An effective and regioselective bromination of 1,4,5,8- naphthalenetetracarboxylic dianhydride using tribromoisocyanuric acid

Article abstract of DOI:10.1016/j.tetlet.2013.09.029

A highly efficient and cost-effective reagent for the bromination of 1,4,5,8-naphthalenetetracarboxylic dianhydride under mild reaction conditions is reported. Bromination of 1,4,5,8-naphthalenetetracarboxylic dianhydride using tribromoisocyanuric acid (TBCA) in concentrated H₂SO₄ is very effective and regioselective. 1,4,5,8-Naphthalenetetracarboxylic dianhydride was brominated smoothly under optimized reaction conditions to give mono-, di- and tetra-brominated products in good to excellent yields using TBCA. As a proof of principle, the potential of this bromination methodology is demonstrated by converting brominated naphthalenetetracarboxylic dianhydrides into N-imide and core functionalized 1,4,5,8-napthalenetetracarboxylic diimides by treating with n-butylamine to yield corresponding mono-, di- and tetra-(n-butylamino)-naphthalene diimides in good yields in one-step reactions.

Full text of DOI:10.1016/j.tetlet.2013.09.029

Tetrahedron Letters 54 (2013) 6314–6318
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
An effective and regioselective bromination of 1,4,5,8-naphthalene-
tetracarboxylic dianhydride using tribromoisocyanuric acid
⇑
Y. V. Suseela, M. Sasikumar, T. Govindaraju
Bioorganic Chemistry Laboratory, New Chemistry Unit, Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Jakkur P.O., Bangalore 560064, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 16 July 2013
Revised 5 September 2013
Accepted 11 September 2013
Available online 17 September 2013
A highly efficient and cost-effective reagent for the bromination of 1,4,5,8-naphthalenetetracarboxylic
dianhydride under mild reaction conditions is reported. Bromination of 1,4,5,8-naphthalenetetracarboxy-
lic dianhydride using tribromoisocyanuric acid (TBCA) in concentrated H2SO4 is very effective and regio-
selective. 1,4,5,8-Naphthalenetetracarboxylic dianhydride was brominated smoothly under optimized
reaction conditions to give mono-, di- and tetra-brominated products in good to excellent yields using
TBCA. As a proof of principle, the potential of this bromination methodology is demonstrated by
converting brominated naphthalenetetracarboxylic dianhydrides into N-imide and core functionalized
1,4,5,8-napthalenetetracarboxylic diimides by treating with n-butylamine to yield corresponding
mono-, di- and tetra-(n-butylamino)-naphthalene diimides in good yields in one-step reactions.
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Bromination
Tribromoisocyanauric acid
Naphthalene dianhydride
Core substitution
Naphthalene diimide
Fluorescence
Naphthalene diimides (NDIs) are the rapidly emerging class of
aromatic compounds with significant implications in organic, bio-
supramolecular chemistry, biomedicine and materials science ow-
ing to their remarkable electronic, spectroscopic and self-assembly
properties.1 The imide substituted NDIs and core substituted NDIs
(cNDIs) have been shown to have wide-ranging applications in the
field of supramolecular chemistry1,2 and biomedicine that is gener-
ation of nanostructures,2,3 DNA intercalation,4 supramolecular chi-
rality,5 artificial photosynthesis,6 self-cleaning,7 sensors,8 organic
solar cell applications,9 host–guest systems,10a,b synthetic ion
channels10c and n-type organic field effect transistors (OFETs).11
Functionalization through imide nitrogens or via core substitution
(substitution on the naphthalene core) produces analogues that al-
ter their electrical, optical and redox properties.12 Varying the nat-
ure of substituents either electron donating or withdrawing on
cNDIs has been shown to exhibit colourful rainbow fluorescence.13
The versatility in structure and properties of NDIs is responsible for
its wide spread application in various fields.
