Competitive one-pot reactions: Simultaneous synthesis of decahydroacridine-1,8-diones and 1,8-dioxo-octahydroxanthenes and photophysical characterization

Article abstract of DOI:10.1080/00397911.2013.831903

A simple and convenient one-pot method for simultaneously obtaining decahydroacridine-1,8-diones and 1,8-dioxo-octahydroxanthene derivatives is described. A high conversion yielding both products was obtained under the reaction conditions. To understand the optical behavior of the model compounds and their potential use as antenna moieties in bichromophoric systems, the photophysical properties of all samples were studied using ultraviolet-visible absorption and steady-state fluorescence spectroscopy in methanol solutions. For the case of the acridinediones, the fluorescence spectra were found to exhibit the typical emission profile of the locally excited state, whereas, contrary to previous published experimental results, reliable fluorescence emission spectra for the xanthenes derivatives could not be obtained. On the other hand, the poor quantum yields of the synthesized decahydroacridine-1,8-diones were explained based on the benzene-like substitution effect, which favors the intersystem crossing relaxation mechanism. [Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications for the following free supplemental resource(s): Full experimental and spectral details.] Copyright

Full text of DOI:10.1080/00397911.2013.831903

Synthetic Communications1, 44: 648–659, 2014
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2013.831903
COMPETITIVE ONE-POT REACTIONS: SIMULTANEOUS
SYNTHESIS OF DECAHYDROACRIDINE-1,8-DIONES
AND 1,8-DIOXO-OCTAHYDROXANTHENES AND
PHOTOPHYSICAL CHARACTERIZATION
Sugey M. Martinez Gomez,1 Diego M. Alzate Sanchez,1
2
William Rodrıguez-Cordoba, Cesar A. Sierra, and
1
´
´
Cristian Ochoa-Puentes1
1
´
Departamento de Quımica, Universidad Nacional de Colombia,
´
Bogota, Colombia
Escuela de Fısica, Universidad Nacional de Colombia Sede Medellın,
2
´
´
´
Medellın, Colombia
GRAPHICAL ABSTRACT
Abstract
A simple and convenient one-pot method for simultaneously obtaining
decahydroacridine-1,8-diones and 1,8-dioxo-octahydroxanthene derivatives is described. A
high conversion yielding both products was obtained under the reaction conditions. To
understand the optical behavior of the model compounds and their potential use as antenna
moieties in bichromophoric systems, the photophysical properties of all samples were stud-
ied using ultraviolet–visible absorption and steady-state fluorescence spectroscopy in meth-
anol solutions. For the case of the acridinediones, the fluorescence spectra were found to
exhibit the typical emission profile of the locally excited state, whereas, contrary to previous
published experimental results, reliable fluorescence emission spectra for the xanthenes
derivatives could not be obtained. On the other hand, the poor quantum yields of the synthe-
sized decahydroacridine-1,8-diones were explained based on the benzene-like substitution
effect, which favors the intersystem crossing relaxation mechanism.
[Supplementary materials are available for this article. Go to the publisher’s online
edition of Synthetic Communications1 for the following free supplemental resource(s):
Full experimental and spectral details.]
Keywords Acridinediones; one-pot-synthesis; photophysical characterization; xanthenes
Received June 13, 2013.
Address correspondence to Cristian Ochoa-Puentes, Departamento de Quımica, Universidad
´
´
Nacional de Colombia, Bogota, D.C., Colombia. E-mail: cochoapu@unal.edu.co
648

