Synthesis and photochemical reactivity of new 4-substituted naphtho[1,2-b]pyran derivatives

Article abstract of DOI:10.1016/j.jphotochem.2010.09.009

A new naphtho[1,2-b]pyran possessing an ester substituent in position 4 was prepared from 2,3-dihydro-2,2-diphenyl-4H-naphtho[1,2-b]pyran-4-one and then converted to the carboxylic acid derivative. The photochromic behaviour of these two compounds was studied by UV-vis spectroscopy and the structures of the photoproducts elucidated by NMR. Under UV irradiation the uncoloured ester derivative afforded a single coloured photoisomer having a transoid-trans (TT) configuration while the acid was irreversibly transformed into degradation products. In strong acid medium both compounds were converted to a spiro derivative formed through the opening of the pyran ring followed by an intramolecular lactone ring formation and electrophilic aromatic substitution.

Full text of DOI:10.1016/j.jphotochem.2010.09.009

Journal of Photochemistry and Photobiology A: Chemistry 216 (2010) 73–78
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Synthesis and photochemical reactivity of new 4-substituted
naphtho[1,2-b]pyran derivatives
a
a,∗
b
b
b
Céu M. Sousa , Paulo J. Coelho , Gaston Vermeersch , Jérôme Berthet , Stephanie Delbaere
a
Centro de Química - Vila Real, Universidade de Trás-os-Montes e Alto Douro, 5001-801 Vila Real, Portugal
Université Lille Nord de France, CNRS UMR 8516, UDSL, Faculté des Sciences Pharmaceutiques et Biologiques, F-59006 Lille, France
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 2 July 2010
Received in revised form 3 September 2010
Accepted 8 September 2010
Available online 17 September 2010
A new naphtho[1,2-b]pyran possessing an ester substituent in position 4 was prepared from 2,3-dihydro-
,2-diphenyl-4H-naphtho[1,2-b]pyran-4-one and then converted to the carboxylic acid derivative. The
2
photochromic behaviour of these two compounds was studied by UV–vis spectroscopy and the structures
of the photoproducts elucidated by NMR. Under UV irradiation the uncoloured ester derivative afforded
a single coloured photoisomer having a transoid-trans (TT) configuration while the acid was irreversibly
transformed into degradation products. In strong acid medium both compounds were converted to a
spiro derivative formed through the opening of the pyran ring followed by an intramolecular lactone
ring formation and electrophilic aromatic substitution.
Keywords:
Photochromism
Naphthopyran
NMR
©
2010 Elsevier B.V. All rights reserved.
Lactone
Triflic acid
UV irradiation
Mukaiyama aldol condensation
1
. Introduction
One possible way to prevent the formation of this long-lived
photoisomer is to connect the pyran double bond to the naph-
thalene core (Scheme 2). The introduction of an alkyl bridge
between carbons 4 and 5 would give rise to a new type of fused-
naphthopyrans that should produce only one photoisomer and
therefore exhibit mono-exponential fading kinetic, although prob-
ably very fast, thus avoiding the persistence of the residual colour
[5]. In this paper we describe the photochromic properties of
two new naphthopyrans substituted in position 4 by an ester or
a carboxylic acid chain and an attempt to prepare such fused-
naphthopyran that surprisingly afforded a spiro lactone formed
through a multi-step mechanism.
Naphthopyrans are one of the most important classes of pho-
tochromic systems with excellent photochromic performance
that met considerable success in the production of variable-
transmission optical materials, namely photochromic plastic
ophthalmic lenses, which darken in the sunlight [1,2].
Under near-UV light irradiation, these uncoloured or faintly
coloured molecules, either in solution or incorporated in polymeric
matrices, undergo an electrocyclic pyran-ring opening with for-
mation of the transoid-cis isomer (TC, major product) that, upon
isomerization of the double bond, leads to the transoid-trans iso-
mer (TT, minor product) (Scheme 1) [3]. A photostationary state
is usually reached after several minutes of irradiation. These two
photoisomers, with a strong absorption in the visible part of the
spectrum have different lifetimes. As a result, in the absence of
light the system returns to the original colourless state by a pro-
cess following a bi-exponential kinetic. While the TC isomer rapidly
returns to the uncoloured closed form, the TT isomer is thermally
more stable and is responsible for the persistence of a residual
colour for several minutes or hours after the removal of the light
source [4].
