Synthesis and intramolecular ring transformation of: N, N ′-dialkylated 2,6,9-triazabicyclo[3.3.1]nonadienes

Article abstract of DOI:10.1039/d0ob01950j

The first and facile synthesis of N,N′-dialkylated 2,6,9-triazabicyclo[3.3.1]nonadienes was achieved by the [4 + 4] self-condensation of β-formyl-β-nitroenamine in the presence of ammonium acetate. The 2,6- A nd 2,9-dialkylated products were found to be interconvertible when dissolved in a solvent. This isomerization proceeds through intramolecular ring transformation via a common intermediate under equilibrium. This journal is

Full text of DOI:10.1039/d0ob01950j

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Synthesis and intramolecular ring transformation
of N,N’-dialkylated 2,6,9-triazabicyclo[3.3.1]
nonadienes†
Cite this: DOI: 10.1039/d0ob01950j
Yumi Nakaike, a Yusuke Yoshida,b Soichi Yokoyama, b,c,d Akitaka Ito b,c and
b,c
Nagatoshi Nishiwaki
*
The first and facile synthesis of N,N’-dialkylated 2,6,9-triazabicyclo[3.3.1]nonadienes was achieved by the
[4 + 4] self-condensation of β-formyl-β-nitroenamine in the presence of ammonium acetate. The 2,6-
and 2,9-dialkylated products were found to be interconvertible when dissolved in a solvent. This isomeri-
Received 23rd September 2020,
Accepted 28th October 2020
DOI: 10.1039/d0ob01950j
zation proceeds through intramolecular ring transformation via
a common intermediate under
rsc.li/obc
equilibrium.
dones are synthesized through this process.5 In these reac-
tions, a secondary amine such as piperidine is found to be a
Introduction
β-Formyl-β-nitroenamine 1 possesses multiple functionalities suitable base for condensation, while a tertiary amine such as
such as a formyl, nitro, and amino group, and a carbon– triethylamine causes no reaction, indicating that the inter-
carbon double bond with biased electron density, which bring mediate formation of iminium species is crucial (Scheme 1, b).
about diverse reactivities.1 Two electrophilic sites of 1 react Furthermore, the [4 + 2] self-condensation of 1 proceeds in the
with dinucleophiles such as hydrazines, 1,2-diamines, and presence of sulfonic acid to form a dinitropyridinium salt
ketones to afford nitrated pyrazoles,2 diazepines2 and phenols in situ, which can be trapped by electron-rich benzenes
(Scheme 1, a),3 respectively, in which nitroenamine 1 serves as leading to the formation of 4-arylated 1,4-dihydropyridines
a synthetic equivalent of nitromalonaldehyde (NMA-H). Its (Scheme 1, c).6
sodium salt (NMA-Na) component has been used for this
purpose for a long time. However, NMA-Na should be handled
carefully because of the explosive impurity, and aqueous or
alcoholic media should be used.4 In contrast, nitroenamine 1
is safely handleable, and its high solubility in common
organic solvents allows its reaction with versatile reagents in
organic media.
The dipolar properties of nitroenamine 1 facilitate its reac-
tions with 1,3-dicarbonyl compounds possessing both nucleo-
philic and electrophilic sites, and polyfunctionalized pyri-
aDepartment of Energy and Hydrocarbon Chemistry, Graduate School of Engineering,
Kyoto University, Yoshidahonmachi, Sakyo-ku, Kyoto 606-8501, Japan
bSchool of Environmental Science and Engineering, Kochi University of Technology,
Tosayamada, Kami, Kochi 782-8502, Japan.
E-mail: nishiwaki.nagatoshi@kochi-tech.ac.jp
cResearch Center for Molecular Design, Kochi University of Technology, Tosayamada,
Kami, Kochi 782-8502, Japan
dThe Institute of Scientific and Industrial Research, Osaka University, Mihogaoka,
Ibaraki, Osaka 567-0047, Japan
†Electronic supplementary information (ESI) available: Spectral data and copies
of NMR spectra of compounds 2–6, crystallographic data of 2a and 3d, and
temperature-dependent NMR spectra. CCDC 2027731 and 2027735. For ESI and
crystallographic data in CIF or other electronic format see DOI: 10.1039/
d0ob01950j
Scheme 1 Reactions using nitroenamine 1, in which the pink circles
and blue circles indicate electrophilic and nucleophilic sites,
respectively.
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These results prompted us to design a new synthetic work, methylamine also serves as a nitrogen source to form a
method for the triazabicyclic framework, including the [4 + 4] nitrogen bridge, which indicates that the addition of a nitro-
self-condensation of nitroenamine 1. Tröger’s base7 (3,7- gen source to our reaction is also necessary. In our study of
dibenzo-2,6-diazabicyclo[3.3.1]nonane) with a V-shaped struc- three-component ring transformation using dinitropyridone,
ture has attracted much attention because of its chirality,8 bio- ammonium acetate was found to serve as an excellent nitrogen
logical activity,9 molecular recognition ability,10 and opto- source and an activator of the substrate (Scheme 2, b),16 which
electronic properties.11 However, the bridgehead nitrogen prompted us to study the synthesis of TABNs using nitroena-
atoms cannot be modified anymore. Hence, researchers’ atten- mine 1 and ammonium acetate (Scheme 1, d).
tion has recently turned towards its aza-analogue, 2,6,9-triaza-
bicyclo[3.3.1]nonane (TABN), because of the availability of
further interactions and modifiability of nitrogen atoms in the
scaffold.12 However, it is still difficult to introduce a functional
group into the bicyclic framework,13 except for two examples.14,15
We focused on one of the examples, Ostercamp’s work. The
functionalized TABN derivative was first synthesized by the
treatment of NMA-Na with methylamine (Scheme 2, a).15 The
use of safely handleable nitroenamine 1 was considered to rep-
resent a general synthetic method for diverse TABNs because
the N-substituent of 1 can be easily modified. In Ostercamp’s
Results and discussion
When a solution of nitroenamine 1a in ethanol was heated at
80 °C for 1 d in the presence of ammonium acetate, four kinds
of TABNs 2a–5a were formed, among which 2a and 3a could
not be separated by column chromatography (Table 1, entry 1).
