Photochromic fused-naphthopyrans without residual color

Article abstract of DOI:10.1021/jo3003216

A series of new photochromic fused-naphthopyrans with an alkyl bridge between the pyran ring and the naphthalenic core was synthesized in several steps from 4-(bromomethyl)benzocoumarin. The presence of the alkyl bridge in these new fused-naphthopyrans prevents the formation of one long-lived photoisomer and therefore has a dramatic effect on their photochromic properties: UV irradiation of common naphthopyrans gives rise to two isomeric colored photoisomers, one of which fades very slowly and is responsible for a persistent residual color. UV excitation of these new uncolored fused-naphthopyrans leads to the formation of only one colored photoisomer that fades completely to the uncolored state in few seconds/minutes following a monoexponential decay law, thus avoiding the problem of the residual coloration typically observed with naphthopyrans.

Full text of DOI:10.1021/jo3003216

Article
pubs.acs.org/joc
Photochromic Fused-Naphthopyrans without Residual Color
Ceu M. Sousa,† Jerome Berthet,‡ Stephanie Delbaere,‡ and Paulo J. Coelho*,†
́
†Centro de Química−Vila Real, Universidade de Tras
́
-os-Montes e Alto Douro, 5001-801 Vila Real, Portugal
‡CNRS UMR 8516, UDSL, Faculte
France
́
des Sciences Pharmaceutiques et Biologiques, Universite Lille Nord de France, F-59006, Lille,
́
S
* Supporting Information
ABSTRACT: A series of new photochromic fused-naphthopyrans with
an alkyl bridge between the pyran ring and the naphthalenic core was
synthesized in several steps from 4-(bromomethyl)benzocoumarin. The
presence of the alkyl bridge in these new fused-naphthopyrans prevents
the formation of one long-lived photoisomer and therefore has a
dramatic effect on their photochromic properties: UV irradiation of
common naphthopyrans gives rise to two isomeric colored photo-
isomers, one of which fades very slowly and is responsible for a
persistent residual color. UV excitation of these new uncolored fused-
naphthopyrans leads to the formation of only one colored photoisomer
that fades completely to the uncolored state in few seconds/minutes
following a monoexponential decay law, thus avoiding the problem of
the residual coloration typically observed with naphthopyrans.
systems.16−25 The synthesis of naphthopyrans with large optical
density and fast return to the uncolored closed form, at ambient
temperature, is a key requirement for their industrial
application. Although hundreds of naphthopyrans have been
prepared in the last two decades, a problem still persists with
these molecules: since the two colored photoisomers have
different thermal stabilities, they exhibit different fading rates;
most of the coloration fades rapidly, typically in few seconds/
minutes (TC decay), but 10−20% of the coloration fades very
slowly (several minutes/hours) because of the formation of the
more stable TT isomer.26−31 Therefore, although the
coloration of the photochromic ophthalmic lenses under
sunshine is quite fast (less than one minute), their complete
INTRODUCTION
■
Naphthopyrans are well-known for their photochromic proper-
ties. UV irradiation of these uncolored molecules leads to the
formation of highly conjugated colored species that, in the
absence of light, return thermally, with variable speed, to the
closed form.1 The phenomen occurs in solution or when the
molecules are dispersed in polymeric matrices, although the
kinetics of the process is highly affected by the nature of the
host matrix.2−8 The relative ease of chemical synthesis, the
versatility of the photochromic activity, the thermal stability,
and the notable fatigue resistance made these compounds the
most commercially important class of photochromic molecules
used for the production of photochromic plastic ophthalmic
lenses that show a rapid and reversible color change at room
temperature when exposed to the sunlight.9−12
Under near-UV light irradiation, naphthopyrans undergo an
electrocyclic pyran-ring-opening with the formation of two
colored photoisomers with a strong absorption in the visible
part of the spectrum. UV and NMR studies revealed that the
two photoisomers have similar absorption characteristics but
different stabilities. The cleavage of the C(sp3)-O bond of the
closed form leads initially to the transoid-cis (TC) photoisomer,
which is thermally unstable and rapidly returns to the
uncolored state, or through light promoted CC isomeri-
zation is converted to the more stable transoid-trans (TT)
isomer that returns slowly to the uncolored form through the
TC isomer (Scheme 1).13−15
discoloration, once the user returns indoors, is very slow.32,33
A
biexponential color decay is observed, and only after a long
time, all the photoisomers are converted back to the closed
uncolored form (Scheme 2, black line).
One way to avoid the formation of the TT isomer and
overcome the problem of the residual color is to prevent the
CC isomerization of the short-lived TC isomer to the more
stable TT isomer. This can be done by incorporating an alkyl
bridge between the pyran double bond and the naphthalenic
ring (Scheme 3).34,35 The opening of the pyran ring in such
fused-naphthopyrans should lead to only one colored photo-
isomer (TC), since the isomerization of the CC bond
(leading to TT isomer) is precluded. This photoisomer ought
to exhibit a fast monoexponential color decay to the initial
uncolored form (Scheme 2, line in red), thus avoiding the
persistency of the residual color of the long-lived colored TT
Diarylnaphthopyrans are very sensitive to structural
modifications. A great number of substitutions and/or
annelations have been studied in order to increase the ability
to produce intense colored forms (colorability), to tailor
chromatic properties, or to change the fading rates of these
Received: February 15, 2012
Published: March 29, 2012
© 2012 American Chemical Society
3959
dx.doi.org/10.1021/jo3003216 | J. Org. Chem. 2012, 77, 3959−3968

The Journal of Organic Chemistry
Article
Scheme 1. Photochromic Equilibrium for 2,2-Diphenyl-2H-naphtho[1,2-b]pyrans
isomer. In this paper, we describe the synthesis and
photochromic properties of three new fused-naphthopyrans
with such an innovative structure (Scheme 3).
Scheme 2. Color Forming and Color Bleaching for Common
Naphthopyrans (in Black) and a Hypothetical Fused-
Naphthopyran (in Red) Measured at λmax
RESULTS AND DISCUSSION
■
Synthesis of Fused-Naphthopyrans 11−13. For the
synthesis of the proposed fused-naphthopyran with a fused ring
between carbons 4 and 5, we first explored the synthesis of a
naphthopyran bearing an ester chain at carbon 4 that could
form a five-membered cycle by an intramolecular ring closure
leading to the desired fused-naphthopyran. Although this
precursor was easily prepared from 2,2-diphenylnaphtho[1,2-
b]pyran-4-one, we were unable to perform the intramolecular
cyclization reaction under classic Friedel−Crafts conditions
(conversion to the acyl chloride followed by Lewis acid
treatment) or by the direct action of strong acids. Treatment of
this 4-substituted naphthopyran with triflic acid at room
temperature gave an unexpected cyclic lactone formed by an
initial acid-promoted opening of the pyran ring followed by
C−C bond rotation, intramolecular electrophilic aromatic
substitution, and acid catalyzed lactone formation (Scheme
4).36
Scheme 3. Photochromic Equilibrium for a Fused-
Naphtho[1,2-b]pyran
Because of the high reactivity of the pyran ring under acidic
conditions and since naphthopyrans can also be prepared from
coumarins, although usually in low yields,37,38 we decided to
prepare the target fused-naphthopyrans using a different
synthetic approach: first the synthesis of a 4-substituted
coumarin, then building the fused ring, and in the final step,
formation of the pyran ring.