2. Results and discussion
The reaction of 2,3-dihydro-2,2-diphenyl-4H-naphtho[1,2-
b]pyran-4-one
1 [5,6] with the silyl enol ether 1-methyl
trimethylsilyl dimethylketene acetal in the presence of an excess
of TiCl4 afforded the naphtho[1,2-b]pyran 2 directly. Subsequent
hydrolysis in a basic medium provided the corresponding car-
boxylic acid 3 (Scheme 3).
−
3
In toluene solution (10 M) naphthopyrans 2 and 3 are colour-
less with a very strong absorption in the near UV region. Continuous
◦
UV light irradiation of a solution of naphthopyran 2 at 20 C leads to
the slow development of a pale yellow colouration with a maximal
absorption at 420 nm but a photostationary state was not achieved
even after 40 min of irradiation (Fig. 1).
∗ Corresponding author. Tel.: +351 259 350284; fax: +351 259 350480.
E-mail address: pcoelho@utad.pt (P.J. Coelho).
1
010-6030/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jphotochem.2010.09.009

7
4
C.M. Sousa et al. / Journal of Photochemistry and Photobiology A: Chemistry 216 (2010) 73–78
Ph
Ph
order kinetics pointing to a photoreversible process involving only
one photoisomer (Fig. 1).
Ph Ph
O
O
O
Ph
Ph
UV
To investigate the structure of the products formed upon UV
irradiation of naphthopyran 2, NMR studies were carried out in
+
Δ, vis
−
2
toluene-d8 (10 M) after UV irradiation with a 1000 W UV lamp,
1
directly in the NMR tube at room temperature. The H NMR spectra
Closed form
Colourless
TC
TT
were recorded at regular time intervals to monitor the changes in
peak-intensities and thus to obtain information about the number
of photoproducts and the evolution of their concentration in time
Coloured
Scheme 1. Photochromic equilibrium for 2H-naphtho[1,2-b]pyran.
[
7].
As displayed in Figs. 2 and 3, UV irradiation results in the forma-
Ph
Ph Ph
tion of only one photoproduct (20% at the photostationary state).
In the 1H NMR spectrum, one can observe two distinct resonances
at 1.61 and 1.41 ppm for the two methyl groups, which are not
equivalent probably due to sterical hindrance, preventing a rapid
rotation. The singlet signal at 6.59 ppm was assigned to proton H-3
which was more deshielded than in the closed form, due to the
extension of the conjugation. A 1D selective NOESY experiment
O
O
Ph
UV
4
Δ, vis
5
Closed Form
Colourless
TC
Coloured
indicated a dipolar correlation between H-3 and a doublet sig-
Scheme 2. Photochromic equilibrium for a fused-naphthopyran.
nal at 7.06 ppm, attributed to H-5. Both 2D 1H–1H COSY and 1D
selective-TOCSY experiments have been recorded to identify the
scalar coupling between H-10 at 8.20 ppm and three signals at 6.89,
0.12
0.10
0.08
0.06
0.04
0.02
0.00
7
.01 and 6.76 ppm assigned to H-9, H-8 and H-7, respectively, and
between H-6 at 6.17 ppm and H-5 at 7.06 ppm. From this set of data,
the photoproduct was identified as the open form of compound 2
with a transoid-trans configuration (TT) (Scheme 4).
Vis Light On
UV light off
The relatively high thermal stability of this photoproduct and
the fact that visible light irradiation is very effective to regenerate
the initial naphthopyran are also in agreement with the TT config-
uration. The same experiment was repeated at low temperature to
examine whether the second possible photoisomer (transoid-cis) is
formed or not, as this open form is usually less thermally stable than
the TT isomer. However, at 228 K, UV irradiation generated only the
TT isomer. Therefore the presence of the ester chain in C-4 increases
the difference in the stability of the two possible photoisomers and
probably the more unstable TC isomer is rapidly converted through
UV light on
0
20
40
60
80
100
120
140
160
180
Time (min)
C
C double bond isomerization to the more stable TT form [8].
The photochemical behaviour of naphthopyran 3 was also
Fig. 1. Colour forming and colour bleaching for naphtho[1,2-b]pyran 2 measured at
20 nm.
examined by UV–vis spectroscopy and then by NMR. In contrast
to naphthopyran 2, no colouration and consequently no absorp-
tion in the visible range of the spectrum was observed when a
toluene solution of naphthopyran 3 was irradiated with a 150 W
UV lamp, suggesting that this compound would not be sensitive to
UV light. However, NMR investigations on irradiated solutions of
naphthopyran 3 with a 1000 W UV lamp evidenced the formation
4
When the UV light was turned off, a nearly constant absorbance
was observed underlining the formation of a long-lived coloured
compound (t1/2 = 18 h). The visible light irradiation (ꢀmax > 420 nm)
of this solution induces a slow absorption decrease following a first
Ph Ph
O
Ph Ph
O 2
Ph Ph
O
OSiMe3
OMe
1
O
4
1) NaOH, EtOH
O
O
H CO
3
2) HCl
60%
TiCl4 75%
HO
1
2
3
Scheme 3. Synthesis of naphthopyrans 2 and 3.