In the 1H NMR spectrum of one major product 2a, a singlet
signal assigned to two equivalent olefinic protons and an NH
signal showing coupling with the adjacent bridgehead protons
were observed. Hence, this isomer was determined to be a 2,6-
dipropyl derivative. The other major product 3a possesses an
unsymmetrical structure; one of the olefinic protons was
observed as a singlet, and the other was observed as a doublet
coupled with the adjacent NH proton, which was also sup-
1
ported by the H–1H COSY 2D NMR spectrum. The recrystalli-
zation of the 2a and 3a mixture afforded a single crystal of 2a,
which was subjected to X-ray crystallography to confirm the
structure (Fig. 1, left). Fortunately, a single crystal of dibenzyl
derivative 3d was obtained, and the structure was confirmed to
be a 2,9-disubstituted isomer (Fig. 1, right). The use of lower
Scheme 2 Synthetic equivalents of NMA-H: (a) sodium salt NMA-Na reaction temperature increased the total yield of products 2a–
and (b) 1-methyl-3,5-dinitro-2-pyridone.
5a, presumably because the competitive decomposition of
Table 1 Formation of four kinds of triazabicyclic compounds 2–5
Yielda (%)
Entry
R
NH4OAc (equiv.)
Temp. (°C)
2
3
4
5
Total
Recovery of 1a (%)
1
2
3
4
Pr
Pr
Pr
Pr
Pr
i-Pr
t-Bu
–CH2Ph
–CH2CHvCH2
–CH2CH2OH
a
a
a
a
a
b
c
d
e
f
1
1
1
2
4
1
1
1
1
1
80
50
rt
50
50
50
50
50
50
50
25
51
45
47
39
27
0
26
21
37
12
20
12
21
18
4
7
2
1
0
2
1
0
0
3
3
46
90
75
93
97
51
0
93
80
81
20
10
18
4
19
18
23
39
20
0
11
15
8
5
1
6
29
30
4
6
4
7b
8
0
53
41
24
9
10
12
a Determined by 1H NMR. b Non-alkylated bicyclic compound 6 was obtained in 26% yield.
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the formation of any detectable byproduct. A different behav-
ior was observed when 2a was dissolved in chloroform-d,
which might be due to a trace amount of hydrochloric acid in
the solvent. Conversely, the formation of 2d was also observed
when 3d was dissolved in deuterated solvents. The equilibrium
constants (K = [3]/[2]) were temperature-dependent, as shown
in Fig. 3. The K value for 3a/2a increased upon increasing the
temperature, whereas that for 3d/2d decreased. The Gibbs
energy differences between 2 and 3 determined by the
Arrhenius-type fittings (ln K = −ΔG/RT) reveal that 3d is more
stable than 2d (ΔG < 0) in contrast to the 2a/3a system
(Table 2). The difference originated from the existence of
π-stacking between the benzyl groups in 3d. In addition, the K
values in CD3CN were smaller than the relevant values in
CDCl3, presumably due to the polarity and/or Lewis acidity/
basicity of the solvent. These tendencies were qualitatively
reproduced by theoretical calculations. Furthermore, when a
mixture of 2a and 3a was heated in the presence of ammonium
acetate, nitroenamine 1a was formed in 10% yield in the reac-
tion mixture, indicating the existence of equilibrium between
1a and TABNs 2a and 3a.
Fig. 1 ORTEP views of 2a (left, 2,6-di-Pr) and 3d (right, 2,9-di-Bn).
Thermal ellipsoids are represented at probably the 50% level. CCDC:
2027731 (2a) and 2027735 (3d).†
ammonium acetate was suppressed (entry 2). Although this
reaction proceeded even at room temperature, the total yield
decreased to an extent (entry 3). The yields of dealkylated pro-
ducts 4a and 5a increased when larger amounts of ammonium
acetate were used (entries 4 and 5).
The optimized conditions were applied to other nitroena-
mines 1b–f. Bicyclic products 2b–5b possessing bulkier isopro-
pyl groups could be prepared by altering nitroenamine to 1b
(entry 6). When tert-butyl-substituted nitroenamine 1c was
employed, the corresponding bicyclic products 2c–5c were not
formed, and non-alkylated bicyclic product 6 was obtained
with 26% yield, which was due to the easy elimination of the
stable tert-butyl cation under acidic conditions (entry 7). It was
also possible to introduce functional groups to the ring nitro-
gen atoms, such as benzyl, allyl, and 2-hydroxyethyl groups,
efficiently (entries 8–10).
Based on these results, bicyclic products 2 and 3 are con-
sidered to be formed as shown in Scheme 3. The reaction is
initiated by the conversion of a formyl group of 1 to iminium
All attempts to control the selectivity between 2 and 3
failed. During this study, we noticed that the 2/3 ratio changed
each time we performed 1H NMR. This observation suggests
that there is a relationship of equilibrium between 2 and 3. To
confirm this, the single crystals of 2a and 3d used for X-ray
crystallography were dissolved in deuterated solvents, and the
1
change in the mole fraction ([2]/[2] + [3]) was monitored by H
NMR at intervals of several minutes/hours (Fig. 2). Conversion
from 2a to 3a was observed by only dissolving them in the sol-
vents at room temperature, irrespective of the solvent, without
Fig. 3 Temperature dependences of equilibrium constants K for 3a/2a
(closed squares) and 3d/2d (open squares) in CDCl3 (green) and CD3CN
(red).
