A novel chromatism switcher with double receptors selectively for Ag + in neutral aqueous solution: 4,5-diaminoalkeneamino-N-alkyl-l,8- naphthalimides

Article abstract of DOI:10.1016/j.tetlet.2004.03.105

Two novel fluorosensors of 4,5-disubstituted-N-alkyl-l,8-naphthalimide derivatives (H1, H2, H3) with double ethylenediamino receptors, double propylenediamino receptors, or one methylpiperazine receptor were synthesized, respectively. Their fluorescence and absorption in the presence or absence of nine metal ions were studied. In the presence of Ag⁺, H1's absorption moved to long wavelength with color change from yellow-green to red, its quenching and red shift in fluorescence were also remarkable. Similarly, H1's fluorescence was also strongly quenched in the presence of Cu²⁺. In addition, H1 and H2 show high pH sensitively. There was 139-folds fluorescence enhancement for H1, 22-folds for H2, and 4-folds for H3 when pH was changed from 8 to 3, respectively.

Full text of DOI:10.1016/j.tetlet.2004.03.105

Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 3969–3973
A novel chromatism switcher with double receptors selectively for
Ag in neutral aqueous solution: 4,5-diaminoalkeneamino-N-alkyl-
l,8-naphthalimides
+
a,b
Lihua Jia, Yu Zhang, Xiangfeng Guo and Xuhong Qian
b,c
a,b
a,
*
a
State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116012, China
b
Qiqihar University, Qiqihaer 161006, China
Shanghai Key Laboratory of Chemical Biology, Institute of Pesticides and Pharmaceuticals, East China University of Science
and Technology, Shanghai 200237, China
c
Received 9 June 2003; revised 15 January 2004; accepted 1 March 2004
Abstract—Two novel fluorosensors of 4,5-disubstituted-N-alkyl-l,8-naphthalimide derivatives (H1, H2, H3) with double ethylene-
diamino receptors, double propylenediamino receptors, or one methylpiperazine receptor were synthesized, respectively. Their
þ
fluorescence and absorption in the presence or absence of nine metal ions were studied. In the presence of Ag , H1’s absorption
moved to long wavelength with color change from yellow-green to red, its quenching and red shift in fluorescence were also
2
þ
remarkable. Similarly, H1’s fluorescence was also strongly quenched in the presence of Cu . In addition, H1 and H2 show high pH
sensitively. There was 139-folds fluorescence enhancement for H1, 22-folds for H2, and 4-folds for H3 when pH was changed from 8
to 3, respectively.
ꢀ
2004 Elsevier Ltd. All rights reserved.
1
4
15
The development of fluorescent devices for the sensing
and reporting of chemical species is currently of signif-
icant importance for both chemistry and biology. More
lators, and fluorescent markers in medicine and
biology. More recently, 1,8-naphthalimide derivatives
with ethylenediamine functionality or analogs as a guest
binding site, have been developed as signaling molecules
to respond to transition metal ions by fluorescence
1
specifically, chemsensors for the detection and mea-
surement of transition metal ions are actively being
investigated, because transition metal ions are essential
trace elements in biological systems and significant ele-
1
6;17
enhancement in organic solvent.
However few selec-
tive fluoroionophores derived from them were reported.
In addition, transition metal ions are easier to chelate
and detect in organic solvents, because of their relatively
small solvation energies. It is rather difficult to recognize
transition metal ions in aqueous solvents because of their
strong hydration, which is relevant to biological and
environmental applications.
2–10
ments in environmental chemistry.
Essential requi-
sites of such a sensor are high sensitivity and selectivity,
since its main applications are addressed to the analysis
of environmental or biological samples. In addition, its
9
ability to operate in water is extremely important.
We have focused on the use of 4,5-diamino-1,8-naph-
thalimide derivatives as fluorescence sensors to detect
transition metal ions in water. It is known that the highly
fluorescent and photo-stable 1,8-naphthalimide deriva-
tives, for example, 4-amino-1,8-naphthalimides, function
as fluorescent dyes for synthetic polymers and textile
4-Aminonaphthalimide fluorophore is an electronic
push–pull system containing one electron-donating
group and is usually connected to one ethylenediamino
receptor in PET (Photo-induced Electron Transfer)
based sensors, we hypothesized that its fluorescence
intensity would increase with the introduction of two
electron-donating ethylenediamino groups or analogs to
the para-positions of electron-withdrawing carboximide
moiety and if such two receptors in coordination with
each other would improve sensitivity and selectivity for
transition metal cations, as well as hydrophilic ability.
