Base-induced chemiluminescent decomposition of bicyclic dioxetanes bearing a (benzothiazol-2-yl)-3-hydroxyphenyl group: A radiationless pathway leading to marked decline of chemiluminescence efficiency

Article abstract of DOI:10.1021/jo300417e

Charge-transfer-induced decomposition (CTID) of bicyclic dioxetanes 1b-d bearing a 3-hydroxylphenyl moiety substituted with a benzothiazol-2-yl group at the 2-, 6-, or 5-position was investigated, and their chemiluminescence properties were compared to ea

Full text of DOI:10.1021/jo300417e

Article
pubs.acs.org/joc
Base-Induced Chemiluminescent Decomposition of Bicyclic
Dioxetanes Bearing a (Benzothiazol-2-yl)-3-hydroxyphenyl Group: A
Radiationless Pathway Leading to Marked Decline of
Chemiluminescence Efficiency
Masatoshi, Tanimura, Nobuko Watanabe, Hisako K. Ijuin, and Masakatsu Matsumoto*
Department of Chemistry, Kanagawa University, Tsuchiya, Hiratsuka, Kanagawa 259-1293, Japan
S
* Supporting Information
ABSTRACT: Charge-transfer-induced decomposition
(CTID) of bicyclic dioxetanes 1b−d bearing a 3-hydrox-
ylphenyl moiety substituted with a benzothiazol-2-yl group at
the 2-, 6-, or 5-position was investigated, and their
chemiluminescence properties were compared to each other,
based on those for a 4-benzothiazolyl analogue 1a. Dioxetanes
1c and 1d underwent CTID to give the corresponding oxido
anions of keto esters 8c or 8d in the singlet excited state with
high efficiencies similarly to the case of 1a. On the other hand, 1b showed chemiluminescence with quite low efficiency, though it
gave exclusively keto ester 2b. The marked decline of chemiluminescence efficiency for 1b was attributed to 1b mainly being
decomposed to 8b through a radiationless pathway, in which intramolecular nucleophilic attack of nitrogen in the benzothiazolyl
group to dioxetane O−O took place to give cyclic intermediate cis-11.
hydroxyphenyl) group, to which a benzothiazolyl group was
attached at the 2-, 5-, or 6-position. These precursors 3b−d
were synthesized according to the synthetic process of 1a9
through several steps starting from the corresponding 4-tert-
butyl-3,3-dimethyl-2,3-dihydrofurans 4b−d bearing a 5-(form-
yl-3-methoxyphenyl) group, as illustrated in Scheme 1. The
initial step was condensation of 4b−d with 2-aminobenzene-
thiol to give exclusively the corresponding benzothiazolinyl
derivatives 5b−d, which were used for the next reaction
without further purification. The oxidation of benzothiazolines
5b−d was achieved by the use of 2,3-dichoro-5,6-dicyano-1,4-
benzoquinone (DDQ) in toluene to give dihydrofurans 6b−d
in high yields. Dihydrofurans 6b−d were finally demethylated
with sodium methanethiolate in hot DMF to give the desired
precursors 3b−d in 95, 85, and 89% yields, respectively. All of
3b−d underwent 1,2-addition of singlet oxygen to selectively
give the corresponding dioxetanes 1b−d in 69 (conversion
yield 97%), 100, and 98% yields. The structures of dioxetanes
INTRODUCTION
■
Dioxetanes substituted with an aromatic electron donor such as
the phenoxide anion undergo intramolecular charge-transfer-
induced decomposition (CTID) with an accompanying
emission of bright light.1−4 The phenomenon has received
considerable attention from the viewpoints of mechanistic
interest related to bioluminescence and application to clinical
and biological analysis.5−7 Thus, up to the present, a wide
variety of CTID-active dioxetanes have been designed and
synthesized. One such dioxetane is bicyclic dioxetane 1a
bearing a 4-(benzothiazol-2-yl)-3-hydroxyphenyl group, which
effectively emits light even in an aqueous system.8,9 To
understand how the benzothiazol-2-yl group functioned to
achieve high-performance chemiluminescence, we investigated
CTID of three isomeric dioxetanes 1b−d, in which a
benzothiazolyl group was attached at the 2-, 6-, or 5-position
on the 3-hydroxyphenyl group. We report here that these
isomeric dioxetanes 1b−d showed characteristic chemilumi-
nescence depending on the structure of the aromatic electron
donor, and that a radiationless decomposition of dioxetane 1b
concurrently took place with the chemiluminescent CTID,
though both decompositions gave the same keto ester 2b
(Chart 1).
1
1b−d were determined by H NMR, 13C NMR, IR, mass
spectral data, and elemental analyses. Furthermore, X-ray single
crystallographic analysis was successfully achieved for all
dioxetanes 1b−d. ORTEP views of dioxetanes 1b−d are
shown in the Supporting Information. All of these benzothia-
zolyl-substituted dioxetanes 1b−d were thermally stable
enough to permit handling at room temperature, though they
decomposed into the corresponding keto esters 2b−d when
heated in refluxing p-xylene.
RESULTS AND DISCUSSION
■
Synthesis of Bicyclic Dioxetanes 1b−d Bearing a 3-
Hydroxyphenyl Moiety Substituted with a Benzothia-
zol-2-yl Group. All of the dioxetanes 1b−d investigated here
were prepared by singlet oxygenation of the corresponding 4-
tert-butyl-3,3-dimethyl-2,3-dihydrofurans 3b−d bearing a 5-(3-
Received: March 13, 2012
Published: April 23, 2012
© 2012 American Chemical Society
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Chart 1. Bicyclic Dioxetanes 1a−d Bearing a 3-Hydroxyphenyl Moiety Substituted with a Benzothiazol-2-yl Group and Their
Decomposition Products 2a−d
Scheme 1. Synthetic Pathway of Dioxetanes 1b−d
Chemiluminescent Decomposition of Bicyclic Dioxe-
tanes Bearing a 3-Hydroxyphenyl Moiety Substituted
with a Benzothiazol-2-yl Group in a TBAF/Acetonitrile
System. Dioxetane 1a has been reported to decompose
Scheme 2. Base-Induced Decomposition of Dioxetanes 1b−
d and 7
according to the pseudo-first-order kinetics to give bright green
CL
light (maximum wavelength λmax
= 492 nm) with
chemiluminescence efficiency ΦCL = 0.28 and rate constant
of CTID kCTID = 4.2 × 10−4 s−1 at 45 °C (half-life t1/2 = ln 2/
kCTID = 1600 s) when treated with a large excess of
tetrabutylammonium fluoride (TBAF) in acetonitrile.8,9
Comparing chemiluminescence properties for 1a with those
for parent dioxetane 7 bearing an unsubstituted 3-hydrox-
yphenyl group (λmaxCL = 467 nm, ΦCL = 0.11, and t1/2 = 25 s in
TBAF/acetonitrile at 25 °C) (Scheme 2),10 we can see that the
benzothiazolyl group acts to considerably improve ΦCL, while
decreasing t1/2 by 2 orders.
