1 : 0
1 : 0.4
1 : 0
17
3
9
35
45
35
21 27
22 30
31 25
* The molar ratios of products were determined from the 1H NMR
spectra. Nitramine 2a was completely converted within 5 min at
20 °C. The total yield of products 1a—d is close to quantitative.
The denitration process can be avoided, if the nitraꢀ
mine is exchanged with its Oꢀmethyl derivative, for examꢀ

[1,2,5]Oxadiazolo[3,4ꢀc]cinnoline 5ꢀoxides
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 3, March, 2011
539
leads to a complex consisting of oxodiazonium ion, moleꢀ
cule of methanol, and molecule of H2SO4 (for more deꢀ
tails see the last section of the paper).
well as small amount of FCO 5b, are observed in the reacꢀ
tion mixture (Scheme 7, Table 3, the last line). About the
same proportion of products is observed after 1 h, if amine
1b and 1 equiv. of conc. HNO3 are taken in the reaction
instead of nitramine 2b (Scheme 7, Table 3).
It was found that compound 3a in solutions of concenꢀ
trated acids is converted to FCO 5a in good yields (Scheme 6,
Table 2). The rate of cyclization strongly depends on the
acid strength. For example, in H2SO4 (the Hammett acidity
function H0 = –11.94)9 compound 3a completely disapꢀ
pears within 5 min (TLC monitoring), in weaker MeSO3H
(H0 = –7.74)10 within 30 min, and in CF3COOH (H0 =
= –2.71)11 the reaction comes to completion within 3 days.
Scheme 7
Scheme 6
i. H+ or BF3•OEt2, 20 °C.
For the transformation of compound 3a to FCO 5a,
a Lewis acid can be also used, for example, BF3•OEt2 (see
Scheme 6, Table 2). However, the yield of FCO 5a is
considerably lower than when acids were used.
Generation of oxodiazonium cation from Oꢀmethyl
compound 3a upon the action of BF3•Et2O is likely to
proceed according to Scheme 4 (Eq. (3´)).
Another approach, which allows one to accomplish
generation of oxodiazonium cation from nitramine upon
the action of acids, consists in that as to make the denitraꢀ
tion process of nitramine reversible. This can be achieved,
if exclude a possibility of nitration of the phenyl substituꢀ
ent by the use of nitramine 2b as a model, which contains
an electronꢀwithdrawing nitro group in the ring. After this
nitramine was kept in 93% H2SO4 during 1 h, approxiꢀ
mately equal amounts of amine 1b and nitramine 2b, as
Position of the NO2 group: 4´ (1b, 2b), 3´ (1c, 2c), 2´ (1d, 2d),
7 (5b), 8 (5c), 6 (5c´), 9 (5d).
If the reaction time is increased to 24 h, almost comꢀ
plete conversion of nitramine is observed, and the yield of
FCO 5b reaches 77%. An increase in concentration of
H2SO4 to 96% accelerates the reaction, whereas an inꢀ
crease to 100% somewhat slows it down (see Table 3).
For evaluation of comparative rates of cyclization of
compounds with different positions of the nitro group in
the benzene ring, aminofurazans 2b—d were involved into
the reaction with HNO3 under the same conditions (100%
H2SO4, 1 equiv. of conc. HNO3, 20 °C, 10 h). The reacꢀ
1
tion products were analyzed by H NMR spectroscopy.
Conversion of the compounds (a degree of transformation
of amine 1 and nitramine 2 into the reaction products:
FCO 5 and unidentified products, was from 16 to 31%
Table 2. Formation of FCO 5a by the reaction of compound 3a
with acids or BF3•Et2O
1
with respect to FCO 5) was determined using H NMR
Acid
(concentꢀ
ration (%))
Ratio
acid : H2O
(mol)
Reaction
time
Yield of
FCO 5a
(%)a
spectroscopy. For the 4ꢀ, 3ꢀ, and 2ꢀnitrophenylꢀsubstitutꢀ
ed compounds, the conversion was 61, 54, and 20%, reꢀ
spectively. Apparently, the low rate of cyclization of
2ꢀnitrophenylꢀsubstituted nitramine 2d is due to the steric
reasons. Significant amount of unidentified byꢀproducts
does not allow one to evaluate the relative rates of cyclizaꢀ
tion more accurate.
A plausible mechanism of the formation of FCO 5 is
shown in Scheme 4 (see Eqs (2) and (4)). At the same
time, one cannot completely exclude an alternative mechꢀ
anism either, which includes nitration of nitramine with
H2SO4 (100)
H2SO4 (93)
СH3SO3H (100)
CF3COOH (100)
BF3•Et2O (100)
1 : 0
1 : 0.4
1 : 0
1 : 0
1 : 0
5 min
5 min
30 min
3 days
1 days
78
70
83
79
31b
a The yields of FCO 5a were determined from the 1H NMR
spectra. Conversion of compound 3a was complete.
b The yield of FCO 5a is calculated for the isolated product.

540
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 3, March, 2011
Klenov et al.
Table 3. Formation of FCO 5b from aminofurazan 1b and nitraminofurazan 2b in the presence of 1 equiv. of HNO3
Starting
compound
Concentration of
H2SO4 (%)
Ratio
H2SO4 : H2O (mol)
ta/h
Molar ratio (%)b
1b
2b
5b
Pс
1b
1b
1b
1b
2bd
93
93
96
100
93
1 : 0.4
1 : 0.4
1 : 0.23
1 : 0
1
24
24
24
1
32
0
2
9
29
39
3
7
19
37
11
77
79
62
6
18
20
12
10
28
1 : 0.4
a Reaction time.
b The molar ratios of products were determined from the 1H NMR spectra.
c Unidentified products.
d In the absence of HNO3.
nitric acid at the O atom to form the intermediate E
(Scheme 8). Nitric acid can be liberated in the process of
denitration (see Scheme 4, Eq. (1)). The intermediate E is
able to dissociate with the formation of oxodiazonium
cation (see Scheme 8). We considered such a mechanism
in the preceding work12 for the generation of oxodiazoꢀ
nium cation from nitramines upon the action of N2O5 in
organic solvents.