11
12
materials, liquid-crystal additives, electrooptically
sensitive materials in laser technology, DNA interca-
13
*
Corresponding author. Tel./fax: +86-411-3673466; e-mail: xhqian@
dlut.edufor.cn
0
040-4039/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2004.03.105

3970
L. Jia et al. / Tetrahedron Letters 45 (2004) 3969–3973
Here we report the synthesis and signaling properties of
þ
2þ
H1, H2, and H3. H1 is able to detect Ag and Cu ions
þ
in Tris–HCl aqueous at pH 7.5. In the presence of Ag ,
the absorption of H1’s aqueous solution was red shifted,
observable by a change in color from yellow-green to
red, its quenching and red shift in fluorescence were also
remarkable, therefore H1 is a two-channel molecular
Figure 1. The color response of H1 to different transition metal ions.
þ 18
switcher for the optical detection of Ag . And the
fluorescence quenching of H1 was very strong in the
2þ
presence of Cu . In addition, there is a 139-folds fluo-
rescence enhancement for H1, 22-folds for H2, and
By comparison with the other transition metal ions,
Cu -induced fluorescence quenching of the H1 was the
strongest, while its emission and absorption wavelength
2þ
4-folds for H3 when pH value was changed from 8 to 3,
respectively.
þ
changed slightly. In the presence of Ag , the H1’s
fluorescence was quenched with a red shift about 17 nm
(H1 in Fig. 2a), a red shift about 76 nm in its absorption
was found by comparing with its absolute buffer solu-
tion (H1 in Fig. 2c). It implies that there is a strong
interaction between H1 with Ag or Cu in Tris–HCl
aqueous solution.
The syntheses of targets were shown in Scheme 1. Fol-
lowing the literatures,
19–21
1 was prepared from
acenaphthalene via chlorination and oxygenation.
Compound 1 was condensed with dodecyl amine in eth-
anol at reflux for 10 h, and was cooled to room temper-
ature to afford a yellow solid 2 after filtration, and
purified by silica gel column chromatography using di-
chloromethane as eluent. H1 and H2 were prepared as
follows with 77% and 52% yield, respectively. Compound
þ
2þ
The electron densities of these naphthalimide fluoro-
phores are very high due to the electron donors at 4- and
5-position, which strengthens the quenching between
transition metal ions and electron-rich fluorophore. This
is very different from the naphthalimide fluoroiono-
phores with one electron-donating group, which showed
the fluorescence enhancement through the inhibition of
PET in the presence of transition metal ions and the
weakness of the quenching between cation and the
2
reacted with the corresponding amine in acetonitrile
with reflux for 7 h under a nitrogen atmosphere, the
reaction mixture was poured into water, extracted with
ethyl acetate, dried over K CO , and evaporated, then the
2 3
residue was dissolved in methanol and further purified by
column chromatography using methanol–triethylamine
17;23;24
(
10:1, v/v) as eluent. While H3 (yield 70%) was obtained
electron-deficient fluorophore.
when 2 reacted with methylpiperazineat the same condi-
tions, H4 was not obtained, as the methylpiperazine is a
secondary amine, its steric hindrance is larger by com-
parison with that of dimethylaminoethylene (or propyl-
ene)amine. The structures of all products were identified
2
þ
þ
The influence of the concentrations of Cu or Ag on
H1’s fluorescence intensity was shown in Figure 3a,
respectively. The fluorescence intensity was quenched
2þ
more than 90% during the concentration of Cu at
lmol/L level (Fig. 3a), and decreased linearly upon the
1
13
22
by using H NMR, C NMR, and MS.