Dioxetane 1b has a π-electron system of o-(benzothiazol-2-
yl)phenol formally the same as that of 1a, though the
benzothiazolyl group suffers the steric hindrance of the adjacent
dioxetane ring and a hydroxy group at the opposite side. On
treatment with TBAF (large excess) in acetonitrile at 25 °C,
dioxetane 1b decomposed far more rapidly than 1a with the
accompanying chemiluminescence, the λmaxCL of which was the
same as that for 1a, as shown in Table 1, though the spectrum
was broader than that for 1a, as shown in Figure 1. However,
Φ
CL for 1b was unexpectedly low (ΦCL = 0.0036)11,12 and only
1/80 of that for 1a.
Careful neutralization of the spent reaction mixture of 1b
gave selectively keto ester 2b as in the case of 1a giving 2a.
Oxido anion 8b generated from 2b in situ in TBAF/acetonitrile
showed fluorescence, the spectrum of which practically
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in Figure 1 and Table 1. Value of ΦCL for 1c was considerably
higher than that for 1b, though the rate of CTID markedly
decreased.
Table 1. TBAF-Induced Chemiluminescence of Dioxetanes
1a−d and 7
a
CL
λmax
/
b
Benzothiazolyl group of dioxetane 1d does not directly lie in
π-conjugation system with a hydroxy group and receives steric
effect from neither a dioxetane ring nor a hydroxyl group since
these three groups are in meta-relation among each other.
Therefore, the aromatic system of 1d lies in a different situation
from those for 1a, 1b, and 1c. Dioxetane 1d also underwent
TBAF-induced decomposition to give light, the spectrum of
which is shown in Figure 1. As shown in Table 1 and Figure 1,
comparing that for dioxetane 7 rather than 1a, the
chemiluminescence spectrum shifted to a longer wavelength
region, but both ΦCL and kCTID decreased for 1d: low ΦCL was
fl
dioxetane
nm
ΦCL
Φ
ΦS
kCTID/s−1
t1/2/s
c
1a
492
493
528
535
467
0.28
0.66
0.42
4.2 × 10−4
2.0 × 10−2
6.9 × 10−5
7.2 × 10−3
2.8 × 10−2
1600
34
1b
1c
1d
0.0036
0.011
0.044
0.11
0.67
0.0054
(0.46)
0.73
0.024
0.060
11000
96
d
e
7
0.24
0.46
25
a
Unless otherwise stated, reactions were carried out in a TBAF/
b
acetonitrile system at 45 °C. Based on a value reported for the
chemiluminescent decomposition of 3-adamantylidene-4-(3-tert-butyl-
dimethylsiloxyphenyl)-4-methoxy-1,2-dioxetane in TBAF/DMSO.11,12
c
d
From ref 9. From ref 10. Chemiluminescent decomposition was
fl
e
attributed to low Φ of the emitter (vide infra). Such a
carried out at 25 °C. From ref 13.
tendency has been observed for various dioxetanes bearing a 5-
aryl-3-hydroxyphenyl group (1,3,5-trisubstitution pattern).14
Both dioxetanes 1c and 1d gave also the corresponding keto
esters 2c and 2d in high yields after careful neutralization of
spent reaction mixtures, as in the case of 1a and 1b.
Fluorescence spectrum of authentic emitter 8d generated
from 2d coincided with the chemiluminescence spectrum of
dioxetane 1d (Figure 2). On the basis of fluorescence efficiency
fl
Φ (0.060) for 8d, singlet chemiexcitation efficiency ΦS for 1d
was estimated to be as high as or rather higher than for 1a, as
shown in Table 1. On the other hand, authentic emitter 8c
fl
generated from 2c showed fluorescence (Φ = 0.024), the
spectrum of which did not coincide with the chemilumines-
cence spectrum of 1c and showed two peaks, differently from
the case of 8a, 8b, and 8d (Figure 2). Notably, the
concentration of 8c did not affect the shape of the spectrum.
Thus, the fluorescence spectrum of 8c was analyzed to
comprise two fluorescence spectra: the first coincided with
Figure 1. Chemiluminescence spectra of dioxetanes 1a−d.
coincided with chemiluminescence spectrum of 1b (Figure 2).
This result showed that 8b was the emitter produced through
fl
the chemiluminescence spectrum of 1c (λmax = 528 nm), and
fl
the second was one with λmax = 466 nm (Figure 2 and the
Supporting Information). This finding suggests that 8c should
exist as an equilibrium mixture of at least two species.15 Here,
chemiexcitation efficiency ΦS for 1c was formally estimated to
be as high as that for 1a (Table 1), though it could not reliably
be estimated because of a discrepancy in the spectrum between
chemiluminescence of 1c and the fluorescence of 8c.
As described above, singlet chemiexcitation effectively
occurred for CTID of 1a, 1c, and 1d but not for 1b.
Considering that 1a and 1b both have an ortho-benzothiazolyl-
substituted phenol group as an important aromatic electron
donor as well as a fluorophore and that the authentic emitters
8a and 8b both effectively show fluorescence, the marked
decrease in ΦS for CTID of 1b was unexpected. Thus, we
thought that 1b may decompose to keto ester 8b through a
new concurrent pathway(s) that did not lead to chemilumi-
nescence. A clue to understanding this radiationless decom-
position was found when we measured the melting point of 1b.
After a sample of crystalline 1b was heated to melting (100
°C), we found the unusual decomposition product trans-10 in
addition to intact dioxetane 1b and keto ester 2b. Chromato-
graphic purification (SiO2) gave crystalline trans-10, the
structure of which was determined by X-ray single crystallo-
Figure 2. Fluorescence spectra of authentic 8a−d generated from 2a−
d in TBAF/acetonitrile.
9b from 1b (Scheme 2). On the basis of fluorescence efficiency
fl
Φ = 0.67 measured for 8b, singlet chemiexcitation efficiency
fl
ΦS (=ΦCL/Φ ) for 1b was estimated to be only 0.0054 and 1/
80 of that for 1a. Therefore, unexpected decline of ΦCL for 1b
was attributed to quite low ΦS. Thus, we decided to investigate
TBAF-induced decomposition of analogous dioxetanes 1c and
1d to understand why 1b gave such a poor chemiluminescence.
Benzothiazolyl group of dioxetane 1c lies in a π-conjugation
system with a hydroxy group, though at the para-position
differently from the case of 1a and 1b, and receives steric effect
of the adjacent dioxetane ring as 1b. When 1c was treated in a
TBAF/acetonitrile system similarly to the case of 1b, 1c
showed chemiluminescence, the spectrum of which shifted to a
longer wavelength region from the case of 1a and 1b, as shown
1
graphic analysis (Supporting Information). However, the H
NMR and 13C NMR spectra of pure trans-10 could not be
measured because of its instability: trans-10 was contaminated
by ca. 10% of keto ester 2b. Notably, crystalline 1a, 1c, and 1d
exclusively gave the corresponding keto esters 2a, 2c, and 2d
when heated to melting.