O
2
H CO
O
3
O
3
O
O
1
0
10
hv-UV
9
8
9
OCH3
OCH3
3
5
8
5
O
7
6
hv-Vis / Δ
7
6
TT
TC Not observed
2
Scheme 4. Photochromic reaction for naphtho[1,2-b]pyran 2.

C.M. Sousa et al. / Journal of Photochemistry and Photobiology A: Chemistry 216 (2010) 73–78
75
Fig. 2. Parts of 1H NMR spectra of naphtho[1,2-b]pyran 2 (a) before and (b) after UV irradiation at room temperature.
Fig. 3. Kinetics of colouration under UV irradiation (left) and photobleaching with visible light (right) of naphtho[1,2-b]pyran 2.
of three photoproducts labeled P , P and P3 which are thermally
P1 is a conjugated phenol formed by pyran ring opening fol-
lowed by decarboxylation of the acid function. The phenol function
is characterized by a broad signal at 5.18 ppm while the two methyl
groups give two distinct signals at 1.48 ppm and 1.70 ppm and
1
2
and photochemically (with visible light) stable (Fig. 4). P , P and
1
2
P3 were therefore assigned to degradation photoproducts and their
structures deduced from 1 and 2D NMR experiments (Scheme 5).
H
O
Ph
1
0
10b
4
2
Ph
4
a
H
3
O
O
Ph
O
H
5
10
10b
2'
Ph
3
O
O
7
6
P1
2
2
4
O
3
O
1
0
4
a
hv
5
6'
4
Ph
Ph
P3
1
0b
OH hv-UV
Ph
O
Ph
3
6
O2
5
-CO2
2
+
6
10
7
4
3
10b
O
5
6
P2
Scheme 5. Photochemical behaviour of naphtho[1,2-b]pyran 3.

7
6
C.M. Sousa et al. / Journal of Photochemistry and Photobiology A: Chemistry 216 (2010) 73–78
Fig. 4. Parts of 1H NMR spectra of naphtho[1,2-b]pyran 3 (a) before, (b) after 30 min of UV irradiation and (c) after 60 min of UV irradiation.
are thus diastereotopic. P1 evolves thermally through cyclisation
O
towards P . Such bond-reforming between C-2 and oxygen requires
2
O 24 1'
the hydrogen-migration from the phenol to C-3.
O
CF SO H
3
3
The pyran ring in P2 was characterized by a 2D 1H–13C HMBC
experiment which displayed long-range correlations between the
quaternary carbon C-2 at 83.9 ppm, the methylene protons in C-3 at
5
6
'
O
86%
r.t.
RO
ꢀ ꢀꢀ ꢀ ꢀꢀ
.17 ppm and the aromatic protons H-2 /2 /6 /6 at 7.81 ppm. The
3
2
(R=CH3)
3 (R=H)
1
13
4
presence of an ethylenic function was apparent from H– C long
range correlations between the quaternary carbon assigned to C-4
at 122.9 ppm and the diastereotopic methyl protons at 1.56 ppm
and 1.73 ppm, and between the quaternary carbon bearing the two
methyls at 127.7 ppm and the methylene protons (H-3) at 3.17 ppm.
P3 was identified as a conjugated phenol containing a car-
bonyl function resulting from the opening of the pyran ring
and oxidation of the double bond at C-4. The formation of ace-
Scheme 6. Synthesis of lactone 4.
14.78 ppm, due to hydrogen-bonding with the C
O function at C-
. In the 2D 1H– C HMBC spectrum long-range correlations were
13
4
observed between the quaternary carbon at 154 ppm (C-2) and
the aromatic protons at 6.94 ppm (H-3) and 7.25 ppm (H-2 = H-
), and between the quaternary carbon C-10b at 163.8 ppm and
1
tone in the sample was also observed (ı H = 1.6 ppm) [9]. The
ꢀ
phenolic proton exhibited a highly deshielded chemical shift,
ꢀ
6
Ph
Ph
Ph
Ph
O
Ph Ph
O
H
RO
OH
O
OH
Ph
Rotation
CF SO H
3
3
O
O
O
RO
(R= CH3)
(R= H)
RO
RO
2
3
EAS
CF SO H
3
3
O
O
RO
OH
Ph Ph
O
O
Ph
Ph
H+
O
Not formed
4
Scheme 7. Mechanism for the formation of lactone 4.