Table 2 Observed and calculated Gibbs energy differences in chloro-
form and acetonitrile
ΔG (kJ mol−1
)
R
Solvent
Obsda
Calcdb
–Pr
Chloroform
Acetonitrile
Chloroform
Acetonitrile
+2.40 0.09
+1.58 0.12
−1.36 0.22
−2.38 0.14
+5.22
+5.29
+1.87
+0.69
–CH2Ph
a Determined using deuterated solvents. b Calculated at the B3LYP/6-
311+G(d,p) level.
Fig. 2 Time courses of the mole fraction of 2a (closed squares) and 3d
(open squares) in C6D6 (black), CDCl3 (green) and CD3CN (red).
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the conversion of nitroenamine 1 or iminium ion 7 to nitroe-
namine 11 (Scheme 4), which affords dealkylated products 4
and 5 in a manner similar to that shown in Scheme 3.
Products 4 and 5 are also inseparable because there is a
relationship between these compounds.
Conclusions
TABN frameworks were efficiently constructed by the [4 + 4]
self-condensation of nitroenamine 1 in the presence of
ammonium acetate. Since the N-alkyl group of 1 is easily modi-
fied, versatile TABNs were available by this protocol. The major
products, 2,6- and 2,9-dialkylated TABNs 2 and 3, were found
to be interconvertible when dissolved in a solvent and this iso-
merization proceeds through intramolecular ring transform-
ation under equilibrium via the common intermediate 10.
Further studies on the physical properties of TABNs and
chemical conversion using the functionalities are in progress,
and the results will be presented in due course.
Scheme 3 A plausible mechanism for the formation of bicyclic com-
pounds 2 and 3.
Experimental section
General
ion 7, which facilitates the attack of the less nucleophilic
amino group of another molecule of 1 forming 8. After the
elimination of ammonia, the formed iminium ion is attacked
by the imino group intramolecularly to form a six-membered
ring. Dihydropyrimidine 10 is a common intermediate of 2
and 3. When the amino group in the side chain attacks the
4-position (Path A), 2,6-dialkyl product 2 is formed. On the
other hand, 2,9-dialkyl product 3 is formed when the amino
group attacks the 6-position of 10 (Path B). A direct rearrange-
ment between 2 and 3 is also possible if a stable cation such
as a benzyl and allyl cation is released. However, ring trans-
formation via intermediate 10 is considered to be more plaus-
ible based on our previous findings; 4,6-dinitro-2,8-diazabicy-
clo[3.3.1]nona-2-ene and 3-nitropyridine are interconvertible
under equilibrium in the presence of ammonium acetate.17
The use of larger amounts of ammonium acetate is subject to
The melting points were determined using an SRS-Optimelt
automated melting point system. All the reagents and solvents
were commercially available and used as received. The 1H
NMR spectra were measured on a Bruker Ascend-400 at
400 MHz with tetramethylsilane as an internal standard. The
13C NMR spectra were measured on a Bruker Ascend-400 at
100 MHz, and the assignments of the 13C NMR spectra were
performed by DEPT experiments. The high-resolution mass
spectra were measured on an AB SCIEX Triple TOF 4600. The
IR spectra were recorded on a JASCO FT/IR-4200 spectrometer.
Preparation of nitroenamines 1a–f
Nitroenamines 1a–f were prepared according to our estab-
lished method.18 Nitropyrimidinone was prepared in 70%
overall yield by the condensation of commercially available
1,1,3,3-tetramethoxypropane and N-methylurea in 12 M hydro-
chloric acid followed by nitration with nitric acid in sulfuric
acid. To a solution of pyrimidinone (310 mg, 2 mmol) in
methanol (40 mL), propylamine (410 μL, 5 mmol) was added,
and the mixture was heated under reflux for 3 h. After evapor-
ation, the residue was extracted with hexane (3 × 30 mL), and
the removal of hexane afforded NMR pure azadienamine
(390 mg, 1.96 mmol, 98%) as a pale yellow oil. A solution of
azadienamine (200 mg, 1 mmol) in chloroform (5 mL) was
charged on silica gel (20 g) in a column and allowed to stand
at room temperature for 1 day, and then it was eluted with
chloroform. The solvent was removed under reduced pressure
to give nitroenamine 1a (150 mg, 93%). Other nitroenamines
1b–f were prepared in the same way by using the corres-
ponding amines instead of propylamine (Scheme 5).
Scheme 4 Conversion of an alkylamino group to an amino group in
the nitroenamine moiety.
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(400 MHz, CDCl3) δ 4.16 (br dd, J = 5.8, 5.8 Hz, 2H), 5.3–5.5
(m, 2H), 5.8–6.0 (m, 1H, overlapped with signals of E-isomer),
7.91 (d, J = 15.2 Hz, 1H), 9.5–9.9 (br, 1H), 10.06 (s, 1H).
4-Aza-6-hydroxy-2-nitro-2-hexenal (1f)
Brown solid; mp 125.4–126.5 °C (E/Z = 71/29). (E)-Isomer; 1H
NMR (400 MHz, CD3CN) δ 3.1–3.4 (br, 1H), 3.5–3.6 (m, 2H),
3.70 (t, J = 5.2 Hz, 2H), 8.58 (br d, J = 8.8 Hz, 1H), 10.10 (d, J =
3.6 Hz, 1H), 10.3–10.7 (br, 1H); 13C NMR (100 MHz, CD3CN)
δ 53.3 (CH2), 60.8 (CH2), 126.8 (C), 157.4 (CH), 186.3 (CH). (Z)-
Scheme 5 Outline of the preparative method for nitroenamines 1a–f.
1
Isomer; H NMR (400 MHz, CD3CN) δ 3.2–3.4 (br, 1H), 3.62 (t,
J = 4.7 Hz, 2H), 3.6–3.8 (m, 2H), 7.96 (d, J = 15.2 Hz, 1H),
9.5–9.9 (br, 1H), 9.98 (s, 1H); 13C NMR (100 MHz, CD3CN)
δ 53.4 (CH2), 60.8 (CH2), 125.6 (C), 152.7 (CH), 183.8 (CH).
