Green Synthesis of 1,3-Dibenzylimidazolidine-2,4,5-triones by Oxidation of Hexabenzylhexaazaisowurtzitanes

Article abstract of DOI:10.1002/jhet.2831

Herein, a novel and convenient procedure is described for the preparation of 1,3-dibenzylimidazolidine-2,4,5-triones. This method is based on a multi-stage oxidation of hexabenzylhexaazaisowurtzitanes by hydrogen peroxide in acetic acid, leading to the title compounds in relatively good yields.

Full text of DOI:10.1002/jhet.2831

Month 2017
Green Synthesis of 1,3-Dibenzylimidazolidine-2,4,5-triones by Oxidation
of Hexabenzylhexaazaisowurtzitanes
a
a
b
*
Ahmad Khorramabadi-zad, Mohammad Azadmanesh, and Yadollah Bayat
aFaculty of Chemistry, Bu-Ali Sina University, Hamedan 6517838695, Iran
bDepartment of Chemistry, Malek Ashtar University of Technology, P.O. Box 16765-3454, Tehran, Iran
*
E-mail: khoram@gmail.com
Additional Supporting Information may be found in the online version of this article.
Received September 12, 2016
DOI 10.1002/jhet.2831
Published online 00 Month 2017 in Wiley Online Library (wileyonlinelibrary.com).
Herein, a novel and convenient procedure is described for the preparation of 1,3-dibenzylimidazolidine-
2,4,5-triones. This method is based on a multi-stage oxidation of hexabenzylhexaazaisowurtzitanes by
hydrogen peroxide in acetic acid, leading to the title compounds in relatively good yields.
J. Heterocyclic Chem., 00, 00 (2017).
INTRODUCTION
reported without going into details. Because of the
importance of CL-20 in areas such as missile industry,
developing new procedures for its preparation may be of
economic value. One way to achieve CL-20 is to start with
hexaacetylhexaazaisowurtzitane (HAIW). This compound
has been prepared from HBIW through a costly, multi step,
and time-consuming reaction.
Therefore, direct conversion of HBIW into HAIW, by
the reaction of N-oxide intermediate with acetyl chloride
(through the presumed Polonovski rearrangement) was
attempted. For this purpose, HBIW was treated with
H2O2 in acetic acid. However, instead of the above said
intermediate, a white crystalline compound was formed,
which was found to be 1,3-dibenzylimidazolidine-2,4,5-
trione (Fig. 1, R=H). The successful synthesis of 1,3-
dibenzylimidazolidine-2,4,5-trione, prompted us to
prepare other derivatives of this compound. For this
purpose, three other derivatives of HBIW were
synthesized according to the procedure of Nielsen and
coworkers [16], and subjected to the above said oxidation
reaction (Fig. 1, R= 2-Cl, 4-CH3, 4-OCH3).
Five-membered rings containing two heteroatoms are
privileged structures with proven utility in medicinal
chemistry [1]. One example of such a heterocycle
comprises imidazoline and imidazolidine. Imidazolines
are biologically active pharmacophores and synthetic
intermediates in medicinal chemistry [2–12]. Another
member of this family is imidazolidine-2,4,5-trione
(commonly known as parabanic acid) and its derivatives;
they are used in preparation of alkylidene and imino-
substituted hydantoins by their reactions with Wittig
reagents [13]. Parabanic acid has a pronounced herbicidal
action, controlling the growth of unwanted plants.
Although parabanic acid, the main skeleton of the titled
compounds, is produced as a byproduct during synthesis of
1,1-diamino-2,2-dinitroethylene (DADE) as an energetic
material [14], few processes have been published for the
preparation of substituted parabanic acid and its
derivatives, for example, reaction of trimethylsilyl
cyanide with aryl isocyanates [15] and the reaction of
urea derivatives with oxalyl chloride [13].
It is interesting that in our laboratory, however, 1,3-
dibenzylimidazolidine-2,4,5-trione (a derivative of
parabanic acid sold at about 40 $ per 1mg), was
unexpectedly formed during oxidation of hexabenzyl-
hexaazaisowurtzitane (HBIW). The latter compound is
itself the very starting material for the synthesis of
hexanitrohexaazaisowurtzitane (also called HNIW and
CL-20). CL-20 is the most powerful explosive known
having higher performance than other conventional
explosives for which various synthesis methods have been
RESULTS AND DISCUSSION
As was mentioned earlier, our main purpose was to
synthesize HAIW from HBIW by Polonovski
rearrangement of the N-oxide intermediate in the
presence of acetyl chloride. However, instead of N-oxide
intermediate, the oxidation of HBIW led merely to a
crystalline compound which was confirmed to be 1,3-
dibenzylimidazolidine-2,4,5-trione.
© 2017 Wiley Periodicals, Inc.