C.M. Sousa et al. / Journal of Photochemistry and Photobiology A: Chemistry 216 (2010) 73–78
77
the phenolic proton at 14.78 ppm, H-10 at 8.57 ppm and H-5 at
.51 ppm. Finally, the carbonyl function (C O at 196.9 ppm) is cor-
related with the aromatic protons H-3 at 6.94 ppm and H-5 at
angle to the monitoring beam using an optical fiber system (77654
−
2
7
Oriel Instruments). 40 W m light flux was used (Goldilux Pho-
tometer with UV-A probe). Visible irradiation experiments were
performed using a long-pass filter, Schott GG 420 (Oriel 59480). A
7
.51 ppm.
◦
The presence of the acid chain at C-4 allows the pyran ring open-
thermostated (20 C) 10 mm quartz cell (3.5 mL sample solution)
ing but leads to an open form that rapidly loses CO , affording
compounds P1 and P2 that cannot reform the pyran ring and upon
equipped with magnetic stirring was used. In a preliminary exper-
iment, the UV–vis absorption spectra of the closed and open forms
and the ꢀmax of the open form were determined. In a second exper-
iment the absorbance at the photostationary equilibrium, Aeq, was
measured at ꢀmax and then the decrease in the absorbance vs. time
was monitored.
2
in situ oxidation give compound P . Therefore naphthopyran 3 does
3
not show a reversible photochemical behaviour and is irreversibly
converted to P3.
The intramolecular cyclisation of naphthopyran
3 was
attempted by converting this acid to the acyl chloride using
SOCl2 followed by Lewis acid treatment and by the direct action of
strong acids (H SO , H PO , PPA) at room or low temperature, but
4.2. NMR studies
2
4
3
4
under these conditions only degradation products were observed.
We were unable to obtain the desired fused-naphthopyran using
this approach. However, the treatment of naphthopyran 3 with
triflic acid (CF SO H) [10] at room temperature gave a clean
reaction and afforded a new lactone 4 in 86% yield (Scheme 6).
The same compound was obtained under identical conditions
from naphthopyran 2 even when the reaction was performed in
the dark. In the 1H NMR spectrum of lactone 4, the two signals at
For NMR investigations, samples in toluene-d8 were irradiated
directly in the NMR tube (5 mm), thermo-regulated, using a 1000 W
Xe–Hg HP filtered short-arc lamp (Oriel) equipped with a filter for
UV irradiation (Schott 011FG09, 259 < ꢀ < 388 nm + 313 nm inter-
ferential filter). After irradiation had been stopped, the samples
were transferred to the thermoregulated probe of the NMR spec-
3
3
1
trometer ( H, 300 MHz).
The complete NMR data (1 and 2 D spectra and assignments)
of compounds 2–4 and the NMR characterization of the photo-
products of compounds 2 and 3 are reported in the supplementary
data.
1
.14 ppm and 1.46 ppm were assigned to the two methyl groups
ꢀ
and the singlet at 6.61 ppm was attributed to H-1 . Long range
scalar correlations in the HMBC spectrum between the quaternary
carbon C-4 at 60.5 ppm and the methyl protons at 1.14 and
ꢀ
1
7
.46 ppm, the aromatic protons H-1 at 6.61 ppm, proton H-5 at
4.3. Synthesis
ꢀ
.08 ppm and proton H-6 at 7.34 ppm were observed. The lactone
function was identified from correlation between the carbonyl C-2
at 173.4 ppm and the methyl protons at 1.14 ppm and 1.46 ppm.
The formation of this compound from naphthopyrans 2 and 3
can be explained by considering an initial acid-promoted opening
of the pyran ring followed by C–C bond rotation, intramolecu-
lar aromatic substitution and acid catalyzed lactone formation
Methyl
2-methyl-2-(2,2-diphenyl-2H-naphtho[1,2-b]pyran-4-
yl)propanoate 2. TiCl4 (0.70 mL, 6.7 mmol) was added to a solution
of naphtho[1,2-b]pyranone 1 (200 mg, 0.677 mmol) and 1-methyl
trimethylsilyl dimethylketene acetal (0.700 mL, 3.4 mmol) in
CH Cl (0.5 mL) at r.t. After 30 min the solution was quenched
2
2
with HCl (5%, 25 mL) and extracted with ethyl acetate (3× 25 mL).