HRMS (ESI/TOF) calcd for C5H8N2O4(M − H+): 159.0411,
found: 159.0416; IR (KBr, cm−1) 3494, 3216, 1674, 1589, 1491,
1314.
4-Aza-2-nitro-2-heptenal (1a)18
Brown solid (E/Z = 76/24). (E)-Isomer; 1H NMR (400 MHz,
CDCl3) δ 1.01 (t, J = 7.4 Hz, 3H), 1.74 (tq, J = 7.3, 7.4 Hz, 2H),
3.45 (dt, J = 6.8, 7.3 Hz, 2H), 8.48 (dd, J = 3.6, 14.5 Hz, 1H),
10.14 (d, J = 3.6 Hz, 1H), 10.3–10.8 (br, 1H). (Z)-Isomer; 1H
NMR (400 MHz, CDCl3) δ 1.01 (t, J = 7.4 Hz, 3H), 1.76 (tq, J =
7.3, 7.4 Hz, 2H), 3.53 (dt, J = 6.8, 7.3 Hz, 2H), 8.48 (d, J =
15.3 Hz, 1H), 9.5–9.9 (br, 1H), 10.05 (s, 1H).
Synthesis of triazabicyclic compounds
To a solution of formylnitroenamine 1a (158.2 mg, 1.0 mmol)
in ethanol (4 mL), ammonium acetate (78.5 mg, 1.0 mmol)
was added, and the resultant mixture was heated at 50 °C for
1 day. After the removal of the solvent under reduced pressure,
the residual brown solid was dissolved in dichloromethane
(30 mL) and washed with water (30 mL × 1). The aqueous layer
was extracted with dichloromethane (30 mL × 3). The com-
bined organic layer was dried over magnesium sulfate and
evaporated to afford a brown solid as a residue. The solid was
subjected to column chromatography on silica gel using ethyl
acetate/dichloromethane (1/9) as an eluent to afford a mixture
of 2a and 3a as a yellow solid (81.0 mg, 0.27 mmol, 55%) and a
mixture of 3a and 4a as a brown solid (17.9 mg, 0.07 mmol,
14%). However, further separation could not be achieved.
When other nitroenamines 1b–f were used, the experiments
were performed in the same way. In the cases of 1b and 1f,
ethyl acetate was used as an extraction solvent instead of di-
chloromethane. In the case of 1f, ethyl acetate was used as an
eluent for column chromatography.
4-Aza-5-methyl-2-nitro-2-hexenal (1b)19
Brown solid (E/Z = 76/24). (E)-Isomer; 1H NMR (400 MHz,
CDCl3) δ 1.40 (d, J = 6.6 Hz, 6H), 3.75 (sep, J = 6.6 Hz, 1H), 8.52
(ddd, J = 0.6, 3.6, 14.6 Hz, 1H), 10.15 (d, J = 3.6 Hz, 1H),
10.3–10.8 (br, 1H). (Z)-Isomer; 1H NMR (400 MHz, CDCl3)
δ 1.42 (d, J = 6.6 Hz, 6H), 3.84 (sep, J = 6.6 Hz, 2H), 7.95 (d, J =
15.4 Hz, 1H), 9.4–9.9 (br, 1H), 10.56 (s, 1H).
4-Aza-5,5-dimethyl-2-nitro-2-hexenal (1c)18
White solid (E/Z = 79/21). (E)-Isomer; 1H NMR (400 MHz,
CDCl3) δ 1.45 (s, 9H), 8.57 (dd, J = 3.6, 14.9 Hz, 1H), 10.15 (d,
J = 3.6 Hz, 1H), 10.3–10.8 (br, 1H). (Z)-Isomer; 1H NMR
(400 MHz, CDCl3) δ 1.47 (s, 9H), 7.99 (d, J = 15.7 Hz, 1H),
9.7–10.1 (br, 1H), 9.94 (s, 1H).
4-Aza-2-nitro-5-phenyl-2-pentenal (1d)
White solid; mp 119.2–120.0 °C (E/Z = 77/23). (E)-Isomer; 1H
NMR (400 MHz, CDCl3) δ 4.64 (d, J = 5.9 Hz, 2H), 7.2–7.5 (m,
5H), 8.54 (dd, J = 3.6, 14.3 Hz, 1H), 10.16 (d, J = 3.6 Hz, 1H),
10.6–11.0 (br, 1H); 13C NMR (100 MHz, CDCl3) δ 54.5 (CH2),
126.3 (C), 127.8 (CH), 129.1 (CH), 129.5 (CH), 133.9 (CH), 155.0
The NMR spectra were analyzed using a mixture of 2 and 3
because these products are interconvertible under equilibrium
when dissolved in solvents. Hence, the content ratio varied in
each measurement. With regard to bicyclic products 3 and 4,
the NMR spectra were measured using a mixture because they
were inseparable despite several attempts. The yields of 3 and
4 were determined on the basis of the integral ratio.
1
(C), 186.4 (CH). (Z)-Isomer; H NMR (400 MHz, CDCl3) δ 4.71
(d, J = 6.0 Hz, 2H), 7.2–7.5 (m, 5H), 7.98 (d, J = 15.1 Hz, 1H),
9.7–10.0 (br, 1H), 10.07 (s, 1H); 13C NMR (100 MHz, CDCl3)
δ 54.7 (CH2), 125.1 (C), 127.9 (CH), 129.2 (CH), 129.5 (CH),
133.9 (CH), 150.3 (C), 183.4 (CH). HRMS (ESI/TOF) calcd for
C10H10N2O3(M − H+): 205.0619, found: 205.0624; IR (KBr,
cm−1) 3212, 1656, 1606, 1505, 1317.
