New syntheses of [1,2,5]oxadiazolo[3,4-e][1,2,3,4]tetrazine 4,6-dioxide

Article abstract of DOI:10.1134/S107042801303024X

New methods were developed for the synthesis of [1,2,5]oxadiazolo[3,4-e][1, 2,3,4]tetrazine 4,6-dioxide from 4-(tert-butyl-NNO-azoxy)-N-nitro-1,2,5- oxadiazol-3-amine or its alkali metal salts and acid anhydrides (or chlorides) in the presence of strong acids. The yield of [1,2,5]oxadiazolo[3,4-e][1,2,3,4] tetrazine 4,6-dioxide in acetic anhydride in the presence of sulfuric acid or sulfuric anhydride at 20 C in 20 min attained 83%. A general mechanism was proposed for the reactions under study. Acetyl group behaved for the first time as departing group in the synthesis 1,2,3,4-tetrazine 1,3-dioxides, and [1,2,5]oxadiazolo[3,4-e][1,2,3,4]tetrazine 4,6-dioxide was obtained in 47% yield from N-[4-(acetyl-NNO-azoxy)-1,2,5-oxadiazol-3-yl]acetamide.

Full text of DOI:10.1134/S107042801303024X

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2013, Vol. 49, No. 3, pp. 455–465. © Pleiades Publishing, Ltd., 2013.
Original Russian Text © V.P. Zelenov, A.A. Lobanova, S.V. Sysolyatin, N.V. Sevodina, 2013, published in Zhurnal Organicheskoi Khimii, 2013, Vol. 49,
No. 3, pp. 467–477.
Dedicated to Full Member of the Russian Academy of Sciences
I.P. Beletskaya on her jubilee
New Syntheses of [1,2,5]Oxadiazolo[3,4-e][1,2,3,4]tetrazine
4,6-Dioxide
V. P. Zelenova, A. A. Lobanovab, S. V. Sysolyatinc, and N. V. Sevodinab
a Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, Leninskii pr. 47, Moscow, 119991 Russia
e-mail: viczel2008@rambler.ru
b Altay Federal Research and Production Center, Biysk, Altay krai, Russia
c Institute for Problems of Chemical and Energetic Technologies, Siberian Branch, Russian Academy of Sciences,
Biysk, Altay krai, Russia
Received December 11, 2012
Abstract—New methods were developed for the synthesis of [1,2,5]oxadiazolo[3,4-e][1,2,3,4]tetrazine 4,6-di-
oxide from 4-(tert-butyl-NNO-azoxy)-N-nitro-1,2,5-oxadiazol-3-amine or its alkali metal salts and acid
anhydrides (or chlorides) in the presence of strong acids. The yield of [1,2,5]oxadiazolo[3,4-e][1,2,3,4]tetrazine
4,6-dioxide in acetic anhydride in the presence of sulfuric acid or sulfuric anhydride at 20°C in 20 min attained
83%. A general mechanism was proposed for the reactions under study. Acetyl group behaved for the first time
as departing group in the synthesis 1,2,3,4-tetrazine 1,3-dioxides, and [1,2,5]oxadiazolo[3,4-e][1,2,3,4]tetrazine
4,6-dioxide was obtained in 47% yield from N-[4-(acetyl-NNO-azoxy)-1,2,5-oxadiazol-3-yl]acetamide.
DOI: 10.1134/S107042801303024X
[1,2,5]Oxadiazolo[3,4-e][1,2,3,4]tetrazine 4,6-diox-
ide (I, furazano-1,2,3,4-tetrazine 1,3-dioxide) occupies
a specific place among known 1,2,3,4-tetrazine 1,3-di-
oxides [1]. First, it is the only known representative of
five-membered heterocycles fused to a tetrazine diox-
ide ring. Second, compound I is characterized by
a high standard enthalpy of formation (158–160.9 kcal×
mol–1) [2, 3], which makes it promising as component
of energetic compositions [4–6]. Third, the conditions
of synthesis of [1,2,5]oxadiazolo[3,4-e][1,2,3,4]tetra-
zine 4,6-dioxide (I) differ essentially from those for
the preparation of aromatic analogs or tetrazine diox-
ides fused to a six-membered heteroring.
tert-butyl group is the leaving group [1, 7] (Scheme 1).
Both ionic systems (NO2BF4, HNO3–H2SO4, HNO3–
oleum, PCl5) and low-polar compounds (N2O5, P4O10)
were successfully used to prepare tetrazine dioxides
of the aromatic series [1]. It is believed that tetrazine
dioxides are formed through intermediate oxodi-
azonium ion A.
Tetrazine dioxide I was synthesized in 52% yield
from amine IIa with the use of NO2BF4 (Scheme 2)
[1, 8]. In the reaction of N-nitroamine IIIa with P4O10
in acetonitrile the yield of I was poor even when the
reaction was carried out under fairly severe conditions
(30% at 80°C) [1], whereas N-nitroanilines readily
reacted with P4O10 at 20°C in 15–40 min to afford 63–
88% of the corresponding benzotetrazine dioxides [7].
Tetrazine dioxides are generally synthesized from
o-(N-nitroamino)-tert-butylazoxyarenes in which the
Scheme 1.
O
N
O
NO2
t-Bu
N
O
N
NH2
O
N
HN
N
N
N
N
N
N
t-Bu
t-Bu
–t-Bu+
N
N
O
O
A
455

ZELENOV et al.
456
Even more contrasting results were obtained in synthe-
ses with N2O5. Anilines reacted with nitric anhydride
to form 51–83% of tetrazine dioxides [9], whereas the
reaction of N2O5 with IIa, which is obviously mediat-
ed by N-nitroamine IIIa, gave only the oxidation prod-
uct, nitro derivative IV [10] (Scheme 2). No reason-
able explanation was given to the observed pattern.