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Scheme 3. Radiationless Decomposition of Dioxetane 1b to Keto Ester 2b
The unusual decomposition product trans-10 was thought to
be derived from an intramolecular redox reaction between the
benzothiazolyl nitrogen and the O−O in dioxetane 1b. A redox
reaction between an amine and a dioxetane has been reported
by Adam and his co-workers: a primary or secondary amine
attacks a dioxetane to give the corresponding 2-amino-
oxyethanol, while tertiary amine catalyzes the decomposition
of dioxetane to two carbonyl fragments through an as-yet-
undetected aminooxy intermediate.16 Thus, trans-10 was the
first example of an aminooxy intermediate for the tert-amine-
catalyzed decomposition of dioxetane. In fact, when heated at
>100 °C, trans-10 changed exclusively to 2b. However, such a
redox reaction would directly give isomeric cis-10 but not trans-
10. Although product cis-10 could not be isolated in pure form
after thermolysis of crystalline 1b (vide infra),17 its structure
was fortunately determined by X-ray single crystallographic
analysis of a eutectic crystal of 1b and cis-10 (1:1) obtained
during the recrystallization of 1b (Supporting Information).
The results described above encouraged us to investigate
whether or not 1b produced 10 or its anion cis-11 even in
TBAF/acetonitrile. Upon treatment with even only 1 equiv of
TBAF in acetonitrile at 45 °C, 1b exclusively gave 2b after 30
min. However, when the amount of TBAF was further
decreased to 0.3 equiv, 1b was found to produce cis-10
(29%) and 2b (64%) along with a trace amount of 1b and
trans-10 after 10 h. Thus, cis-10 contaminated with ca. 10% of
2b was obtained as yellow crystals by rinsing from a reaction
mixture after usual workup. The product cis-10 was, of course,
rapidly and exclusively transformed to 2b on further treatment
with TBAF.
contrast to CTID of 9b. Hence, the base-induced decom-
position of 1b gave only weak light.
CONCLUSION
■
CTID of bicyclic dioxetanes 1b−d bearing a benzothiazolyl-
substituted 3-hydroxylphenyl group was investigated, and their
chemiluminescence properties were compared, based on those
for 1a. While dioxetanes 1c and 1d underwent CTID to give
the corresponding keto esters 8c and 8d in a singlet excited
state with high efficiencies as with 1a, 1b led to singlet
chemiexcitation with quite low efficiency. The unusually low
singlet chemiexcitation efficiency for 1b was attributed to the
decomposition of oxido anion 9b to 8b mainly through a
radiationless pathway in which intramolecular nucleophilic
attack of the nitrogen of benzothiazolyl group took place on the
dioxetane O−O to give cis-11.
EXPERIMENTAL SECTION
■
General. Melting points were uncorrected. IR spectra were taken
1
on a FT/IR infrared spectrometer. H and 13C NMR spectra were
recorded on a 400 and 500 MHz spectrometers. Mass spectra were
obtained by using double-focusing mass spectrometers and an ESI-
TOF mass spectrometer. X-ray diffraction data were collected on a
CCD diffrectometer with graphite monochromated MoKα
(λ=0.71070 Å) radiation. Column chromatography was carried out
using silica gel.
4-tert-Butyl-5-(2-formyl-3-methoxyphenyl)-3,3-dimethyl-
2,3-dihydrofuran (4b): Pale yellow oil; 1H NMR (400 MHz,
CDCl3) δH 1.01 (s, 9H), 1.35 (s, 6H), 3.92 (s, 2H), 3.93 (s, 3H), 6.94
(dd, J = 7.6 and 1.0 Hz, 1H), 6.99 (d, J = 8.4 Hz, 1H), 7.48 (dd, J = 8.4
and 7.6 Hz, 1H), 10.35 (s, 1H) ppm; 13C NMR (125 MHz, CDCl3) δC
27.0, 32.0, 32.5, 47.2, 55.9, 83.5, 112.1, 123.5, 124.0, 127.1, 134.1,
140.0, 146.1, 160.6, 190.8 ppm; IR (liquid film) ν 2957, 2867, 2762,
1698, 1652, 1587, 1577 cm−1; mass (m/z, %) 288 (M+, 8), 273 (12),
232 (16), 231 (100), 217 (24), 201 (17), 189 (11), 163 (11); HRMS
(ESI) 311.1656, calcd for C18H24O3Na [M + Na+] 311.1623.
4-tert-Butyl-5-(2-formyl-5-methoxyphenyl)-3,3-dimethyl-
2,3-dihydrofuran (4c): Colorless plates, mp 61.5−62.0 °C (from
The results described above showed that the decomposition
of 9b (oxido anion of 1b) to 8b (isolated as 2b) through
intermediate cis-11 (isolated as cis-10) should occur con-
currently with chemiluminescent CTID to give 8b in TBAF/
acetonitrile. Scheme 3 offers a plausible process, in which
nucleophilic attack of the nitrogen in the benzothiazolyl group
takes place on O−O of dioxetane 9b to give intermediate cis-11,
which spontaneously undergoes cleavage of a C−C bond of the
tetrahydrofuran ring to finally give keto ester 8b. This process
would not cause chemiexcitation of any carbonyl fragment, in
1
hexane); H NMR (500 MHz, CDCl3) δH 1.03 (s, 9H), 1.37 (s, 6H),
3.89 (s, 3H), 3.94 (s, 2H), 6.84 (d, J = 2.4 Hz, 1H), 6.97 (dd, J = 8.8
and 2.4 Hz, 1H), 7.93 (d, J = 8.8 Hz, 1H), 10.04 (s, 1H) ppm; 13C
NMR (125 MHz, CDCl3) δC 27.1, 32.1, 32.5, 47.4, 55.5, 83.4, 114.7,
116.1, 128.0, 129.0, 129.1, 141.7, 144.9, 163.5, 190.5 ppm; IR (KBr) ν
2981, 2861, 2763, 1655, 1690, 1601 cm−1; mass (m/z, %) 288 (M+, 7),
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233 (58), 232 (16), 231 (68), 217 (35), 201 (17), 189 (17), 163
(100); HRMS (ESI) 311.1613, calcd for C18H24O3Na [M + Na+]
311.1623.
coupling, J = 8.2 Hz, 1H) ppm; 13C NMR (125 MHz, CDCl3) δC 27.4,
32.5, 32.5, 47.2, 55.6, 83.2, 112.0, 118.6, 121.5, 121.8, 123.2, 125.2,
126.3, 126.3, 134.5, 135.0, 138.2, 148.8, 154.0, 159.6, 167.6 ppm; IR
(KBr) ν 3442, 2982, 2955, 2924, 2854, 1605, 1584, 1508, 1458, 1422,
1337 cm−1; mass (m/z, %) 394 (M+ + 1, 7), 393 (M+, 25), 379 (24),
378 (100), 322 (26). HRMS (ESI): 394.1844, calcd for C24H28NO2S
[M + H+] 394.1841, 416.1666, calcd for C24H27NO2SNa [M + Na+]
416.1660. Anal. Calcd for C24H27NO2S: C, 73.25; H, 6.92; N, 3.56.
Found: C, 73.25; H, 7.08; N, 3.57.