Position of the nitro group in the phenyl ring of the
starting compounds significantly affects the rate of the
ring closure. The cyclization is the fastest in the case of
pꢀnitroꢀsubstituted compound 1b (2 h), oꢀnitroꢀsubstitutꢀ
ed compound 1d cyclizes slower (5 h), the lowest rate of
the reaction is observed for mꢀnitroꢀsubstituted compound
1c (7 h). Apparently, these differences in the reaction
rates are due to the different thermodynamic stability of
the corresponding σꢀcomplexes 6b, 6d, 6c, and 6c´ formed
Scheme 8
Generation of oxodiazonium ions from Nꢀnitramines
upon the action of H2SO4—HNO3 nitrating mixture. As it
was shown above, cyclization of 3ꢀaminoꢀ4ꢀ(nitrophenyl)ꢀ
furazans 1b—d to FCO 5b—d takes place upon the action
of 1 equiv. of conc. HNO3 in sulfuric acid. However, the
rate of the reaction is low under such conditions and
a prolonged time is required to reach high conversion of
aminofurazans. In this case, if 24 h is required for the
synthesis of 7ꢀnitro derivative 5b in ~80% yield, then for
obtaining 9ꢀnitro derivative 5d in the same yield already
a few days are needed. In order to develop convenient
preparative procedure, a 10ꢀfold excess of the nitrating
agent was used in the reaction. To simplify the procedure,
conc. HNO3 was replaced with the corresponding amount
of KNO3. Such a method allowed us to synthesize FCO
5b—d in 92—95% yields (Table 4). 3ꢀAminoꢀ4ꢀ(mꢀnitroꢀ
phenyl)furazan 1c gave a mixture of isomeric 8ꢀnitroꢀ and
6ꢀnitro derivatives 5c and 5c´, respectively, which was
separated by preparative TLC. Apparently, oxodiazonium
cation in this case was formed in accordance with Scheme 8.
Table 4. Synthesis of nitroꢀsubstituted FCO 5b—d
a
Starting
compound
τ /h FCO
Position of
substituent
Yield of
FCO 5
(%)b
NO2 to FCO 5
1b
1c
2
7
5b
5c
5с´
5d
7
8
6
9
95
42
51
92
1d
5
a Reaction time.
b The yields of FCO 5b—d were determined from the
1H NMR spectra. Conversion of compounds 1b—d were
complete.

[1,2,5]Oxadiazolo[3,4ꢀc]cinnoline 5ꢀoxides
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 3, March, 2011
541
Table 5. 1H and 14N NMR spectra of FCO 5a—d in acetoneꢀd6
Comꢀ
pounda
1H NMR, δ (J/Hz)
14N NMR,
δ (Δν1/2/Hz)
H(6)
H(7)
H(8)
H(9)
5ab
8.66 (dd, J = 8.6,
J = 1.1)
9.33 (d, J = 2.0)
8.16 (ddd, J = 8.6,
J = 7.5, J = 1.3)
—
8.22 (ddd, J = 7.8,
J = 7.5, J = 1.1)
8.99 (dd, J = 8.6,
J = 2.0)
8.59 (dd, J = 7.8,
J = 1.3)
8.94 (d, J = 8.6)
–50 (N→O, Δν1/2 = 12)
5b (7)
5c (8)
5c´ (6)
5d (9)
–17 (С—NO2, Δν1/2 = 100),
–52 (N→O, Δν1/2 = 20)
–13 (С—NO2, Δν1/2 = 80),
–48 (N→O, Δν1/2 = 12)
–11 (С—NO2, Δν1/2 = 50),
–57 (N→O, Δν1/2 = 15)
–13 (С—NO2, Δν1/2 = 60),
–53 (N→O, Δν1/2 = 20)
8.95 (d, J = 9.3)
—
8.90 (dd, J = 9.3,
J = 2.4)
8.43 (dd, J = 7.8,
J = 1.1)
—
9.33 (d, J = 2.4)
8.48 (t, J = 7.8)
8.92 (dd, J = 7.8,
J = 1.1)
—
9.00 (d, J = 8.5)
8.40 (t, J = 8.2)
8.67 (dd, J = 8.0,
J = 1.0)
a Position of NO2 group is given in parentheses.
b The 1H—1H COSY was used to assign the signals.
upon the attack of oxodiazonium cation on the phenyl
ring, which is determined by both the electronic and
steric factors.
ucts, whereas FCO 5a is formed in the trace amounts
(3%). Apparently, the small excess of SO3 mainly gives
irreversible denitration of nitramine 2a.
Furazano[3,4ꢀc]cinnoline 5ꢀNꢀoxides 5 are represenꢀ
tatives of a new heterocyclic system. Their structure was
confirmed by 1H, 14N (Table 5), and 13C NMR spectrosꢀ
copy (Table 6), IR spectroscopy, and mass spectrometry.
The full assignment of signals for the compounds in the
13C NMR spectra was performed using the 1H—13C twoꢀ
dimensional correlations.
Scheme 9
The method of generation of oxodiazonium ions from
nitramines upon the action of nitrating agents (see Scheme 7)
does not allow one to synthesize FCO 5a, the compound
containing no electronꢀwithdrawing substituents in the
benzene ring. In this connection, we studied a possibility
of generation of oxodiazonium cations by the reaction of
Nꢀnitramines with SO3 and P4O10.