2,6,9-Triaza-4,8-dinitro-2,6-dipropylbicyclo[3.3.1]nona-3,7-diene
(2a) and 2,6,9-triaza-4,8-dinitro-2,9-dipropylbicyclo[3.3.1]nona-
3,7-diene (3a)
Yellow solid, mp 152.5–153.3 °C, Rf = 0.43 (SiO2, dichloro-
methane/methanol = 20/1). 2a; 1H NMR (400 MHz, CDCl3)
δ 0.98 (t, J = 7.4 Hz, 6H), 1.6–1.9 (m, 4H), 2.2–2.3 (br, 1H), 3.43
4-Aza-2-nitro-2,6-pentadienal (1e)5
1
Yellow oil (E/Z = 78/22). (E)-Isomer; H NMR (400 MHz, CDCl3) (ddd, J = 7.7, 7.7, 13.9 Hz, 2H), 3.98 (ddd, J = 5.8, 7.8, 13.9 Hz,
δ 4.09 (br dd, J = 5.7, 5.7 Hz, 2H), 5.3–5.5 (m, 2H), 5.90 (ddt, J = 2H), 5.68 (d, J = 2.8 Hz, 2H), 8.20 (s, 2H); 13C NMR (100 MHz,
5.7, 11.2, 17.0 Hz, 1H), 8.48 (dd, J = 3.6, 14.4 Hz, 1H), 10.15 (d, CDCl3) δ 11.1 (CH3), 23.3 (CH2), 56.9 (CH2), 61.9 (CH), 122.4
J = 3.6 Hz, 1H), 10.3–10.8 (br, 1H). (Z)-Isomer; 1H NMR (C), 144.6 (CH). 3a; 1H NMR (400 MHz, CDCl3) δ 0.93 (t, J =
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7.4 Hz, 3H), 1.00 (t, J = 7.4 Hz, 3H), 1.56 (ddq, J = 7.2, 7.2, 2,6,9-Triaza-4,8-dinitro[3.3.1]nona-3,7-diene (6)
7.4 Hz, 2H), 1.6–1.9 (m, 2H), 2.37 (dt, J = 7.2, 12.6 Hz, 1H),
Yellow solid, mp 207.0–208.1 °C (dec.). 1H NMR (400 MHz,
2.41 (dt, J = 7.4, 12.6 Hz, 1H), 3.39 (ddd, J = 7.8, 7.8, 14.0 Hz,
1H), 3.95 (ddd, J = 5.4, 8.1, 14.0 Hz, 1H), 5.34 (d, J = 1.4 Hz,
1H), 5.32 (s, 1H), 7.0–7.2 (br, 1H), 8.16 (s, 1H), 8.29 (d, J = 4.7,
1H); 13C NMR (100 MHz, CDCl3) δ 11.1 (CH3), 11.6 (CH3), 20.8
(CH2), 23.2 (CH2), 51.4 (CH2), 56.8 (CH2), 61.3 (CH), 66.9 (CH),
122.2 (C), 122.7 (C), 142.2 (CH), 144.4 (CH). HRMS (ESI/TOF)
calcd for C12H19N5O4 (M + H+): 298.1510, found: 298.1515;
IR (KBr, cm−1) 3291, 2965, 1613, 1304, 1226. A single crystal of
2a was obtained as yellow needles by recrystallization from di-
chloromethane/hexane.
DMSO-d6) δ 3.72 (t, J = 2.7 Hz, 1H), 5.51 (d, J = 2.7 Hz, 2H),
8.24 (s, 2H); 13C NMR (100 MHz, DMSO-d6) δ 56.2 (CH), 123.1
(C), 142.8 (CH); HRMS (ESI/TOF) calcd for C6H7N5O4 (M − H+):
212.0425, found: 212.0427; IR (KBr, cm−1) 3166, 3012, 1607,
1353, 1223.
2,6,9-Triaza-2,6-dibenzyl-4,8-dinitrobicyclo[3.3.1]nona-3,7-diene
(2d) and 2,6,9-triaza-2,9-dibenzyl-4,8-dinitrobicyclo[3.3.1]nona-
3,7-diene (3d)
Brown solid, mp 155.8–157.5 °C, Rf = 0.29 (SiO2, hexane/ethyl
acetate/triethylamine = 6/4/0.5). 2d; 1H NMR (400 MHz, CDCl3)
δ 1.9–2.1 (br, 1H), 4.68 (d, J = 14.8 Hz, 2H), 5.08 (d, J = 14.8 Hz,
2H), 5.65 (d, J = 2.6 Hz, 2H), 6.9–7.5 (m, 10H), 8.26 (s, 2H). 3d;
1H NMR (400 MHz, CDCl3) δ 3.29 (d, J = 13.4 Hz, 1H), 3.35 (d,
J = 13.4 Hz, 1H), 4.63 (d, J = 14.7 Hz, 1H), 4.99 (d, J = 14.7 Hz,
1H), 5.24 (d, J = 1.3 Hz, 1H), 5.35 (d, J = 1.3 Hz, 1H), 6.9–7.5
(m, 10H), 8.30 (s, 1H), 8.38 (s, 1H). A signal of N–H was
absent, which was presumably due to overlapping. The 13C
NMR (100 MHz, CDCl3) measurement was performed using a
mixture of two isomers 2d and 3d. δ 53.7 (CH2), 59.1 (CH2),
59.1 (CH2), 60.7 (CH), 61.1 (CH), 65.8 (CH), 121.8 (C), 122.8
(C), 123.0 (C), 128.2 (CH), 128.4 (CH), 128.6 (CH), 128.7 (CH),