Synthesis of 5-[2-(Benzothiazol-2-yl)-3-hydroxyphenyl]-4-
tert-butyl-3,3-dimethyl-2,3-dihydrofuran (3b). Typical Proce-
dure: A solution of 5-[2-(benzothiazol-2-yl)-3-methoxyphenyl]-4-tert-
butyl-3,3-dimethyl-2,3-dihydrofuran (6b) (537 mg, 1.36 mmol) and
sodium thiomethoxide (200 mg, 2.85 mmol, 2.09 equiv) in dry DMF
(5 mL) was stirred under a nitrogen atmosphere at 140 °C for 10 min.
The reaction mixture was poured into saturated aqueous NH4Cl and
extracted with AcOEt. The organic layer was washed three times with
saturated aqueous NaCl, dried over anhydrous MgSO4, and
concentrated in vacuo. The residue was chromatographed on silica
gel and eluted with AcOEt−hexane (1:9) to give 493 mg of 5-[2-
(benzothiazol-2-yl)-3-hydroxyphenyl]-4-tert-butyl-3,3-dimethyl-2,3-di-
hydrofuran (3b) as a pale yellow solid in 95% yield.
4-tert-Butyl-5-(3-formyl-5-methoxyphenyl)-3,3-dimethyl-
1
2,3-dihydrofuran (4d): Colorless oil; H NMR (400 MHz, CDCl3)
δH 1.06 (s, 9H), 1.35 (s, 6H), 3.87 (s, 3H), 3.89 (s, 2H), 7.11 (s with
fine coupling, 1H), 7.35 (s with fine coupling, 1H), 7.41 (s, 1H), 9.96
(s, 1H) ppm; 13C NMR (125 MHz, CDCl3) δC 27.3, 32.5, 32.6, 47.3,
55.6, 83.3, 112.0, 122.8, 125.2, 126.8, 137.4, 138.4, 148.2, 159.8, 191.8
ppm; IR (liquid film) ν 2958, 2868, 2729, 1700, 1463, 1335, 1054
cm−1; mass (m/z, %) 288 (M+, 24), 274 (19), 273 (100), 217 (14),
163 (32); HRMS (ESI) 311.1653, calcd for C18H24O3Na [M + Na+]
311.1623.
Synthesis of 5-[2-(Benzothiazol-2-yl)-3-methoxyphenyl]-4-
tert-butyl-3,3-dimethyl-2,3-dihydrofuran (6b). Typical Proce-
dure: A solution of 4-tert-butyl-5-(2-formyl-3-methoxyphenyl)-3,3-
dimethyl-2,3-dihydrofuran (4b) (7.12 g, 24.7 mmol) and 2-amino-
benzenethiol (2.90 mL, 27.2 mmol, 1.1 equiv) in dry EtOH (140 mL)
was mixed under a nitrogen atmosphere at room temperature and
stirred for 5 h. The reaction mixture was concentrated in vacuo to give
10.5 g of crude 4-tert-butyl-5-[2-(2,3-dihydrobenzothiazol-2-yl)-3-
methoxyphenyl]-3,3-dimethyl-2,3-dihydrofuran 5b as a pale yellow
oil. The crude 5b was used for the next reaction without further
purification.
A solution of crude 5b and 2,3-dichloro-5,6-dicyano-1,4-benzoqui-
none (DDQ) (5.60 g, 24.7 mmol, 1.00 equiv) in dry toluene (80 mL)
was refluxed for 50 min. After cooling, the reaction mixture was filtered
and concentrated in vacuo. The residue was chromatographed on silica
gel and eluted with AcOEt−hexane (1:4) to give 9.01 g of 5-[2-
(benzothiazol-2-yl)-3-methoxyphenyl]-4-tert-butyl-3,3-dimethyl-2,3-di-
hydrofuran (6b) as a colorless solid in 93% yield based on 4b.
According to the procedure described above, 5-[2-(benzothiazol-2-
yl)-5-methoxyphenyl]-4-tert-butyl-3,3-dimethyl-2,3-dihydrofuran (6c)
and 5-[3-(benzothiazol-2-yl)-5-methoxyphenyl]-4-tert-butyl-3,3-di-
methyl-2,3-dihydrofuran (6d) were synthesized by using the
corresponding benzaldehydes 4c and 4d instead of 4b in 62 and
77% yield, respectively.
(Benzothiazol-2-yl)-3-methoxyphenyl-substituted dihydrofurans 6c
and 6d were similarly demethylated with sodium thiomethoxide to
give 5-[2-(benzothiazol-2-yl)-5-hydroxyphenyl]-4-tert-butyl-3,3-di-
methyl-2,3-dihydrofuran (3c) and 5-[3-(benzothiazol-2-yl)-5-hydrox-
yphenyl]-4-tert-butyl-3,3-dimethyl-2,3-dihydrofuran (3d) in 85 and
89% yield, respectively.
3b: Pale yellow granules, mp 171.0−171.5 °C (from AcOEt−
1
hexane); H NMR (400 MHz, CDCl3) δH 1.05 (s, 9H), 1.42 (s, 3H),
1.51 (s, 3H), 4.03 (d, J = 8.3 Hz, 1H), 4.17 (d, J = 8.3 Hz, 1H), 6.87
(dd, J = 7.3 and 1.3 Hz, 1H), 7.13 (dd, J = 8.3 and 1.3 Hz, 1H), 7.33
(dd, J = 8.3 and 7.3 Hz, 1H), 7.42 (ddd, J = 7.9, 7.2, and 1.2 Hz, 1H),
7.51 (ddd, J = 8.2, 7.2, and 1.2 Hz, 1H), 7.93 (d with fine coupling, J =
7.9 Hz, 1H), 8.01 (d with fine coupling, J = 8.2 Hz, 1H), 13.93 (s, 1H)
ppm; 13C NMR (125 MHz, CDCl3) δC 25.7, 29.0, 31.7, 32.9, 47.6,
83.4, 116.2, 118.7, 121.1, 121.9, 123.5, 125.4, 126.5, 127.7, 131.3,
133.9, 135.4, 147.7, 149.4, 159.4, 167.3 ppm; IR (KBr) ν 3435, 2984,
2952, 2928, 2866, 2700, 2586, 1575, 1466, 1454, 1444 cm−1; mass (m/
z, %) 379 (M+, 0.3), 364 (20), 323 (21), 322 (100), 308 (17), 254
(10), 57 (12). HRMS (ESI): 380.1682, calcd for C23H26NO2S [M +
H+] 380.1684, 402.1512, calcd for C23H25NO2SNa [M + Na+]
402.1504. Anal. Calcd for C23H25NO2S: C, 72.79; H, 6.64; N, 3.69.
Found: C, 72.79; H, 6.75; N, 3.78.