À6
concentrations (0–1.2 · 10 mol/L, DI ¼ À13:47xÀ
2
2þ
Addition of transition metal ions to the buffer solution
of H1 resulted in changes of color, which were sharply
1:03, R ¼ 0:9836). When the concentration of Cu was
À6
increased to 5.4 · 10 mol/L, which was half of that of
H1, the fluorescence was quenched to constant mini-
þ
different (Fig. 1). When Ag was added to the H1 buffer
solution, its color changed from yellow-green to red, yet
mum. Similarly, the fluorescence decreased linearly
À5
þ
the color of the H1 solution did not change when other
2þ
upon the concentrations of Ag (0–1.0 · 10 mol/L,
2þ
2þ
2þ
2þ
2
þ
transition metal ions (Co , Pb , Zn , Mg , Hg ,
2þ
DI ¼ À1:63x À 1:29, R ¼ 0:9824) up to a ratio H1–Ag
2
þ
Cd , Ca ) were added.
of 1:1 and then leveled off. These phenomena were
O
O
O
SO
2
Cl
2
/CH Cl2
K Cr O +CrO
C
12
H25NH
2
2
2
2
7
3
ice bath
HAc
Cl Cl
Cl Cl
1
O
R
R
RNH
2
H1: R=NHCH
H2: R=NHCH CH CH N(CH )
3 2
2
2 3 2
CH N(CH )
C12H25
N
C12H25
O
N
O
2
2
2
O
O
Cl
N
C12H25
N
H3
H4
N
Cl Cl
2
HN
N
O
O
N
N
N
N
C
12
H
25
N
O
X
Scheme 1. Synthetic procedures for H1, H2, and H3.

L. Jia et al. / Tetrahedron Letters 45 (2004) 3969–3973
3971
6
0
2
1
1
1
1
1
0
8
6
4
2
0
8
6
4
2
0
No one
No one
2
+
H1
2+
50
40
30
Hg
Cd
H2
2+
2
+
Pb
Cd
Cu
Hg
2
+
2+
+
Pb
Ag
Cu
2+
+
2
+
Ag
2
1
0
0
0
450
500
550
Em/nm
600
650
700
460
510
560
Em/nm
610
660
(
a)
(b)
0
0
0
0
0
0
.6
.5
.4
.3
.2
.1
0
0.6
0.5
0.4
0.3
+
H2
2+
H1
Ag
Pb
Pb
2+
+
Ag
Noone
No one
2+
2+
Hg
Hg
2
2
+
+
2+
Cd
Cu
Cu
2+
Cd
0
0
.2
.1
0
Ag+
2
40
340
440
λ/nm
540
2
40
340
440
λ/nm
540
(
c)
(d)
À5
Figure 2. Fluorescence and absorption of H1 (a, c) and H2 (b, d) (1 · 10 mol/L) in Tris–HCl aqueous solution (0.01mol/L, methanol–water ¼ 1:19,
À5
v/v, pH ¼ 7.5) in the presence of different metal ions (5 · 10 mol/L).
3
2
2
1
1
0
5
0
5
0
N
O
HN
H
Ag+
12 25
C H
N
O
N
H1-Ag
+
N
N
N
O
O
O
O
NH
NH
HN
H
Cu++
C
12
H
25
C
12
H
25
N
5
N
H1-Cu++
0
0
10
20
30
40
50
(a)
C/µmol/L
(b)
À5
2þ
þ
Figure 3. (a) The fluorescence intensity of H1 (1 · 10 mol/L) responds to the different concentrations of Cu (j) and Ag (m) in Tris–HCl aqueous
þ
2þ
.
(
pH ¼ 7.5, methanol–water ¼ 1:19, v/v). (b) Structure of the complex H1–Ag and the complex H1–Cu
diagnostic for the formation of a complex with 2:1
stoichiometry between H1 and Cu , and a complex
with 1:1 between H1 and Ag (Fig. 3b).
Because of far distances and weak interaction between
2þ
2þ
Cu and H1’s fluoropfores, absorption and fluores-
cence wavelength of H1 were almost unchanged in the
þ
2
þ
presence of Cu .
þ
2þ
Ag and Cu resulted in different response in the
absorption or fluorescence of H1. Comparatively
The fluorescence and absorption of H2 did not change
in the presence of transition metal ions (H2 in Fig. 2b
and d), which were different from the case of H1. The
þ
speaking, 4d orbital is far from the nucleus of Ag with
large radius, the attraction of its nucleus to 4d electrons
is relatively weaker than compared with the case for
molecular modeling calculation (Pcmodel 6.0) suggested
that, the two ethylenediamino groups of H1 formed a
2þ
Cu with small radius and 3d electrons. As a result, the
þ
þ
intramolecular d–p interaction of the complex Ag –H1
cavity-like receptor with appropriate size for Ag , which
resulted in strong interaction and short distance between
was very strong, which resulted in a red shift in the
absorption and emission as well as the color change of
H1’s solution. In fact, some researchers have confirmed
that there was an intramolecular d–p interaction in some
þ
ꢀ
Ag and H1’s fluorophore (6.144 and 6.565 A from Ag
þ
to 4- or 5-position of naphthalene ring, respectively).