Generation of oxodiazonium ion from Nꢀnitramine upon
the action of SO3. The reaction of nitramine 2a with oleꢀ
um of different concentrations was studied (Scheme 9,
Table 7). The reagents were mixed with cooling (0 °C) to
avoid for the reaction mixture to be strongly heated and
turn black. The reaction is complete within 5 min. It turned
out that when the molar ratio 2a : SO3 = 1 : 8, 3ꢀaminoꢀ4ꢀ
(nitrophenyl)furazans 1b—d are the main reaction prodꢀ
i. Oleum, 0 → 20 °C, 5 min; ii. 1 equiv. of conc. HNO3, 14%
oleum, 0 → 20 °C, 5 min.
Table 6. 13C NMR spectra of FCO 5a—d in acetoneꢀd6
a
Comꢀ
poundb
δ
C(3a)
C(5a) (br.s)
C(6)
C(7)
C(8)
C(9)
C(9a)
С(9b)
5a
157.5
158.1
157.0
156.6
156.9
141.8
142.3
143.4
131.2
141.1
123.9
119.7
125.6
144.1 (br.s)
127.0
134.7
151.6 (br.s)
128.0
128.4
134.4
135.9
130.0
150.6 (br.s)
136.4
129.5
126.2
128.7
120.9
128.0
119.5
124.5
120.0
121.1
112.6
138.2
138.0
137.3
137.0
134.3
5b (7)
5c (8)
5c´ (6)
5d (9)
146.4 (br.s)
a The 1H—13C (HMBC and HSQC procedures) twoꢀdimensional correlations were used to assign the signals.
b Position of NO2 group is given in parentheses.

542
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 3, March, 2011
Klenov et al.
Table 7. Formation of FCO 5a from nitramine 2a in oleum
Starting
compound
Content of SO3
in oleum (wt.%)
Ratio
2a (1a) : SO3 (mol)
Molar ratioa (%)
5а
1b
1c
1d
1a
2а
1.5
4
7
14
14
1 : 8
3
23
52
70
0
30
21
17
10
35
30
31
12
11
41
24
22
19
9
13
3
0
0
0
1 : 20
1 : 35
1 : 70
1 : 70
1аb
24
1
a The molar ratios of products were determined from the H NMR spectra. Conversion of the starting
compounds was complete.
b
HNO3 was added as a reagent.
An increase in concentration of SO3 in the reaction
tions of 2ꢀ(tertꢀbutylꢀNNOꢀazoxy)(Nꢀnitramino)benzene
and 3ꢀ(tertꢀbutylꢀNNOꢀazoxy)ꢀ4ꢀ(Nꢀnitramino)furazan
with P4O10 in MeCN as a solvent leading to annulated
1,2,3,4ꢀtetrazine 1,3ꢀdioxides. Supposedly, the course of
these reactions includes transformation of the —NHNO2
group to the [—N=N=O]+ cation. To confirm this sugꢀ
gestion, we carried out the reaction of nitramine 2a with
P4O10 under similar conditions. Heating nitramine 2a in
anhydrous MeCN with a 20ꢀfold excess of P4O10 gave
FCO 5a in 66% yield (Scheme 11). The byꢀproducts
formed in this reaction can be easily separated by chromaꢀ
tography on silica gel. Apparently, under phosphorylation
conditions the oxodiazonium cation is generated from
Oꢀphosphorylated nitramine G.
mixture leads to the increase in the yield of FCO 5a, and for
the molar ratio 2a : SO3 = 1 : 70 it reaches 70%. If aminoꢀ
furazan 1a is taken instead of nitramine 1a and added to a
solution of equivalent amount of conc. HNO3 in 14%
oleum, no FCO 5a is formed, rather nitration of the phenyl
ring takes place, that leads to a mixture of amines 1b—d (see
Table 7). It is obvious that the Cꢀnitration takes place sigꢀ
nificantly faster than the Nꢀnitration under these conditions.
It is probable that under conditions of sulfation, the
oxodiazonium cation is formed from nitramine Oꢀsulfo
derivative F (Scheme 10).
Generation of oxodiazonium ion from Nꢀnitramine upon
the action of P4O10. Earlier,3 we have described the reacꢀ
Scheme 10
Scheme 11
i. P4O10, MeCN, 70 °C, 10 h (66%).

[1,2,5]Oxadiazolo[3,4ꢀc]cinnoline 5ꢀoxides
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 3, March, 2011
543
Theoretical study of generation of oxodiazonium ion from
Oꢀmethyl compound 3a in H2SO4 by the B3LYP functional
density method. To confirm existence of oxodiazonium
ion as a kinetically independent species, we studied the
potential energy surface (PES) of combined molecular
system Oꢀmethylated 3ꢀnitraminoꢀ4ꢀphenylfurazan (3a)
+ [H3SO4]+ in the gas phase by the B3LYP/6ꢀ311G(d,p)
functional density method.13,14 For the confirmation of
local minima on the PES, we performed calculations of
vibrational spectra of the species studied.
Taking into account acidity of the reaction medium,
we considered a protonated molecule of sulfuric acid
[H3SO4]+ as a protonating agent. Earlier,15,16 it has been
shown that ions [H3SO4]+ can exist in 100% sulfuric acid
in the form of complexes containing one or two molecules
of H2SO4. It is known that protonation of alkyl sulfates
promotes formation of carbenium ions.17
H
O
C
S
The study of PES (Fig. 1) showed that protonation of
Oꢀmethyl compound 3a at the O atom of the MeO group
with [H3SO4]+ leads to a nonactivated elongation of the
N...O(H)Me bond with the formation of the complex conꢀ
sisting of oxodiazonium ion, molecule of methanol,
and molecule of H2SO4 (Fig. 2, Table 8), in which the
N...O(H)Me bond length is 1.923 Å. As it follows from
the calculated Mulliken effective charges, the —N=N=O
fragment in the oxodiazonium ion (Fig. 3) is characterꢀ
ized by a positive total charge (0.37 e) and, therefore,
tends to be involved into intramolecular electrostatic inꢀ
teraction with the phenyl fragment. In addition, accordꢀ
ing to the calculated data the LUMO localized on the
—N=N=O fragment can efficiently interact with the
HOMO localized on the phenyl fragment. To sum up, in
the framework of the molecular orbitals perturbation theꢀ
ory, proceeding from the geometrical and electronic strucꢀ
ture of the considered oxodiazonium ion, one can predict
the readiness of the corresponding reaction leading to the
Fig. 2. Geometry of the complex oxodiazonium cation + MeOH +
+ H2SO4 optimized by the DFT/B3LYP method and obtained
in the study of PES of combined molecular system 3a + [H3SO4]+.