128.9 (CH), 129.0 (CH), 129.0 (CH), 129.4 (CH), 129.4 (CH),
134.5 (C), 134.7 (C), 135.0 (C), 142.8 (CH), 144.6 (CH), 144.8
2,6,9-Triaza-4,8-dinitro-2-propylbicyclo[3.3.1]nona-3,7-diene (4a)
and 2,6,9-triaza-4,8-dinitro-9-propylbicyclo[3.3.1]nona-3,7-diene
(5a)
Yellow solid, mp 91.5–93.6 °C (4a/5a = 89/11). 4a; 1H NMR
(400 MHz, CD3CN) δ 0.92 (t, J = 7.4 Hz, 3H), 1.6–1.9 (m, 2H),
2.7–2.9 (br, 1H), 3.45 (ddd, J = 7.7, 7.7, 13.8 Hz, 1H), 3.87 (ddd,
J = 5.5, 7.8, 13.8 Hz, 1H), 5.57 (d, J = 1.6 Hz, 1H), 5.68 (d, J =
2.0 Hz, 1H), 7.6–8.1 (br, 1H), 8.20 (s, 1H), 8.22 (s, 1H); 13C
NMR (100 MHz, CDCl3) δ 11.1 (CH3), 23.6 (CH2), 55.6 (CH2),
55.7 (CH), 61.5 (CH), 124.0 (C), 124.3 (C), 143.5 (CH), 145.35
(CH). 5a; 1H NMR (400 MHz, CD3CN) δ 0.87 (t, J = 7.4 Hz, 3H),
1.51 (ddq, J = 6.7, 6.8, 7.4 Hz, 2H), 2.34 (dt, J = 6.7, 14.7 Hz,
1H), 2.36 (dt, J = 6.8, 14.7 Hz, 1H), 5.33 (s, 2H), 7.6–8.1 (br,
2H), 8.22 (s, 2H); 13C NMR (100 MHz, CDCl3) δ 11.7 (CH3), 21.2
(CH2), 51.3 (CH2), 62.0 (CH), 124.0 (C), 142.8 (CH). HRMS (ESI/
(CH); HRMS (ESI/TOF) calcd for C20H19N5O4(M
+
H+):
394.1510, found: 394.1525; IR (KBr, cm−1) 3279, 3057, 1614,
1318, 1209. A single crystal of 3d was obtained as yellow blocks
by recrystallization from ethanol/diethyl ether.
TOF) calcd for C9H13N5O4 (M
−
H+): 254.0895, found:
254.0890; IR (KBr, cm−1) 3283, 2965, 1611, 1340, 1225, 1139,
926.
2,6,9-Triaza-2-benzyl-4,8-dinitrobicyclo[3.3.1]nona-3,7-diene (4d)
and 2,6,9-triaza-9-benzyl-4,8-dinitrobicyclo[3.3.1]nona-3,7-diene
(5d)
2,6,9-Triaza-2,6-di(2-methylethyl)-4,8-dinitrobicyclo[3.3.1]nona-
3,7-diene (2b) and 2,6,9-triaza-2,9-di(2-methylethyl)-4,8-dinitro-
bicyclo[3.3.1]nona-3,7-diene (3b)
Yellow solid, mp 155.0–155.8 °C. 4d; 1H NMR (400 MHz,
CD3CN) δ 2.6–2.8 (br, 1H), 4.78 (d, J = 15.0 Hz, 1H), 4.99 (d, J =
15.0 Hz, 1H), 5.56 (dd, J = 1.0, 2.7 Hz, 1H), 5.63 (d, J = 2.7 Hz,
1H), 7.1–7.5 (m, 5H), 8.24 (s, 1H), 8.26 (s, 1H). 5d; 1H NMR
(400 MHz, CD3CN) δ 3.54 (d, J = 13.3 Hz, 1H), 3.59 (d, J =
13.3 Hz, 1H), 5.25 (s, 2H), 7.1–7.5 (m, 5H), 8.27 (s, 2H). A
signal of N–H was absent, which was presumably due to over-
lapping. The 13C NMR (100 MHz, CD3CN) measurement was
performed using a mixture of two isomers 4d and 5d. δ 53.7
(CH2), 57.1 (CH), 58.9 (CH2), 61.5 (CH), 62.5 (CH), 123.8 (C),
124.1 (C), 124.9 (C), 128.8 (CH), 129.2 (CH), 129.3 (CH), 129.6
(CH), 129.9 (CH), 130.0 (CH), 136.9 (C), 137.4 (C), 142.9 (CH),
143.5 (CH), 145.3 (CH); HRMS (ESI/TOF) calcd for C13H13N5O4
(M − H+): 302.0895, found: 302.0895; IR (KBr, cm−1) 3276,
1705, 1610, 1320, 1204, 928.
Yellow solid, mp 160.6–162.1 °C. Signals of 3b were too small
to be assigned. 2b; 1H NMR (400 MHz, CDCl3) δ 1.36 (d, J =
6.6 Hz, 12H), 2.1–2.3 (br, 1H), 4.36 (sep, J = 6.6 Hz, 2H), 5.69
(d, J = 2.7 Hz, 2H), 8.27 (s, 2H); 13C NMR (100 MHz, CDCl3)
δ 21.3 (CH3), 24.2 (CH3), 55.5 (CH), 63.4 (CH), 122.7 (C), 140.9
(CH); HRMS (ESI/TOF) calcd for C12H18N5O4 (M − H+):
296.1364, found: 296.1375; IR (KBr, cm−1) 3291, 2973, 1609,
1338, 1259, 1230, 1181.