The key step of this synthesis was the preparation of 4-
(bromomethyl)benzocoumarin 2 (Scheme 5). Since the allylic
Scheme 4. Unexpected Rearrangement of a 4-Substituted Naphthopyran in Triflic Acid
3960
dx.doi.org/10.1021/jo3003216 | J. Org. Chem. 2012, 77, 3959−3968

The Journal of Organic Chemistry
Article
a
Scheme 5. Synthesis of Fused Coumarin 6
a
(a) BrCH2COCH2COOEt 1, H2SO4, 56%; (b) diethyl malonate, NaH, DMSO, 39%; (c) (1) EtOH, NaOH, (2) DMSO, reflux, 97%; (d) SOCl2,
AlCl3, 29%.
a
Scheme 6. Synthesis of Fused-Naphthopyran 11
a
(e) NaBH4/EtOH, 68%; (f) PhMgBr/Et2O, H3O+, 40%; (g) t-BuMe2SiCl/Imidazole/DMF, 79%; (h) PhMgBr/Et2O, H3O+, 18%.
bromination of the known 4-methylbenzocoumarin39 using
NBS or LDA/Br2 did not afford the desired brominated
benzocoumarin, we chose to prepare the ethyl γ-bromo-
acetoacetate 1 by direct bromination of ethyl acetoacetate,40
and then perform the reaction with 1-naphthol in sulfuric acid,
which gave directly the desired 4-(bromomethyl)-
benzocoumarin 2 in medium yield (56%) (Scheme 5).41 The
Friedel−Crafts reaction in the presence of AlCl3 gave the fused
benzocoumarin 6 isolated in 29% yield after elution from silica.
The formation of the fused ketone 6 was confirmed by H
NMR spectroscopy, which displayed a key singlet signal at δ
8.40 ppm due to the benzenic proton H-7 and a signal at δ
195.7 ppm in the 13C NMR spectrum assigned to the ketone
carbonyl carbon (C-6) (Scheme 5).
1
1
formation of the coumarin ring was confirmed by H NMR
The reduction of ketone 6 with NaBH4 gave the alcohol 7
that was then treated with PhMgBr and hydrolyzed in diluted
spectroscopy, which displayed two key singlets at δ 6.56 (1H)
and δ 4.54 ppm (2H) assigned to the ethylenic H-3 proton and
1
HCl (aq) to afford the fused-naphthopyran 8 (Scheme 6). H
CH2Br and by the signals at δ 160.3 and δ 27.2 ppm in the 13
C
NMR analysis (see the Supporting Information) showed that
this compound is not stable in CDCl3 solution and is slowly
(for two days) converted to the aromatized anthracene
derivative 9 by migration of the double bond followed by
dehydration. In particular, the progressive disappearance of the
signals at δ 2.95 (m) and δ 2.60 (m) ppm assigned to protons
H-4 was observed with the concomitant appearance of a singlet
at δ 3.4 ppm that can be attributed to H-3 after the double
bond migration, and later with the appearance of the signals at
δ 4.00 (s), 7.71 (d), 7.4 (t), and 7.15 (d) ppm assigned to
NMR spectrum assigned to the carbonyl and CH2Br carbons,
respectively.
To build the alkyl bridge we performed the reaction of 2 with
diethyl malonic ester in basic medium, which afforded the
diester 3 along with a minor amount of product 4 formed by
dialkylation of the malonic ester.42 Basic hydrolysis and
decarboxylation of the diester 3 under thermal conditions
gave the monoacid 5 in good yield, which was then converted
to the corresponding acyl chloride. Finally, the intramolecular
3961
dx.doi.org/10.1021/jo3003216 | J. Org. Chem. 2012, 77, 3959−3968

The Journal of Organic Chemistry
Article
Scheme 7. Synthesis of Fused-Naphthopyrans 12 and 13
protons H-3, H-6, H-5, and H-4, respectively, of the anthracene
derivative 9 (Scheme 6).
found to be too difficult because of their low and equal polarity
in different mixtures of eluants. Their structural characterization
was possible by 2D NMR spectroscopy (see the Supporting
Information). At room temperature, the 1H NMR signals of 13
are broad because of the exchange between different
conformations. To increase the resolution, NMR spectra were
recorded at high temperature (T = 343 K). Compound 13 is
characterized by the sp3 C-2 in the pyran ring at δ 85.8 ppm,
whereas the aliphatic quaternary carbon, C-4, in compound 14
with a naphthyl substituent is much less deshielded at δ 42.2
ppm. The two naphthyl substituents for naphthopyran 13 are
symmetrical with the same chemical shift for the equivalent
protons in each group. On the contrary, the two naphthyl
groups of 14 are magnetically unequivalent, as they are attached
to two different carbons, thus resulting in a set of different
signals for the protons of each naphthyl group.
Photochromic Behavior of Fused-Naphthopyrans 11−
13. In toluene solution (1.0 × 10−4 M), fused-naphthopyrans
11−13 are nearly colorless with a very strong absorption in the
UV region between 320 and 370 nm. Continuous UV−vis light
irradiation (150 W ozone free Xe lamp) at 20 °C leads to the
development of orange solutions with maximal absorption
between 450 and 455 nm (Figure 1, Table 1).
When the UV irradiation was turned off, the absorbance at
the maximum wavelength of absorption decreased, following a
monoexponential kinetic decay law, and after several seconds,
the absorbance reached exactly the initial value (Figure 2). This
monoexponential decay contrasts with the usual behavior of
naphthopyrans and is indicative of the formation of only one
colored species.24
The fading rate constants and therefore the lifetime of the
colored species are very dependent on the nature of the aryl
substituents at the sp3 carbon atom. While naphthopyran 11
with two phenyl groups gave rise to rather unstable colored
opened forms with an half-life time of 0.30 s, naphthopyrans 12
and 13, which have two sterically hindered groups at C-2,
generated more stable colored species with a much higher
lifetime. The lifetime of the colored forms of naphthopyran 13
bearing two naphth-1-yl groups (t1/2 = 32 s) is 100 times higher
than for the parent 2,2-diphenyl-naphthopyran 11, while for
naphthopyran 12, with two o-methoxyphenyl groups, the
lifetime (t1/2 = 66 s) is 220 times higher.