on NDIs including supramolecular chemistry, organic electronics
and biomedicine. Therefore developing an efficient and econom-
ical brominating reagent for the regioselective synthesis of bro-
mo-derivatives of NDA is of high priority. Various bromination
methods known till date in the literature for bromination of
NDA involve (i) molecular bromine as a brominating reagent in
the presence of catalytic amount of iodine either in oleum or mix-
ture of conc. H2SO4 and oleum as a solvent,14 (ii) use of sodium
bromide (NaBr) as a brominating agent in oleum15 and (iii) dibro-
moisocyanuric acid (DBI) in oleum as a source of bromine.16
However all these literature methods suffer from many draw-
backs like molecular bromine involved reactions produce low
yields and handling bromine is a difficult task due to its toxicity
and high vapour pressure. Moreover, hazardous and corrosive
nature of molecular bromine makes it difficult to handle as a bro-
minating reagent under milder reaction conditions. Furthermore,
prolonged reaction time and high reaction temperatures were
needed to carry out the reaction (i.e., the tetra-bromo NDA was
synthesized at 140 °C). The NaBr method required harsh reaction
conditions and a special equipment to carry out the reaction.15
DBI is highly expensive, not readily available in large quantities,
reactions were performed at high temperature (130 °C)16b and
gave mixture of brominated products.16d Moreover, purification
and isolation of the bromo-derivatives of NDA have not been de-
scribed with full details in the literature reports. All the above
discussed methods typically report purification and characteriza-
tion of bromo-derivatives of NDAs by converting them into corre-
sponding imides. These drawbacks further reiterate the need for
The bromo-derivatives of 1,4,5,8-naphthalenetetracarboxylic
dianhydride (NDA) serve as precursors for the preparation of
numerous functionalized NDIs. The area of NDIs has been wit-
nessing a rapid progress due to interesting properties and novel
functional applications of N-imide and core functionalized NDIs.
The availability of precursor materials in abundance to prepare
functionalized NDIs accelerates the ongoing research activities
⇑
Corresponding author.
E-mail address: tgraju@jncasr.ac.in (T. Govindaraju).
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.09.029

Y. V. Suseela et al. / Tetrahedron Letters 54 (2013) 6314–6318
6315
O
O
O
Br
O
O
1
O
O
a
O
O
O
O
O
O
O
O
Br
Br
Br
O
N
N
b
c
+
Br
O
N
Br
O
O
O
2
O
O
O
NDA
TBCA
O
Br
Br
Br
Br
O
O
O
3
Scheme 1. Reagents and conditions: (a) TBCA (0.5 equiv), concd H2SO4, rt, 8 h, 70%; (b) TBCA (1 equiv), concd H2SO4, rt, 12 h, 76%; (c) TBCA (2.5 equiv), concd H2SO4, rt, 8 h
then at 80 °C, 8 h, 87%.
Table 1
Optimized reaction conditions for the bromination of NDA using TBCA as a reagent.
Compound
TBCA (equiv)
aSolvent (mL)
Reaction time (h)
Reaction temperature (°C)
dCrude yield (%)
eYield after recrystallization (%)
1
2
3
0.5
1.0
2.5
25
25
25
8
brt
89
92
98
70
76
87
12
rt
b8 + c
8
rt and c80
aConcentrated H2SO4.
brt = room temperature.
cHeating.
dAfter product precipitation.
eRecrystallized from dimethylformamide.
developing an efficient brominating reagent for the rapid and
regioselective bromination of NDA to preferred bromo-products
in high yield and purity. In addition, research in our laboratory
is focused on exploring the potential of functionalized NDIs for
their self-assembly, optical and chiroptical properties with the
aim of developing biomimetic systems and materials for opto-
electronic, chiroptical and biomedical applications.2,5,7 Therefore
we intended to develop an efficient and regioselective bromina-
tion methodology to obtain mono-, di- and tetra-brominated
NDAs in high yield and purity. Recently, we have developed a
5,5-dimethyl-1,3-dibromohydantoin (DBH) reagent for the regio-
selective bromination of NDAs.17 However, the DBH method
requires relatively prolonged reaction times, fairly high reaction
temperature and excess brominating reagent to give bromo-
NDAs with relatively low yields. These shortcomings and our
desire to develop a superior bromination method for NDA in
terms of bromine-atom economy, reaction efficiency and cost
effectiveness motivated us to develop newer and effective bromi-
nating reagent. For this purpose we chose TBCA as the potential
brominating reagent due to its inexpensive synthesis from isoc-
yanuric acid ($22/25 g, www.sigma–aldrich.com) in large quanti-
ties and high atom-economy with respect to transferable
bromine atoms compared to other brominating reagents.
TBCA is a white solid which is less toxic and expected to be a
safe brominating reagent that can be easily synthesized in bulk
from isocyanuric acid and NaBr in the presence of OxoneÒ.18a TBCA
has been used for the bromination of simple alkenes and aromatic
substrates18 but has not been exploited for bromination of NDA.