The goals of the present study were to develop
efficient procedures for the synthesis of [1,2,5]oxa-
diazolo[3,4-e][1,2,3,4]tetrazine 4,6-dioxide (I), eluci-
date reasons for considerably different reaction paths
of nitric anhydride with N-nitroamine IIIa and aro-
matic analogs, and estimate the effect of some factors
on the synthesis of compound I.
Scheme 2.
O
N
NO2BF4, MeCN
20°C, 4 h
N
N
N
O
52%
N
N
O
I
O
N
NO2
O
N
NH2
N2O5 (3–5 equiv)
0°C, MeCN
t-Bu
t-Bu
P4O10, MeCN
80°C
N
N
N
O
N
O
30%
N
N
NO2
IV
IIa
O
HN
N2O5 (1 equiv)
MeCN
t-Bu
N
N
N
52%
N
O
IIIa
Scheme 3.
O
NH2
NO2
t-Bu
N
O
N
N
N
O
NO2
R1
N
N
O
O
N
HN
N
N
N
N
N
N
E+
R1
IIa
N
O
–[R1]+, –EtOH
O
N
Ac
N
N
O
HN
N
IIIa, IIIb
O
N
N
O
O
NO2, H+, Ac2O
R1
N
A
I
N
N
NO2
N
O
E+
O
N
N
R1
VIIa, VIIb
M+
N
N
N
Va, VIa
O
O
O
+ AlCl3
R2–C=O [AlCl3·Hlg]–
R2
O
Hlg
R3
O
+
H+ An–
R3–C=O An–
+
R3COOH
O
R3
O
O
N
+
H2SO4
O2N HSO4
+
N
N
–O
O
O–
HO
O–
R1 = t-Bu (a), Ac (b); E+ = NO2+, R2C(O)+, R3C(O)+, SO3, P4O10; R2 = Me; Hlg = Cl, Br; R3 = Me, Et, Ph; H+An– = HClO4, H2SO4,
HBF4, H3PO4; Va, M = Na; VI, M = K.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 49 No. 3 2013

NEW SYNTHESES OF [1,2,5]OXADIAZOLO[3,4-e][1,2,3,4]TETRAZINE 4,6-DIOXIDE
Table 1. Synthesis of tetrazine dioxide I from N-nitroamine IIIa
457
Run no.
Acid (Lewis acid)a
Solvent
AcCl
Temperature, °C
Reaction time,b h
Yield of I, %
01
AlCl3
5–10
25
0.25
2.00
30
3
02
ZnCl2
Ac2O
03c
HClO4
Ac2O
20
0.25
55
83
56
3
04
H2SO4
Ac2O
20
0.33
05c
06d
07
HBF4
Ac2O
20
7.00
H3PO4
Ac2O
20
48.000
0.33
H2SO4
(EtCO)2O
AcOH
ClCH2CH2Cl
Ac2O
20
55
53
57
82
60
23
08e
Oleum (60% SO3)
SO3
22
30.000
0.25
09
–10 to –5
25
10
SO3
0.25
11
12f
P4O10
Ac2O
10
0.50
H2SO4–(PhCO)2O
MeNO2
20
7.00
a
b
c
d
e
f
Molar ratio acid–IIIa 2:1, unless otherwise stated.
The reaction time was determined by the disappearance of initial compound IIIa according to the TLC data.
The required amount of acid was added to excess Ac2O, and AcOH was then removed under reduced pressure.
Anhydrous acid was preliminarily prepared by adding a required amount of P2O5 to 82% H3PO4.
6.2 mol of SO3 per mole of IIIa.
Molar ratio (PhCO)2O-IIIa 2:1.
We have developed new methods of synthesis of
catalyzed by less strong acids, 7 h in the presence of
HBF4 and 48 h in the presence of H3PO4 (H0 = –5.2
[12]). Strong acids (HClO4, H2SO4, HBF4) ensured
a good yield of I (55–83%), while the yield was close
to zero with the use of weaker acids such as H3PO4
(3%) and CF3COOH (~0.1%; H0 = –2.71 [13]).
compound I, the first communication being reported in
2004 [11]. Tetrazine dioxide I was obtained by reac-
tions of N-nitroamines IIIa and IIIb or their salts Va
and VIa with organic acid anhydrides and chlorides in
the presence of strong mineral acids as ionizing agents,
as well as with mineral acid anhydrides in the absence
(SO3, P4O10) or in the presence of strong acid (N2O5)
(Scheme 3).
Presumably, the high yield of I in Ac2O in the
presence of P4O10 (Table 1, 60%) or SO3 (82%; cf. run
no. 9) is favored by the additive effect of anhydrides
ionized by the acid liberated during the reaction.
Unlike acids, the reaction of N2O5 with Ac2O gives
weakly polar mixed anhydride, acetyl nitrate [14]
(Scheme 4). Strong acid (HNO3) that may be formed
via abstraction of hydroxide ion from N-nitroamine
IIIa reacts with Ac2O to produce very weak acid
(AcOH) and acetyl nitrate [15]. The lack of a strong
electrophile is responsible for the failure to obtain
tetrazine dioxide I in the reaction of N-nitroamine IIIa
with N2O5 in Ac2O.
It is advisable to use polar solvents having no basic
properties. Strong Brønsted (HClO4, H2SO4, HBF4,
H3PO4) or Lewis acid (AlCl3, BF3 ·Et2O, ZnCl2) pro-
motes ionization of weakly polar anhydride (acid
halide) to form an ion pair E+An– (Scheme 3). Attack
by electrophilic species E+ on N-nitroamine molecule
yields intermediate oxodiazonium ion A which under-
goes cyclization to tetrazine dioxide I via elimination
of tert-butyl or acetyl cation. The conditions of synthe-
sis and yields of compound I from N-nitroamine IIIa
are collected in Table 1.