Although this aromatization was only observed when
compound 8 was dissolved in CDCl3, we decided to protect
the secondary hydroxyl function of compound 7 in the form of
a silyl ether to improve its chemical stability. The TBDMS
ether 10 was easily formed in DMF, and it is stable under the
acid conditions needed to prepare the final diaryl naphtho-
pyrans. Finally, the protected naphthopyran-2-one 10 was
treated with PhMgBr/Et2O and hydrolyzed in HCl (5%)
overnight to afford the stable fused-naphthopyran 11 in low
yield (18%). The NMR spectra of this compound showed an
upfield shift of proton H-3 from δ 6.29 ppm to δ 5.87 ppm and
a signal for C-2 at δ 83.2 ppm, characteristic of the pyran ring.1
In 2006, Heron et al. showed that the kinetics of the ring
closure reaction could be slowed down, placing substituents,
such as methoxy, chlorine, fluorine, or methyl in the ortho
position of the phenyl rings.43 This structural change increased
4−20 times the lifetime of colored open form, and it has been
attributed to a steric effect in which the ortho substituent
hinders the thermal ring closure of the photogenerated colored
species, and therefore an appreciable concentration of these
colored species is obtained, which is manifest by an
intensification of the developed color. More recently, Guo
and Chen showed that the substitution of the phenyl groups by
two 1-naphthyl groups also increases significantly the lifetime of
the open colored species leading to high steady-state optical
density at room temperature.44 Taking into account these
results, we prepared the diaryl naphthopyrans 12 and 13 with
2-methoxyphenyl and 1-naphthyl substituents at C-2, by
reaction of naphthopyran-2-one 10 with the Grignard reagents
derived from 1-bromoanisole and 1-bromonaphthalene,
followed by acid treatment (Scheme 7). The reaction afforded
the expected compounds, but their isolation was complicated
because of their low polarity and the presence of side products.
After column chromatography and two preparative thin layer
chromatographies, compounds 12 and 13 were isolated in 13−
1
19% yield. H NMR analysis of compound 13 showed that it
was contaminated with the pyran 14 (the ratio of 13/14 is 40/
60) formed by 1,2- and 1,4-addition of the Grignard reagent to
the coumarin ring, followed by hemicetal formation and
dehydration.37,38 The separation of these two isomers was
3962
dx.doi.org/10.1021/jo3003216 | J. Org. Chem. 2012, 77, 3959−3968

The Journal of Organic Chemistry
Article
Figure 1. UV−vis absorption spectra of fused-naphthopyran 12 before
and after UV irradiation.
Under continuous UV irradiation, the absorbance at the
photostationary state is inversely related to the kinetic rate of
the discoloration process, and therefore the slower photo-
chromic systems give rise to more colored solutions. Hence,
UV irradiation of slow fading naphthopyrans 12 and 13
originates highly colored orange solutions, while for the fast
fading fused-naphthopyran 11, the color variation (A = 0.01) is
too small and not easily perceivable by the eye at room
temperature.
The remarkable reproducibility of the UV−vis irradiation/
dark cycles can be seen in the fact that after each coloration/
fading sequence, the absorbance returns to the same initial
value, and no residual color is formed. The modulation of the
fading kinetic obtained by changing the nature of the sp3 aryl
substituents allows us to go from very fast interconversion
between the uncolored and colored forms (naphthopyran 11
that, as a result, exhibits at room temperature a very small color
change) to considerably slow switching systems (naphthopyran
12). The fused-naphthopyran 13 shows an intermediate
behavior: the UV−vis irradiation for 4 min gave an orange
solution (A = 0.36) that faded completely in 4 min without any
residual color (Figure 2).
It is also noteworthy that the coloration/fading process for
these naphthopyrans is reproducible, and after several cycles,
the same maximal absorbance is attained, which is indicative
that these compounds are resistant to photodegradation even
when exposed for several minutes to UV−vis light (40 W)
(Figure 2).
Figure 2. UV−vis irradiation/dark cycles for fused-naphthopyrans
11−13.
formed upon UV irradiation of fused-naphthopyrans 11−12,
NMR studies were carried out before and after UV irradiation.
Since the lifetimes of the colored species of these compounds
are low at rt, fresh samples of naphthopyrans 11 and 12 in
toluene-d8 were directly irradiated in the NMR tube (5 mm) at
low temperature (−60 °C) using a 1000 W Xe−Hg short-arc
lamp. After irradiation, the sample was rapidly transferred into
the thermoregulated probe of a 500 MHz NMR spectrometer.
The 1H NMR spectra were recorded at regular time intervals to
monitor the changes in peak-intensities and thus obtain
information about the formation of photoproducts and the
evolution of their concentration in time.
Structural Elucidation of the Colored Open Form by
NMR. Recently, NMR has emerged as a very powerful
technique for the study of the mechanism of the photochromic
phenomenon.45 NMR analysis of irradiated solutions gives
information about the structure and number of species formed
under irradiation, their evolution in time, and the individual
fading rates.46 To investigate the structure of the products
UV irradiation of fused-naphthopyrans 11−12 leads to the
formation of a set of new signals that are typical of an opened
Table 1. Maximal Wavelengths of the Colored Forms (λmax, nm), Colorability (Maximum Absorbance at λmax Attained at the
Photostationary State), Fading Rate Constants (K, min−1), and Half-Life (s) for Fused-Naphthopyrans 11−13 in Toluene
Solutions (1.0 × 10−4 M at 20 °C) under UV−vis Continuous Irradiation
naphthopyran
Ar
λmax (open form)
ΔAbs
K (min−1
)
t1/2 (s)
11
12
13
Ph
450
455
455
0.01
0.65
0.36
127
0.63
1.39
0.30
66
2-methoxyphenyl
1-naphthyl
32
3963
dx.doi.org/10.1021/jo3003216 | J. Org. Chem. 2012, 77, 3959−3968

The Journal of Organic Chemistry
Article
1
Figure 3. H NMR spectrum of fused-naphthopyran 11 before (a) and after (b) UV irradiation at −60 °C.
1
Figure 4. H NMR spectrum of fused-naphthopyran 12 (a) before and (b) after UV irradiation at −60 °C.
pyran ring conjugated photoisomer. In particular, a high
deshielding singlet at δ 7.90 ppm for 11 and δ 8.40 ppm for 12,
characteristic of proton H-3, was observed, which is indicative
of a trans−cis configuration (TC) for these colored opened
species (Figures 3 and 4). The fast bleaching at −60 °C of the
opened form of naphthopyran 11 did not allow us to record 2D
experiments. Therefore, to establish the structure of the opened
form, a ROESY-1D experiment was performed that confirmed a
strong correlation between protons H-3 and H-2′/6′ and
between H-7/H-6 and H-8 (Figure 5).
The colored species of naphthopyran 12 is more stable at
−60 °C. 2D HMBC experiment (see the Supporting
Information) evidenced a carbonyl group at δ 184.7 ppm (C-
1), characteristic of an open form and correlated with H-11.
The high deshielding of the H-3 signal at δ 8.40 ppm,
correlated with C-1′/1″, confirms the TC configuration of this
opened colored species.
During thermal evolution at −20 °C, the signals of the
opened species decreased following a monoexponential kinetic
decay law (t1/2= 32 min), and the signals of the closed forms
increased (see the Supporting Information). The results
3964
dx.doi.org/10.1021/jo3003216 | J. Org. Chem. 2012, 77, 3959−3968

The Journal of Organic Chemistry
Article
on the sp3 carbon atom was observed, which led to an increase
of the lifetime of the colored form, and therefore, a colored
solution with an high optical density was obtained. The
structure of the photoisomer was proven by NMR to have a
trans−cis configuration. Unlike common naphthopyrans, which
under UV light originates two isomeric photomerocyanines
(TC and TT) with different stabilities and consequently
different fading kinetics, this type of fused-naphthopyrans
produces only one colored compound, and thus, when the light
source is removed, the color fades monoexponentially and
completely to the uncolored state without the formation of a
residual coloration.