H
O
C
Fig. 3. Geometry of oxodiazonium cation optimized by the
DFT/B3LYP method.
formation of the σꢀcomplex of phenyl group with oxodiꢀ
azonium ion.
Results of calculation of cationic σꢀcomplex by the
B3LYP method with full optimization of geometrical paraꢀ
meters (Fig. 4) indicates its stability, though thermodyꢀ
namically it is less favorable (endothermicity of the reacꢀ
tion of its formation is equal to 2.3 kcal mol–1 at T = 298 K)
than the corresponding oxodiazonium ion. The final eleꢀ
mentary reaction of the proton transfer from this σꢀcomplex
to the molecule of sulfuric acid leading to the formation of
FCO 5a (Fig. 5) is exothermic (ΔH = –15.6 kcal mol–1 at
T = 298 K). To sum up, the calculated data obtained
H
O
C
S
Fig. 1. The initial geometry of the complex used in the study of
PES of combined molecular system 3a + [H3SO4]+.

544
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 3, March, 2011
Klenov et al.
Table 8. Selected geometric parameters (bond lengths and bond
angles) calculated by the B3LYP/6ꢀ311G(d,p) method for
the fragment C—N=N=O in the complex oxodiazonium
ion + MeOH + H2SO4 (see Fig. 2) (I) and in the "free" oxodiꢀ
azonium ion (see Fig. 3) (II)
Parameter
I
II
Parameter
I
II
Bond length
d/Å
Bond angle
N—N—O
ω/deg
C—N
N—N
N—O
1.406 1.386
1.202 1.147
1.180 1.150
151
169
N...OH*
1.923
—
H
O
* The distance between the central nitrogen atom of the fragment
C—N=N=O and the oxygen atom of MeOH in the complex.
C
allows one to suggest a plausible mechanism of the formaꢀ
tion of FCO 5a from Oꢀmethyl compound 3a as a seꢀ
quence of the elementary reactions (Scheme 12).
Fig. 5. Geometry of FCO 5a optimized by the DFT/B3LYP
method.
Scheme 12
ΔH = –20.0 kcal mol–1, ΔG = –29.5 kcal mol–1). When
concentrated, but not 100%, sulfuric acid is used, an oxoꢀ
nium ion [H3O]+ can also be the protonating species.
However, if comparable values of proton affinity for the
molecules of water and sulfuric acid are taken into acꢀ
count,18 then the thermodynamics of the process of forꢀ
mation of FCO 5a from Oꢀmethyl compound 3a can
3а + [H3SO4]+
[Ar—N=N=O]+ + MeOH + H2SO4 (a)
(ΔH = –6.7 kcal mol–1
)
[Ar—N=N=O]+
[σꢀComplex]+
(b)
(c)
change within 3 kcal mol–1
.
(ΔH = +2.3 kcal mol–1
)
In conclusion, transformation of nitramines 2a—d to
FCO 5a—d upon the action of nitrating, phosphorylating,
and sulfating agents is a serious argument in favor of
the intermediate formation of oxodiazonium cation
[—N=N=O]+. The ability of this cation to be involved
into intramolecular reaction of aromatic electrophilic subꢀ
stitution with the phenyl ring containing no substituents,
as well as with deactivated aromatic ring containing nitro
groups in orthoꢀ, metaꢀ, and paraꢀpositions were deꢀ
monstrated.
[σꢀComplex]+ + H2SO4
5а + [H3SO4]+
(ΔH = –15.6 kcal mol–1
)
The calculated data indicate that the reactions (a) and
(c) are strongly exothermic, whereas the reaction (b) is
weakly endothermic. The sequence of these reactions reꢀ
sults in irreversible formation of FCO 5a (at T = 298 K
A new method for the generation of oxodiazonium ion
from methoxy(oxido)diazenyl group —N=N(O)OMe
upon the action of acids was developed. Theoretical studꢀ
ies of the mechanism of this reaction by the B3LYP funcꢀ
tional density method were performed.
Experimental
1
H
O
H, 13C, and 14N NMR spectra were recorded on a Bruker
DRXꢀ500 spectrometer (500.13, 125.76, and 36.14 MHz, reꢀ
spectively) in acetoneꢀd6. Chemical shifts are given relatively to
Me4Si (1H, 13C) or MeNO2 (14N, external standard, the highꢀ
field chemical shifts have negative values). IR spectra were reꢀ
corded on a Specord Mꢀ80 spectrometer (KBr pellets), mass
spectra were recorded on a Kratos MSꢀ300 instrument (EI,
70 eV). Reaction progress was monitored by TLC (Silufol UVꢀ254
C
Fig. 4. Geometry of the σꢀcomplex optimized by the
DFT/B3LYP method.

[1,2,5]Oxadiazolo[3,4ꢀc]cinnoline 5ꢀoxides
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 3, March, 2011
545
and Merck 60 F254). Column chromatography on silica gel was
used. 3ꢀAminoꢀ4ꢀphenylꢀ1,2,5ꢀoxadiazole19 and ethereal soluꢀ
tion of diazomethane20 were obtained according to the known
procedures. Distilled colorless HNO3, d = 1.5 g cm–1, was used.