2,6,9-Triaza-2-(2-methylethyl)-4,8-dinitrobicyclo[3.3.1]nona-3,7-
diene (4b)
Brown solid, mp 126.2–127.9 °C. Signals of 5b were too small
to be assigned. 1H NMR (400 MHz, CD3CN) δ 1.30 (d, J =
6.6 Hz, 3H), 1.33 (d, J = 6.6 Hz, 3H), 2.7–2.9 (br, 1H), 4.24 (qq,
J = 6.6, 6.6 Hz, 1H), 5.57 (d, J = 1.1 Hz, 1H), 5.70 (d, J = 1.2 Hz,
1H), 7.7–8.0 (br, 1H), 8.21 (s, 1H), 8.26 (s, 1H); 13C NMR
(100 MHz, CD3CN) δ 21.2 (CH3), 23.9 (CH3), 56.2 (CH), 57.4
(CH), 64.4 (CH), 124.1 (C), 124.9 (C), 141.4 (CH), 143.4 (CH);
2,6,9-Triaza-4,8-dinitro-2,6-di(3-propen-1-yl)bicyclo[3.3.1]nona-
3,7-diene (2e) and 2,6,9-triaza-4,8-dinitro-2,9-di(3-propen-1-yl)
bicyclo[3.3.1]nona-3,7-diene (3e)
1
HRMS (ESI/TOF) calcd for C9H12N5O4 (M − H+): 254.0895, Brown solid, mp 60.5–62.0 °C. 2e; H NMR (400 MHz, CDCl3)
found: 254.0898; IR (KBr, cm−1) 3283, 1609, 1342, 1232.
δ 2.20 (br, 1H), 4.17 (dddd, J = 1.5, 1.5, 5.0, 15.4 Hz, 2H), 3.60
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(br dd, J = 7.1, 15.4 Hz, 2H), 5.82 (dddd, J = 1.2, 1.2, 1.2, NMR (100 MHz, CD3CN) δ 51.9 (CH2), 57.3 (CH2), 60.7 (CH2),
17.2 Hz, 2H), 5.3–5.5 (m, 2H), 5.69 (d, J = 2.8 Hz, 2H), 5.87 61.4 (CH2), 62.1 (CH), 68.4 (CH), 122.9 (C), 123.1 (C), 143.4
(dddd, J = 5.0, 7.1, 10.2, 17.2 Hz, 2H), 8.18 (s, 2H). 3e; 1H NMR (CH), 145.9 (CH). HRMS (ESI/TOF) calcd for C10H15N5O6
(400 MHz, CDCl3) δ 3.01 (dddd, J = 1.2, 1.2, 6.4, 13.5 Hz, 1H), (M − H+): 300.0950, found: 300.0954; IR (KBr, cm−1)1209,
3.08 (dddd, J = 1.2, 1.2, 6.3, 13.5 Hz, 1H), 4.13 (dddd, J = 1.3, 1307, 1612, 2359, 3307.
1.3, 5.1, 15.3 Hz, 1H), 4.44 (br dd, J = 7.2, 15.3 Hz, 1H), 5.26
2,6,9-Triaza-2-(2-hydroxyethyl)-4,8-dinitro[3.3.1]nona-3,7-diene
(4f) and 2,6,9-triaza-9-(2-hydroxyethyl)-4,8-dinitro[3.3.1]nona-
3,7-diene (5f)
(dddd, J = 1.2, 1.2, 1.2, 17.1 Hz, 1H), 5.29 (dddd, J = 1.3, 1.3,
1.3, 10.2 Hz, 1H), 5.3–5.5 (m, 2H), 5.47 (dddd, J = 1.3, 1.3, 1.3,
17.0 Hz, 1H), 5.34 (d, J = 1.5 Hz, 1H), 5.38 (d, J = 1.5 Hz, 1H),
5.82 (dddd, J = 6.3, 6.4, 10.2, 17.1 Hz, 1H), 5.86 (dddd, J = 5.1,
7.2, 10.2, 17.0 Hz, 1H), 6.2–6.8 (br, 1H), 8.18 (s, 1H), 8.30 (s,
1H). The 13C NMR (100 MHz, CDCl3) measurement was per-
formed using a mixture of two isomers 2e and 3e. δ 52.6 (CH2),
57.5 (CH2), 57.5 (CH2), 60.7 (CH), 61.7 (CH), 66.2 (CH), 120.6
(CH2), 121.1 (CH2), 121.4 (CH2), 121.8 (C), 122.8 (C), 122.9 (C),
131.5 (CH), 131.7 (CH), 132.4 (CH), 142.8 (CH), 144.3 (CH),
144.6 (CH); HRMS (ESI/TOF) calcd for C12H15N5O4 (M − H+):
292.1051, found: 292.1054; IR (KBr, cm−1) 3283, 1613, 1482,
1416, 1309, 920, 760.
1
Brown solid, mp 95.6–97.2 °C. 4f; H NMR (400 MHz, CD3CN)
δ 2.8–3.0 (br, 1H), 2.9–3.4 (br, 1H), 3.57 (ddd, J = 3.8, 6.9,
14.3 Hz, 1H), 3.67 (ddd, J = 3.8, 6.2, 11.6 Hz, 1H), 3.77 (ddd, J =
3.5, 6.9, 11.6 Hz, 1H), 3.99 (ddd, J = 3.5, 6.2, 14.3 Hz, 1H), 5.57
(s, 1H), 5.73 (s, 1H), 7.4–8.2 (br, 1H), 8.21 (s, 1H), 8.23 (s, 1H);
13C NMR (100 MHz, CD3CN) δ 57.0 (CH2), 57.2 (CH), 61.5
(CH2), 63.8 (CH), 124.0 (C), 124.7 (C), 143.5 (CH), 145.6 (CH).
5f; 1H NMR (400 MHz, CD3CN) δ 2.49 (ddd, J = 5.5, 5.5,
13.4 Hz, 1H), 2.55 (ddd, J = 5.1, 5.1, 13.4 Hz, 1H), 2.9–3.4 (br,
1H), 3.5–3.7 (m, 2H, overlapped with signals of 4f), 5.44 (s,
2H), 7.4–8.2 (br, 2H), 8.23 (s, 2H); 13C NMR (100 MHz, CD3CN)
δ 51.9 (CH2), 60.7 (CH2), 62.5 (CH), 124.0 (C), 142.7 (CH).
HRMS (ESI/TOF) calcd for C8H11N5O5 (M − H+): 256.0687,
found: 256.0685; IR (KBr, cm−1) 1208, 1226, 1317, 1609, 2359,
3251.