However, the two propylenediamino groups of H2
formed a cavity-like receptor with larger size and
resulted in relatively weak interaction (by comparison of
25;26
2þ
The fact that Cu was bound
coordinated systems.
with two H1 (Fig. 3a) implies that four dimethylamino
groups of two H1 might coordinate with one Cu .
2þ
þ
Fig. 4a and b) and far distance between Ag and H2

3972
L. Jia et al. / Tetrahedron Letters 45 (2004) 3969–3973
Acknowledgements
National Natural Science Foundation of China, the
Natural Science Foundation of Heilongjiang Province
and Key Teacher Aid Financially Project of Teacher
Official of Heilongjiang Province, China, support this
research.
References and notes
1
. (a) Amendable, V.; Fabbrizzi, L.; Licchelli, M.; Mangano,
C.; Pallavicini, P.; Parodi, L.; Poggi, A. Coord. Chem. Rev.
1
Q. N.; Gunnlaugsson, T.; Huxley, A. J. M.; McCoy, C. P.;
999, 190–192, 649–669; (b) de Silva, A. P.; Gunaratne, H.
Figure 4. The calculated results (in CPK model) for the interaction
þ
þ
between Ag and H1 (a), Ag and H2 (b) based on MMX-E of
cmodel 6.0 software.
Rademacher, J. T.; Rice, T. E. Chem. Rev. 1997, 97, 1515–
1
P
566; (c) Mizukami, S.; Nagano, T.; Urano, Y.; Odani, A.;
Kikuchi, K. J. Am. Chem. Soc. 2001, 124, 3920–3925; (d)
He, H.; Mortellaro, M. A.; Leiner, M. J. P.; Fraatz, R. J.;
Tusa, J. K. J. Am. Chem. Soc. 2003, 125, 1468–1469.
. Kim, H.-J.; Moon, D.; Lah, M. S.; Hong, J.-I. Angew.
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F.; Ward, A. D. J. Am. Chem. Soc. 2003, 125, 3889–3895.
. Zheng, Y.; Orbulescu, J.; Ji, X.; Andreopoulos, F. M.;
Pham, S. M.; Leblanc, R. M. J. Am. Chem. Soc. 2003, 125,
600
400
200
0
2
4
5
2
680–2686.
. Zheng, J.; Dickson, R. M. J. Am. Chem. Soc. 2002, 124,
3982–13983.
1
2
3
4
5
6
7
8
9
6. Beltramello, M.; Gatos, M.; Mancin, F.; Tecilla, P.;
Tonellato, U. Tetrahedron Lett. 2001, 42, 9143–9146.
pH
7
8
. Bhattacharya, S.; Thomas, M. Tetrahedron Lett. 2000, 41,
10313–10317.
. Klein, G.; Kaufmann, D.; Schiirch, S.; Reymond, J.-L.
Chem. Commun. 2001, 561–562.
Figure 5. The influence of pH on fluorescence of H1 (j), H2 (m), and
À5
H3 (d) (1 · 10 mol/L) in a solution of ethanol and water (1:4, v/v).
ꢀ
14.424 and 14.504 A, respectively). Similarly, the chain
(
9. Ghosh, P.; Bharadwaj, P. K.; Roy, J.; Ghosh, S. J. Am.
Chem. Soc. 1997, 119, 11903–11909.
length of propylenediamino group is longer than that of
ethylenediamino group, which resulted in far distance
1
1
1
1
0. Rurark, K.; Kollmannsberger, M.; Resch-Genger, U.;
Daub, J. J. Am. Chem. Soc. 2000, 122, 968–969.
1. Grabtchev, I.; Philipova, T.; Meallier, P.; Guittonneau, S.
Dyes Pigments 1996, 31, 31–34.
2. Grabchev, I.; Moneva, I.; Bojinov, V.; Guittonneau, S.
J. Mater. Chem. 2000, 10, 1291–1294.
3. Kukhto, A. V.; Kolesnik, E. E.; Tobi, M. I.; Grabchev, I.
J. Appl. Spectrosc. 2000, 67, 939–942.
14. Yao, W.; Qian, X.; Hu, Q. Tetrahedron Lett. 2000, 41,
2
þ
and weak interaction between Cu and H2’s fluoro-
phore. In addition, almost no fluorescence or absorption
signal response was observed for H3 in the presence of
transition metal cations.