3c: Colorless columns, mp 206.5−207.0 °C (from AcOEt−hexane);
1H NMR (400 MHz, CDCl3) δH 0.94 (s, 9H), 1.36 (s, 6H), 3.90−4.20
(m, 2H), 5.77 (s, 1H), 6.85 (d, J = 2.7 Hz, 1H), 6.91 (dd, J = 8.5 and
2.7 Hz, 1H), 7.37 (ddd, J = 7.9, 7.2, and 1.2 Hz, 1H), 7.47 (ddd, J =
8.2, 7.2, and 1.2 Hz, 1H), 7.90 (d with fine coupling, J = 7.9 Hz, 1H),
8.03 (d, J = 8.5 Hz, 1H), 8.06 (d with fine coupling, J = 8.2 Hz, 1H)
ppm; 13C NMR (125 MHz, CDCl3) δC 26.1 (broad), 28.4 (broad),
31.8, 32.6, 47.2, 83.2, 116.3, 119.0, 121.3, 122.8, 124.8, 126.0, 126.0,
127.0, 131.6, 135.9, 136.6, 146.8, 152.7, 157.4, 166.7 ppm; IR (KBr) ν
3388, 3058, 2966, 2929, 2908, 2864, 2777, 2677, 2586, 1608, 1568,
1465, 1432 cm−1; mass (m/z, %) 379 (M+, 0.3), 364 (14), 323 (20),
322 (100), 308 (15), 254 (11). HRMS (ESI): 380.1696, calcd for
C23H26NO2S [M + H+] 380.1684, 402.1517, calcd for C23H25NO2SNa
[M + Na+] 402.1504. Anal. Calcd for C23H25NO2S: C, 72.79; H, 6.64;
N, 3.69. Found: C, 72.79; H, 6.83; N, 3.75.
6b: Colorless granules, mp 120.0−120.5 °C (from AcOEt−
1
hexane); H NMR (400 MHz, CDCl3) δH 0.88 (s, 9H), 0.75−1.40
(m, 6H), 3.77 (s, 2H), 3.82 (s, 3H), 6.98−7.04 (m, 2H), 7.38 (ddd, J =
7.9, 7.2, and 1.2 Hz, 1H), 7.41 (dd, J = 8.3 and 7.8 Hz, 1H), 7.47 (ddd,
J = 8.2, 7.2, and 1.2 Hz, 1H), 7.92 (d with fine coupling, J = 7.9 Hz,
1H), 8.09 (d with fine coupling, J = 8.2 Hz, 1H) ppm; 13C NMR (125
MHz, CDCl3) δC 26.9 (broad), 31.7, 32.4, 46.7, 56.0, 82.8, 111.3,
121.1, 123.1, 123.2, 123.6, 124.7, 125.5, 126.1, 130.4, 136.4, 137.9,
146.7, 152.9, 157.5, 162.6 ppm; IR (KBr) ν 3434, 2989, 2924, 2864,
1654, 1577, 1468, 1429 cm−1; mass (m/z, %) 393 (M+, 0.2), 378 (16),
337 (22), 336 (100), 322 (15); HRMS (ESI) 394.1852, calcd for
C24H28NO2S [M + H+] 394.1841, 416.1673, calcd for C24H27NO2SNa
[M + Na+] 416.1660. Anal. Calcd for C24H27NO2S: C, 73.25; H, 6.92;
N, 3.56. Found: C, 73.18; H, 7.07; N, 3.67.
1
6c: Colorless oil; H NMR (400 MHz, CDCl3) δH 0.94 (s, 9H),
1.37 (s, 6H), 3.88 (s, 3H), 3.92−4.20 (m, 2H), 6.89 (d, J = 2.7 Hz,
1H), 7.01 (dd, J = 8.8 and 2.7 Hz, 1H), 7.36 (ddd, J = 7.9, 7.2, and 1.2
Hz, 1H), 7.47 (ddd, J = 8.2, 7.2, and 1.2 Hz, 1H), 7.90 (d with fine
coupling, J = 7.9 Hz, 1H), 8.06 (d with fine coupling, J = 8.2 Hz, 1H),
8.11 (d, J = 8.8 Hz, 1H) ppm; 13C NMR (125 MHz, CDCl3) δC 26.2
(broad), 28.4 (broad), 31.8, 32.6, 47.2, 55.5, 83.3, 114.6, 117.2, 121.2,
123.0, 124.6, 125.9, 126.5, 126.6, 131.5, 136.1, 136.4, 147.2, 153.1,
160.5, 166.1 ppm; IR (liquid film) ν 2957, 2934, 2868, 1602, 1566,
1482, 1463, 1433 cm−1; mass (m/z, %) 393 (M+, 0.7), 378 (15), 337
(22), 336 (100), 322 (15), 268 (9). HRMS (ESI): 394.1854, calcd for
C24H28NO2S [M + H+] 394.1841, 416.1673, calcd for C24H27NO2SNa
[M + Na+] 416.1660.
6d: Pale yellow granules, mp 139.0−140.0 °C (from AcOEt−
hexane); 1H NMR (400 MHz, CDCl3) δH 1.10 (s, 9H), 1.37 (s, 6H),
3.91 (s, 2H), 3.92 (s, 3H), 6.98 (dd, J = 2.6 and 1.3 Hz, 1H), 7.39
(ddd, J = 7.9, 7.2, and 1.2 Hz, 1H), 7.49 (ddd, J = 8.2, 7.2, and 1.3 Hz,
1H), 7.59 (dd, J = 1.6 and 1.3 Hz, 1H), 7.64 (dd, J = 2.6 and 1.6 Hz,
1H), 7.90 (d with fine coupling, J = 7.9 Hz, 1H), 8.08 (d with fine
3d: Colorless granules, mp 190.0−191.0 °C (from CH2Cl2−
1
hexane); H NMR (400 MHz, CDCl3) δH 1.06 (s, 9H), 1.33 (s, 6H),
3.89 (s, 2H), 6.95 (t, J = 1.8 Hz, 1H), 7.32 (s, 1H), 7.34 (ddd, J = 8.0,
7.3, and 1.1 Hz, 1H), 7.44 (ddd, J = 8.2, 7.3, and 1.1 Hz, 1H), 7.53 (d,
J = 1.8 Hz, 2H), 7.82 (d with fine coupling, J = 8.0 Hz, 1H), 8.04 (d, J
= 8.2 Hz, 1H) ppm; 13C NMR (125 MHz, CDCl3) δC 27.3, 32.5, 32.5,
47.2, 83.1, 114.2, 120.3, 121.5, 121.6, 123.0, 125.3, 126.4, 126.6, 134.2,
134.8, 138.3, 148.5, 153.6, 156.3, 168.1 ppm; IR (KBr) ν 3494, 2980,
2967, 2910, 2869, 1608, 1597, 1465, 1438, 1429 cm−1; mass (m/z, %)
380 (M+ + 1, 7), 379 (M+, 26), 365 (25), 364 (100), 308 (27), 254
(10), 226 (8); HRMS (ESI) 380.1691, calcd for C23H26NO2S [M +
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H+] 380.1684, 402.1509, calcd for C23H25NO2SNa [M + Na+]
402.1504. Anal. Calcd for C23H25NO2S: C, 72.79; H, 6.64; N, 3.69.
Found: C, 72.79; H, 6.77; N, 3.72.
and eluted with AcOEt−hexane (1:9) to give 2,2,4,4-tetramethyl-3-
oxopentyl 2-(benzothiazol-2-yl)-3-hydroxybenzoate (2b) as a pale
yellow oil (165 mg, 98% yield).