2,6,9-Triaza-4,8-dinitro-2-(3-propen-1-yl)bicyclo[3.3.1]nona-3,7-
diene (4e) and 2,6,9-triaza-4,8-dinitro-9-(3-propen-1-yl)bicyclo
[3.3.1]nona-3,7-diene (5e)
Yellow solid, mp 135.4–137.5 °C. 4e; 1H NMR (400 MHz,
CD3CN) δ 2.7–2.9 (br, 1H), 4.19 (dddd, J = 1.4, 1.4, 5.0, 15.6 Hz,
1H), 4.43 (dddd, J = 1.4, 1.4, 6.8, 15.6 Hz, 1H), 5.30 (dddd, J =
1.4, 1.4, 1.4, 10.2 Hz, 1H), 5.39 (dddd, J = 1.4, 1.4, 1.4, 17.1 Hz,
1H), 5.57 (dd, J = 1.1, 2.7 Hz, 1H), 5.65 (br d, J = 2.8 Hz, 1H),
5.94 (dddd, J = 5.0, 6.9, 10.2, 17.1 Hz, 1H), 7.5–8.1 (br, 1H),
8.18 (s, 1H), 8.22 (s, 1H). 5e; 1H NMR (400 MHz, CD3CN) δ 3.00
(dddd, J = 1.3, 1.3, 6.4, 13.7 Hz, 1H), 3.05 (dddd, J = 1.3, 1.3,
6.4, 13.7 Hz, 1H), 5.30 (dddd, J = 1.3, 1.3, 1.3, 10.2 Hz, 1H),
5.39 (dddd, J = 1.3, 1.3, 1.3, 17.1 Hz, 1H), 5.33 (s, 2H), 5.85
(dddd, J = 6.4, 6.4, 10.2, 17.1 Hz, 1H), 7.5–8.1 (br, 2H), 8.23 (s,
2H). The 13C NMR (100 MHz, CD3CN) measurement was per-
formed using a mixture of two isomers 4e and 5e. δ 52.6 (CH2),
57.1 (CH), 57.7 (CH2), 61.5 (CH), 62.8 (CH), 119.9 (CH2), 119.9
(CH2), 123.8 (C), 124.1 (C), 124.9 (C), 134.0 (CH), 134.4 (CH),
142.8 (CH), 143.4 (CH), 145.1 (CH); HRMS (ESI/TOF) calcd for
C9H11N5O4 (M − H+): 252.0738, found: 252.0740; IR (KBr,
cm−1) 3278, 1610, 1423, 1334, 1215, 927.
X-Ray crystallographic analysis
Diffraction data were collected at 93 or 123 K under a cold N2-
gas stream using a Rigaku XtaLAB Synergy-S/Mo system (λ =
0.71073 Å (Mo-Kα)). The integrated data were analyzed using
the Olex2 crystallographic software package.20 The structures
were solved with the ShelXT structure solution program21
using Intrinsic Phasing and refined with the ShelXL refine-
ment package22 using least-squares minimization. Anisotropic
refinement was performed for all non-hydrogen atoms, and all
the hydrogen atoms were placed at the calculated positions.
Temperature dependent NMR spectra
1H NMR spectra were obtained by using the variable-tempera-
ture (VT) NMR technique. The sample solutions were stored at
−10–50 °C for over 12 h prior to the measurements.
2,6,9-Triaza-2,6-di(2-hydroxyethyl)-4,8-dinitro[3.3.1]nona-3,7-
diene (2f) and 2,6,9-triaza-2,9-di(2-hydroxyethyl)-4,8-dinitro
[3.3.1]nona-3,7-diene (3f)
Theoretical calculations
Density functional theory (DFT) calculations for 2a, 2d, 3a and
3d were conducted using Gaussian 16 W software (revision
A.03)23 using the restricted Becke three-parameter hybrid func-
tionals with the Lee–Yang–Parr correlation (RB3LYP)24,25 and
6-311+G(d,p) basis set.26,27 Ground-state geometries were opti-
mized and, then, the Gibbs energies of the molecules were cal-
culated. Solvation was considered using the conductor-like
polarizable continuum model.28,29
1
Brown solid, mp 68.1–70.7 °C. 2f; H NMR (400 MHz, CD3CN)
δ 2.8–3.0 (br, 1H), 3.0–3.3 (br, 2H), 3.44 (ddd, J = 3.8, 7.0,
14.2 Hz, 2H), 3.69 (ddd, J = 3.8, 6.0, 11.8 Hz, 2H), 3.77 (ddd, J =
3.4, 7.0, 11.8 Hz, 2H), 4.01 (ddd, J = 3.4, 6.0, 14.2 Hz, 2H), 5.71
(d, J = 1.0 Hz, 2H), 8.24 (s, 2H); 13C NMR (100 MHz, CD3CN)
δ57.4 (CH2), 61.5 (CH2), 63.3 (CH), 123.5 (C), 144.6 (CH). 3f; 1H
NMR (400 MHz, CD3CN) δ 2.49 (ddd, J = 5.2, 5.2, 13.7 Hz, 1H),
2.64 (ddd, J = 5.0, 5.0, 13.7 Hz, 1H), 2.9–3.1 (br, 1H), 3.0–3.3
(br, 1H), 3.5–3.8 (m, 5H, overlapped with signals of 3f), 3.97
(ddd, J = 3.3, 6.0, 14.7 Hz, 1H), 5.42 (d, J = 1.5 Hz, 1H), 5.61 (d,
Conflicts of interest
J = 1.5 Hz, 1H), 7.5–8.2 (br, 1H), 8.26 (s, 1H), 8.27 (s, 1H); 13C There are no conflicts to declare.
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15 D. L. Ostercamp and S. Wiles, J. Heterocycl. Chem., 2000,
37, 1357.
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