The pH sensitivities of H1, H2, and H3 as PET fluo-
rescent sensor were also studied for the sake of exploring
its potential application to detect protons in a micro-
environment. As shown in Figure 5, H1, H2, and H3
responded sharply to pH: there was 139-fold fluores-
cence enhancement for H1, 22-fold for H2, and 4-fold
for H3 when pH from 8 to 3, respectively.
7711–7715.
5. Rogers, J. E.; Weiss, S. J.; Kelly, L. A. J. Am. Chem. Soc.
000, 122, 427–436.
6. Ramachandram, B.; Saroja, G.; Sankaran, B.; Samanta,
A. J. Phys. Chem. B 2000, 104, 11824–11832.
7. Ramachandram, B.; Sankaran, B.; Karmakar, R.; Saha,
S.; Samanta, A. Tetrahedron 2000, 56, 7041–7044.
8. Boiocchi, M.; Fabbrizzi, L.; Licchelli, M.; Sacchi, D.;
V ꢁa zquez, M.; Zampa, C. Chem. Commun. 2003, 1812–
1813.
1
1
1
1
2
Obviously, H1 is a novel chemosensor of naphthalimide
þ
with double ethylenediamino receptors for Ag with
high sensitivity and selectivity, it could be used in
aqueous condition, which is very different from the
19. (a) Goto, N.; Nagai, Y. Kogyo Kagaku Zasshi 1954, 57,
236–240; (b) Goto, N. Kogyo Kagaku Zasshi 1959, 62,
þ 27–31
known fluorescent quenching sensors for Ag .
fact, so far, very few papers have been published
In
6
99–705.
20. Tao, Z.-F.; Qian, X.; Tang, J. Dyes Pigments 1996, 30,
47–252.
1. Anikin, V. F.; Kupriyan, D. G. Russ. J. Org. Chem. 2000,
6, 1671–1676.
þ
concerning the selective signaling response between Ag
and fluorescence probes of anthracene with receptor, for
example, polythiazaalkane, polythiaalkane, pyrazolyl-
methyl, thioazacrown, and so on. For silver cation,
H1 probably was the first two-channel molecular
switcher for the optical detection of Ag . Further
applications of H1 in chemical biology and structure–
properties relationships are currently under investigation.
2
2
2
3
27–31
1
2. 2: mp 99.0–101.0 ꢁC, H NMR (400 MHz, CDCl
3
) d 8.49
(
d, J ¼ 8:0 Hz, 2H), 7.85 (d, J ¼ 8:0 Hz, 2H), 4.13 (a-CH
2
,
þ
t, J ¼ 7:4 Hz, 2H), 1.70–1.71 (m, b-CH
2
, 2H), 1.38–1.24
1
3
(m, –CH –, 18H), 0.87 (t, –CH , J ¼ 6:6 Hz, 3H).
2
3
C
3
NMR (400 MHz, CDCl ) d 163.1, 138.2, 131.7, 126.2,

L. Jia et al. / Tetrahedron Letters 45 (2004) 3969–3973
3973
d,
1
22.4, 40.9, 32.2, 29.8, 29.7, 29.6, 28.2, 27.3, 22.9, 14.4. H1:
(C–CH
J ¼ 10:8 Hz, 2H), 2.75 (C–CH
(N–CH , s, 3H), 1.69 (b-CH , m, 2H), 1.37–1.24 (C–CH
m, 18H), 0.86 (–CH
, t, J ¼ 6:8 Hz, 3H). C NMR
(400 MHz, CDCl ) d 163.9, 163.6, 155.2, 137.4, 133.2,
2
,
t, J ¼ 10:8 Hz, 2H), 2.95 (C–CH
2
,
1
mp 131.8–133.2 ꢁC, H NMR (400 MHz, CDCl
J ¼ 8:4 Hz, 2H), 6.69 (d, J ¼ 8:4 Hz, 2H), 4.12 (a-CH
J ¼ 7:6 Hz, 2H), 3.29 (NH–CH , d, J ¼ 4:4 Hz, 4H), 2.70
C–CH –N, s, 4H), 2.29 (N–CH , s, 12H), 1.70 (b-CH
H), 1.40–1.24 (–CH –, m, 18H), 0.87 (–CH
) d 164.6,
2.7, 152.7, 143.1, 133.7, 128.4, 111.9, 111.3, 108.6, 106.5,
3
) d 8.40 (d,
2
, t, J ¼ 10:0 Hz, 2H), 2.48
2
, t,
3
2
2
–,
1
3
2
3
(
2
2
3
2
,
3
2
3
,
t,
132.4, 130.9, 129.6, 122.9, 122.3, 117.1, 116.6, 54.5, 52.9,
45.9, 40.7, 32.2, 29.9, 29.9, 29.6, 29.6, 28.6, 27.4, 22.9, 14.4.