EXPERIMENTAL SECTION
■
Spectrokinetic Studies under Continuous Irradiation. UV−
visible irradiation experiments were made using a UV−vis
spectrometer coupled to a 150 W ozone free Xenon lamp. The light
from the UV lamp was filtered using a water filter and then carried to
the spectrophotometer holder at the right angle to the monitoring
beam using an optical fiber system. 40 W m−2 light flux was used
(measured with a Photometer with UV-A probe). A temperature
controlled (20 °C) stirred 10 mm quartz cell (3.5 mL of sample
solution) was used. In a preliminary experiment, the UV−vis
absorption spectra of the closed and open forms and the λmax of the
open form were determined. In a second experiment, the absorbance
at photostationary equilibrium, Aeq, was measured at λmax and then the
decrease in the absorbance vs time was monitored. The sample
solutions were not deaerated.
1
Figure 5. ROESY-1D spectrum of fused-naphthopyran 11: (a) H
NMR spectrum, (b) 1D NOESY spectrum with an irradiation of H-7,
and (c) 1D NOESY spectrum with an irradiation of H-3.
obtained by NMR are in agreement with those obtained by
UV−vis spectroscopy and confirm that UV irradiation of these
fused-naphthopyrans leads to the opening of the pyran ring
with formation of a single colored TC opened species. The fact
that under UV−vis light these fused-naphthopyrans do not
generate the TT-photoisomer allows the system to return
thermally and completely to the initial uncolored form in few
minutes, thus avoiding the usual residual color due to this
unwanted photoisomer (Scheme 8).
NMR Studies. The 1H and 13C NMR spectra (at 400.13 and
100.62 MHz) were recorded at 298 K in CDCl3, DMSO, or acetone-
d6. Chemical shifts (δ) are reported in ppm. For NMR investigations
of the colored species, samples of the naphthopyrans in toluene-d8
were irradiated directly in the NMR tube (5 mm) and thermoregulated
using a 1000 W Xe−Hg HP filtered short-arc lamp equipped with a
filter for UV irradiation (259 < λ < 388 nm). After irradiation had been
stopped, the samples were transferred to the thermoregulated probe,
QNP or TXI, of an 500 NMR spectrometer (ν0 (1H) = 500 MHz, ν0
(13C) = 125 MHz.
Scheme 8. Photochromic Equilibrium for Fused-
Naphthopyrans 11−13
Ethyl 4-Bromo-3-oxobutanoate (1). To a solution of ethyl
acetoacetate (30 g; 0.23 mol) in dry Et2O (50 mL) at 0 °C was added
bromine (12 mL; 0.23 mol) dropwise over 45 min with vigorous
stirring. After the mixture was stirred at room temperature for 24 h, ice
was added (100 g), and the organic phase washed with a sodium
hydrogenocarbonate solution (5%) saturated with sodium chloride
(200 mL) and again washed with a saturated sodium of chloride
solution (200 mL). The organic phase was dried (Na2SO4) for 2 h,
and the solvent was removed under reduced pressure to give an orange
oil (31.9 g; 65%) stabilized immediately by the addition of barium
carbonate (50 mg; 0.26 mmol). The orange oil contained small
amounts of a highly lachrymatory oil, probably the ethyl α-
bromoacetoacetate.
The irradiation experiments on the mixture of compounds
13/14 at 228 K are less clear because of the superposed signals
of the initial compounds. However, it can be concluded that
compound 13 leads to two TC conformers (characterized by
aliphatic signals C(CH3)3 at 0.97 and 1.06 ppm, H-6 signal at
4.08 and 4.18 ppm, and aromatic signals H-3 at 7.88 and 7.94
ppm and H-11 at 8.79 and 8.90 ppm) that thermally return to
the initial form, while compound 14 is irreversibly converted
into two unidentified photoproducts that stay present in the
sample after the return to room temperature.
4-(Bromomethyl)-2H-naphtho[1,2-b]pyran-2-one (2). A sol-
ution of 1-naphthol (2.00 g, 13.8 mmol) and ethyl 4-bromoacetoa-
cetate 1 (1.9 mL, 13.8 mmol) was cooled to 0 °C, and then H2SO4 (10
mL) was slowly added over 30 min under constant stirring, during
which the solution became darker in color. After stirring for an
additional 2 h at 0 °C, the reaction mixture was treated with ice (100
g), and then NaHCO3 (sat, 100 mL) was carefully added with stirring
for 0.5 h (gas evolution) and stirred for an additional 2 h. The solution
was extracted with CH2Cl2 (3 × 100 mL), and the combined organic
phase was dried (Na2SO4). The solvent was removed under reduced
pressure, yielding a red oil that was dissolved in ethanol (50 mL) at
room temperature and precipitated overnight. Filtration and washing
with cold ethanol gave the benzocoumarin 2 as a yellow solid (2.240 g;
56% yield): mp 155−166 °C; IR (KBr, cm−1) 3028, 2987, 1711, 1634,
CONCLUSION
■
A set of new fused-naphthopyrans with an alkyl bridge between
the pyran ring and the naphthalenic core was synthesized in
seven steps from 1-naphthol using a synthetic approach
involving benzocoumarins. UV light irradiation of these
compounds in solution originates one colored compound that
fades completely to the uncolored state in few seconds/
minutes. A significant steric effect of the aromatic substituents
1
1598, 1475, 1375, 1121; H NMR (400 MHz, CDCl3) 8.50 (dd, J =
2.5, 6.5 Hz, 1H), 7.86 (dd, J = 2.5, 6.4 Hz, 1H), 7.71 (d, J = 8.8 Hz,
1H), 7.68−7.60 (m, 3H), 6.56 (s, 1H), 4.54 (s, 2H); 13C NMR (100
3965
dx.doi.org/10.1021/jo3003216 | J. Org. Chem. 2012, 77, 3959−3968

The Journal of Organic Chemistry
Article
MHz, CDCl3) 160.3, 151.4, 150.8, 134.9, 129.0, 127.7, 127.3, 124.4,
123.2, 122.6, 119.8, 115.2, 112.6, 27.2; EI-MS (TOF) m/z (%) 290
(4.3, [M + 2]+), 288 (4.35, M+), 210 (76), 182 (100), 181 (86), 153
(25), 152 (48). HRMS calculated for C14H9BrO2: 287.9786. Found:
287.9783.
were added dry CH2Cl2 (5 mL) and AlCl3 (0.990 g, 7.41 mmol) at
room temperature with constant stirring. After 1 h, another equivalent
of AlCl3 was added, and the solution was kept at room temperature for
1 h. The solution was then quenched with water (30 mL) and
extracted with EtOAc (3 × 20 mL). The combined organic phases
were dried (Na2SO4), and the solvent was evaporated under reduced
pressure, leaving a solid residue that was purified by column
chromatography on silica (0−40% EtOAc/petroleum ether) to give
the fused anthracenopyran-2,6-dione 6 as an orange solid (538 mg;
29%): mp 203−207 °C; IR (KBr, cm−1) 3046, 2948, 1733, 1687, 1587,
1299; 1H NMR (400 MHz, CDCl3) 8.58 (d, J = 8.0 Hz, 1H), 8.40 (s,
1H), 8.05 (d, J = 8.0 Hz, 1H), 7.79 (t, J = 7.1 Hz, 1H), 7.73 (t, J = 6.9
Hz, 1H), 6.48 (t, J = 1.5 Hz, 1H), 3.30 (td, J = 7.3 Hz, J = 1.5 Hz, 2H),
2.99 (t, J = 7.3 Hz, 2H); 13C NMR(100 MHz, CDCl3) 195.7, 160.2,
151.7, 150.5, 133.9, 130.2, 129.7, 129.5, 126.3, 125.4, 123.9, 122.7,
113.9, 112.6, 37.1, 28.0; EI-MS (TOF) m/z (%) 250 (100, M+), 248
(51), 222 (71, [M − CO]+), 220 (71), 194 (69), 165 (71), 164 (57),
163 (53). HRMS calculated for C16H10O3: 250.0630. Found:
250.0638.