Singlet Oxygenation of 5-[2-(Benzothiazol-2-yl)-3-hydrox-
yphenyl]-4-tert-butyl-3,3-dimethyl-2,3-dihydrofuran (3b). Typ-
ical Procedure: A solution of dihydrofuran 3b (202 mg, 0.532 mmol)
and tetraphenylporphyrin (TPP) (1.5 mg) in CH2Cl2 (10 mL) was
irradiated externally with a 940 W Na lamp under an oxygen
atmosphere at 0 °C for 8.5 h. After the concentration of the
photolysate in vacuo, the residue was chromatographed on silica gel
and eluted with CH2Cl2−hexane (4:1) and then with AcOEt−hexane
(1:1) to give intact 3b (60 mg, 30%) and 1-[2-(benzothiazol-2-yl)-3-
hydroxyphenyl]-5-tert-butyl-4,4-dimethyl-2,6,7-trioxabicyclo[3.2.0]-
heptane (1b) as a pale yellow solid (150 mg, 69% yield (CY = 97%)).
Dihydrofurans 3c and 3d were similarly oxygenated with singlet
oxygen to give the corresponding dioxetanes 1c and 1d in 100 and
98% yields, respectively.
1b: Colorless granules, mp 100.5−101.0 °C (dec) (from CH2Cl2−
hexane); 1H NMR (500 MHz, CDCl3) δH 0.95 (s, 9H), 1.03 (broad s,
3H), 1.06 (s, 3H), 3.81 (d, J = 8.2 Hz, 1H), 4.55 (d, J = 8.2 Hz, 1H),
7.14 (dd, J = 8.2 and 1.1 Hz, 1H), 7.28−7.36 (m, 1H), 7.42 (dd, J =
8.2 and 7.8 Hz, 1H), 7.43 (ddd, J = 8.0, 7.3, and 1.1 Hz, 1H), 7.52
(ddd, J = 8.0, 7.3, and 1.1 Hz, 1H), 7.92 (d, J = 8.0 Hz, 1H), 8.10 (d, J
= 8.0 Hz, 1H), 8.36 (s, 1H) ppm; 13C NMR (125 MHz, CDCl3) δC
19.0, 24.6, 26.9, 36.7, 45.1, 80.4, 106.1, 117.0, 118.1, 118.7, 121.2,
122.2, 123.0, 125.4, 126.1, 130.5, 135.1, 136.8, 151.8, 155.4, 165.5
ppm; IR (KBr) ν 3493, 3314, 3218, 3065, 2974, 2919, 2806, 2681,
1586, 1463 cm−1; mass (m/z, %) 412 (M+ + 1, 14), 411 (M+, 57), 271
(13), 255 (17), 254 (100), 253 (33), 227 (27), 198 (12), 57 (15);
HRMS (ESI) 412.1597, calcd for C23H26NO4S [M + H+] 412.1583,
434.1422, calcd for C23H25NO4SNa [M + Na+] 434.1402. Anal. Calcd
for C23H25NO4S·1/2CH2Cl2: C, 62.17; H, 5.77; N, 3.09. Found: C,
62.19; H, 6.08; N, 3.19.
Dioxetanes 1c and 1d were similarly decomposed to give the
corresponding keto esters 2c and 2d in 98 and 97% yields,
respectively.
1
2b: Colorless oil; H NMR (500 MHz, CDCl3) δH 1.12 (s, 9H),
1.28 (s, 6H), 4.40 (s, 2H), 7.10 (dd, J = 7.4 and 1.4 Hz, 1H), 7.22 (dd,
J = 8.4 and 1.4 Hz, 1H), 7.38 (dd, J = 8.4 and 7.4 Hz, 1H), 7.45 (ddd, J
= 7.8, 7.3, and 1.2 Hz, 1H), 7.53 (ddd, J = 8.1, 7.3, and 1.4 Hz, 1H),
7.93 (d with fine coupling, J = 7.8 Hz, 1H), 8.04 (d with fine coupling,
J = 8.1 Hz, 1H), 12.68 (s, 1H) ppm; 13C NMR (125 MHz, CDCl3) δC
23.5, 27.8, 45.7, 48.7, 73.7, 114.7, 120.3, 120.6, 121.3, 122.3, 125.8,
126.7, 131.7, 133.1, 134.2, 150.4, 158.1, 166.1, 168.7, 215.6 ppm; IR
(liquid film) ν 3351, 2974, 2872, 1724, 1685, 1579, 1477, 1454 cm−1;
mass (m/z, %) 412 (M+ + 1, 11), 411 (M+, 40), 255 (17), 254 (100),
253 (32), 227 (29), 198 (12), 57 (20); HRMS (ESI) 412.1598, calcd
for C23H26NO4S [M + H+] 412.1583, 434.1415, calcd for
C23H25NO4SNa [M + Na+] 434.1402.
1
2c: Colorless oil; H NMR (500 MHz, CDCl3) δH 1.04 (s, 6H),
1.10 (s, 9H), 4.23 (s, 2H), 6.92 (dd, J = 8.4 and 2.6 Hz, 1H), 7.13 (d, J
= 2.6 Hz, 1H), 7.39 (ddd, J = 8.0, 7.2, and 1.1 Hz, 1H), 7.47 (d, J = 8.4
Hz, 1H), 7.48 (ddd, J = 8.1, 7.2, and 1.2 Hz, 1H), 7.88 (d with fine
coupling, J = 8.0 Hz, 1H), 8.02 (d, J = 8.1 Hz, 1H), 8.76 (broad s, 1H)
ppm; 13C NMR (125 MHz, CDCl3) δC 23.1, 27.9, 45.7, 48.7, 72.8,
117.1, 118.5, 121.5, 122.9, 124.3, 125.2, 126.3, 132.1, 133.0, 135.6,
153.1, 158.6, 167.5, 167.7, 217.0 ppm; IR (liquid film) ν 3355, 3060,
2976, 2934, 2873, 2793, 2683, 2607, 1726, 1685, 1605, 1576, 1479,
1434, 1367 cm−1; mass (m/z, %) 411 (M+, 6), 355 (10), 255 (16), 254
(100), 227 (42), 57 (23); HRMS (ESI) 434.1414, calcd for
C23H25NO4SNa [M + Na+] 434.1402.