3ꢀNitraminoꢀ4ꢀphenylꢀ1,2,5ꢀoxadiazole (2a). The compound
NO2BF4 (0.23 g, 1.72 mmol) was added in small portions to
a solution of 3ꢀaminoꢀ4ꢀphenylꢀ1,2,5ꢀoxadiazole 1a (0.2 g,
1.24 mmol) in anhydrous acetonitrile (6 mL) with vigorous stirꢀ
ring at –30 °C. The cooling bath was removed and the stirring
was continued until the temperature reached –10 °C, then
the reaction mixture was poured into the aqueous solution of
NaHCO3 (0.5 g in 20 mL). The aqueous layer was separated,
washed with Et2O (2×10 mL), and acidified with 10% aq. HCl to
pH 2, then extracted with CH2Cl2 (5×10 mL). The extract was
dried with MgSO4 and concentrated in vacuo to obtain nitrꢀ
amine 2a (176 mg, 69%) as yellowish crystals, after recrystallizaꢀ
tion from light petroleum m.p. 69—71 °C (decomp.). Found (%):
C, 46.53; H, 2.87; N, 26.91. C8H6N4O3. Calculated (%):
C, 46.61; H, 2.90; N, 27.18. IR, ν/cm–1: 1280, 1312, 1324, 1404,
1468, 1504, 1616, 3308. 1H NMR, δ: 7.61—7.64 (m, 3 H, H(3´),
H(4´), H(5´)); 7.88 (dd, 2 H, H(2´), H(6´), J = 7.3 Hz, J = 2.2 Hz);
9.25 (br.s, 1 H, NH). 13C NMR, δ: 125.5 (C(1´)); 128.3 (C(2´),
C(6´)); 130.3 (C(3´), C(5´)); 132.3 (C(4´)); 149.0 (C(3)); 152.8
(C(4)). The HMBC and HSQC experiments were used to assign
1.86 mmol) in 93% aq. H2SO4 (1 mL) was added dropwise to
a solution of aminofurazan 1a (0.3 g, 1.86 mmol) in 93%
aq. H2SO4 (4 mL) with vigorous stirring at 20 °C. The reaction
mixture was stirred for 10 min and then poured onto finely
crushed ice (15 g). A suspension formed was extracted with
CH2Cl2 (5×10 mL). The combined organic layer was washed
with brine (2 mL), dried with MgSO4, and concentrated in vacuo
to obtain a mixture of 3ꢀaminoꢀ4ꢀ(nitrophenyl)ꢀ1,2,5ꢀoxadiꢀ
azoles 1b—d (345 mg, 90%), which was separated by preparative
TLC on silica gel (eluent: light petroleum—AcOEt (2 : 1)). Comꢀ
pound 1b (132 mg, 34%), compound 1c (107 mg, 28%), and
compound 1d (104 mg, 27%) were finally obtained.
3ꢀAminoꢀ4ꢀ(4´ꢀnitrophenyl)ꢀ1,2,5ꢀoxadiazole (1b), m.p.
173—175 °C. Found (%): C, 46.47; H, 2.95; N, 26.85.
C8H6N4O3. Calculated (%): C, 46.61; H, 2.93; N, 27.18. IR,
ν/cm–1: 1312, 1348, 1476, 1516, 1604, 1632, 3328, 3452.
1H NMR, δ: 5.80 (br.s, 2 H, NH2); 8.15 (d, 2 H, H(2´), H(6´),
J = 9.0 Hz); 8.44 (d, 2 H, H(3´), H(5´), J = 9.0 Hz). 13C NMR,
δ: 125.1 (C(3´), C(5´)); 130.1 (C(2´), C(6´)); 133.5 (C(1´)); 146.8
(C(4)); 150.0 (br.s, C(4´)); 156.3 (C(3)). 13C NMR (DMSOꢀd6),
δ: 124.0 (C(3´), C(5´)); 129.1 (C(2´), C(6´)); 131.8 (C(1´));
145.6 (C(4)); 148.2 (C(4´)); 155.3 (C(3)). The HMBC and
HSQC experiments were used to assign the signals. 14N NMR (acetꢀ
oneꢀd6), δ: –13 (NO2, Δν1/2 = 130 Hz). MS, m/z: 206 [M]+, 176
[M – NO]+.
the signals. 14N NMR, δ: –37 (N—NO2, Δν = 20 Hz). MS,
1/2
m/z: 206 [M]+.
3ꢀAminoꢀ4ꢀ(3´ꢀnitrophenyl)ꢀ1,2,5ꢀoxadiazole (1c), m.p.
123—125 °C (from MeOH). Found (%): C, 46.78; H, 2.89;
N, 27.01. C8H6N4O3. Calculated (%): C, 46.61; H, 2.93;
N, 27.18. IR, ν/cm–1: 1308, 1320, 1352, 1472, 1516, 1532, 1636,
Reaction of compound 2a with diazomethane. A solution of
diazomethane, obtained from NꢀmethylꢀNꢀnitrosourea (0.2 g),
in Et2O (3 mL) was added dropwise to a stirred solution of nitraꢀ
mine 2a (90 mg, 0.44 mmol) in Et2O (3 mL) at 20 °C until
evolution of the gas was ceased and the solution turned slightly
yellowish. Then the solvent was evaporated in vacuo to obtain
a mixture of Oꢀ and Nꢀmethyl derivatives 3a and 4a (94 mg, 98%)
as yellowish crystals. The mixture was separated by preparative
TLC on silica gel (eluent: light petroleum—AcOEt (4 : 1)) to
yield Oꢀmethyl compound 3a (60 mg, 63%) and Nꢀmethyl comꢀ
pound 4a (34 mg, 35%).