Alkylation of Diethyl Malonate with 2. Diethyl malonate (550
μL, 3.60 mmol) was added to a suspension of NaH (60% dispersion in
mineral oil, 266 mg, 6.65 mmol) in DMSO (6.0 mL). After the
foaming subsided and the suspension cleared to a solution, 4-
(bromomethyl)benzocoumarin 2 (1.00 g, 3.47 mmol) was added all at
once. After 5 min of stirring, the solution was quenched with HCl (5%,
50 mL) and extracted with EtOAc (3 × 50 mL). The combined
organic phases were dried (Na2SO4), and the solvent was evaporated
under reduced pressure, leaving a yellow oil that was dissolved in
ethanol (50 mL). The solid formed after standing overnight at room
temperature was filtered and washed with cold ethanol to give the
diester 3 as slightly yellow crystals. Recrystallization from CH2Cl2/
Et2O gave diester 3 as white crystals. The filtered ethanol solution and
the recrystallization mother liquid were gathered and evaporated,
leaving a yellow solid that was purified by column chromatography on
silica (20% EtOAc/5% CH2Cl2/petroleum ether), affording an extra
amount of diester 3 and the pure 4.
4H-5,6-Dihydroanthraceno[9,1-bc]pyran-6-ol-2-one (7).
NaBH4 (44 mg; 1.28 mmol) was added to a solution of
anthracenopyran-2,6-dione 6 (321 mg; 1.28 mmol) in pure ethanol
(5 mL) at room temperature with constant stirring. After standing for
1 h, the ethanol was removed under reduced pressure, and HCl (5%,
50 mL) was added. The solution was extracted with EtOAc (2 × 50
mL), and the organic phases were combined and dried (Na2SO4). The
solvent was removed under reduced pressure to give alcohol 7 as
slightly yellow crystals (220 mg; 68%): mp 179.2−181.6 °C; IR (KBr,
Diethyl 2-((2-Oxo-2H-naphtho[1,2-b]pyran-4-yl)methyl)-
malonate (3). Spectral data (498 mg, 39% yield): mp 109.6−112.2
1
°C; IR (KBr, cm−1) 3040, 2987, 1722, 1328, 1269, 1222, 1145; H
NMR (400 MHz, CDCl3) 8.50 (m, 1H), 7.84 (m, 1H), 7.68 (d, J = 8.8
Hz, 1H), 7.63−7.57 (m, 3H), 6.33 (s, 1H), 4.22 (m, 4H), 3.78 (t, J =
7.5 Hz, 1H), 3.45 (d, J = 7.4 Hz, 2H), 1.25 (t, J = 7.1 Hz, 6H); 13C
NMR (100 MHz, CDCl3) 168.0, 160.3, 152.8, 150.9, 134.7, 128.8,
127.6, 127.2, 124.4, 123.2, 122.6, 119.5, 114.2, 113.8, 62.1, 50.4, 30.7,
14.0; EI-MS (TOF) m/z (%) 368 (100, M+), 323 (9, [M −
OCH2CH3]+), 295 (24, [M − CO2CH2CH3]+), 267 (17), 249 (64),
222 (29), 221 (79), 194 (39), 181 (30), 165 (75). HRMS calculated
for C21H20O6: 368.1260. Found: 368.1263.
Diethyl 2,2-bis((2-Oxo-2H-naphtho[1,2-b]pyran-4-yl)-
methyl)malonate (4). Spectral data (200 mg, 10%): mp 199.9−
202.1 °C; IR (KBr, cm−1) 3076, 2976, 1710, 1475, 1374, 1245, 1198;
1H NMR (400 MHz, CDCl3) 8.53 (m, 2H), 7.80 (m, 2H), 7.70−7.60
1
cm−1) 3358, 3046, 2928, 1710, 1463, 1198; H NMR (400 MHz,
acetone-d6) 8.6 (d, J = 7.4 Hz, 1H), 7.99 (d, J = 8.3 Hz, 1H), 7.90 (s,
1H), 7.71−7.65 (m, 2H), 6.32 (s, 1H), 5.10 (m, 1H, OH), 4.70 (d, J =
5.2 Hz, 1H), 3.20 (m, 1H), 2.95 (m, 1H), 2.25 (m, 1H), 2.05 (m, 1H);
13C NMR (100 MHz, acetone-d6) 161.5, 156.6, 152.4, 138.7, 136.7,
130.5, 129.9, 128.6, 124.1, 123.7, 122.9, 114.0, 112.9, 69.1, 32.9, 27.9;
EI-MS (TOF) m/z (%) 252 (42, M+), 234 (54, [M − H2O]+), 206
(100), 178 (50), 177 (32), 176 (44), 165 (15), 152(17), 151 (19).
HRMS calculated for C16H12O3: 252.0786. Found: 252.0796.
2,2-Diphenyl-2H-anthraceno[9,1-bc]pyran (9). A solution of
PhMgBr (prepared from bromobenzene (0.50 g, 3.2 mmol) and
magnesium (1.0 g)) in dry Et2O (10 mL) was slowly added to a stirred
solution of dihydroanthracenopyran-6-ol-2-one 7 (184 mg, 0.73
mmol) in dry Et2O (5 mL). After 15 min at room temperature, the
solvent was removed under reduced pressure, and then HCl (5%, 20
mL) was added, and the solution was stirred overnight. The solution
was then extracted with EtOAc (3 × 25 mL), and the combined
organic layers were dried (Na2SO4). The solvent was removed under
reduced pressure, and the residue was purified by chromatography
column on silica (25% EtOAc/petroleum ether) to give 8 as a white
solid (114 mg, 40%): 1H NMR (400 MHz, CDCl3) 8.45 (d, 1H), 7.75
(d, 1H), 7.6−7.5 (m), 7.5−7.4 (m), 7.5−7.2 (m), 7.64 (s, 1H), 5.95 (s,
1H), 4.95 (m, 1H), 2.95 (m, 1H), 2.60 (m, 1H), 2.20−2.0 (m, 2H);
EI-MS (TOF) m/z (%) 390 (8, M+), 372 (92, [M − H2O]+), 313
(45), 295 (100), 265 (75), 252 (32), 205 (86), 165 (22). HRMS
calculated for C28H22O2: 390.1620. Found: 390.1631. In CDCl3
solution, this compound is not stable and in two days is converted
by dehydration and double bond migration to the anthracenopyran 9:
1H NMR (100 MHz, CDCl3) 8.45 (dd, J = 1.5, 6.7 Hz, 1H), 7.91 (d, J
= 8 Hz, 1H), 7.90 (s, 1H), 7.71 (d, J = 8.6 Hz, 1H), 7.59−7.55 (m,
4H), 7.52−7.44 (m, 2H), 7.33−7.30 (t, J = 6.6 Hz, 1H), 7.25−7.10
(m, 7H), 4.00 (s, 2H); EI-MS (TOF) m/z (%) 372 (71, M+), 281
(18), 265 (13), 205 (100), 177 (24), 176 (19), 167 (16). EI-HRMS
calculated for C28H20O: 372.1514. Found: 372.1518.
6-t-Butyldimethylsilyloxy-4H-5,6-dihydroanthraceno[9,1-
bc]pyran-2-one (10). A solution of the alcohol 7 (981 mg; 2.71
mmol), t-butyldimethylsilyl chloride (490 mg; 3.25 mmol), and
imidazole (662 mg, 9.72 mmol) in dimethylformamide (10 mL) was
stirred at room temperature. After 24 h, another 1.2 equiv of t-
butyldimethylsilyl chloride was added, and the solution was kept at
room temperature for 2 days with stirring. After the reaction was
confirmed complete by TLC, NH4Cl (22%, 50 mL) was added, and
(m, 6H), 7.53 (t, J = 8.9 Hz, 2H), 6.47 (s, 2H), 4.04 (m, 4H), 3.64 (s,
4H), 1.05 (t, J = 7.1 Hz, 6H); 13C NMR (100 MHz, CDCl3) 169.4,
160.1, 151.3, 150.8, 134.7, 129.0, 127.6, 127.4, 124.3, 123.2, 122.6,
119.6, 115.9, 114.6, 62.6, 50.5, 34.3, 13.6; EI-MS (TOF) m/z (%) 576
(45, M+), 548 (12), 368 (60), 275 (50), 221 (85), 210 (97), 182
(100), 165 (77). HRMS calculated for C35H28O8: 576.1784. Found:
576.1769.
3-(2-Oxo-2H-naphtho[1,2-b]pyran-4-yl)propanoic Acid (5). A
mixture of diester 3 (540 mg, 1.47 mmol) and NaOH (640 mg, 16
mmol) in pure EtOH (20 mL) was heated under reflux for 2 h. After
returning to room temperature, the solvent was removed under
reduced pressure, and a solution of HCl (5%, 50 mL) was added and
stirred for 20 min. The solid thus formed was filtered to afford the
corresponding diacid as a yellow solid. This compound was dissolved
in DMSO (5 mL) and heated at reflux for 10 min, during which some
CO2 evolution occurs. After the mixture returned to room
temperature, water (25 mL) was added, and the solid thus formed
was filtered, washed with water, and dried under a high vacuum to
afford the monoacid 5 as a white powder (382 mg, 97%): mp 187−
191 °C; IR (KBr, cm−1) 2940 (large), 1716, 1610, 1369, 1263, 1169;
1H NMR (400 MHz, DMSO) 12.4 (s, 1H, OH), 8.39 (m, 1H), 8.06
(m, 1H), 7.90−7.85 (m, 2H), 7.73−7.70 (m, 2H), 6.45 (s, 1H), 3.16
(t, J = 7.0 Hz, 2H), 2.71 (t, J = 7.5 Hz, 2H); 13C NMR (100 MHz,
DMSO) 173.2, 169.7, 159.6, 156.1, 149.8, 134.3, 128.8, 127.9, 127.4,
124.1, 121.6, 120.7, 114.2, 112.8, 31.7, 26.5; EI-MS (TOF) m/z (%)
268 (90, M+), 240 (31), 223 (9, [M − COOH]+), 222 (11), 195 (100,
[M − CH2CH2COOH]+), 181 (38), 165 (30), 152 (47), 139 (22).
HRMS calculated for C16H12O4: 268.0736. Found: 268.0733.
4H-5,6-Dihydroanthraceno[9,1-bc]pyran-2,6-dione (6). A sol-
ution of the carboxylic acid 5 (1.986 g; 7.41 mmol) in SOCl2 (1 mL)
was heated at reflux for 1 h, and after cooling to room temperature, the
SOCl2 excess was removed under reduced pressure. To the residue
3966
dx.doi.org/10.1021/jo3003216 | J. Org. Chem. 2012, 77, 3959−3968

The Journal of Organic Chemistry
Article
the solution was extracted with EtOAc (2 × 30 mL). The combined
organic layers were dried (Na2SO4) and concentrated under a vacuum
to afford the crude silyl ether, which was purified by chromatography
on silica gel (0−6% EtOAc/petroleum ether) to give the silyl ether 10
as slightly yellow crystals (790 mg; 79%): mp 149.8−151.1 °C; IR
(KBr, cm−1) 3070, 2952, 2858, 1716, 1463, 1245; 1H NMR (400
MHz, CDCl3) 8.51 (d, J = 7.3 Hz, 1H), 7.83 (d, J = 7.3 Hz, 1H), 7.64
(s, 1H), 7.63−7.55 (m, 2H), 6.29 (s, 1H), 5.05 (m, 1H), 3.18 (m, 1H),
2.83 (m, 1H), 2.20−2.0 (m, 2H), 0.935 (s, 9H), 0.21 (s, 3H), 0.15 (s,
3H); 13C NMR (100 MHz, CDCl3) 161.0, 154.3, 150.8, 135.4, 134.6,
128.7, 127.8, 126.7, 122.5 (two signals), 121.2, 112.1, 111.3, 68.8, 31.5,
26.2, 25.8, 18.2, −4.4, −4.5; EI-MS (TOF) m/z (%) 366 (3, M+), 309
(100, [M − C4H9]+), 235 (53, [M − OSiMe2(t-Bu)]+), 207 (25), 206
(21), 205 (21), 165 (7), 75(82). EI-HRMS calculated for C22H26O3Si:
366.1651. Found: 366.1650.
General Procedure for the Reaction of Dihydroanthraceno-
pyran-2-one 10 with Grignard Reagents. A solution of the
Grignard reagent (5 equiv) in dry Et2O (10 mL) was slowly added to a
stirred solution of dihydroanthracenopyran-2-one 10 (270 mg; 0.73
mmol) in dry Et2O (5 mL). After 15 min at room temperature, the
Et2O was removed under reduced pressure, and then HCl (5%, 20
mL) was added, and the solution was stirred overnight. The solution
was then extracted with EtOAc (3 × 25 mL), and the combined
organic layers were dried (Na2SO4). The solvent was removed under
reduced pressure, and the residue was purified by chromatography
column on silica (petroleum ether) followed by preparative TLC (5%
EtOAc/petroleum ether).
205 (15), 165 (13), 121 (65). EI-HRMS calculated for C36H40O4Si:
564.2696. Found: 564.2701.
6-t-Butyldimethylsilyloxy-2,2-(naphth-1-yl)-2H,4H-5,6-
dihydroanthraceno[9,1-bc]pyran (13). Prepared from dihydroan-
thracenopyran-2-one 10 (270 mg; 0.73 mmol) and 1-NpMgBr (from
1-bromonaphthalene (0.66 g, 3.2 mmol) and magnesium (1.0 g)) and
obtained as a white solid (91 mg; 19%) (mixture of isomeric
dihydroanthracenopyran 13 and 14): IR (KBr, cm−1) 3052, 2940,
2858, 1374, 1251, 1074; for NMR details see the Supporting
Information; EI-MS (TOF) m/z (%) 604 (6, M+), 547 (2, [M −
C4H9]+), 472 (100), 345 (58), 344 (62), 343 (47), 315 (25). EI-
HRMS calculated for C42H40O2Si: 604.2798. Found: 604.2792.
ASSOCIATED CONTENT
■
S
* Supporting Information
NMR spectra (1H and 13C) for all new compounds, 2D NMR
data for the new fused-napthopyrans 11−13, NMR data for
irradiated solutions of compounds 11 and 12. This material is
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: pcoelho@utad.pt.
■
Notes
The authors declare no competing financial interest.
6-t-Butyldimethylsilyloxy-2,2-diphenyl-2H,4H-5,6-
dihydroanthraceno[9,1-bc]pyran (11). Prepared from dihydroan-
thracenopyran-2-one 10 (270 mg; 0.73 mmol) and PhMgBr (from
bromobenzene (0.50 g, 3.2 mmol) and magnesium (1.0 g)) and
obtained as a white solid (92 mg; 18%): 1H NMR (400 MHz, CDCl3)
8.30 (m, 1H), 7.83 (m, 1H), 7.50−7.42 (m, 4H), 7.40−7.36 (m, 2H),
7.35 (s, 1H), 7.31−7.17 (m, 5H), 5.87 (s, 1H), 4.93 (m, 1H), 2.87 (m,
1H), 2.60 (m, 1H), 2.05 (m, 1H), 1.90 (m, 1H), 0.935 (s, 9H), 0.16
(s, 3H), 0.10 (s, 3H) or 1H NMR (400 MHz, toluene-d8) 8.44 (dd, J =
8.2 Hz, J = 1.5 Hz, 1H), 7.6−7.55 (m, 5H), 7.42 (s, 1H), 7.27 (ddd, J
= 8.2 Hz, J = 6.9 Hz, J = 1.4 Hz, 1H), 7.21 (ddd, J = 8.2 Hz, J = 6.9 Hz,
J = 1.4 Hz, 1H), 7.17−7.07 (m, 4H), 7.07−6.97 (m, 2H), 5.76 (t, J =
1.6 Hz, 1H), 4.77 (dd, J = 6.6 Hz, J = 4.4 Hz, 1H), 2.81 (m, 1H), 2.38
(m, 1H), 1.87 (m, 2H), 1.02 (s, 9H), 0.14 (s, 3H), 0.04 (s, 3H); 13C
NMR (100 MHz, toluene-d8) 147.3, 145.8, 135.9, 134.2, 129.9, 127.8,
127.5, 127.3, 127.0, 126.2, 125.0, 124.2, 122.0, 120.9, 117.9, 113.3,
83.2, 69.5, 32.1, 25.6, 24.9, 18.0, −4.8, −5.0; EI-MS (TOF) m/z (%)
504 (10, M+), 447 (6, [M − C4H9]+), 427 (14, [M − C6H5]+), 372
(26), 295 (100), 281 (10), 265 (16), 252 (10), 205(26), 75 (33). EI-
HRMS calculated for C34H36O2Si: 504.2485. Found: 504.2493.
6-t-Butyldimethylsilyloxy-2,2-(2′-methoxyphenyl)-2H,4H-
5,6-dihydroanthraceno[9,1-bc]pyran (12). Prepared from dihy-
droanthracenopyran-2-one 10 (270 mg; 0.73 mmol) and o-
CH3OPhMgBr (from 2-bromoanisole (0.60 g, 3.2 mmol) and
magnesium (1.0 g)) and obtained as a white solid (53 mg; 13%):
ACKNOWLEDGMENTS
The authors acknowledge FCT (Portugal’s Foundation for
Science and Technology) and FEDER for financial support
through the research unit Centro de Quimica-Vila Real
(POCTI-SFA-3-616) and Project PTDC/QUI/66012/2006.
The 300 and 500 MHz NMR facilities were funded by the
■
́
Reg
Jeunesse de l'Education Nationale et de la Recherche
(MJENR), and the Fonds Europeens de Developpement
́ ̀
ion Nord-Pas de Calais (France), the Ministere de la
́
́
Reg
́
ional (FEDER).
REFERENCES
■
(1) Hepworth, J. D.; Heron, B. M. Functional Dyes; Sung-Hoon, K.,
Ed.; Elsevier: Amsterdam, 2006.
(2) Malic, N.; Campbell, J. A.; Ali, A. S.; Francis, C. L.; Evans, R. A. J.
Polym. Sci., Polym. Chem. 2011, 49, 476.
(3) Xie, B. J.; Wang, G.; Zhao, X. C. J. Appl. Polym. Sci. 2011, 122,
3377.
(4) Pardo, R.; Zayat, M.; Levy, D. Chem. Soc. Rev. 2011, 40, 672.
(5) Coelho, P. J.; Carvalho, L. M.; Goncalves, L.; Silva, C. J. R.;
Campos, A. M.; Gomes, M. J. J. Sol-Gel Sci. Technol. 2010, 56, 203.
(6) Pardo, R.; Zayat, M.; Levy, D. J. Photochem. Photobiol., A. 2008,
198, 232.
1
IR (KBr, cm−1) 3070, 2940, 1469, 1239, 1080; H NMR (400 MHz,
(7) Favaro, G.; Ortica, F.; Romani, A.; Smimmo, P. J. Photochem.
Photobiol., A. 2008, 196, 190.
(8) Sriprom, W.; Neel, M.; Gabbutt, C. D.; Heron, B. M.; Perrier, S. J.
Mater. Chem. 2007, 17, 1885.
(9) Tomasulo, M. US Patent 0108781A1 (2011).
(10) Aiken, S.; Cano J.-P.; Gabbutt C. D.; Heron, B. M.; Kosa, T.; Su
L.; Sukhomlinova, L.; Taheri, B. US Patent 0202033A1 (2010)
(11) Kim, B.-K.; Deng, J.; Xiao, W.; Van gemert, B.; Chopra, A.;
Molock, F.; Mahadevan, S. US Patent 0072206A1 (2009).
(12) Breyne, O.; Chan Y.-P.; Jean, P. US Patent 6506538B1 (2003).
(13) Delbaere, S.; Micheau, J. C.; Teral, Y.; Bochu, C.; Campredon,
M.; Vermeersch, G. Photochem. Photobiol. 2001, 74, 694.
(14) Coelho, P. J.; Salvador, M. A.; Heron, B. M.; Carvalho, L. M.
Tetrahedron 2005, 61, 11730.