2d: Colorless needles, mp 185.5−186.0 °C (from AcOEt−hexane);
1H NMR (400 MHz, CDCl3) δH 1.33 (s, 9H), 1.43 (s, 6H), 4.44 (s,
1c: Colorless granules, mp 181.0−181.5 °C (dec) (from AcOEt−
hexane); 1H NMR (500 MHz, CDCl3) δH 0.89 (broad s, 3H), 1.00 (s,
3H), 1.01 (s, 9H), 3.61 (d, J = 8.2 Hz, 1H), 4.42 (d, J = 8.2 Hz, 1H),
6.85 (dd, J = 8.5 and 2.7 Hz, 1H), 7.25 (d, J = 8.5 Hz, 1H), 7.31
(broad s, 1H), 7.40 (ddd, J = 8.0, 7.3, and 1.1 Hz, 1H), 7.47 (ddd, J =
8.0, 7.3, and 1.1 Hz, 1H), 7.63 (broad s, 1H), 7.87 (d, J = 8.0 Hz, 1H),
8.04 (d, J = 8.0 Hz, 1H) ppm; 13C NMR (125 MHz, CDCl3) δC 19.1,
24.4 (broad), 27.0, 36.7, 45.2, 80.3, 106.1, 116.5, 116.8, 117.9, 121.1,
123.0, 125.1, 125.1, 126.0, 133.7, 136.3, 136.5, 151.9, 157.1, 169.3
ppm; IR (KBr) ν 3441, 3067, 3007, 2982, 2959, 2896, 1605, 1479,
1432, 1306 cm−1; mass (m/z, %) 411 (M+, 8), 355 (11), 255 (17), 254
(100), 227 (40), 57 (16); HRMS (ESI) 412.1594, calcd for
C23H26NO4S [M + H+] 412.1583, 434.1420, calcd for C23H25NO4SNa
[M + Na+] 434.1402. Anal. Calcd for C23H25NO4S: C, 67.13; H, 6.12;
N, 3.40. Found: C, 67.11; H, 6.23; N, 3.45.
1d: Colorless columns, mp 141.0−141.5 °C (dec) (from CH2Cl2−
hexane); 1H NMR (400 MHz, CDCl3) δH 1.02 (s, 9H), 1.17 (s, 3H),
1.39 (s, 3H), 3.84 (d, J = 8.3 Hz, 1H), 4.60 (d, J = 8.3 Hz, 1H), 6.35
(s, 1H), 7.27 (dd, J = 2.4 and 1.5 Hz, 1H), 7.40 (ddd, J = 8.1, 7.2, and
1.2 Hz, 1H), 7.49 (ddd, J = 8.2, 7.2, and 1.3 Hz, 1H), 7.71 (dd, J = 2.4
and 1.5 Hz, 1H), 7.84 (dd, J = 1.5 and 1.5 Hz, 1H), 7.89 (d with fine
coupling, J = 8.1 Hz, 1H), 8.08 (d with fine coupling, J = 8.2 Hz, 1H)
ppm; 13C NMR (100 MHz, CDCl3) δC 18.5, 25.2, 27.0, 36.8, 45.7,
80.3, 105.2, 115.1, 116.0, 118.3, 120.2, 121.6, 123.2, 125.4, 126.4,
134.5, 135.0, 138.7, 153.7, 156.1, 167.3 ppm; IR (KBr) ν 3388, 3073,
2979, 2967, 2696, 1600, 1488, 1433, 1346 cm−1; mass (m/z, %) 411
(M+, 5), 355 (39), 354 (10), 272 (10), 271 (19), 255 (15), 254 (100),
227 (30), 226 (28), 57 (20); HRMS (ESI) 412.1598, calcd for
C23H26NO4S [M + H+] 412.1583, 434.1409, calcd for C23H25NO4SNa
[M + Na+] 434.1402. Anal. Calcd for C23H25NO4S: C, 67.13; H, 6.12;
N, 3.40. Found: C, 67.03; H, 6.19; N, 3.43.
2H), 6.01 (s, 1H), 7.41 (ddd, J = 8.1, 7.2, and 1.2 Hz, 1H), 7.50 (ddd,
J = 8.2, 7.2, and 1.2 Hz, 1H), 7.56 (dd, J = 2.6 and 1.3 Hz, 1H), 7.86
(dd, J = 2.6 and 1.6 Hz, 1H), 7.91 (d with fine coupling, J = 8.1 Hz,
1H), 8.06 (d with fine coupling, J = 8.2 Hz, 1H), 8.16 (dd, J = 1.6 and
1.3 Hz, 1H) ppm; 13C NMR (125 MHz, CDCl3) δC 23.7, 28.1, 46.0,
49.2, 72.6, 118.1, 119.2, 120.9, 121.6, 123.1, 125.6, 126.5, 132.1, 134.7,
134.9, 153.4, 157.0, 165.4, 167.1, 216.7 ppm; IR (KBr) ν 3434, 2973,
1696, 1685, 1614, 1601, 1437, 1374, 1334 cm−1; mass (m/z, %) 411
(M+, 5), 355 (39), 354 (10), 272 (10), 271 (19), 255 (16), 254 (100),
227 (28), 226 (25), 57 (22); HRMS (ESI) 412.1605, calcd for
C23H26NO4S [M + H+] 412.1583, 434.1411, calcd for C23H25NO4SNa
[M + Na+] 434.1402. Anal. Calcd for C23H25NO4S: C, 67.13; H, 6.12;
N, 3.40. Found: C, 67.06; H, 6.11; N, 3.44.
Time Course of Thermal Decomposition of Crystalline 1b at
80 °C. Crystalline 1b (20.0 mg) was heated at 80 °C, and after 1, 2, 3,
1
and 4 h, product distribution was monitored by H NMR in CDCl3
(Figure S1).
Thermal Decomposition of Crystalline 1b To Isolate trans-
10. Crystalline 1b (21.5 mg) was heated at 90 °C for 45 min to give a
mixture of 2b and trans-10. After cooling, the crude product was
chromatographed on NH−silica gel and eluted with AcOEt−MeOH
(9: 1) to give a mixture of 2b and trans-10 (37:63) as a pale yellow oil
(13.2 mg), which was crystallized from CHCl3−hexane to give
colorless plates of trans-10 including 10% of 1b. Further purification of
trans-10 was unsuccessful because of its thermal and chemical (silica
gel) instability: trans-10 gradually decomposed to 2b during isolation
and purification process even though at low temperature.
1
trans-10: H NMR (500 MHz, CDCl3) δH 1.19 (s, 9H), 1.38 (s,
3H), 1.89 (s, 3H), 2.47 (s, 1H), 3.88 (d, J = 8.7 Hz, 1H), 4.01 (d, J =
8.7 Hz, 1H), 6.84 (d, J = 8.9 Hz, 1H), 7.13 (d, J = 7.3 Hz, 1H), 7.34
(dd, J = 8.9 and 7.3 Hz, 1H), 7.47 (dd with fine coupling, J = 8.0 and
7.3 Hz, 1H), 7.61 (dd with fine coupling, J = 8.0 and 7.3 Hz, 1H), 7.66
(d, J = 8.0 Hz, 1H), 7.89 (d, J = 8.0 Hz, 1H) ppm; 13C NMR (125
MHz, CDCl3) δC 25.2, 28.7, 29.1, 39.3, 46.8, 82.2, 90.9, 107.5, 110.8,
111.4, 117.5, 123.9, 124.0, 125.5, 126.3, 127.9, 130.0, 135.3, 136.7,
151.0, 174.4 ppm.