ACRIDINEDIONES DIOXO-OCTAHYDROXANTHENES
649
INTRODUCTION
During recent decades, a large number of studies have been focused on the
development of new classes of laser dyes. Among the new fluorophores developed,
acridinedione and xanthene dyes have emerged as new materials with advance
optical properties.[1–3] Specifically, acridinedione and xanthenes derivatives, includ-
ing rhodamines and fluoresceins, have lasing efficiency comparable to the well-know
standard, coumarin-102. The most important photophysical properties of these dyes
include high extinction coefficients in the ultraviolet–visible (UV-vis), excellent quan-
tum yields, great photostability, and relatively long emission wavelengths. All these
features make these systems highly favorable dyes to be used as light receptors or
antennas in the synthesis of new multichromophore compounds.[4]
Acridones and acridinediones are well-known nitrogenated heterocycles in
which one or two carbonyl groups are attached to the structure. Acridinedione dyes
act as both electron donors and acceptors because of their bichromophoric structure,
which include both the heterocyclic nitrogen and the carbonyl groups.[5–13] Addition-
ally, depending on the chemical structure, these dyes can undergo interesting
reactions in the excited states including excited-state intramolecular proton
transfer,[14–19] energy transfer,[20] and intramolecular charge transfer.[21] The photo-
physical and photochemical properties of several acridinedione dyes in solution
and in poly(methyl methacrylate) (PMMA) matrix have been extensively investi-
gated.[13,17,21–23] Several reports show that these heterocycles present a broad range
of biological activities[24–27] as well as applications in bioanalytical chemistry as
fluorescent probes.[28] Within this class of compounds, the 9-aryl-decahydroacridine-
1,8-dione derivatives have emerged as very interesting systems not only because of
easy synthesis and biological activity as SITR1 inhibitors,[29] DNA intercalator,[30]
calcium,[31] and potassium[32,33] channel modulators but also for their photophysical
and photochemical properties. Additionally, the acridinedione derivatives have been
widely used as chemosensors,[34,35] as laser dyes,[2,36,37] as initiators in photopoly-
merization,[38,39] in the preparation of blue light-emitting devises,[40] in dye-sensitized
solar cells,[41] and as fluorescent probes for monitoring of polymerization
processes.[42] These dyes are also important because of their structural similarity to
the coenzyme nicotinamide adenine dinucleotide (NADH), which acts as a coenzyme
in biological systems.[9,43–46]
The synthesis of these derivatives usually involves the reaction of dimedone or
1,3-ciclohexanedione with aromatic or aliphatic aldehydes and a source of nitrogen
in a stepwise sequence reaction or in a one-pot multicomponent reaction. In the first
methodology, two equivalents of the cyclic diketone is condensed with one equiva-
lent of the aldehyde to form a tetraketone 1, which reacts with an amine to yield
the decahydroacridine-1,8-dione derivative 2[2] (Scheme 1). Furthermore, in the mul-
ticomponent reaction approach, conventional heating using different solvents and
catalyst such as HCl,[47] CeCl3 ꢀ 7H2O,[48] ambelyst 15,[49] p-dodecylbenezenesulfonic
acid,[50] and ceric ammonium nitrate (CAN)[51] have been reported. Alternative pro-
cedures involve the use of microwave irradiation,[52] ionic liquids,[53] and solvent-free
reactions.[54]
On the other hand, xanthenes are a very interesting class of oxygen-containing
heterocycles. In particular, the 1,8-dioxo-octahydroxanthenes have shown potential

650
S. M. M. GOMEZ ET AL.
Scheme 1. Synthetic procedures commonly used for the synthesis of decahydroacridine-1,8-diones and
1,8-dioxo-octahydroxanthenes.
in different applications both in the field of medicinal chemistry[55] and materials
science.[56] As in the synthesis of decahydroacridine-1,8-dione derivatives, the syn-
thesis of 1,8-dioxo-octahydroxanthenes 3 is commonly performed by the conden-
sation of the appropriate aldehyde and dimedone or 1,3-ciclohexanedione
(Scheme 1). Several synthetic procedures with solvent-free conditions using different
catalysts,[57–63] ionic liquids,[53,64–66] homogeneous[67,68] and heterogeneous[69–73]
catalysts, and microwave-[74] and ultrasound- assisted[75–77] synthesis have been
reported.
During recent years, our research group has been interested in developing
efficient synthetic routes that allow us to obtain different laser dyes based on the
acridinedione and=or xanthenes dyes and use them to photosensitize macromolecu-
lar systems. The indirect electronic excitation of a molecular system through auxili-
ary chromophores is of great importance for light-harvesting applications. For
example, recently, we have reported a photoinduced energy transfer study in bichro-
mophoric pyrene– phenylenevinylene (PV) systems (antenna–bridge–acceptor
systems with variable length) and showed that the energy-transfer process is
especially efficient in systems where the linker is formed by eight atoms.[78] In this
preliminary work we explore the possibility of using heterocyclic compounds to per-
form a study in which the heterocycle can be used as antenna in a multichromopho-
ric system. Taking into account that the acridinedione dyes operate in the blue-green
region of the UV-vis spectrum and their efficient lasing yield, we believe that these
systems can be used as light receptors in the synthesis of new multichromophore oli-
gomers derived from PV. In this study, we report both the unexpected results
obtained with the one-pot method for the synthesis and the steady-state spectro-
scopy for 9-aryl-decahydroacridine-1,8-diones.
RESULTS AND DISCUSSION
To obtain a set of 9-aryl-decahydroacridine-1,8-dione derivatives, we perfor-
med the synthesis of the desired molecules using dimedone as cyclic diketone. Our
synthetic methodology was based on the reaction of aromatic aldehydes, dimedone,