Thus we performed bromination of NDA using TBCA which was
prepared by following the literature procedure18a and optimized
the reaction conditions for regioselective preparation of mono-,
di- and tetra-brominated NDA core. Further it should be noted that
TBCA is particularly advantageous because of high atom-economy
as it can transfer three Br+ to one substrate which accelerates the
rate of reaction compared to any currently used brominating re-
agents including dibromoisocyanuric acid (DBI). Easy and straight
forward synthesis of TBCA reagent18 in large quantity makes it
an industrially viable reagent for the bromination of NDA while
DBI is highly expensive and not readily available in bulk quantity.
The bromination reactions of NDA using TBCA were fast, required
low equivalents of TBCA and performed under milder conditions
compared to any other brominating reagent reported in the litera-
ture. Interestingly mono-, di- and tetra-bromination of NDA core
was performed at ambient conditions by varying equiv of TBCA.
It should be noted that the reaction time of tetra-bromination of
NDA was greatly reduced by heating the reaction mixture towards

6316
Y. V. Suseela et al. / Tetrahedron Letters 54 (2013) 6314–6318
C4H9
O
N
O
O
O
O
C4H9HN
Br
n-C4H9NH2
reflux, 10 h
O
N
O
O
O
O
O
O
C4H9
4
1
C4H9
N
O
O
O
NHC4H9
Br
n-C4H9NH2
reflux, 24 h
C4H9HN
Br
O
O
N
O
O
O
O
O
O
O
C4H9
5
2
C4H9
N
O
C4H9HN
C4H9HN
NHC4H9
NHC4H9
Br
Br
Br
Br
n-C4H9NH2
reflux, 32 h
O
N
O
O
O
O
C4H9
6
3
Scheme 2. Core substitution of bromo-NDAs (1–3) with n-butylamine (n-C4H9NH2).
the end. Thus TBCA is an efficient, economical, industrially viable
and ecofriendly reagent for the regioselective bromination of
NDA core.
was obtained by converting it into core substituted product as
discussed in the following sections. We believe that the observed
regioselective bromination of NDA using TBCA particularly in
dibromo-NDA 2 is attributed to (i) in highly deactivated NDA, the
potential bromination sites lie on opposite sides of the ring to give
stable and symmetrical product, (ii) first bromination deactivates
the potential bromination site on the same side and hence the next
bromination occurs on opposite side of the ring and (iii) interaction
of reagent (TBCA) and substrate (NDA) in regioselective transfer of
bromination cannot be neglected. Therefore, thorough investiga-
tion is necessary to understand the mechanism of observed
bromination regioselectivity in NDA.
The mono-, di- and tetra-bromo-NDAs were prepared as shown
in Scheme 1.19 The reaction conditions were optimized by varying
the equivalents of TBCA and reaction time as shown in Table 1.
NDA was treated with TBCA (0.5 equiv) in 98% H2SO4 at room tem-
perature for 8 h in a stoppered round bottomed flask (100 mL). The
reaction afforded crude product consisting of mainly 2-bromo-
NDA (1), trace of dibromo-NDA (2) and unreacted starting material.
The crude product was recrystallized in dimethylformamide to
obtain 120 in 70% yield (Scheme 1). Reaction of NDA and 1 equiv
of TBCA in 98% H2SO4 at room temperature for 12 h gave crude
product which was further recrystallized in dimethylformamide
to obtain 2,6-dibromo-NDA 221 in 76% yield. The purity and
integrity of the product were further confirmed by converting
Imide and core substitution of brominated NDAs
Imide (N,N0) substitution of NDA improves solubility, aggrega-
tion and intermolecular packing in the solid state of resulting NDIs.
However, imide substituents of NDI have relatively less influence
on the optical and electronic properties, while naphthalene core
substitution in NDI facilitates the tuning of optical and electronic
properties. Therefore imide and core substitutions cooperatively
act together to impart various properties as discussed above to
the NDI molecular system.
Here we demonstrate the utility of our new brominating re-
agent (TBCA) by carrying out the imide and core substitution of
brominated NDAs (1–3) with n-butylamine as outlined in
Scheme 2.23 Monobromo-NDA 1 in n-butylamine was refluxed
for 10 h to obtain N,N0-bis-(n-butyl)-2-(n-butylamino)-NDI (4)24
2,6-dibromo-NDA
2
into corresponding N,N0-bis-(n-butyl)-2,6-
di(n-butylamino)-1,4,5,8-naphthalenetetracarboxylic diimide (5).