1
3316, 3412. H NMR, δ: 5.81 (br.s, 2 H, NH2); 7.91 (t, 1 H,
H(5´), J = 8.1 Hz); 8.27 (d, 1 H, H(6´), J = 7.3 Hz); 8.43 (dd, 1 H,
H(4´), J = 8.1 Hz, J = 1.5 Hz); 8.66 (t, 1 H, H(2´), J = 1.5 Hz).
13C NMR, δ: 123.6 (C(2´)); 125.8 (C(4´)); 128.8 (C(1´)); 131.7
(C(5´)); 134.9 (C(6´)); 146.7 (C(4)); 149.7 (br.s, C(3´)); 156.2
(C(3)). The HMBC and HSQC experiments were used to assign
the signals. 14N NMR, δ: –13 (NO2, Δν1/2 = 100 Hz). MS, m/z:
206 [M]+, 176 [M – NO]+.
Eꢀ3ꢀ[Methoxy(oxido)diazenyl]ꢀ4ꢀphenylꢀ1,2,5ꢀoxadiazole
(3a), m.p. 72—73 °C (from MeOH). Found (%): C, 49.33;
H, 3.70; N, 25.21. C9H8N4O3. Calculated (%): C, 49.09;
H, 3.66; N, 25.45. IR, ν/cm–1: 1240, 1300, 1452, 1544, 1556.
1H NMR, δ: 4.23 (s, 3 H, Me); 7.53—7.59 (m, 3 H, H(3´),
H(4´), H(5´)); 7.96 (dd, 2 H, H(2´), H(6´), J = 7.8 Hz, J = 1.9 Hz).
13C NMR, δ: 59.1 (Me); 124.8 (C(1´)); 128.3 (C(2´), C(6´));
129.1 (C(3´), C(5´)); 131.1 (C(4´)); 150.6 (C(4)); 153.1 (C(3)).
The HMBC and HSQC experiments were used to assign the
3ꢀAminoꢀ4ꢀ(2´ꢀnitrophenyl)ꢀ1,2,5ꢀoxadiazole (1d), m.p.
113—114 °C (from MeOH) (cf. Ref. 21: m.p. 111—112 °C).
Found (%): C, 46.74; H, 2.95; N, 26.99. C8H6N4O3. Calculatꢀ
ed (%): C, 46.61; H, 2.93; N, 27.18. IR, ν/cm–1: 1312, 1352,
1476, 1524, 1532, 1632, 3340, 3444. 1H NMR, δ: 5.63 (br.s, 2 H,
NH2); 7.75 (dd, 1 H, H(6´), J = 7.3 Hz, J = 2.2 Hz); 7.91 (td, 1 H,
H(4´), J = 7.3 Hz, J = 2.2 Hz, J = 1.5 Hz); 7.98 (td, 1 H, H(5´),
J = 7.3 Hz, J = 1.5 Hz); 8.34 (dd, 1 H, H(3´), J = 8.1 Hz, J = 1.5 Hz).
13C NMR, δ: 121.8 (C(1´)); 126.2 (C(3´)); 132.9 (C(4´)); 133.6
(C(6´)); 135.2 (C(5´)); 147.2 (C(4)); 149.4 (br.s, C(2´)); 156.8
(C(3)). The HMBC and HSQC experiments were used to assign
signals. 14N NMR, δ: –50 (N→O, Δν = 90 Hz). MS, m/z:
1/2
220 [M]+, 189 [M – OMe]+.
3ꢀ[Methyl(nitro)amino]ꢀ4ꢀphenylꢀ1,2,5ꢀoxadiazole (4a),
m.p. 69—71 °C (from light petroleum). Found (%): C, 49.27;
H, 3.69; N, 25.13. C9H8N4O3. Calculated (%): C, 49.09; H, 3.66;
the signals. 14N NMR, δ: –12 (NO2, Δν = 85 Hz). MS, m/z:
1/2
206 [M]+, 176 [M – NO]+.
3ꢀNitraminoꢀ4ꢀ(4´ꢀnitrophenyl)ꢀ1,2,5ꢀoxadiazole (2b). The
compound NO2BF4 (32 mg, 0.24 mmol) was added in small
portions to a solution of compound 1b (38 mg, 0.18 mmol) in
anhydrous acetonitrile (3 mL) with vigorous stirring at –30 °C.
The cooling bath was removed and the stirring was continued
until the temperature reached 0 °C. Then, a solution of K2CO3
(0.1 g) in water (0.5 mL) was added to the reaction mixture,
which was stirred for another 30 min at 0 °C. The mixture obꢀ
tained was concentrated at 0 °C. The residue was thoroughly
triturated and washed with Et2O (5 mL) with vigorous stirring
over 30 min. The washing was repeated another 2 times. A preꢀ
1
N, 25.45. IR, ν/cm–1: 1292, 1424, 1452, 1480, 1568. H NMR,
δ: 3.95 (s, 3 H, Me); 7.54—7.60 (m, 3 H, H(3´), H(4´), H(5´));
7.78 (dd, 2 H, H(2´), H(6´), J = 7.7 Hz, J = 1.3 Hz). 13C NMR,
δ: 40.0 (Me); 124.7 (C(1´)); 127.2, 127.3 (C(2´), C(6´)); 129.4,
129.5 (C(3´), C(5´)); 131.4 (C(4´)); 152.0 (C(4)); 152.4 (C(3)).
The HMBC and HSQC experiments were used to assign the
signals. 14N NMR, δ: –35 (N—NO2, Δν = 30 Hz). MS, m/z:
1/2
220 [M]+.