ACRIDINEDIONES DIOXO-OCTAHYDROXANTHENES
651
and benzylamine via one-pot, three-component reaction synthesis under conven-
tional heating using acetic acid as solvent. Initially, benzaldehyde (1 eq.), dimedone
(2 eq.), and benzylamine (1 eq.) were mixed in 10 mL of acetic acid. The progress of
the reaction was monitored by thin-layer chromatography (TLC) and the mixture
was refluxed until the starting materials were consumed. After completion of
reaction, the product was purified by chromatography on silica gel using ethyl
acetate–n-hexane 2:3 as eluent to give two compounds.
The structure of the first compound isolated, labeled as 8a, was elucidated
by Fourier transform–infrared (FT-IR), 1H NMR, 13C NMR, and gas
chromatography–mass spectrometry (GCMS). FT-IR spectra showed characteristic
absorptions between 2957 and 3000 cmꢁ1, which were assigned for the aromatic
rings, while absorptions between 2928 and 2868 cmꢁ1 were attributed to asymmetric
and symmetric aliphatic stretches. The carbonyl group was remarked at a strong
1
stretch absorption in 1632 cmꢁ1. In the H NMR spectra the signals corresponding
to the aromatic protons from the phenyl and benzyl ring are located at 7.15–7.20 and
7.28–7.41 ppm, respectively. Two singlets at 5.34 and 4.90 ppm were assigned to pro-
tons at C9 and the CH2 in the benzyl group, respectively. Signals at 2.30–2.49 and
2.19 ppm were assigned to protons at C4, C5 and C2, C7. The signals observed at
0.99 and 0.88 ppm correspond to the methyl protons. 13C NMR spectra showed
characteristic peaks at 195.6 ppm for the carbonyl group and 125.4–145.8 ppm for
=
the aromatic substituent. Signals at 150.5 and 115.4 ppm were attributed to C C
in the pyridyl core, while peaks at 50.0 and 48.8 ppm were assigned to the carbon
atoms at C2, C7, and the CH2 of the benzyl group respectively. The remaining sig-
nals correspond to C4, C5 at 40.2 ppm, quaternary carbons C3, C6 at 32.7 ppm,
methine carbon C9 at 32.1 ppm, and methyl carbons of dimedone at 28.4 and
28.2 ppm. The mass spectra showed the corresponding molecular ion peak at 439
(40%). All this information supports the desired acridinedione 8a.
1
For the second compound labeled as 10a, the H NMR spectra showed three
aromatic signals between 7.21 and 7.03 ppm corresponding to five aromatic protons,
two singlets at 4.08 ppm and 2.39 ppm corresponding to one and four protons
respectively, a double doublet at 2.13 ppm for four protons, and two singlets at
1.03 and 0.92 ppm for six protons each. The 13C NMR spectra showed seven peaks
between 196.5 and 115.8 ppm and six peaks between 50.9 and 27.5 ppm for each one
of the nonequivalent carbons present in 10a. FT-IR spectra for this compound
showed absorptions between 3032 and 3061 cmꢁ1, which were assigned for the
aromatic rings.
Absorptions between 2956 and 2854 cmꢁ1 were attributed to asymmetric and
symmetric aliphatic stretches. A strong stretch absorption band at 1662 cmꢁ1 was
assigned to a cyclic carbonyl group. The mass spectra exhibited a molecular ion peak
at 350 (71%). All this information indicates that the structure of the compound cor-
responds to the octahydroxanthene 10a. These results show that under the reaction
conditions two competitive processes occur simultaneously: the formation of the
decahydroacridine-1,8-dione 8a and the formation the of 1,8-dioxo-octahydrox-
anthene derivative 10a. The obtention of the first heterocycle can be explained by
the mechanism proposed by Shi et al.[79] and Rostamizadeh et al.[54] According
to the proposed mechanism, one equivalent of dimedone reacts with benzylamine
to yield the enamine 4. The second equivalent of dimedone reacts with benzaldehyde to

652
S. M. M. GOMEZ ET AL.
Scheme 2. Mechanism proposed to obtain 8a.
yield the condensation intermediate 5, which undergoes a Michael addition with 4, afford-
ing the intermediate 6. Then isomerization of intermediate 6 occurred to give 7, which after
an intramolecular cyclization and dehydration yields the product 8a (Scheme 2).
Similarly, obtaining the octahydroxantene can be explained by the mechanism
proposed by Kantevari et al.[59] and Verma et al.[62] in which the enol form of the dime-
done reacts with benzaldehyde to give the Knoevenagel adduct 5. Then 5 may further
undergo Michael addition with another molecule of dimedone to form the intermediate
9, which after a dehydration reaction yields the compound 10a (Scheme 3).
Based on these results we concluded that this methodology may allow us to
obtain two heterocyclic compounds in one single procedure. Then, following the same
procedure described before for obtaining compounds 8a and 10a, we performed the
synthesis of a set of structural analogs, obtaining always both the target acridine-1,8-
dione and the octahydroxantene. The results are summarized in Scheme 4.
Steady-State Spectroscopy
Because of the extended electronic conjugation both products are expected to
exhibit optical properties according to the literature reports of analogous systems,[62]
and therefore, it was important to perform a study of the photophysical character-
ization of the acridinediones and the xanthenes. The steady-state absorption and
emission spectra of compounds 8a–e in methanol solutions are shown in Figs. 1
and 2. The absorption spectra of the different acridinedione derivates show an
Scheme 3. Mechanism proposed to obtain 10a.

ACRIDINEDIONES DIOXO-OCTAHYDROXANTHENES
653
Scheme 4. Simultaneous one-pot synthesis of decahydroacridine-1,8-diones 8a–e and 1,8-dioxo-
octahydroxanthenes 10a–e.
intense broad band at 350–425 nm. This band has been assigned to the intramolecu-
lar charge-transfer (ICT) due to the transfer of charge from the ring nitrogen to the
carbonyl oxygen in the acridinedione fluorophore.[80] The rigid structure of the acri-
dinediones favors the charge-transfer transition, which is sensitive to the solvent
environment as reported by Srividya et al.[80] The absorption spectra of the acridine-
diones 8b–e do not display any significant change in the shape and position relative
to the absorption spectrum of 8a, maintaining the characteristic broad band despite
the different substituents on the phenyl ring.
The emission spectra of the acridinediones 8a–e in methanol solutions were
recorded using an excitation wavelength tuned at the ICT band. The fluorescence
spectra of the acridinediones (Fig. 2) exhibit a single structureless broad band with
a maximum approximately at 430 nm that has been assigned to the emission of the
local excited state.[81] In contrast to the absorption spectrum, the position of the
emission band is shifted depending on the nature of the substituent over the phenyl
moiety. Also, it is well known that the position of the emission band is red shifted
with increasing the solvent polarity.[10] This result indicates that the charge-transfer
excited state is stabilized in polar media. The absorption, emission, and Stokes shift
values for all the compounds in methanol are given in Table 1.
Figure 3 shows the absorption spectra of the xanthene derivates 10a–e in
methanol solutions. In general, the UV–vis absorption spectra of the substituted
Figure 1. Absorption spectra for the acridinedione derivates 8a–e.

654
S. M. M. GOMEZ ET AL.
Figure 2. Emission spectra for the acridinedione derivates 8a–e.
1,8-dioxo-octahydroxanthenes show an intense band around 260–314 nm, very
short-wavelength spectral range compared with the absorption spectra of standard
xanthene derivatives such as rhodamine and fluorescein derivatives. These differ-
ences can be explained based on the different degree of conjugation between the
octahydroxanthenes and xanthenes. Additionally, as can be observed in Fig. 3, the
absorption spectrum of compound 10e extends to longer wavelengths and shows a
shoulder at 360 nm.
On the other hand, reliable emission spectra from the 1,8-dioxo-
octahydroxanthenes 10a–e in methanol solution could not be obtained. This contra-
dicts the early report of Verma et al.,[62] who detected fluorescence emission for
compounds 10a–d in several solvents, including methanol, tetrahydrofuran, cyclohex-
ane, and acetonitrile. After performing careful unsuccessful attempts to detect fluores-
cence in all these solvents, and based on the previously reported spectroscopic
data[59,64,73] and our NMR spectra, mass spectrometry, and FTIR data that clearly
proved chemical structure of the 1,8-dioxo-octahydroxanthenes 10a–e, we can assume
that the emission spectra in that report could be due to the presence of some impurities.
Quantum Yield of Fluorescence
The fluorescence quantum yields (Qy) in methanol for all the acridinediones
are given in Table 1. As can be observed, the quantum yield values of the acridine-
diones 8a–e are between 0.04 and 0.18. According to literature reports, acridine-
diones with N-H or N-CH3 functional groups present quantum yields of about
Table 1. Optical properties of the acridinediones 8a–e in methanol solution
Compound Absorption kmax (nm) Emission kmax (nm) Quantum yield (U) Stokes shift (cmꢁ1
)
8a
8b
8c
8d
8e
373
380
378
375
381
443
440
424
438
422
0.10
0.06
0.18
0.05
0.04
4236
3588
2870
3836
2550

ACRIDINEDIONES DIOXO-OCTAHYDROXANTHENES
655
Figure 3. Absorption spectra of xanthene derivates 10a–e.
0.9, whereas, modification either on the nitrogen or in the carbon at the 9-position
with aromatic groups results in a considerable decrease of the Qy. These results have
been explained by Srividya et al.[10] based on the well-known behavior of the substi-
tution with benzene-like groups, which favor the intersystem crossing relaxation
mechanism, and therefore, result in systems with greater triplet yields. Also, it is
important to note that all the acridinediones synthesized in this work have a benzyl
substituent in the nitrogen atom, which can increase the efficiency of the singlet-
triplet transition. Finally, the lower fluorescence quantum yield of acridinediones
8b, 8d, and 8e compared to 8a and 8c is also attributed to the presence of
electron-donating (ED) methoxy and chloride groups in the para-position of the
phenyl ring.[16] The presence of these ED groups results in the photoinduced electron
transfer process through space between –OCH3 or –Cl group and the acridinedione
moiety, as has been shown by Rajendran et al.[18] The low Qy values presented in
Table 1 agree very well with the aforementioned optoelectronic mechanisms. Photo-
physical properties of the acridinedione compounds are summarized in Table 1.
EXPERIMENTAL
A solution of dimedone (3.56 mmol), benzylamine (1.78 mmol), and the selected
aldehyde (1.78 mmol) in acetic acid (4 mL) was heated under reflux for the appropri-
ate time. After completion of the reaction (TLC) and distillation of acetic acid, the
crude was washed with a solution of potassium carbonate (10%) and extracted with
chloroform (3 ꢂ 10 mL). The organic layers were recovered and dried over anhydrous
sodium sulfate, and the solvent was evaporated. Finally, the crude product was
purified by silica-gel column chromatography (ethyl acetate–n-hexane 2:3).
10-Benzyl-9-phenyl-3,3,6,6-tetramethyldecahydroacrydin-1,8-dione
(8a)
Yellow solid. Yield 38% (300.2 mg, 0.68 mmol), mp 182–184 ꢃC.[82] FT-IR
1
(KBr pellet, cmꢁ1): 3000, 2957, 2928, 2868, 1632, 1565, 1380. H NMR (400 MHz,
CDCl3) d (ppm): 7.28–7.41 (m, 5H), 7.15–7.20 (m, 5H), 5.34 (s, 1H), 4.90 (s, 2H),

656
S. M. M. GOMEZ ET AL.
2.49 (d, 2H, J ¼ 16.6 Hz), 2.30 (d, 2H J ¼ 16.6 Hz), 2.19 (m, 4H), 0.99 (s, 6H), 0.88 (s,
6H). 13C NMR (100 MHz, CDCl3) d (ppm): 195.6, 150.5, 145.8, 137.1, 129.2, 128.7,
127.9, 125.9, 125.4, 115.4, 50.0, 48.8, 40.2, 32.7, 32.1, 28.8, 28.2. GCEM (EI) (m=z):
439 [M]þ. Anal. calcd. for C30H33NO2: C, 81.97; H, 7.57; N, 3.19; O, 7.28. Found: C,
81.87; H, 3.10; N, 7.38; O, 7.45.
3,3,6,6-Tetramethyl-9-phenyl-3,4,5,6,7,9-hexahydro-1H-xanthene-
1,8-(2H)-dione (10a)
White solid. Yield 55% (344.1 mg, 0.98 mmol), mp 201–203 ꢃC.[59,64] FT-IR
(KBr pellet, cmꢁ1): 2956, 2854, 1662, 1491.1H NMR (400 MHz, CDCl3) d (ppm):
7.21 (dd, 2H, J1 ¼ 7.0 Hz, J2 ¼ 1.5 Hz), 7.14 (t, 2H, J ¼ 5.6 Hz), 7.03 (t, 1H,
J ¼ 7.3 Hz), 4.08 (s, 1H), 2.39 (s, 4H), 2.13 (m, 4H), 1.03 (s, 6H), 0.92 (s, 6H).13C
NMR (100 MHz, CDCl3) d (ppm): 196.5, 162.4, 144.2, 128.5, 128.2, 126.5, 115.8,
50.9, 41.0, 32.3, 32.0, 29.4, 27.5. GCEM (EI) (m=z): 350 [M]þ. Anal. calcd. for
C23H26O3: C, 78.83; H, 7.48; O, 13.70. Found: C, 78.67; H, 7.39; O, 13.75.
CONCLUSIONS
We describe a simple, practical, and economically viable one-pot method for
easy simultaneous access to functionalized decahydroacridine-1,8-diones and 1,8-
dioxo-octahydroxanthenes by the condensation of aldehydes, benzylamine, and
5,5-dimethyl-1,3-cyclohexanedione. By means of steady-state spectroscopy, we have
studied the photophysics of the acridinediones in methanol solution. The results
showed that both the substitution on the nitrogen atom by a benzyl group and
the carbon-9 with p-aromatic groups results in a highly fluorescence quenching
because these substituents favor the intersystem crossing relaxation mechanism.
On the other hand, the shape and position of the absorption band of the local excited
state remain constant upon the aforementioned chemical modifications. Addition-
ally, despite the poor quantum yields of the model acridinedione systems, we believe
these systems could be good candidates, acting as antennas in bichromophoric
system, for energy-transfer applications because of the expected long-lived triplet
excited states.
SUPPORTING INFORMATION
General experimental information, spectroscopic and characterization data for
1
compounds 8b–e 10b–e, H and 13C NMR, GCMS spectra for selected compounds,
and quantum yield calculations can be found via the Supplementary Content section
of this article’s Web page.
ACKNOWLEDGMENT
The authors are thankful to the Universidad Nacional de Colombia for the
support of this work.

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657
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