(
(
Scheme 7). Instead of an electrophilic aromatic substitution
EAS) promoted by the triflic acid that could lead to the desired
The combined organic phases were dried (Na SO ) and the solvent
2
4
evaporated under reduced pressure leaving a brown oil that was
purified by column chromatography (2% EtOAc/ether petroleum,
silica gel) to give 2 as slightly yellow crystals (187 mg, 75% yield).
fused-naphthopyran, these molecules behave differently and in
strong acid medium a series of reactions occurred affording a
non-photochromic spiro compound with a completely different
structure to the expected one.
◦
−1
Mp 118–121 C. IR (KBr, cm ): 3054, 2944, 2866, 1728, 1642, 1587,
1493, 1446, 1383, 1265, 1187, 1132, 983. 1H NMR (toluene-d ):
8
8
7
6
.45 (d, J = 8.4 Hz, 1H), 7.64 (d, J = 8.4 Hz, 4H), 7.35 (d, J = 8.6 Hz, 1H),
.31 (d, J = 8.7 Hz, 1H), 7.24 (dd, J = 8.4, 6.8 Hz, 1H), 7.14 (dd, J = 8.6,
.8 Hz, 1H), 7.08 (dd, J = 8.4, 7.9 Hz, 4H), 7.03 (d, J = 8.7 Hz, 1H), 6.96
3
. Conclusion
(
dd, J = 7.9, 2H), 3.36 (s, 3H), 1.45 (s, 6H). 13C NMR (toluene-d ):
8
UV irradiation of naphtho[1,2-b]pyran 2 substituted on the
1
1
2
1
4
77.0, 148.4, 145.2, 137.8, 134.1, 127.9, 127.8, 127.4, 127.2, 126.4,
25.6, 125.5, 124.2, 122.5, 121.4, 120.5, 116.2, 82.3, 51.6, 44.4,
5.5. MS: m/z (%): 434 (45), 357 (100), 334 (96), 333 (99), 283 (38),
65 (45). EI-HRMS: calculated for C30H26O : 434.1882; found:
34.1884.
pyran double bond by an ester chain leads to the slow formation
of only one photoisomer possessing a transoid-trans (TT) configura-
tion that shows a high thermal stability and is converted back to the
original naphthopyran under visible irradiation. The corresponding
acid derivative 3 exhibits a different behaviour under UV irradia-
tion and is irreversibly converted to several degradation products
involving decarboxylation and oxidation of one double bond. Upon
treatment with CF SO H, both naphthopyrans were converted to a
non-photochromic spirolactone 4 formed by opening of the pyran
ring followed by intramolecular cyclisation.
3
2
-Methyl-2-(2,2-diphenyl-2H-naphtho[1,2-b]pyran-4-
yl)propanoic acid 3. mixture of naphthopyran
.739 mmol) and NaOH (1.5 g, 37.5 mmol) in EtOH (30 mL) was
A
2 (320 mg,
0
3
3
heated under reflux for 24 h. After return to r.t., the solvent was
removed under reduced pressure and water (50 mL) and ethyl
acetate (20 mL) were added. The organic phase was discarded
and the aqueous phase acidified with HCl (25 mL, 5%) and then
extracted with ethyl acetate (3× 50 mL). The combined organic
phases were dried (Na SO ) and the solvent evaporated under
4
. Experimental part
2
4
4.1. Spectrokinetic studies under continuous irradiation
reduced pressure leaving an off-white solid that was washed
with Et O (5 mL) to give 3 as white solid (187 mg, 60% yield). Mp
2
◦
−1
UV–vis irradiation experiments were made using a CARY 50
Varian spectrometer coupled to a 150 W Ozone free Xenon lamp
224–226 C. IR (KBr, cm ): 3062, 2989, 2885, 2657, 2530, 1691,
1639, 1446, 1378, 1262, 1147, 1100, 970. 1H NMR (toluene-d ):
8
(
(
6255 Oriel Instruments), equipped with a filter Schott 011FG09
259 < ꢀ < 388 nm with ꢀmax = 330 nm and T = 79%). The light from
8.44 (d, J = 8.4 Hz, 1H), 7.63 (d, J = 8.4 Hz, 4H), 7.39 (d, J = 8.8 Hz,
1H), 7.35 (d, J = 8.2 Hz, 1H), 7.24 (dd, J = 8.4, 6.9 Hz, 1H), 7.15 (dd,
J = 8.2, 6.9 Hz, 1H), 7.13–6.91 (m, 7H), 6.06 (s, 1H), 1.41 (s, 6H).