CDCl3) 8.28 (m, 1H), 7.68−7.64 (m, 2H), 7.60 (dd, J = 1.7, 7.7 Hz,
1H), 7.38−7.33 (m, 2H), 7.31 (s, 1H), 7.20−7.13 (m, 2H), 6.93−6.82
(m, 2H), 7.80 (t, J = 7.2 Hz, 2H) 1H), 6.08 (s, 1H), 4.92 (m, 1H),
3.49 (s, 6H), 2.85 (m, 1H), 2.58 (m, 1H), 2.04 (m, 1H), 1.90 (m, 1H),
1
0.95 (s, 9H), 0.16 (s, 3H), 0.11 (s, 3H) or H NMR (400 MHz,
toluene-d8) 8.60 (d, J = 8.2 Hz, 1H), 8.01 (dd, J = 7.9 Hz, J = 1.7 Hz,
1H), 7.89 (dd, J = 7.9 Hz, J = 1.7 Hz, 1H), 7.61 (d, J = 8.0 Hz, 1H),
7.28 (td, J = 7.9 Hz, J = 1.4 Hz, 1H), 7.21 (td, J = 8.0 Hz, J = 1.4 Hz,
1H), 6.55 (dd, J = 8.0 Hz, J = 0.9 Hz, 1H), 6.52 (dd, J = 8.0 Hz, J = 0.9
Hz, 1H), 6.36 (t, J = 1.6 Hz, 1H), 4.81 (dd, J = 6.5 Hz, J = 4.8 Hz,
1H), 3.19 (s, 3H), 3.17 (s, 3H), 2.87 (m, 1H), 2.44 (m, 1H), 1.90 (m,
2H), 1.03 (s, 9H), 0.15 (s, 3H), 0.08 (s, 3H); 13C NMR (100 MHz,
toluene-d8) 156.4, 147.8, 136.1, 133.8, 133.4, 128.8, 128.6, 128.3,
127.9, 127.4, 125.7, 124.8, 124.4, 122.6, 120.1, 119.9, 117.4, 113.1,
112.3, 81.6, 69.7, 32.2, 25.6, 25.1, 17.7, −4.7, −4.9; EI-MS (TOF) m/z
(%) 564 (17, M+), 507 (4, [M − C4H9]+), 457 (6, [M −
C6H4OCH3]+), 432 (72), 401 (11), 325 (100), 311 (32), 227 (29),
(15) Delbaere, S.; Luccioni-Houze, B.; Bochu, C.; Teral, Y.;
Campredon, M.; Vermeersch, G. J. Chem. Soc., Perkin Trans. 2 1998,
1153.
3967
dx.doi.org/10.1021/jo3003216 | J. Org. Chem. 2012, 77, 3959−3968

The Journal of Organic Chemistry
Article
(16) Guo, K. P.; Chen, Y. J. Phys. Org. Chem. 2010, 23, 207.
(17) Delbaere, S.; Vermeersch, G.; Frigoli, M.; Mehl, G. H. Org. Lett.
2010, 12, 4090.
(18) Gabbutt, C. D.; Heron, B. M.; Kilner, C.; Kolla, S. B. Org.
Biomol. Chem. 2010, 8, 4874.
(19) Coelho, P. J.; Carvalho, L. M.; Vermeersch, G.; Delbaere, S.
Tetrahedron 2009, 65, 5369.
(20) Alberti, A.; Teral, Y.; Roubaud, G.; Faure, R.; Campredon, M.
Dyes Pigm. 2009, 81, 85.
(21) Gabbutt, C. D.; Heron, B. M.; Kolla, S. B.; McGivern, M. Eur. J.
Org. Chem. 2008, 2031.
(22) Kumar, S.; Hernandez, D.; Hoa, B.; Lee, Y.; Yang, J. S.;
McCurdy, A. Org. Lett. 2008, 10, 3761.
(23) Gabbutt, C. D.; Heron, B. M.; Instone, A. C.; Horton, P. N.;
Hursthouse, M. B. Tetrahedron 2005, 61, 463.
(24) Coelho, P. J.; Salvador, M. A.; Oliveira, M. M.; Carvalho, L. M. J.
Photochem. Photobiol., A. 2005, 172, 300.
(25) Coelho, P. J.; Salvador, M. A.; Oliveira, M. M.; Carvalho, L. M.
Tetrahedron 2004, 60, 2593.
(26) Ercole, F.; Malic, N.; Harrisson, S.; Davis, T. P.; Evans, R. A.
Macromolecules 2010, 43, 249.
(27) Berthet, J.; Coelho, P. J.; Carvalho, L. M.; Vermeersch, G.;
Delbaere, S. J. Photochem. Photobiol., A. 2009, 208, 180.
(28) Moorthy, J. N.; Koner, A. L.; Samanta, S.; Roy, A.; Nau, W. M.
Chem.Eur. J. 2009, 15, 4289.
(29) Ercole, F.; Davis, T. P.; Evans, R. A. Macromolecules 2009, 42,
1500.
(30) Oliveira, M. M.; Salvador, M. A.; Delbaere, S.; Berthet, J.;
Vermeersch, G.; Micheau, J. C.; Coelho, P. J.; Carvalho, L. M. J.
Photochem. Photobiol., A. 2008, 198, 242.
(31) Sallenave, X.; Delbaere, S.; Vermeersch, G.; Saleh, A.; Pozzo, J.
L. Tetrahedron Lett. 2005, 46, 3257.
(32) Nabais, C.; Heron, B. M.; de Sousa, H. C.; Gil, M. H.; Sobral, A.
J. Biomater. Sci., Polym. Ed. 2011, 22, 139.
(33) Corns, S. N.; Partington, S. M.; Towns, A. D. Color. Technol.
2009, 125, 249.
(34) Sousa, C. M.; Pina, J.; de Melo, J. S.; Berthet, J.; Delbaere, S.;
Coelho, P. J. Org. Lett. 2011, 13, 4040.
(35) Sousa, C. M.; Pina, J.; de Melo, J. S.; Berthet, J.; Delbaere, S.;
Coelho, P. Eur. J. Org. Chem. 2012, 1768−1773.
(36) Sousa, C. M.; Coelho, P. J.; Vermeersch, G.; Berthet, J.;
Delbaere, S. J. Photochem. Photobiol., A. 2010, 216, 73.
(37) Tickle, R. W.; Tickle, W.; Melton, T.; Elvidge, J. A. J. Chem. Soc.,
Perkin Trans. 1 1974, 569.
(38) Cotterill, W. D.; Iqbal, M.; Livingstone, R. J. Chem. Res., Synop.
1998, 2.
(39) Valizadeh, H.; Shockravi, A. Tetrahedron Lett. 2005, 46, 3501.
(40) Burger, A.; Ullyot, G. E. J. Org. Chem. 1947, 12, 342.
(41) Basanagouda, M.; Shivashankar, K.; Kulkarni, M. V.; Rasal, V. P.;
Patel, H.; Mutha, S. S.; Mohite, A. A. Eur. J. Med. Chem. 2010, 45,
1151.
(42) Celebuski J. E.; US patent 5,247,099 (1993).
(43) Gabbutt, C. D.; Heron, B. M.; Instone, A. C. Tetrahedron 2006,
62, 737.
(44) Guo, K. P.; Chen, Y. J. Mater. Chem. 2010, 20, 4193.
(45) Delbaere, S.; Vermeersch, G. J. Photochem. Photobiol., C 2008, 9,
61.
(46) Delbaere, S.; Vermeersch, G.; Micheau, J. C. J. Photochem.
Photobiol., C 2011, 12, 74.
3968
dx.doi.org/10.1021/jo3003216 | J. Org. Chem. 2012, 77, 3959−3968