Nitration of 3ꢀaminoꢀ4ꢀphenylꢀ1,2,5ꢀoxadiazole (1a) with
the H2SO4—HNO3 mixture. A solution of KNO3 (188 mg,

546
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 3, March, 2011
Klenov et al.
cipitate was dissolved in H2O (10 mL) and the aqueous layer was
washed with Et2O (2×5 mL). Then, the aqueous layer was aciꢀ
dified with 10% aq. H2SO4 to pH 2 and extracted with AcOEt
(3×5 mL). The organic extracts were combined, dried with
MgSO4, and concentrated in vacuo to obtain nitramine 2b (32 mg,
69%) as yellowish crystals, m.p. 104—109 °C (decomp.).
Found (%): C, 38.19; H, 2.07; N, 27.62. C8H5N5O5. Calculatꢀ
ed (%): C, 38.26; H, 2.01; N, 27.88. IR, ν/cm–1: 1280, 1292,
Reaction of 3ꢀnitraminoꢀ4ꢀ(4´ꢀnitrophenyl)ꢀ1,2,5ꢀoxadiazole
(2b) with 93% H2SO4. The reaction was carried out according to
the general procedure for the reaction of 3ꢀnitraminoꢀ4ꢀphenylꢀ
1,2,5ꢀoxadiazole 2a with acids. The reaction mixture was kept at
20 °C for 1 h. The molar ratio of products was determined by
1H NMR (see Table 3).
Synthesis of cinnoline 5ꢀNꢀoxides 5b—d (general procedure).
A solution of KNO3 (196 mg, 2 mmol) in 100% H2SO4 (2 mL)
was added in one portion to aminofurazan 1b—d (40 mg,
0.2 mmol) at 20 °C with vigorous stirring. The reaction mixture
was stirred until compounds 1b—d were completely dissolved
and kept at 20 °C for the time indicated in Table 4. Then the
mixture was poured into icy water (5 mL) and extracted with
CH2Cl2 (5×4 mL). The organic extracts were combined, washed
with brine (2 mL), dried with MgSO4 and concentrated in vacuo.
The yields of products 5b—d were determined by 1H NMR (see
Table 4). Cinnoline 5ꢀNꢀoxides 5b—d were purified by preparaꢀ
tive TLC on silica gel (eluent: CHCl3—AcOEt (4 : 1)).
7ꢀNitro[1,2,5]oxadiazolo[3,4ꢀc]cinnoline 5ꢀNꢀoxide (5b),
m.p. 128—130 °C (from MeOH). Found (%): C, 41.36; H, 1.34;
N, 29.75. C8H3N5O4. Calculated (%): C, 41.21; H, 1.30; N, 30.04.
IR, ν/cm–1 (the region 1200—1600 cm–1): 1272, 1348, 1428,
1440, 1472, 1540, 1608. MS, m/z: 233 [M]+, 203 [M – NO]+.
8ꢀNitro[1,2,5]oxadiazolo[3,4ꢀc]cinnoline 5ꢀNꢀoxide (5c),
m.p. 164—166 °C (from CH2Cl2). Found (%): C, 41.08; H, 1.32;
N, 30.27. C8H3N5O4. Calculated (%): C, 41.21; H, 1.30;
N, 30.04. IR, ν/cm–1 (the region 1200—1600 cm–1): 1268, 1348,
1440, 1480, 1552. MS, m/z: 233 [M]+.
6ꢀNitro[1,2,5]oxadiazolo[3,4ꢀc]cinnoline 5ꢀNꢀoxide (5c´),
m.p. 150—152 °C (from CH2Cl2). Found (%): C, 41.38; H, 1.33;
N, 29.81. C8H3N5O4. Calculated (%): C, 41.21; H, 1.30; N, 30.04.
IR, ν/cm–1 (the region 1200—1600 cm–1): 1268, 1376, 1420,
1476, 1552. MS, m/z: 233 [M]+.
9ꢀNitro[1,2,5]oxadiazolo[3,4ꢀc]cinnoline 5ꢀNꢀoxide (5d),
m.p. 204—207 °C (from acetone). Found (%): C, 41.11; H, 1.28;
N, 29.79. C8H3N5O4. Calculated (%): C, 41.21; H, 1.30;
N, 30.04. IR, ν/cm–1 (the region 1200—1600 cm–1): 1272, 1348,
1408, 1424, 1480, 1544, 1584. MS, m/z: 233 [M]+; 203 [M – NO]+.
Reaction of nitramine 2a with oleum of different concentraꢀ
tions (general procedure). Oleum (1 mL) was added in one porꢀ
tion to nitramine 2a (10 mg, 0.05 mmol) (see Table 7) at 0 °C
with vigorous stirring. The reaction mixture was heated to 20 °C
over 5 min, then poured into icy water (3 mL), and extracted
with CH2Cl2 (5×3 mL). The organic extracts were combined,
washed with brine (1 mL), dried with MgSO4, and concentrated
in vacuo. The molar ratios of products were determined by
1H NMR (see Table 7).
Reaction of 3ꢀaminoꢀ4ꢀphenylꢀ1,2,5ꢀoxadiazole (1a) with
HNO3 in 14% oleum. The reaction was carried out according to
the general procedure for the reaction of 3ꢀaminoꢀ4ꢀ(nitropheꢀ
nyl)ꢀ1,2,5ꢀoxadiazoles 1b—d with HNO3 in H2SO4. The reagents
were mixed at 0 °C, then the reaction mixture was heated to
20 °C and kept for 5 min at this temperature. The molar ratios of
products were determined by 1H NMR (see Table 7).
1
1328, 1344, 1520, 1604, 1616, 3316. H NMR, δ: 8.17 (d, 2 H,
H(2´), H(6´), J = 8.6 Hz); 8.44 (d, 2 H, H(3´), H(5´), J = 8.6 Hz).