A. Khorramabadi-zad, M. Azadmanesh, and Y. Bayat
Vol 000
Figure 1. Synthesis of 1,3-dibenzylimidazolidine-2,4,5-triones from HBIWs.
To explain this phenomenon, it is reasonable to first
consider the structure of HBIW. Its X-ray analysis shows
that C1–C7 bond length (Fig. 2, circled atoms) is longer
than normal sp3–sp3 carbon bond [17], which may be due
to the strained molecular skeleton of this compound
weakening the C1–C7 bond.
In addition, according to a previous report, the C1–C7
bond in HBIW is broken in the presence of CuCl2 (as a
mild oxidizing agent) in pyridine [18]. It is therefore
logical to conclude that the reaction may follow a similar
pathway in the presence of H2O2 and acetic acid (Fig. 3).
Furthermore, based on a reported oxidative cleavage of
HBIW in the presence of CAN [19], it is plausible that in
the first step of the proposed mechanism a dication
species (II) is formed. This dication is then hydroxylated
by H2O to III (step 2) which is itself oxidized to IV. In
the following steps, the remaining C―H bonds are
successively oxidized to C-OOAc ones (V), the oxidative
cleavage of which leads to the desired product (VI).
2,4,5-triones from HBIWs with good yields. H2O2/AcOH
mixture is equivalent to peracetic acid which is a strong
and benign oxidizing agent. The advantages of this
procedure over previously reported ones (which have
made use of an unsafe reagent such as oxalyl chloride
[13] or the highly toxic trimethylsilyl chloride [15]) are
that it is highly efficient and sustainable using a cheap,
easily available, green, and non-toxic environmentally
friendly reagent for defragmentation of HBIW and its
derivatives. In short, while highly expensive 1,3-
dibenzylimidazolidine-2,4,5-trione has been previously
prepared from urea and oxalyl chloride, it was shown that
this compound and its analogues could be synthesized
from corresponding HBIW derivatives.
EXPERIMENTAL
IR spectra were recorded using KBr. 1H NMR, 13C
NMR, and DEPT spectra were run in CDCl3. Mass
spectra were recorded on a Shimadzu QP 1100 BX Mass
Spectrometer All chemicals and solvents were purchased
and used as received. HBIW and its derivatives were
synthesized according to the procedure of Nielsen and
coworkers [16], primarily washed with ethanol and then
recrystallized from ethyl acetate. All spectral data of the
products are fully consistent with those of the reported
ones.
CONCLUSION
In summary, a new oxidation system (H2O2/AcOH) was
developed for the synthesis of 1,3-dibenzylimidazolidine-
General
procedure
for
the
synthesis
of
1,3-dibenzylimidazolidine-2,4,5-triones.
In 20 mL of
acetic acid, 10 mmol of HBIW was dissolved; the
reaction vessel was placed in ice bath into which was
poured 40 mL of 35% H2O2 by dropping funnel in
5 min. Reaction temperature was raised to 70°C during
5 h after which the solution color was changed from red
to orange. The mixture was then cooled to room
temperature, 30 mL of water was added, and the yellow
precipitate was collected and washed with two portions
of 20 mL of 50% ethanol. Recrystallizing the crude solid
in acetone/water (5/2) afforded white crystals (see
Table 1 for melting points and reaction yields).
Figure 2. HBIW structure.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2017
Green Synthesis of 1,3-Dibenzylimidazolidine-2,4,5-triones
Figure 3. Plausible mechanism for the oxidation of HBIW by H2O2/AcOH.
Spectral data of the unsubstituted product (Table 1,
entry 1) is fully compatible with the previously
reported ones [20]. The other derivatives of 1,3-
dibenzylimidazolidine-2,4,5-trione, synthesized by this
Spectral data of 1,3-dibenzylimidazolidine-2,4,5-trione
derivatives. 1,3-dibenzylimidazolidine-2,4,5-trione (2a).
1H-NMR (250 MHz, CDCl3) δ4.76 (s,4H), 7.25–7.38
(m,10H); 13C-NMR (62.5 MHz, CDCl3) δ43.0, 128.7,
129.0, 134.4, 153.4, 156.4; DEPT (135, CDCl3): 43.0
(CH2), 128.6, 129.0; MS (m/z): 294 (M+); IR (KBr, cmÀ1):
3032, 1728, 1448, 1412, 1146, 731, 696, 613, 562, 454.
1
procedure, were fully characterized by their H NMR,
13C NMR, IR, and Mass spectra (see vide infra and
supplementary document).
Table 1
Synthesis of 1,3-dibenzylimidazolidine-2,4,5-trione derivatives.
Entry
Ar
Product
Melting point (°C)
Yield (%)
1
2
3
4
C6H5
2-ClC6H4
4-CH3C6H4
4-OCH3C6H4
2a
2b
2c
2d
167–169
198–201
151–153
145–147
53
45
57
15
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

A. Khorramabadi-zad, M. Azadmanesh, and Y. Bayat
Vol 000
REFERENCES AND NOTES
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Acknowledgements. We gratefully acknowledge the support of
this work by the Research Council of Bu-Ali Sina University.
We specially thank Professor Issa Yavari (Tarbiat Modares
University, Tehran, Iran) for his highly fruitful discussions.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet