Chemically-induced geometrical isomerization of stilbenes during peroxyoxalate chemiluminescence reaction: Revisit to 'photochemistry without light'

Article abstract of DOI:10.1016/j.tetlet.2013.11.094

The chemically-induced isomerization of stilbenes during the peroxyoxalate chemiluminescence (PO-CL) reactions was reinvestigated. The PO-CL reactions using bis(2,4,6-trichlorophenyl) oxalate in the presence of several stilbenes (type A reaction) produced cis-stilbenes in 0-4% yields, which was dependent on the singlet excitation energy of the stilbenes. On the other hand, the PO-CL reactions of the oxalates, containing the stilbene moieties in the molecules (type B reaction), produced cis-stilbenes 0-9.3% yields, some of which were much more effective than the type A reactions considering the amount of the oxalate moiety as the energy supplier.

Full text of DOI:10.1016/j.tetlet.2013.11.094

Tetrahedron Letters 55 (2014) 619–622
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Chemically-induced geometrical isomerization of stilbenes
during peroxyoxalate chemiluminescence reaction: revisit to
‘photochemistry without light’
⇑
Jiro Motoyoshiya , Kanako Watanabe, Airi Takizawa, Hikaru Shimizu, Takayuki Maruyama
Course of Applied Chemistry, Division of Chemistry and Materials, Faculty of Textile Science and Technology, Shinshu University, Ueda, Nagano 386-8567, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 17 July 2013
Revised 11 November 2013
Accepted 18 November 2013
Available online 28 November 2013
The chemically-induced isomerization of stilbenes during the peroxyoxalate chemiluminescence (PO-CL)
reactions was reinvestigated. The PO-CL reactions using bis(2,4,6-trichlorophenyl) oxalate in the pres-
ence of several stilbenes (type A reaction) produced cis-stilbenes in 0–4% yields, which was dependent
on the singlet excitation energy of the stilbenes. On the other hand, the PO-CL reactions of the oxalates,
containing the stilbene moieties in the molecules (type B reaction), produced cis-stilbenes 0–9.3% yields,
some of which were much more effective than the type A reactions considering the amount of the oxalate
moiety as the energy supplier.
Keywords:
Peroxyoxalate chemiluminescence
Geometrical isomerization
Stilbene
Ó 2013 Elsevier Ltd. All rights reserved.
Photochemistry without light
Chemiluminescence reactions produce energy for the excitation
of the fluorescent molecules to emit light, while the energy can be
used for sensitization of the coexisting photochemically reactive
molecules instead of the chemiluminescence. A few significant
reports documented such a chemical sensitization called ‘photo-
chemistry without light’,1 in which some typical photoreactions
were induced during the chemiluminescent reactions that in-
cluded the thermal decomposition of the 1,2-dioxetanes, oxidation
of the phthalhydrazides,2 and the peroxyoxalate chemilumines-
cence (CL) reactions.3 One of the representative examples is the
cis–trans isomerization of stilbenes during the peroxyoxalate
chemiluminescence (PO-CL) reaction3a instead of a light emission
as shown in Scheme 1. Although the concept of ‘photochemistry
without light’ is very attractive from the viewpoint of the energy
source for the photoreactions without irradiation by a UV lamp,
less attention has been paid to such systems and there have been
only a few examples.2,3 As a part of our continuing study of the per-
oxyoxalate chemiluminescence,4 we revisited this interesting CL
reaction accompanying the geometrical isomerization of stilbenes
and investigated the two types of PO reactions without fluoro-
phores, one of which is the PO reaction in the presence of various
stilbenes (type A reaction) and the other which is that using the
oxalates containing the stilbene unit in the oxalate molecules (type
B reaction).
To investigate the type A reactions, the trans-stilbenes (1a–h)
bearing various substituents (7.5 ꢀ 10ꢁ4 M in THF/H2O = 3/1) were
treated
with
bis(2,4,6-tricholorophenyl)
oxalate
(TCPO)
(3.75 ꢀ 10ꢁ2 M) and hydrogen peroxide (2.5 ꢀ 10ꢁ2 M) under alka-
line conditions (K2CO3, 2.5 ꢀ 10ꢁ5 M). After work-up the stilbenes
were quantitatively obtained and no other product was detected
in this reaction. The reactions were repeated at least three times
for each stilbene and the ratios of the cis- and trans-stilbenes were
determined by their 1H NMR spectra. The results are summarized
in Table 1. Although the ratio varied below 10%, some trans-stilb-
enes (1c, 1d, 1e, 1g, and 1h) isomerized to the cis-stilbenes during
the peroxyoxalate (PO) reactions of TCPO, while three stilbenes
(1a, 1b, and 1f) did not isomerize at all.
To compare the isomerization efficiency for the above PO reac-
tions to that for the photochemical reactions, the trans-stilbenes
were treated in aqueous THF (THF/H2O = 3/1) by irradiation using
a high pressure mercury lamp for 2 min. and the ratios determined
by 1H NMR spectra are shown in Table 1. The tendency of the
substituent-depending cis-isomer ratio in the chemiluminescent
reactions was roughly similar to that in the direct photoisomeriza-
tion as shown in Figure 1, and thus the peroxyoxalate chemilumi-
nescent reaction provides the situation similar to the direct
photoexcitation of the stilbenes. These ratios of the cis-stilbenes
obtained in the present study are lower than that previously
reported in which trans-4-methoxy-40-nitrostilbene was treated
with bis(2,4-dinitrophenyl) oxalate (DNPO) (5 equiv to the
stilbene) and hydrogen peroxide in dimethoxyethane under anhy-
drous conditions to afford a 9% yield of the cis-isomer as the
⇑
Corresponding author. Tel.: +81 268 5402; fax: +81 268 5391.
E-mail address: jmotoyo@shinshu-u.ac.jp (J. Motoyoshiya).
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.11.094

620
J. Motoyoshiya et al. / Tetrahedron Letters 55 (2014) 619–622
Scheme 1. Chemiluminescence and isomerization without light.
Table 1
Isomerization of stibenes (1a–i) in the PO reactions of TCPO (Type A reaction)
trans-Stilbene
R1
R2
R3
cis-Stilbeneb (%)
Entry 2 Entry 3
Ratio of cis-isomer in photoirradiationc
Entry 1
Average
Abs.d (nm)
1a
1b
1c
1d
1e
1f
H
H
OMe
OBu
tBu
H
H
H
H
H
H
Me
H
H
0
0
0
0
0
0
0
0
0
297
320
323
328
322
287
338
338
OMe
OMe
OMe
OMe
OMe
OMe
OMe
12.1
10.3
29.7
11.7
7.2
1.6
0.8
0.5
0
7.9
1.6
0.8
0.6
0.4
0
7.9
1.1
1.2
0.6
0.8
0
6.2
0.6
1.2
0.7
0.6
0
7.3
1.1
1g
1h
CN
COOEt
46.1
2.7
H
a
[Stilbenes (1a–i)] = 7.5 ꢀ 10ꢁ3 M, [TCPO] = 3.75 ꢀ 10ꢁ2 M, [H2O2] = 2.5 ꢀ 10ꢁ1 M, [K2CO3] = 2.5 ꢀ 10ꢁ5 M.
b Determined by 1H NMR after the work-up.
c Direct photoisomerization of trans-stilbenes under irradiation by a high pressure mercury lamp for 2 min in THF/H2O2 (3/1). [trans-stilbene] = 1.0 ꢀ 10ꢁ4 M.
d Absorption with the longer wavelength of two large peaks around 300 nm.
maximum value.3a The lower ratios in the present study, in spite of
the high amount of TCPO (50 equiv to the stilbenes), would be due
to the different reaction conditions, i.e., the reactions were carried
out in aqueous media and the use of TCPO instead of more reactive
DNPO. We examined the concentration effect under the conditions
changing the ratios of stilbene/oxalate (1/10, 1/20, 1/50) and found
that the higher ratio than 1/50 gave no cis-isomer. In the type A
reactions, 1g with the cyano group was transformed into the
cis-isomer the most effectively of all. This would be due to the low-
er singlet excitation energy of 1g than the others, because it
showed the maximum absorption at 338 nm in the solvents the
same as used for the reactions and the emission at 559 nm, which
was the longest wavelength of all except for 1h with the absorp-
tion and emission at 338 nm and 422 nm, respectively. The differ-
ence in the isomerization ratio between 1g and 1h can be
explained by the rapid loss of the excitation energy of 1h, because
the excited 1h decays faster than 1g due to the hydrogen bonding
in the aqueous media due to the very weak emission of 1h in the
aqueous media.6
Next, for the type B reactions, the PO reactions of the oxalates
(2b, 2d, 2e, 2f, 2g, and 2h),4b,5 containing the stilbene moieties
were reacted with aqueous hydrogen peroxide under weak
alkaline conditions. After a work-up similar to the above type A
reactions, the cis/trans ratios of the stilbenes were determined by
their 1H NMR spectra. As shown in Table 2, the ratios of the
cis-stilbenes increased compared to the type A reactions except
for 2g and 2h. To explore the photochemical behavior of 2g and
2h, we examined the photoirradiation of the corresponding pheno-
lic stilbenes such as 4-cycno-40-hydroxystilbene (3) and 4-carbo-
ethoxy-40-hydroxystilbene (4) under the neutral and basic
conditions. The cis-isomers were formed in 4.1% for 3 and 5.1%
for 4, respectively, after 5 min. irradiation under the neutral condi-
tion, and 32% for 3 under the basic condition. These results show
that the cis-isomers formed during the type B reactions can exist
Figure 1. Ratios of cis-stilbenes (%) for the chemiluminescent reaction (CL) and
direct photoisomerization (Photo).

J. Motoyoshiya et al. / Tetrahedron Letters 55 (2014) 619–622
621
Table 2
Peroxyoxalate reaction of the oxalates bearing the stilbene moiety (Type B reaction)
Oxalate
R1
R2
cis-Stilbeneb (%)
Ratio of cis-isomer in photoirradiation of corresponding phenolic stilbenesc (%)
Entry 1
Entry 2
Entry 3
Average
2b
2d
2e
2f
2g
2h
H
H
H
H
Me
H
7.3
2.2
6.5
8.8
0
5.9
2.2
6.2
10.0
0
4.8
1.8
4.2
8.9
0
6.0
2.1
5.6
9.3
0
0
OBu
tert-Bu
H
CN
COOEt
14.2
11.7
3.0
4.1
5.1
H
0
0
0
0
a
b
c
[Oxalate] = 7.5 ꢀ 10ꢁ2 M, [H2O2] = 2.5 ꢀ 10ꢁ1 M, [K2CO3] = 2.5 ꢀ 10ꢁ5 M in THF/H2O2 (3/1).
Determined by 1H NMR after the work-up.
Direct photoisomerization of trans-stilbenes under irradiation by a high pressure mercury lamp for 2 min in THF/H2O2 (3/1). [trans-stilbene] = 1.0 ꢀ 10ꢁ4 M.
during the type B reaction and the photoirradiation are illustrated.
The reason that 2g and 2h gave no cis-stilbenes might be due to the
poor trans to cis isomerization of donor–acceptor type stilbenes in
the protic solvents as previously reported.7 It is also noteworthy
that when perylene was added as a fluorophore to the PO reactions
of 2d and 2f, no or less isomerization was observed due to the con-
sumption of the excitation energy forming the excited perylene,
namely, the ratios of the cis-stilbenes were reduced from 2.1% to
0% and from 9.3% to 3.8% for 2d and 2f, respectively.
There is a remarkable difference in the isomerization efficiency
between the type A and B reactions as described above. The PO-CL
reaction is believed to involve the 1,2-dioxetanone bearing one
stilbene moiety or the 1,2-dioxetanedione as the high-energy
intermediates,4d,8 the former of which is the precursor of the latter
and formed by the initial acyl substitution of the hydroperoxide
Figure 2. Ratios of cis-stilbenes (%) for the chemiluminescent reaction (CL) and
anion to the oxalate followed by the intramolecular nucleophilic
addition of the peroxide end, and the latter of which contains no
stilbene moiety and is ready to decompose to two moles of carbon
dioxide. The type B reactions provided the interesting result as
mentioned above, namely, the appearance in Figure 2 shows an
opposite tendency between two excitation ways. There might be
an excitation process in the type B reactions different from the
energy transfer as in the type A reaction. A plausible explanation
direct photoisomerization of the corresponding phenolic stilbenes (Photo).
in their forms under the reaction conditions and not isomerize to
the trans-isomers. Considering the amount of the oxalate moiety
as an energy supplier, the type B reactions are much more effective
than the type A reactions except for the push–pull type stilbenes
2g and 2h. In Figure 2 the ratios of the cis-isomers generated
Scheme 2. A plausible electron transfer process for the chemically induced isomerization of the oxalates 2.

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J. Motoyoshiya et al. / Tetrahedron Letters 55 (2014) 619–622
4. (a) Motoyoshiya, J.; Sakai, N.; Imai, M.; Yamaguchi, R.; Koike, R.; Takaguchi, Y.;
Aoyama, H. J. Org. Chem. 2002, 67, 7314–7318; (b) Koike, R.; Kato, Y.;
Motoyoshiya, J.; Nishii, Y.; Aoyama, H. Luminescence 2006, 21, 164–173; (c)
Maruyama, T.; Fujie, Y.; Oya, N.; Hosaka, E.; Kanazawa, A.; Tanaka, Y.; Hattori,
Y.; Motoyoshiya, J. Tetrahedron 2011, 67, 6927–6933; (d) Maruyama, T.; Narita,
S.; Motoyoshiya, J. J. Photochem. Photobiol. A: Chem. 2013, 252, 222–231.
5. Compound 2b: To a solution of (E)-4-hydroxystilbene (0.37 g, 1.90 mmol) in
benzene (50 ml) and triethylamine (0.23 g, 2.30 mmol) was added oxalyl
chloride (0.14 g, 1.10 mmol) dropwise under an argon atmosphere. After being
stirred at room temperature for 2 h, the precipitation was filtered and washed
with THF. The washing containing the product was concentrated under a
reduced pressure to give a white crystal, which was recrystallized from ethyl
acetate. Yield: 84% (0.38 g); 1H NMR (400 MHz, DMSO-d6) d 7.28–7.43 (m,
14H), 7.63 (d, 4H), 7.74 (d, 4H); HRMS (ESI): Calcd for C30H22O4Na ([M+Na]+):
469.1410, found 469.1411. Compound 2d: This compound was prepared by the
procedure as described above using (E)-butoxy-40-hydoxystilbene (0.8 g,
3.00 mmol), triethylamine (0.30 g, 3.00 mmol), and oxalyl chloride (0.19 g,
1.50 mmol) in THF (50 ml). Yield 86% (0.76 g); 1H NMR (400 MHz, CDCl3) d 0.99
(t, 6H), 1.50 (m, 4H), 1.78 (m, 4H), 4.00 (t, 4H), 6.90 (d, 4H), 6.97 (d, 2H), 7.06 (d,
2H), 7.24 (d, 4H), 7.44 (d, 4H), 7.56 (d, 4H). HRMS (ESI): The molecular ion peak
was not observed. Compound 2e: This compound was prepared by the
procedure as described above using (E)-tert-butyl-40-hydoxystilbene (0.40 g,
1.60 mmol), triethylamine (0.16 g, 1.6 mmol), and oxalyl chloride (0.10 g,
0.79 mmol) in THF (30 ml). Yield 84% (0.38 g); 1H NMR (400 MHz, CDCl3) d 1.34
(s, 18H), 7.06 (d, 2H), 7.11 (d, 2H), 7.26 (d, 4H), 7.40 (d, 4H), 7.47 (d, 4H), 7.58
is that an intramolecular charge transfer or an electron exchange
process is involved in the type B reactions as can be seen in some
bioluminescence9 or as proposed during the CIEEL process for the
PO-CL,8,10 respectively. In this assumed mechanism the isomeriza-
tion of the formed radical cations of the stilbenes might occur as
shown in Scheme 2.11 The intramolecular charge transfer or an
electron transfer would take place between the 1,2-dioxetanedione
still bearing the stilbene moiety or the 1,2-dioxetanedione and the
liberated stilbenes, once they are formed in the solvent cage. In
contrast, the electron deficient cyano and carboethoxy groups of
2g and 2h prevented the electron transfer from the stilbene unit
to the 1,2-dioxetane moiety, resulting in no isomerization.
The isomerization efficiency of this electron transfer system is
comparable or higher comparing the fumaronitrile or 9,10-dicy-
anoanthracene sensitized isomerization of trans-stilbene whose
Ucs were reported to be 0.011–0.31,9a,b because Ucs for 2b was cal-
culated to be 0.24 from the equation, UPO-cs = (yield of cis-stilbene)
ꢀ [initial trans-stilbene]/([oxalate] ꢀ Utrans?cis) defined for the
stilbene’s trans–cis isomerization during the peroxyoxalate chemi-
luminescence reaction, using 0.50 for Utrans?cis as the tentative
value of trans-stilbene.7 However, this mechanism is based on a
little evidence and more detailed study is necessary, which will
make the peroxyoxalate chemiluminescence reaction clearer.
In conclusion, the chemically-induced geometrical isomeriza-
tion of the stilbenes during the peroxyoxalate chemiluminescent
reactions was investigated again and some new results were
obtained. The isomerization efficiency was dependent upon the
singlet excitation energy of the stilbenes for the type A reactions,
while the isomerization occurred much more effectively in the
type B reactions in which an intramolecular or quasi-intramolecu-
lar electron transfer might take place.
(d, 4H); HRMS (ESI): Calcd for
C
38H38O4Na ([M+Na]+): 581.2662, found
581.2664. Compound 2f: This compound was prepared by the procedure as
described above using (E)-1-(40-hydoroxyphenyl)-2-phenylpropene (0.30 g,
1.30 mmol), triethylamine (0.16 g, 1.60 mmol), and oxalyl chloride (0.10 g,
0.80 mmol) in benzene (10 ml). Yield 80% (0.25 g); 1H NMR (400 MHz, CDCl3) d
2.30 (br s, 6H), 6.82 (s, 2H), 7.28–7.32 (m, 6H), 7.38 (t, 4H), 7.44 (d, 4H), 7.53 (d,
4H); HRMS (ESI): Calcd for C32H26O4Na ([M+Na]+): 497.1723, found 497.1724.
Compound 2g: This compound was prepared according to the established
procedure.4b Compound 2h: This compound was prepared by the procedure as
described
above
using
(E)-4-carbethoxy-40-hydroxystilbene
(0.80 g,
3.00 mmol), triethylamine (0.30 g, 3.00 mmol), and oxalyl chloride (0.19 g,
1.50 mmol) in THF (30 ml). Yield 72% (0.64 g); 1H NMR (400 MHz, CDCl3) d 1.40
(t, 6H), 4.38 (q, 4H), 6.84 (d, 1H), 7.13 (d, 2H), 7.22 (d, 2H), 7.30 (d, 3H), 7.43 (d,
1H), 7.53 (d, 1H), 7.59 (m, 6H), 8.01 (d, 1H), 8.05 (d, 3H). HRMS (ESI): Not
measured because of thermal lability.
6. Nakatsuji, S.; Matsuda, K.; Uesugi, Y.; Nakashima, K.; Akiyama, S.; Katzer, G.;
Fabian, W. J. Chem. Soc. Perkin Trans. 2 1991, 861–867.
7. Gegiou, D.; Muszkat, K. A.; Fischer, E. J. Am. Chem. Soc. 1968, 90, 3907–3918.
8. Ciscato, L. F. M. L.; Augusto, F. A.; Weiss, D.; Bartoloni, F. H.; Albrecht, S.; Brandl,
H.; Zimmermann, T.; Baader, W. Arkivoc 2012, 391–430.
9. Koo, J.-Y.; Schmidt, S. P.; Schuster, D. B. Proc. Natl. Acad. Sci. U.S.A. 1978, 75, 30–
33.
10. (a) Stevani, C. V.; Silva, S. M.; Baader, W. Eur. J. Org. Chem. 2000, 4037–4046; (b)
Augusto, F. A.; de Souza, G. A.; de Souza, S. P.; Khakid, M.; Baader, W.
Photochem. Photobiol. 2013, 89, 1299–1317.
11. (a) Hub, W.; Klueter, U.; Schneider, S.; Doerr, F. J. Phys. Chem. 1984, 88, 2308–
2315; (b) Lewis, F. D.; Petisce, J. R.; Oxman, J. D.; Nerpras, M. J. J. Am. Chem. Soc.
1985, 107, 203–207.
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