Our effort in synthesizing tribromo-NDA was not fruitful, as this
compound is highly unstable and instantaneously converted to
more stable and symmetrical tetrabromo-NDA. Tetrabromination
of NDA was carried out in 98% sulphuric acid with 2.5 equiv of
TBCA at room temperature for 8 h and at 80 °C for 8 h to give
2,3,6,7-tetrabromo-NDA (3)22 in 87% yield. The product was
recrystallized in DMF to obtain pure tetrabromo-NDA 3. The 1H
NMR spectrum (DMSO-d6) did not show any proton signals, indi-
cating the absence of mono- and di-brominated compounds in
the product. Additional confirmation for the tetrabromo-NDA 3

Y. V. Suseela et al. / Tetrahedron Letters 54 (2013) 6314–6318
6317
(b)
(a)
4
5
6
4
5
6
1.0
0.8
0.6
0.4
0.2
0.0
1.0
0.8
0.6
0.4
0.2
0.0
300 400 500 600 700
Wavelength (nm)
550 600 650 700 750
Wavelength (nm)
(d)
(c)
4
6
5
5
6
4
Figure 1. (a) UV–vis absorption spectra of core substituted NDIs 4–6 in chloroform. (b) Normalized emission spectra of NDIs 4–6 (kex = 497, 577 and 600 nm respectively). (c)
Photographs of solutions of NDIs 4–6 in chloroform (red, blue and green respectively) under day light. (d) Photographs of solutions of NDIs 4–6 in chloroform show bright
fluorescence emission under UV-light (365 nm).
in good yield. Similarly, dibromo- and tetra-bromo-NDAs 2 and 3
in n-butylamine were refluxed for 24 and 32 h respectively to
obtain corresponding imide and core substituted NDIs 525 and
626 in good to moderate yields.
commercially available, straightforward and single-step large
scale synthesis from abundant and least expensive isocyanuric
acid makes it the most economical reagent for bromination of
NDA. The cost effectiveness of the reagent along with relatively
high rate of reaction, simple procedure and excellent yields make
this a preferred methodology for the synthesis of mono-, di- and
tetrabromo-derivatives of NDA. The significance of the TBCA-bro-
mination method worth mentioning includes high conversions,
mild reaction conditions, short reaction times, regioselectivity
and product isolation through generally preferred recrystalliza-
tion technique in high purity. The TBCA-bromination method
provides easy access to large scale preparation (industrially via-
ble) of bromo-NDAs which are utilized for the construction of di-
verse functionalized NDIs. As a proof of principle we have
demonstrated the effect of core substitution with electron donat-
ing groups which tune the absorption and emission of NDI over a
wide visible spectral range. This method can be exploited for the
bromination of various other aromatic systems. Our future work
will be focused on understanding the bromination regiochemistry
in NDA.
The optical properties of NDIs are mainly influenced by the core
substitution. We studied UV–vis absorbance and fluorescence
spectral properties of core substituted NDIs 4, 5 and 6 (Fig. 1). NDIs
4 and 5 with one and two core substituted n-butylamine respec-
tively exhibited band I absorption in the region 300–400 nm. The
NDI 6 with four n-butylamino substituents on the core interest-
ingly showed band I absorption at 458 nm with red-shift of 88
and 94 nm from band I absorption of NDI 4 and 5 respectively.
Moreover, NDIs 4, 5 and 6 showed new absorption bands in the
visible region with kmax at 526, 618 and 638 nm respectively
(Fig. 1a). These new absorption bands of 4–6 cover most of the
visible region of the electromagnetic spectrum. Interestingly, NDIs
5 and 6 displayed a remarkable bathchromic-shift of 92 and
112 nm compared to mono-n-butylamino- substituted NDI 4
confirming the effect of increase in number of electron-donating
substituents on the naphthalene core. The solutions of core substi-
tuted NDIs 4–6 upon excitation with wavelengths corresponding
to their new absorption bands (497, 577, and 600 nm respectively)
as shown in Figure 1a exhibited bright fluorescence emission with
emission maxima at 561, 655 and 692 nm respectively (Fig. 1b).