Scheme 4.
O2N–O–NO2
The reaction time in acetic anhydride and the yield
of I (Table 1, run nos. 3–6) depended on the strength
of the added acid. In the presence of strong acids such
as H2SO4 (H0 = –11.94 [12]) or HClO4 (H0 = –10.31
for 78.6% HClO4 [12]), N-nitroamine IIIa disappeared
completely in 15–20 min (TLC), whereas considerably
longer time was necessary to complete the reaction
Ac–O–Ac
Ac–O–Ac
+
2 Ac–O–NO2
Ac–O–NO2 AcOH
+
HO–NO2
+
We presume that the strength of the added acid
determines the ionic character of the acylium (nitro-
nium) ion–anion couple (E+An–) and cation A–anion
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 49 No. 3 2013

ZELENOV et al.
Scheme 5.
Y–
458
+X
·
·
·
O
·
·
O
O
N
·
N
H
N
R1
X
N
N
NO2
O
N
Y
H
O
O
N
HN
N
O
O
O
N
N
N
+X–Y–
R1
B
N
O
N
N
N
–O=X–Y–H
R1
R1
N
H
·
·
·
Y
N
O
N
N
O
N
N
X
IIIa, IIIb
N
N
O
O
O
O
N
C
A
N
R1
N
N
N
O
B'
O
N
N
N
N
–[R1]+
O
N
N
O
I
O
P
O
N
N
S
E+ = X–Y =
,
,
,
,
.
R2(3)
O
O
O–
O
O
O
O
O
O
couple (Scheme 5) and thus affects the reaction time
and the yield of I.
from N-nitroamine salts Va and VIa (Scheme 3,
Table 2) in the system Ac2O–H2SO4 almost does not
differ from the reaction with N-nitroamine IIIa since
the salts in acid medium are rapidly converted into free
N-nitroamine IIIa.
The role of the inductive (+I) or mesomeric (+M)
effect of the substituent R3 in the anhydride should be
noted (Scheme 3; Table 1, run nos. 4, 7, 12). The
substituents rank as follows with respect to their ef-
ficiency: Me > Et > Ph. Obviously, the yield of com-
pound I increases in parallel with the electrophilicity
of the reagent generated from the anhydride and
H2SO4. Increased negative charge on the oxygen atom
also favors the reaction. Potassium salt VIa reacted
with NO2BF4 in MeCN (Table 2) at an appreciably
higher rate as compared to N-nitroamine IIIa, and the
yield of I was higher (2 h, 52%) [7]. The synthesis of I
Aminofurazans are considerably weaker bases
(pKBH+ of 4-nitrofurazan-3-amine is –4.4 [16]) than
monosubstituted o-nitroanilines (pKBH+ = –0.3 [17]),
and their basicity approaches that of dinitroanilines
(pKBH+ = –5.4) [17]. Obviously, the difference in the
basicity of N-nitro derivatives of o-nitroaniline and
N-nitroaminofurazan IIIa should be similar to the dif-
ference in the basicity of the initial amines. Therefore,
the results of the reactions with the same non-ionized
Table 2. Synthesis of tetrazine dioxide I from salts Va and VIa at 20°C
Salt
Reagent
Solvent
Reaction time, min
Yield of I, %
Va, VIaa
VIab
VIaa
H2SO4–Ac2O
NO2BF4
Ac2O
MeCN
Ac2O
20
20
82–83
68
BF3·Et2O–Ac2O
17 h
36
a
Molar ratio acid–salt 3:1.
Molar ratio NO2BF4–salt 2:1, 25ºC.
b
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 49 No. 3 2013

NEW SYNTHESES OF [1,2,5]OXADIAZOLO[3,4-e][1,2,3,4]TETRAZINE 4,6-DIOXIDE
459
electrophile (e.g., N2O5 or P4O10) under analogous
conditions differ so strongly: the reaction with N-nitro-
aminofurazan IIIa either requires more severe condi-
tions than with aromatic analogs or gives no tetrazine
dioxide I.
appropriate for all known methods of synthesis of
tetrazine dioxides.
We previously [19] developed a procedure for the
preparation of NO2BF4 from N2O5 and Bu4NBF4
(Scheme 6). Addition of nitric acid to the reaction
mixture (in methylene chloride) initiates ion exchange
leading to precipitation of NO2BF4. The presence of
an acid increases the polarity of the medium, and
weakly polar N2O5 molecule undergoes ionization to
give NO2+NO–3 couple.
Electrophile E+ (or X–Y in Scheme 5) is a polarized
molecular entity consisting of atoms with different
electronegativities, and its coordination with N-nitro-
amine III is governed by electrostatic interactions. In
this context, the known syntheses of I by reactions
with NO2BF4 [7] and P4O10 in MeCN [1] may be re-
garded as particular cases of the proposed mechanism.
We presume that the initial step in the reaction of
electrophile E+ with N-nitroamine IIIa or IIIb is
formation of two-center associate B or B′ which is
converted into tetrazine dioxide I through intermediate
O-adduct C and diazonium oxide A. The contribution
of structure B or B′ may depend on the ionic strength
of the reaction medium and the form of N-nitroamine
(nitroamine, aci-nitro form or its salt). The lifetime of
covalent O-adduct C is determined by the rate of
ionization and dissociation of the N–OX bond in
intermediate B (B′). We believe that the reaction of
N-nitroamine with electrophile E+ is a version of
β-elimination [18] and that the proposed mechanism is
Scheme 6.