the UV lamp was filtered using a water filter (61945 Oriel Instru-
ments) and then carried to the spectrometer holder at the right
13
C NMR (toluene-d ): 179.9, 148.6, 145.3, 137.7, 134.5, 128.2,
8

7
8
C.M. Sousa et al. / Journal of Photochemistry and Photobiology A: Chemistry 216 (2010) 73–78
1
1
27.7 (two signals), 127.5, 126.7, 125.8, 122.7, 120.9, 120.7, 122.0,
24.8, 116.4, 82.7, 44.5, 25.7. MS: m/z (%): 420 (3), 402 (2), 376 (21,
References
[
1] (a) J.D. Hepworth, B.N. Heron, Photochromic naphthopyrans, in: S.-H. Kim (Ed.),
Functional Dyes, Elsevier, Amsterdam, 2006, pp. 35–85;
M-CO ), 334 (24), 333 (100), 299 (89), 209 (23), 165 (21). EI-HRMS:
calculated for C29H24O : 420.1725; found: 420.1720.
2
3
(b) B. Van Gemert, Benzo and naphthopyrans (chromenes), in: J.C. Crano, R.
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ꢀ
ꢀ
ꢀ
Spiro[3-phenyl-1H-indene-1,4 -3 ,3 -dimethylnaphtho[1,2-
ꢀ
b]pyran-2 -one] 4. Trifluoromethanosulfonic acid (0.4 mL,
4
and the mixture stirred for 3 h at r.t. Water (10 mL) was added and
the solid formed filtered and dissolved in Et O (10 mL). The organic
solution was dried (Na SO ) and the solvent evaporated under
reduced pressure leaving compound 4 as a white solid (89 mg,
[
[
.5 mmol) was added to naphthopyran 2 (100 mg, 0.23 mmol)
6
8 (1996) 1395–1398;
(b) B. Van Gemert, Mol. Cryst. Liq. Cryst. 344 (2000) 57–62;
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(
2
2
4
8
(b) S. Delbaere, G. Vermeersch, J. Photochem. Photobiol. A: Chem. 159 (2003)
227–232;
(c) K.P. Guo, Y. Chen, J. Mater. Chem. 20 (2010) 4193–4197;
◦
−1
8
1
1
6
6
6%). Mp.89–92 C. IR (KBr, cm ): 3061, 2962, 2920, 2852, 1770,
1
463, 1375, 1244, 1098. H NMR: 8.42 (d, J = 8.4, 1H), 7.82 (d, J = 8.0,
(
(
d) N. Malic, J.A. Campbell, R.A. Evans, Macromolecules 41 (2008) 1206–1214;
e) S. Jockusch, N.J. Turro, R.R. Blackburn, J. Phys. Chem. 106 (2002)
H), 7.73 (d, J = 8.3, 2H), 7.63 (dd, J = 8.4, 7.0, 1H), 7.60–7.45 (m,
H), 7.34 (d, J = 8.0, 1H), 7.32 (dd, J = 7.2, 6.9, 1H), 7.20 (dd, J = 8.0,
.9, 1H), 7.08 (d, J = 8.6, 1H), 6.61 (s, 1H), 1.46 (s, 3H), 1.14 (s, 3H).
C NMR: 173.4, 148.3, 148.1, 146.7, 142.0, 134.9, 133.9, 133.0,
28.9, 128.6, 127.9, 127.7, 127.6, 126.8, 126.7, 126.6, 124.3, 123.6,
23.2, 123.0, 121.4, 121.3, 119.8, 60.6, 43.2, 23.0, 18.7. MS: m/z (%):
02 (46), 374 (7), 359 (44), 332 (100), 302 (24), 300 (19), 255 (47).
A
9236–9241.
[
[
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9
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(
(
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To FCT (Portugal’s Foundation for Science and Technology)
and FEDER for financial support through the research unit
Centro de Química-Vila Real (POCTI-SFA-3-616) and project
PTDC/QUI/66012/2006. The 300 MHz NMR facilities were funded by
the Région Nord-Pas de Calais (France), the Ministère de la Jeunesse
de l’Education Nationale et de la Recherche (MJENR) and the Fonds
Européens de Développement Régional (FEDER).
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Appendix A. Supplementary data
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(
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jphotochem.2010.09.009.