Solutions of NDIs 4–6 in chloroform exhibited bright colours
(red, blue and green respectively) visible to naked eye under day
light due to absorption in the visible region (Fig. 1c). Similarly,
these solutions exhibited bright fluorescence colours (yellow, red
and blue respectively) under UV-light (365 nm) as shown in Fig-
ure 1d. Thus, absorption and emission wavelengths of NDIs can
be tuned in wide visible spectral region by varying electron donat-
ing alkylamino core substituents. The absorbance and fluorescence
data of NDI 4–6 were found to be in agreement with the NDIs
substituted with n-octylamine reported in the literature.16a,f This
study further confirms the utility of our TBCA bromination method
to access core substituted NDIs which subsequently tune the
electronic and optical properties of NDI molecular system.
Acknowledgments
Authors thank Professor C.N.R. Rao FRS for constant support,
JNCASR, DBT-IYBA (BT/03/IYBA/2010), Govt. of India, New Delhi,
for financial support.
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2011, 44, 4721.
12. (a) Jones, B. A.; Facchetti, A.; Marks, T. J.; Wasielewski, M. R. Chem. Mater. 2007,
19, 2703–2705; (b) Hu, Y.; Gao, X.; Di, C.-A.; Yang, X.; Zhang, F.; Liu, Y.; Li, H.;
Zhu, D. Chem. Mater. 2011, 23, 1204–1215; (c) Oh, J. H.; Suraru, S.-L.; Lee, W.-Y.;
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C
14H3BrO6.
21. Compound 2: Dibromo-NDA 2 obtained as pale yellow solid (crude yield 3.91 g,
92%), which was recrystallized from DMF to obtain the pure product as white
crystals (2.42 g, 76%). IR (KBr, cmꢀ1): 1787, 1733, 1191, 1172, 1150, 1093, 985,
936; 1H NMR (400 MHz, DMSO-d6): 1H NMR (400 MHz, DMSO-d6): dH 8.78 (s,
2H); 13C NMR (100 MHz, DMSO-d6): dC157.9, 156.4, 137.5, 129.4, 127.4, 124.2,
123.4. Elemental analysis. Found: C, 39.42; H, 0.45%; Calcd: C, 39.47; H, 0.47%
for C14H2Br2O6.
22. Compound 3: Tetrabromo-NDA 3 obtained as pale yellow solid (crude 5.72 g,
98%), which was recrystallized from DMF to obtain the pure product as white
crystals (5.07 g, 87%). IR (KBr, cmꢀ1): 1787, 1733, 1507, 1499, 1421, 1373,
1335, 1188, 1146, 1096, 988, 937, 778, 702, 570; Elemental analysis. Found: C,
28.67%; Calcd: C, 28.80% for C14Br4O6.
23. General procedure for one-step synthesis of imide and core substituted NDIs(4–6):
The mono-, di- and tetra-brominated NDA compounds 1–3 (2 mmol each)in n-
butylamine were refluxed under nitrogen atmosphere for 10, 24 and 32 h
respectively. The reaction progress was monitored by thin layer
chromatography (TLC). After completion of the reaction, excess n-butylamine
was removed on rotary evaporator and the products were purified by column
chromatography on silica gel (100–200 mesh) to obtain imide and core
functionalized NDIs 4, 5, and
6 with overall 60%, 50% and 46% yields
respectively.
24. Compound 4: IR (CHCl3, cmꢀ1): 3254, 2959, 2926, 2854, 1704, 1673, 1634,
1589, 1519, 1460, 1324, 1016, 786; 1H NMR (400 MHz, CDCl3): dH 10.13 (broad
t, 1H, N–H), 8.66–8.64 (d, J = 8 Hz, 1H, Ar-H), 8.35–8.33 (d, J = 8 Hz, 1H, Ar-H),
8.22 (s, 1H, Ar-H), 4.21–4.15 (m, 4H, 2CH2), 3.61–3.56 (q, J = 6.8 Hz, 2H, CH2),
1.86–1.78 (quin, J = 7.2 Hz, 2H, CH2), 1.75–1.68 (quin, J = 7.2 Hz, 4H, 2CH2),
1.49–1.28 (m, 6H, 3CH2), 1.04–0.97 (m, 9H, 3CH3); 13C NMR (100 MHz, CDCl3):
dC 166.4, 163.5, 163.24, 163.22, 152.5, 131.4, 129.7, 128.1, 126.3, 124.5, 123.7,
119.9, 119.5, 99.9, 43.1, 40.8, 40.3, 31.6, 30.3, 20.6, 20.4, 20.3, 14.0, 13.95,
13.92; HRMS (APCI) (m/z): calcd for C26H31N3O4 [M+H]+, 450.2393, found
450.2395.