Bu4N+ BF4
+
NO2 NO3
HNO3, CH2Cl2
NO2 BF4
+
Bu4N+ NO3
↓
This procedure was utilized in the synthesis of
tetrazine dioxide I. The latter is not formed in the
reaction of N2O5 with N-nitroamine IIIa in MeCN
(Scheme 2) [9], as well as in Ac2O. Addition of 1 equiv
of moderately strong HNO3 (d20 = 1.5 g/cm3)
(65% HNO3, H0 = –3.78, 20°C [12]) to a solution of
N2O5 in an inert polar solvent (MeNO2) ensured
formation of 2% of I (0°C, 48 h, molar ratio IIIa–
N2O5–HNO3 1:3:1). Under analogous conditions, the
Scheme 7.
Ac
HNO3 (1 equiv)
H2SO4, Ac2O
20°C, 3 h
NO2
O
N
NH2
O
N
HN
O
N
HN
Ac2O, H+
t-Bu
t-Bu
t-Bu
N
N
N
N
N
N
30%
N
N
N
O
O
O
IIa
IXa
IIIa
t-BuNBr2
t-BuNBr2
O
N
Ac
Ac
HNO3 (1 equiv)
H2SO4, Ac2O
20°C, 0.5 h
NH2
N
HN
O
N
HN
N
N
N
Ac2O, H+
AcNBr2
N
N
Ac
N
N
O
O
O
N
N
N
47%
N
N
N
N
O
O
O
O
VII
VIII
IXb
I
AcNBr2
O
N
O
O
N
NH2
N
N
N
O
N
Ac
AcNBr2
N
N
N
VII
N
N
O
IIb
O
O
N
N
N
N
O
X
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 49 No. 3 2013

ZELENOV et al.
460
Scheme 8.
O
O
N
O2N
O
N
Ac
Ac
OAc
Br
N
N
N
O
N
HN
N
O
N
N
HNO3, H2SO4
Ac2O
20°C, 3 h
22%
t-Bu
t-Bu
N
t-Bu
+
O
N
N
N
Br
Br
Br
XII
XIII
XIV
XV
O2N
O
Ac
O
N
NH2
N
HNO3, H2SO4, Ac2O
0°C, 15 min
H2SO4, Ac2O
20°C, 3 h
t-Bu
t-Bu
N
N
N
XV
73%
22%
Br
Br
XI
XIII
stronger sulfuric acid converted N2O5 into NO2+HSO4 ;
and tetrazine dioxide I was obtained in a good yield
(57%, 0°C, 0.5 h). It should be noted that N-nitroamine
IIIa failed to react with N2O5 in the presence of
anhydrous HCl (4 days, 0 to 20°C). This result may be
expected, for N2O5 is known to react with HCl yielding
NO2Cl and HNO3. Nitrosyl chloride NO2Cl (μ = 0.42)
is less polar than N2O5 (μ = 1.39) [20], and it tends to
undergo homolytic dissociation [21], i.e., the degree of
ionization of the N–Cl bond is low. Thus the electro-
philicity of E+ species (Scheme 3) generated from
nitric or acetic anhydride is directly related to the
strength of the added acid.
acted initial compound was recovered from the reac-
tion mixture. The reaction with IXa was slower than
with amine IIa (0.4 h, 0 to 20°C, 62%), the reactant
ratio being the same. Comparison of the results of syn-
thesis of compound I from IXa and IXb shows that
acetyl group in the azoxy fragment is a better leaving
group than tert-butyl.
–
Aniline XI reacted with HNO3–H2SO4–Ac2O to
give 73% of benzotetrazine dioxide XV in 15 min at
0°C (Scheme 8) [23]. Analogous reaction with acet-
amide XII occurred at a considerably lower rate, and
the yield of XV was poor (3 h, 20°C, 22%). After
5 min, the reaction mixture contained N-nitro-N-acetyl
derivative XIII and only a small amount of tetrazine
dioxide XV. Insofar as the syntheses of benzotetrazine
dioxide XV from both acetamide XII and pure com-
pound XIII in H2SO4–Ac2O ensured similar yields in
similar reaction times, we presumed [21] that the
cyclization involves O-acetyl derivative XIV rather
than N-acetyl-N-nitroamine XIII as intermediate. The
synthesis of I from acetamide IXa (Scheme 7) also
required a longer time, and the yield was lower (3 h,
20°C, 30%) than in the reaction with amine IIa (0.4 h,
0 to 20°C, 62%), but no N-nitro-N-acetyl derivative
was detected in the reaction mixture (TLC). It is
known that N-nitration is a reversible process [17].
Presumably, the initial step is reversible deacylation–
nitration of amide IXa with formation of N-nitroamine
IIIa; theoretically, this process may follow two alter-
native paths, with or without participation of proton
(Scheme 9).
Tetrazine dioxide I was also synthesized in 62%
yield (Scheme 3) by one-pot reaction of IIa with the
system HNO3–H2SO4 (molar ratio 1:2)–Ac2O.
With a view to elucidate the effect of the distal sub-
stituent (azoxy group) on the synthesis of tetrazine di-
oxide I we have developed alternative methods for its
preparation from acetamides IXa and IXb (Scheme 7).
We failed to obtain acetyldiazene oxide IIb by the
Kovacic reaction [22] from amine VII; instead, com-
pound VII was oxidized with N,N-dibromoacetamide
to macrocycle X. Therefore, nitrosofurazanamine VII
was initially converted into acetamide VIII, and treat-
ment of the latter with N,N-dibromo-2-methylpropan-
2-amine or N,N-dibromoacetamide afforded the corre-
sponding diazene oxides IXa and IXb. N-[4-(Acetyl-
NNO-azoxy)-1,2,5-oxadiazol-3-yl]acetamide (IXb) in
the system HNO3–H2SO4–Ac2O (20°C, molar ratio
IXb–HNO3–H2SO4 1:1:2) was converted in 0.5 h into
tetrazine dioxide I (yield 47%). Increase of the reac-
tion time to 3 h reduced the yield to 28%.
The yield of tetrazine dioxide I did not change
(30%) when the amount of H2SO4 was increased three-
fold (20°C, 3 h, IXa–HNO3–H2SO4 1:1:6; Scheme 7).