API-ES-MS: [MþH]þ (m=z 499).
1
3
J ¼ 6:8 Hz, 3H). C NMR (400 MHz, CDCl
3
6
1
2
03.0, 57.5, 45.3, 43.4, 41.9, 41.6, 40.2, 36.3, 32.2, 31.9,
9.9, 29.7, 29.6, 29.3, 28.5, 27.9, 27.5, 25.5, 22.9, 17.6, 14.4.
23. Ramachandram, B.; Samanta, A. Chem. Commun. 1997,
1037–1038.
þ
þ
API-ES-MS: [MþH] (m=z 538), [MþNa] (m=z 560). H2:
24. Qian, X.; Xiao, Y. Tetrahedron Lett. 2002, 43, 2991–2994.
25. Tajima, K.; Sugimoto, K.; Kanaori, K.; Azuma, N.;
Makino, K. J. Inorg. Biochem. 1997, 67, 182.
26. Manorik, P. A.; Phedorenko, M. A.; Blysnukova, E. I.
J. Inorg. Biochem. 1995, 59, 676.
27. Ostaszewski, R.; Prodi, L.; Montalti, M. Tetrahedron
1999, 5, 11553–11562.
28. Kang, J.; Choi, M.; Kwon, J. Y.; Lee, E. Y.; Yoon, J.
J. Org. Chem. 2002, 67, 4384–4386.
29. Tong, H.; Wang, L.; Jing, X.; Wang, F. Macromolecules
2002, 35, 7169–7171.
30. Qin, W.; Liu, W.; Tan, M. Anal. Chim. Acta 2002, 468,
287–292.
1
À6
mp 71.8–73.1 ꢁC, H NMR (400 MHz, CDCl
3
) d (·10 ):
8
CH
4
1
2
.39 (d, J ¼ 8:4 Hz, 2H), 6.73 (d, J ¼ 8:8 Hz, 2H), 4.11 (a-
2 2
, t, J ¼ 7:6 Hz, 2H), 3.36 (NH–CH
H), 2.45 (C–CH
–N, t, J ¼ 6:4 Hz, 4H), 2.25 (N–CH
2H), 1.90–1.91 (C–CH –C, m, 4H), 1.69–1.70 (b-CH , m,
H), 1.32–1.23 (–CH –, m, 18H), 0.86 (–CH t,
) d 164.7,
52.7, 133.6, 132.4, 111.8, 111.4, 106.6, 58.5, 45.8, 44.2,
0.2, 32.1, 29.9, 29.7, 29.6, 28.5, 27.5, 26.2, 22.9, 14.3. API-
, t, J ¼ 6:4 Hz,
2
3
, s,
2
2
2
3
,
1
3
J ¼ 6:8 Hz, 3H). C NMR (400 MHz, CDCl
3
1
4
þ
þ
ES-MS: [MþH] (566), [MþNa] (m=z 588). H3: mp 86.2–
1
8
6.7 ꢁC,
H
NMR (400 MHz, CDCl
3
)
d
8.53 (d,
J ¼ 8:4 Hz, 1H), 8.43 (d, J ¼ 8:0 Hz, 1H), 7.68 (d,
J ¼ 8:0 Hz, 1H), 7.33 (d, J ¼ 8:4 Hz, 1H), 4.12 (a-CH
t, J ¼ 7:6 Hz, 2H), 3.43 (–CH , d, J ¼ 12:8 Hz, 2H), 3.15
2
,
31. Ishikawa, J.; Sakamoto, H.; Nakao, S.; Wada, H. J. Org.
Chem. 1999, 64, 1913–1922.
2