13. (a) Sakai, N.; Mareda, J.; Vauthey, E.; Matile, S. Chem. Commun. 2010, 4225–
4237.
14. (a) Jacquignon, P.; Buu-Hoi, N. P.; Mangane, M. Bull. Soc. Chim. Fr. 1964, 10,
2517–2523; (b) Gao, X.; Qiu, W.; Yang, X.; Liu, Y.; Wang, Y.; Zhang, H.; Qi, T.;
Liu, Y.; Lu, K.; Du, C.; Shuai, Z.; Yui, G.; Zhu, D. Org. Lett. 2007, 9, 3917–3920; (c)
Piyakulawat, P.; Keawprajak, A.; Chindaduang, A.; Hanusch, M.; Asawapirom,
U. Synth. Metals 2009, 159, 467–472.
15. Bell, T. D. M.; Yap, S.; Jani, C. H.; Bhosale, S. V.; Hofkens, J.; Schryver, F. C. D.;
Langford, S. J.; Ghiggino, K. P. Chem. Asian J. 2009, 4, 1542–1550.
16. (a) Thalacker, C.; Roger, C.; Würthner, F. J. Org. Chem. 2006, 71, 8098–8105; (b)
Chaignon, F.; Falkenstrom, M.; Karlsson, S.; Blart, E.; Odobel, F.; Hammarstrom,
L. Chem. Commun. 2007, 64–66; (c) Krüger, H.; Janietz, S.; Sainova, D.; Dobreva,
D.; Koch, N.; Vollmer, A. Adv. Funct. Mater. 2007, 17, 3715–3723; (d) Kishore, R.
S. K.; Ravikumar, V.; Bernardinelli, G.; Sakai, N.; Matile, S. J. Org. Chem. 2008, 73,
738–740; (e) Doria, F.; Marco di Antonio, M. D.; Michele Benotti, M.; Daniela
Verga, D.; Freccero, M. J. Org. Chem. 2009, 74, 8616–8625; (f) Guo, S.; Wu, W.;
Guo, H.; Zhao, J. J. Org. Chem. 2012, 77, 3933–3943.
25. Compound 5: IR (CHCl3, cmꢀ1): 3286, 2959, 2926, 2854, 1679, 1632, 1596,
1489, 1465, 1320, 1209, 789; 1H NMR (400 MHz, CDCl3): dH9.33-9.30 (t,
J = 5.1 Hz, 2H, N–H), 8.10 (s, 2H, Ar-H), 4.18–4.14 (t, J = 8 Hz, 4H, 2CH2), 3.51–
3.46 (q, J = 6.8 Hz, 4H, 2CH2), 1.83–1.75 (quin, J = 7.2 Hz, 4H, 2CH2), 1.74–1.66
(m, 4H, 2CH2), 1.56–1.41 (m, 8H, 4CH2), 1.03–0.97 (m, 12H, 4CH3); 13C NMR
(100 MHz, CDCl3): dC 166.2, 163.1, 149.2, 125.8, 121.1, 118.3, 101.8, 43.0, 40.3,
31.6, 30.3, 29.8, 20.6, 20.4, 14.0, 13.9; HRMS (APCI) (m/z): calcd for C30H40N4O4
[M+H]+, 521.3128, found 521.3127.
26. Compound 6: IR (CHCl3, cmꢀ1): 3274, 2961, 2916, 2850, 1645, 1629, 1577,
1462, 1263, 1093, 1026, 798; 1H NMR (400 MHz, CDCl3): dH9.38 (broad t, 4H),
4.23–4.19 (t, J = 7.6 Hz, 4H, 2CH2), 3.41–3.36 (q, J = 6.7 Hz, 8H, 4CH2), 2.06–2.01
(m, 24H, 12CH2), 1.01–0.97 (t, 18H, 6CH3); 13C NMR (100 MHz, CDCl3): dC
166.1, 139.4, 114.2, 108.05, 44.9, 40.2, 33.9, 33.5, 32.0, 29.3, 29.1, 22.8, 14.2,
14.1, 14.0; HRMS (APCI) (m/z): calcd. for C38H58N6O4 [M+H]+, 663.4598, found
663.4563.
17. Sasikumar, M.; Suseela, Y. V.; Govindaraju, T. Asian J. Org. Chem. 2013, 2, 779–
785.
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1518; (b) de Almeida, L. S.; Esteves, P. M.; de Mattos, M. C. S. Synthesis 2006,
221–223.