However, raising the concentration of HNO3 by a fac-
Under analogous conditions, the yield of I from
amide IXa was 30% (3 h, 20°C), and 63% of unre-
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 49 No. 3 2013

NEW SYNTHESES OF [1,2,5]OXADIAZOLO[3,4-e][1,2,3,4]TETRAZINE 4,6-DIOXIDE
461
Scheme 9.
Ac
NO2
O
N
NH2
O
N
HN
O
N
HN
H2SO4, 70% AcOH
20°C, 2 h
NO2, –Ac+
t-Bu
t-Bu
t-Bu
N
N
N
N
O
N
N
26%
N
N
N
O
O
IIa
IXa
IIIa
H+
–AcOH
O
NH2
NO2
–H+
t-Bu
N
N
N
N
O
IIa
tor of 6 (IXa–HNO3–H2SO4 1:6:2), other conditions
being equal, increased the yield of I to 42%, which is
very consistent with Scheme 9. Amine IIa was ob-
tained from acetamide IXa in 70% aqueous AcOH in
the presence of H2SO4 (Scheme 9). These findings
indicate fairly ready deacylation of acetamidofurazans
in acid medium.
We also examined the transformation of N-nitro-
aminofurazan IIIc in the system H2SO4–Ac2O
(Scheme 10) in order to estimate the effect of the leav-
ing group R1. After 24 h at 20°C, only traces of I were
detected by TLC. Unlike tert-butyl or acetyl group,
carbocation derived from methyl group is unstable.
Therefore, this result may be regarded as an indirect
proof for the assumed elimination of R1 as carbocation.
EXPERIMENTAL
The H, 13C, and 14N NMR spectra were recorded
on a Bruker AM-300 instrument at 300.13, 75.47, and
21.69 MHz, respectively; the chemical shifts were
measured relative to Me4Si (1H, 13C) or MeNO2 (14N,
upfield shifts are negative). The IR spectra were ob-
tained on a Bruker Alpha-T spectrometer. The progress
of reactions was monitored by TLC on Silica gel 60
F254 plates (Merck). Preparative chromatography was
performed on silica gel. 4-(tert-Butyl-NNO-azoxy)-
1,2,5-oxadiazol-3-amine [9], N,N-dibromoacetamide
[24], 4-nitroso-1,2,5-oxadiazol-3-amine [25], 4-(meth-
yl-NNO-azoxy)-N-nitro-1,2,5-oxadiazol-3-amine [26],
and 4-(tert-butyl-NNO-azoxy)-N-nitro-1,2,5-oxadiazol-
3-amine [26] were synthesized by known methods.
1
Scheme 10.
[1,2,5]Oxadiazolo[3,4-e][1,2,3,4]tetrazine 4,6-di-
oxide (I). a. A solution of 2.30 g (10 mmol) of
N-nitroamine IIIa in 8 ml of acetic anhydride was
added under vigorous stirring at 10±1°C to a suspen-
sion of 3 g (20 mmol) of P4O10 in 25 ml Ac2O, and the
mixture was stirred for 0.5 h. The mixture was then
poured into 150 g of an ice–water mixture, stirred for
0.5 h to hydrolyze Ac2O, and extracted with benzene
(4×50 ml). The combined extracts were evaporated
under reduced pressure, and the residue was purified
by column chromatography using benzene as eluent.
Yield 0.95 g (60%), mp 111–113°C; published data
[8]: mp 110–112°C. The 1H, 13C, and 14N NMR and IR
spectra of the product were identical to those of
an authentic sample of I.
O
NO2
N
O
N
HN
N
N
N
H2SO4, Ac2O
Me
N
O
N
N
N
N
O
O
IIIc
I
To conclude, we have developed new reaction
systems based on acid anhydrides or acid chlorides and
strong acids as ionizing agents for the synthesis of
tetrazine dioxide I from N-nitroamine IIIa or its salts
Va and VIa. The yield of I in acetic anhydride in the
presence of SO3 or sulfuric acid attains 82–83%.
Diazene oxide IXb with acetyl group as leaving group
was used for the first time to synthesize tetrazine
dioxides. The developed procedures for the synthesis
of compound I made it possible to systemize general
principles for construction of both five- and six-mem-
bered rings fused to tetrazine dioxide. The proposed
general mechanism allows for the effects of electro-
philicity and structure of the reactants and the nature of
leaving group R1.
b. Mineral acid, 20 mmol (calculated on 100% acid
or H2SO4 with d20 = 1.83 g/cm3), was added under
stirring at 20±3°C to a solution of 2.30 g (10 mmol) of
N-nitroamine IIIa in 25 ml of liquid acid anhydride
(Table 1) or a solution of 10 mmol of IIIa in 20 ml of
anhydride was added to a solution of mineral acid in
5 ml of anhydride. The mixture was stirred until the
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 49 No. 3 2013

ZELENOV et al.
462
initial compound disappeared (TLC, benzene as
eluent) and poured into 150 ml of ice water (if tri-
fluoroacetic or phosphoric acid or zinc chloride was
used, the mixture was poured into a cold 3–4%
solution of sulfuric acid). The mixture was stirred for
0.5 h to hydrolyze anhydride and extracted with ben-
zene (4 × 30 ml), the solvent was removed under
reduced pressure, and the residue was purified by
column chromatography using benzene as eluent. The
conditions and yields of I are given in Table 1.
under reduced pressure, and the residue was purified
by column chromatography on silica gel using benzene
as eluent. Yield 0.84 g (54%).
g. A stream of gaseous sulfur trioxide was slowly
passed through a solution of 2.30 g (10 mmol) of
N-nitroamine IIIa in 30 ml of acetic anhydride under
stirring at 25–28°C (on cooling with an ice–water mix-
ture). When the initial compound disappeared (TLC,
benzene; Table 1), the mixture was poured into 150 ml
of water, and compound I was isolated according to
the standard procedure. Yield 1.28 g (82%).