13C NMR, δ: 124.3 (C(3´), C(5´)); 129.0 (C(2´), C(6´)); 130.8
(C(1´)); 148.5 (C(3)); 149.6 (br.s, C(4´)); 150.7 (C(4)). The
HMBC experiment was used to assign the signals. 14N NMR, δ:
–12 (C—NO2, Δν1/2 = 150 Hz); –37 (N—NO2, Δν1/2 = 25 Hz).
MS, m/z: 251 [M]+, 206 [M – NO2]+.
Reaction of 3ꢀnitraminoꢀ4ꢀphenylꢀ1,2,5ꢀoxadiazole (2a) with
acids (general procedure). An acid (1 mL) was added in one
portion to nitramine 2a (10 mg, 0.05 mmol) (see Table 1) with
vigorous stirring at 20 °C. The reaction mixture was stirred for 5 min,
then poured into icy water (3 mL), and extracted with CH2Cl2
(5×3 mL). The organic extracts were combined, washed with brine
(1 mL), dried with MgSO4, and concentrated in vacuo. The
yields of products 1a—d were determined by 1H NMR (see Table 1).
Synthesis of [1,2,5]oxadiazolo[3,4ꢀc]cinnoline 5ꢀNꢀoxide (5a)
from Eꢀ3ꢀ[methoxy(oxido)diazenyl]ꢀ4ꢀphenylꢀ1,2,5ꢀoxadiazole
(3a) upon the action of acid (general procedure). An acid (1 mL)
was added in one portion to Oꢀmethyl compound 3a (10 mg,
0.045 mmol) (see Table 2) with vigorous stirring at 20 °C. The
reaction mixture was kept at 20 °C for the time indicated in
Table 2, then poured into icy water (3 mL). When the reaction
was performed in CF3COOH, the reaction mixture was concenꢀ
1
trated and the residue was analyzed by H NMR. After extracꢀ
tion with CH2Cl2 (5×3 mL), the organic extracts were comꢀ
bined, washed with brine (1 mL), dried with MgSO4, and conꢀ
centrated in vacuo. The yield of cinnoline 5ꢀNꢀoxide 5a was
determined by 1H NMR (see Table 2).
Synthesis of cinnoline 5ꢀNꢀoxide 5a from Eꢀ3ꢀ[methoxyꢀ
(oxido)diazenyl]ꢀ4ꢀphenylꢀ1,2,5ꢀoxadiazole (3a) upon the action
of BF3•Et2O. The compound BF3•Et2O (2 mL) was added in
one portion to Oꢀmethyl compound 3a (20 mg, 0.09 mmol) at 20 °C
under dry Ar. The reaction mixture was kept for 24 h at 20 °C,
then poured into water (10 mL), neutralized with NaHCO3 to
pH 8, and extracted with CH2Cl2 (2×5 mL). The organic exꢀ
tracts were combined, washed with brine (2 mL), dried with
MgSO4, and concentrated in vacuo. Cinnoline 5ꢀNꢀoxide 5a
was purified by preparative TLC on silica gel (eluent: light petroꢀ
leum—AcOEt (2 : 1)) to obtain the product (5.3 mg, 31%) idenꢀ
tical to that synthesized earlier.
Reaction of 3ꢀaminoꢀ4ꢀ(nitrophenyl)ꢀ1,2,5ꢀoxadiazoles 1b—d
with HNO3 in H2SO4 (general procedure). Aminofurazan 1b—d
(5 mg, 0.024 mmol) was added in one portion to a solution of
conc. HNO3 (0.001 mL, 0.024 mmol) in sulfuric acid (0.5 mL)
(the concentration of H2SO4 see in Table 3) at 20 °C with vigorꢀ
ous stirring. The reaction mixture was stirred until compounds
1b—d were completely dissolved and kept at 20 °C for the time
indicated in Table 3. Then the mixture was poured into icy water
(2 mL) and extracted with CH2Cl2 (5×2 mL). The organic exꢀ
tracts were combined, washed with brine (1 mL), dried with
MgSO4, and concentrated in vacuo. Degree of conversion of
compounds 1b—d to cinnoline 5ꢀNꢀoxides 5b—d and ratios of
products were determined by 1H NMR (see Table 3).
Synthesis of [1,2,5]oxadiazolo[3,4ꢀc]cinnoline 5ꢀNꢀoxide (5a)
from nitramine 2a upon the action of phosphorus pentoxide. The
compound P4O10 (0.6 g, 2.1 mmol) was added to a solution of
nitramine 2a (20 mg, 0.1 mmol) in anhydrous MeCN at 20 °C
with vigorous stirring. The reaction mixture was heated to 70 °C
over 10 h with vigorous stirring, then cooled to 20 °C, poured
into water (15 mL), and extracted with CH2Cl2 (5×5 mL). The

[1,2,5]Oxadiazolo[3,4ꢀc]cinnoline 5ꢀoxides
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 3, March, 2011
547
organic extracts were combined, washed with brine (2 mL), dried
with MgSO4, and concentrated in vacuo. Cinnoline 5ꢀNꢀoxide
5a was purified by preparative TLC on silica gel (eluent: light
petroleum—AcOEt (2 : 1)) to obtain 12 mg (66%) of this comꢀ
pound as white crystals, m.p. 157—159 °C, after recrystallization
from CH2Cl2 m.p. 167—169 °C. Found (%): C, 49.91; H, 2.17;
N, 29.90. C8H4N4O2. Calculated (%): C, 51.07; H, 2.14;
N, 29.78. IR, ν/cm–1 (the region 1100—1600 cm–1): 1144, 1240,
1272, 1408, 1436, 1440, 1476, 1584. MS, m/z: 188 [M]+.
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This work was financially supported by the Russian
Foundation for Basic Research (Project No. 10ꢀ03ꢀ00752)
and State Contract No. 02.740.11.0258.
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Received April 23, 2010;
in revised form February 1, 2011