Thermal Decomposition of 1-[2-(Benzothiazol-2-yl)-3-hy-
droxyphenyl]-5-tert-butyl-4,4-dimethyl-2,6,7-trioxabicyclo-
[3.2.0]heptane (1b). Typical Procedure: A solution of dioxetane
1b (168 mg, 0.408 mmol) in p-xylene (4 mL) was refluxed under a
nitrogen atmosphere for 4 h. After cooling, the reaction mixture was
concentrated in vacuo. The residue was chromatographed on silica gel
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TBAF-Induced Decomposition of Crystalline 1b To Isolate
cis-10. A solution of 1b (61.4 mg) and TBAF (0.3 equiv) in
acetonitrile (15 mL) was heated at 45 °C for 10 h. The reaction
mixture was poured in aqueous NH4Cl and extracted with AcOEt. The
organic layer was washed with aqueous NaCl, dried over MgSO4, and
concentrated in vacuo. The residue was rinsed with CH2Cl2 to give cis-
10 as a yellow solid (14.0 mg).
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1
cis-10: H NMR (500 MHz, CDCl3) δH 0.68 (broad s, 9H), 1.25
(s, 3H), 1.51 (s, 3H), 2.61 (s, 1H), 3.76 (d, J = 8.6 Hz, 1H), 4.33 (d, J
= 8.6 Hz, 1H), 6.61 (d, J = 7.1 Hz, 1H), 6.85 (d, J = 9.0 Hz, 1H), 7.35
(dd, J = 9.0 and 7.1 Hz, 1H), 7.47 (dd with fine coupling, J = 8.0 and
7.3 Hz, 1H), 7.61 (dd with fine coupling, J = 8.2 and 7.3 Hz, 1H), 7.79
(d, J = 8.2 Hz, 1H), 7.85 (d, J = 8.0 Hz, 1H) ppm; 13C NMR (125
MHz, CDCl3) δC 21.3, 25.9, 27.8 (broad), 39.5, 49.3, 80.4, 91.9, 107.9,
110.5, 111.7, 119.3, 123.7, 125.1, 125.5, 125.7, 128.1, 131.6, 134.8,
136.4, 153.0, 174.3 ppm.
Measurement of Chemiluminescence and Time Course of
the Charge-Transfer-Induced Decomposition of Dioxetanes 1.
General Procedure: Chemiluminescence was measured using a
JASCO FP-750 and/or FP-6500 spectrometer and/or Hamamatsu
Photonics PMA-11 multichannel detector.
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Chemilumin. 1989, 4, 99−111. (b) Schaap, A. P.; Akhavan, H.;
Romano, R. J. Clin. Chem. 1989, 35, 1863−1864. (c) Edwards, B.;
Sparks, A.; Voyta, J. C.; Bronstein, I. J. Biolumin. Chemilumin. 1990, 5,
1−4. (d) Martin, C.; Bresnick, L.; Juo, R. R.; Voyta, J. C.; Bronstein, I.
BioTechniques 1991, 11, 110−113. (e) Mariscal, A.; Garcia, A.;
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16, 888−893. (f) Trofimov, A. V.; Vasil’ev, R. F.; Mielke, K.; Adam, W.
Photochem. Photobiol. 1995, 62, 35−43. (g) Adam, W.; Bronstein, I.;
Edwards, B.; Engel, T.; Reinhardt, D.; Schneider, F. W.; Trofimov, A.
V.; Vasil’ev, R. F. J. Am. Chem. Soc. 1996, 118, 10400−10407.
(h) Buxton, R. C.; Edwards, B.; Juo, R. R.; Voyta, J. C.; Bethell, R.
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(7) Edwards, B.; Sparks, A.; Voyta, J. C.; Bronstein, I. In
Bioluminescence and Chemiluminescence, Fundamentals and Applied
Aspects; Campbell, A. K., Kricka, L. J., Stanley, P. E., Eds.; Wiley:
Chichester, 1994; pp 56−59.
A freshly prepared solution (2.0 mL) of TBAF (1.0 × 10−2 mol/L)
in acetonitrile was transferred to a quartz cell (10 × 10 × 50 mm) and
was placed in the spectrometer, which was thermostatted with stirring
at an appropriate temperature range of 45 °C. After 3−5 min, a
solution of the dioxetane 1 in acetonitrile (1.0 × 10−5 mol/L, 1.0 mL)
was added by means of a syringe and measurement was started
immediately. The intensity of the light emission time-course was
recorded and processed according to first-order kinetics. The total
light emission was estimated by comparing it with that of an
adamantylidene dioxetane, whose chemiluminescent efficiency ΦCL
has been reported to be 0.29 and was used here as a standard.11,12
ASSOCIATED CONTENT
■
S
* Supporting Information
1H NMR/13C NMR spectra of 1b−d, 2b−d, 3b−d, 4b−d, 6b−
d, trans-10, cis-10, and ORTEP views and crystallographic
information files for 1b−d, trans-10, and cis-10. This material is
available free of charge via the Internet at http://pubs.acs.org.
(8) Matsumoto, M.; Akimoto, T.; Matsumoto, Y.; Watanabe, N.
Tetrahedron Lett. 2005, 46, 6075−6078.
AUTHOR INFORMATION
Corresponding Author
*E-mail: matsumo-chem@kanagawa-u.ac.jp.
■
(9) (a) Tanimura, M.; Watanabe, N.; Ijuin, H. K.; Matsumoto, M. J.
Org. Chem. 2010, 75, 3678−3684. (b) Tanimura, M.; Watanabe, N.;
Ijuin, H. K.; Matsumoto, M. J. Org. Chem. 2011, 75, 902−908.
(10) Matsumoto, M.; Mizoguchi, Y.; Motoyama, T.; Watanabe, N.
Tetrahedron Lett. 2001, 42, 8869−8872.
Notes
The authors declare no competing financial interest.
(11) Value of ΦCL was estimated based on the value 0.29 for the
chemiluminescent decomposition of 3-adamantylidene-4-(3-tert-butyl-
dimethylsiloxyphenyl)-4-methoxy-1,2-dioxetane in a TBAF/DMSO
system.12
ACKNOWLEDGMENTS
■
We gratefully acknowledge financial assistance provided by
Grants-in-Aid (No. 22550046 and No. 21550052) for Scientific
Research from the Ministry of Education, Culture, Sports,
Science, and Technology, Japan.
(12) Trofimov, A. V.; Mielke, K.; Vasil’ev, R. F.; Adam, W.
Photochem. Photobiol. 1996, 63, 463−467.
(13) Adam, W.; Matsumoto, M.; Trofimov, A. V. J. Org. Chem. 2000,
65, 2078−2082.
(14) (a) Matsumoto, M.; Kasai, D.; Yamada, K.; Fukuda, N.;
Watanabe, N.; Ijuin, H. K. Tetrahedron Lett. 2004, 45, 8079−8082.
(b) Matsumoto, M.; Yamada, K.; Ishikawa, H.; Hoshiya, N.; Watanabe,
N.; Ijuin, H. K. Tetrahedron Lett. 2006, 47, 8407−8411.
(c) Matsumoto, M.; Yamada, K.; Watanabe, N.; Ijuin, H. K.
Luminescence 2007, 22, 420−429.
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1
(17) H NMR analysis showed that the crystalline was composed of
1b (21%), 2b (35%), cis-10 (23%), and trans-10 (22%) after heating at
80 °C for 2 h, while composed of 1b (7%), 2b (49%), cis-10 (9%), and
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