c. To 20 ml of acetic acid we added under stirring at
22±2°C 4.5 ml of 60% oleum (62 mmol of SO3), and
2.30 g (10 mmol) of N-nitroamine IIIa was then
added. The mixture was stirred until the initial com-
pound disappeared (TLC, benzene; Table 1) and
poured into 100 ml of ice water, and the product was
isolated as described above. Yield 0.83 g (53%).
h. A solution of 1.63 g (15 mmol) of N2O5 in 7 ml
of nitromethane was added under stirring at 0±3°C to
a solution of 1.15 g (5 mmol) of N-nitroamine IIIa in
8 ml of nitromethane, and 5 mmol of H2SO4 (d20
=
1.83 g/cm3) or HNO3 (d20 = 1.5 g/cm3) was added at –5
to 0°C. Gaseous hydrogen chloride was prepared by
adding dropwise sulfuric acid (d20 = 1.83 g/sm3) from
a pressure-equilizing dropping funnel to concentrated
hydrochloric acid; the gas was passed through a U-tube
charged with anhydrous calcium chloride and bubbled
through the reaction mixture at 0±3°C. The mixture
was stirred until the initial compound disappeared (in
the reactions with HNO3 and H2SO4; TLC, benzene;
Table 1) and poured into 100 ml of water, and the
product was isolated according to the standard proce-
dure (as in a), followed by repeated chromatographic
purification using chloroform as eluent. Yield 0.44 g
(57%) in the presence of H2SO4 and 0.02 g (2%) in the
presence of HNO3. No compound I was detected by
TLC in the reaction mixture after passing HCl over
a period of 100 h.
d. Acetyl chloride, 10 ml, was cooled to 0–8°C,
1.34 g (10 mmol) of AlCl3 was added, and 1.15 g
(5 mmol) of N-nitroamine IIIa was then added. The
mixture was stirred for 15 min and poured into 150 g
of an ice–water mixture, and the product was isolated
as described above. Yield 0.24 g (30%).
e. Benzoic anhydride, 2.26 g (10 mmol), was
added under stirring at 20±3°C to a solution of 1.15 g
(5 mmol) of N-nitroamine IIIa in 15 ml of nitro-
methane, 0.58 ml (10 mmol) of H2SO4 (d20 = 1.83 g×
cm–3) was then added, and the mixture was stirred until
the initial compound disappeared (TLC, benzene;
Table 1). The mixture was poured into 100 ml of a cold
4% solution of H2SO4, stirred for 1 h, and extracted
with benzene (4×30 ml). The combined extracts were
evaporated under reduced pressure, the residue was
diluted with 15 ml of CCl4–benzene (4:1), the precip-
itate of benzoic acid was filtered off, and the residue
was purified twice by column chromatography on
silica gel using benzene as eluent. Yield 0.18 g (23%).
i. Nitric acid (d20 = 1.5 g/cm3), 0.42 ml (10 mmol),
was added under stirring at –10 to 0°C to a solution of
1.85 g (10 mmol) of amine IIa in 20 ml of acetic
anhydride, a solution of 1.1 ml (20 mmol) of H2SO4
(d20 = 1.83 g/cm3) in 10 ml of acetic anhydride was
then added at 10–20°C, and the mixture was stirred for
25 min at 20°C, cooled to 0°C, and poured into 150 g
of an ice–water mixture. Compound I was isolated ac-
cording to the standard procedure. Yield 0.96 g (62%).
f. A solution of SO3 in 1,2-dichloroethane was
prepared by shaking 60% oleum with the solvent. The
mixture was kept for 24 h to settle down, and the
organic phase was separated and added dropwise
(using a pressure-equalizing dropping funnel) to a so-
lution of 2.30 g (10 mmol) of N-nitroamine IIIa in
15 ml of 1,2-dichloroethane under stirring at –10 to
–5°C until the initial compound disappeared (TLC,
benzene; Table 1). The mixture was poured into 50 ml
of water and stirred for 5 min, the organic phase was
separated, the aqueous phase was extracted with
1,2-dichloroethane (4×20 ml), the extracts were com-
bined with the organic phase, the solvent was removed
j. Potassium salt VIa, 2.94 g (11 mmol), was added
under stirring at 18–20°C to a solution of 2.92 g
(22 mmol) of NO2BF4 in 15 ml of anhydrous aceto-
nitrile. The mixture was stirred for 20 min at 20°C,
poured into 45 ml of ice water, and extracted with
benzene (3×20 ml). The solvent was removed from the
extract under reduced pressure, and the residue was
purified by column chromatography using benzene as
eluent. Yield 1.17 g (68%).
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NEW SYNTHESES OF [1,2,5]OXADIAZOLO[3,4-e][1,2,3,4]TETRAZINE 4,6-DIOXIDE
463
k. Potassium salt VIa, 1.34 g (5 mmol), was dis-
solved in 15 ml of acetic anhydride, 1.26 ml (10 mmol)
of BF3·Et2O was added under stirring at 19–24°C, and
the mixture was stirred for 17 h at 18–20°C, poured
into 100 g of an ice–water mixture, and treated
according to the standard procedure to isolate 0.28 g
(36%) of I.
C6H9N6NaO4. Calculated, %: C 28.58; H 3.60;
N 33.33.
Potassium salt VIa. Yield 22.8 g (85%), mp 211–
1
213°C (decomp.) H NMR spectrum (acetone-d6):
δ 1.40 ppm (9H, t-Bu). 13C NMR spectrum (ace-
tone-d6), δC, ppm: 25.5 (CMe3), 60.5 (CMe3), 154.3
(C3), 156.7 br.s (C4). 14N NMR spectrum (acetone-d6),
δN, ppm: –12 (NO2, ∆ν1/2 = 40 Hz), –68 (N→O,
∆ν1/2 = 80 Hz). Found, %: C 27.00; H 3.41; N 31.17.
C6H9KN6O4. Calculated, %: C 26.86; H 3.38; N 31.33.
l. Salt Va or VIa, 5 mmol, was added under stirring
at 15–20°C to a solution of 1.47 g (15 mmol) of H2SO4
(d20 = 1.83 g/cm3) in 15 ml of acetic anhydride, and the
mixture was stirred until the initial compound disap-
peared (20 min; TLC, benzene; Table 2). The mixture
was poured into 80 ml of cold water, stirred for 0.5 h,
and treated according to the standard procedure to
isolate 0.64 g (82%, from Va) or 0.65 g (83%, from
VIa) of compound I.
m. Nitric acid (d20 = 1.5 g/cm3), 0.21 ml (0.32 g,
5 mmol), was added under stirring at 10–20°C to a so-
lution of 5 mmol of compound IXa or IXb in 8 ml of
acetic anhydride, a solution of 0.55 ml (10 mmol) of
H2SO4 (d20 = 1.83 g/cm3) in 2 ml of acetic anhydride
was added immediately, and the mixture was stirred
for 3 (IXa) or 0.5 h (IXb) at 20–25°C, poured into
75 ml of cold water, and treated according to the
standard procedure. Yield 0.24 g (30%, from IXa) or
0.37 g (47%, from IXb); in the reaction with IXa,
0.72 g (63%) of the unreacted initial compound was
also isolated. In the reaction of IXa with 30 mmol
(1.92 g) of HNO3 the yield of I in 3 h was 0.33 g
(42%), and in the reaction with 30 mmol of H2SO4
(2.94 g), 0.24 g (30%).
Reaction of 4-nitroso-1,2,5-oxadiazol-3-amine
(VII) with N,N-dibromoacetamide. A solution of
4.64 g (20 mmol) of N,N-dibromoacetamide in 20 ml
of anhydrous acetonitrile was added dropwise under
stirring at 20°C to a solution of 1.14 g (10 mmol) of
compound VII in 20 ml of acetonitrile, and the mixture
was stirred for 1.5 h (TLC). The solvent was removed
under reduced pressure, and the residue was subjected
to column chromatography using dichloroethane as
eluent to isolate 0.92 g (82%) of tris[1,2,5]oxadiazolo-
[3,4-c:3′,4′-g:3″,4″-k][1,2,5,6,9,10]hexaazacyclo-
dodecine 4,9,14-trioxide (X), mp 186–188°C (from
1
CHCl3); published data [27]: mp 187–188°C; the H,
13C, and 14N NMR spectra of the product were iden-
tical to those of an authentic sample. IR spectrum
(KBr), ν, cm–1: 1560, 1520, 1490, 1460, 1340, 1140.
Acylation of aminofurazans. a. One drop of
H2SO4 (~20 mg, 0.2 mmol, d20 = 1.83 g/cm3), was
added under stirring at 20°C to a solution or suspen-
sion of 10 mmol of aminofurazan in 8–10 ml of acetic
anhydride. The initial amine dissolved (if not dissolved
before), and the mixture spontaneously warmed up to
30–40°C. It was stirred for 10 min, poured into 100 ml
of cold (5–10°C) water, stirred for 0.5–1 h, and ex-
tracted with ethyl acetate (3×40 ml). The extract was
dried over MgSO4 and evaporated under reduced
pressure.
4-(tert-Butyl-NNO-azoxy)-N-nitro-1,2,5-oxadi-
azol-3-amine sodium and potassium salts Va and
VIa (general procedure). A solution of 0.1 mol of the
corresponding alkali metal hydroxide in 50 ml of
methanol was added under stirring at 0–12°C to
a solution of 0.1 mol of nitroamine IIIa in 50 ml of
methanol until pH ~6–7. The solvent was removed
under reduced pressure, the residue was dried in air
and dissolved in 40 ml of methanol on heating to
60°C, and the solution was poured into 100 ml of
anhydrous diethyl ether. After cooling, the precipitate
was filtered off.
b. Silica-supported sulfuric acid was used as cata-
lyst. Silica gel was mixed with excess 80–85% sulfuric
acid, the mixture was stirred for 10–15 min, and the
solid material was filtered off and dried for 48 h in
a desiccator over P4O10 until free-flowing powder was
obtained. The amount of the applied acid was deter-
mined by the gain in weight. For acylation of 10 mmol
of amine we used 0.5 g of silica-supported sulfuric
acid containing 55% of sulfuric acid monohydrate. The
mixture was stirred for 10–30 min until the initial
compound disappeared, the catalyst was filtered off,
excess acetic anhydride and acetic acid were distilled
off under reduced pressure, the residue was dissolved
Sodium salt Va. Yield 21.4 g (85%), mp 212–
1
213°C (decomp.). H NMR spectrum (acetone-d6):
δ 1.39 ppm (9H, t-Bu). 13C NMR spectrum (ace-
tone-d6), δC, ppm: 25.5 (CMe3), 60.5 (CMe3), 153.9
(C3), 156.6 br.s (C4). 14N NMR spectrum (acetone-d6),
δN, ppm: –13 (NO2, ∆ν1/2 = 45 Hz), –68 (N→O,
∆ν1/2 = 90 Hz). Found, %: C 28.29; H 3.57; N 33.03.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 49 No. 3 2013

ZELENOV et al.
464
in 50 ml of chloroform or 1,2-dichloroethane, the solu-
tion was washed with water (2×5 ml) and dried over
MgSO4, and the solvent was removed under reduced
pressure.
4-(tert-Butyl-NNO-azoxy)-1,2,5-oxadiazol-3-
amine (IIa). Compound IXa, 1.04 g (4.6 mmol), was
dissolved in 15 ml of 70% aqueous acetic acid, 4.5 g
(46 mmol) of H2SO4 (d20 = 1.83 g/cm3) was added, and
the mixture was stirred for 2 h at 20°C and poured into
80 ml of water. The precipitate was filtered off, washed
with water (2×5 ml), and dried. Yield 0.22 g (26%).
After prolonged storage (3 days), a solid separated
from the mother liquor and was filtered off, washed
with water (2×5 ml), and dried. We thus isolated
an additional amount, 0.55 g (65%), of amine IIa. The
N-(4-Nitroso-1,2,5-oxadiazol-3-yl)acetamide
(VIII) was synthesized from 1.14 g of 4-nitroso-1,2,5-
oxadiazol-3-amine VII as described in a or b. Purifica-
tion by column chromatography (eluent CH2Cl2 or
CHCl3) gave 1.20 g (77%) of blue oily amide VIII
which crystallized on storage, mp 88–90°C. IR spec-
trum (KBr), ν, cm–1: 3280 (NH, dimer), 3240 (NH,
monomer), 1690, 1680 (CO), 1590 (δNH) 1495 (NO,
monomer), 1430, 1390, 1370, 1310, 1280, 1265, 1240
(NO, dimer). 1H NMR spectrum (CDCl3), δ, ppm: 2.36
(3H, CH3), 8.32 (1H, NH). 13C NMR spectrum (CDCl3),
δC, ppm: 23.9 (CH3CO), 136.8 (C3), 166.1 (C4), 168.2
(C=O). Found, %: C 30.72; H 2.49; N 35.96.
C4H4N4O3. Calculated, %: C 30.78; H 2.58; N 35.89.
1
product was identical to an authentic sample in H,
13C, and 14N NMR and IR spectra.
N-[4-(Acetyl-NNO-azoxy)-1,2,5-oxadiazol-3-yl]-
acetamide (IXb). A solution of 0.81 g (3.5 mmol) of
N,N-dibromoacetamide in 20 ml of methylene chloride
was added under stirring at 20°C to a solution of
0.55 g (3.5 mmol) of compound VIII in 30 ml of
methylene chloride. The mixture was stirred for 10 h at
20°C, the solvent was removed under reduced pres-
sure, the residue was dissolved in 15 ml of methylene
chloride on heating to 40°C, 15 ml of diethyl ether was
added to the solution, and the mixture was left to stand
at –20°C for crystallization. Yield 0.32 g (43%). The
mother liquor was evaporated under reduced pressure,
and repeated crystallization gave additionally 0.31 g
(41%) of IXb. Overall yield 0.63 g (85%), mp 120–
123°C (decomp.). IR spectrum (KBr), ν, cm–1: 3332
(NH), 2932 (CH3), 1755, 1708 (CO), 1594 (δNH), 1535,
N-[4-(tert-Butyl-NNO-azoxy)-1,2,5-oxadiazol-3-
yl]acetamide (IXa). a. From 1.85 g of 4-(tert-butyl-
NNO-azoxy)-1,2,5-oxadiazol-3-amine (IIa) we ob-
tained according to method a or b 2.23 g (98%) of oily
amide IXa which crystallized on storage, mp 44–50°C.
IR spectrum (film), ν, cm–1: 3327 (NH), 2976, 2935
(CH3), 1725 (CO), 1596 (δNH), 1539, 1489, 1454,
1
1398, 1384, 1365 [N(O)=N]. H NMR spectrum
(CDCl3), δ, ppm: 1.52 (9H, t-Bu), 2.35 (3H, CH3), 9.43
(1H, NH). 13C NMR spectrum (CDCl3), δC, ppm: 23.6
[C(O)Me], 25.0 (Me3C), 60.9 (Me3C), 144.0 (C3),
151.1 br.s (C4), 167.2 (C=O). 14N NMR spectrum
(CDCl3): δN –69 ppm (N→O, ∆ν1/2 = 80 Hz). Found,
%: C 42.38; H 5.84; N 30.64. C8H13N5O3. Calculated,
%: C 42.29; H 5.77; N 30.82.
1
1497 m, 1386, 1358 m, 1321 [N(O)=N]. H NMR
spectrum (acetone-d6), δ, ppm: 2.31 [3H, NHC(O)Me],
2.45 [3H, MeC(O)N=N(O)], 10.37 (1H, NH).
13C NMR spectrum (acetone-d6), δC, ppm: 22.8 and
23.0 [C(O)Me], 145.9 (C3), 153.5 br.s (C4), 169.3
(NHCO), 181.3 (=NCO). 14N NMR spectrum (ace-
tone-d6): δN –68 ppm (N→O, ∆ν1/2 = 55 Hz). Found,
%: C 33.92; H 3.22; N 32.76. C6H7N5O4. Calculated,
%: C 33.81; H 3.31; N 32.86.
b. One drop of H2SO4, ~20 mg (0.2 mmol, d =
1.83 g/cm3), was added under stirring at 20°C to a so-
lution of 0.57 g (5 mmol) of 4-nitroso-1,2,5-oxadiazol-
3-amine (VII) in 10 ml of acetic anhydride. The mix-
ture was stirred for 10 min, 0.5 g (5 mmol) of Na2CO3
was added, and the mixture was stirred for 10 min
more. The precipitate was filtered off and washed with
15 ml of benzene on a filter, a solution of 2.35 g
(10 mmol) of N,N-dibromo-2-methylpropan-2-amine
in 15 ml of benzene was added to the filtrate under
stirring, and the mixture was stirred for 45 min at
20°C. The solvent was removed under reduced pres-
sure, and the residue was purified by column chroma-
tography using 1,2-dichloroethane as eluent to isolate
1.00 g (88%) of IXa as a light yellow oily liquid which
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