Unexpected formation of new photochromic compounds derived from 3,3-diphenyl-3H-naphtho[2,1-b]pyran-1-one

Article abstract of DOI:10.1016/j.tet.2010.07.044

Two new unexpected photochromic compounds were obtained from naphtho[2,1-b]pyran-1-one 1. The reaction of this ketone with the silyl enol ether methyl trimethylsilyl dimethylketene acetal, catalyzed by TiCl ₄, afforded the photochromic dihydron

Full text of DOI:10.1016/j.tet.2010.07.044

Tetrahedron 66 (2010) 8317e8324
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Unexpected formation of new photochromic compounds
derived from 3,3-diphenyl-3H-naphtho[2,1-b]pyran-1-one
,
a
b,
Céu M. Sousa a, Paulo J. Coelho a , Luis M. Carvalho , Gaston Vermeersch y, Jérôme Berthet b,
*
Stephanie Delbaere b
a Centro de Química e Vila Real, Universidade de Trás-os-Montes e Alto Douro, 5001-801 Vila Real, Portugal
b Université Lille Nord de France, CNRS UMR 8516, UDSL, Faculté des Sciences Pharmaceutiques et Biologiques, F-59006, Lille, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 June 2010
Received in revised form 16 July 2010
Accepted 19 July 2010
Available online 22 July 2010
Two new unexpected photochromic compounds were obtained from naphtho[2,1-b]pyran-1-one 1. The
reaction of this ketone with the silyl enol ether methyl trimethylsilyl dimethylketene acetal, catalyzed by
TiCl4, afforded the photochromic dihydronaphtho[2,1-b]pyranone 2. The Reformatsky reaction of ketone
1 with ethyl bromoacetate led to the formation of the expected alcohol that under acid treatment gave,
unexpectedly, the novel photochromic benzocoumarin 6. UV irradiation compounds 2 and 6 in solution
provided thermally stable photoproducts that returned to the initial uncoloured forms under visible
irradiation. The photochromic behaviour of these compounds and the structures of the photoproducts
formed in these reactions were characterized by 1D and 2D NMR.
Keywords:
Photochromism
NMR analysis
Dihydronaphthopyranone
Benzocoumarin
UV irradiation
Ó 2010 Published by Elsevier Ltd.
1. Introduction
HO
O
R
1
R
Naphthopyrans are well known for their photochromic proper-
ties.1 Under UV irradiation these uncoloured molecules undergo an
electrocyclic reaction of the pyran ring leading to highly conjugated
coloured species that return thermally to the closed form. The
photochromic behaviour of these molecules, in particular the colour
generated and the kinetics of the colouration and fading process, can
be controlled by the introduction of substituents or fused rings,
specially in the aromatic groups linked to the sp3 carbon and in some
positions of the naphthalene core.2 Few reports concern the pho-
tochromic properties of naphthopyrans substituted in the pyran
double bond since it is expected that such molecules should exhibit
very high fading kinetics due to steric constrains and as such, the
coloured species would not be unperceivable to the naked eye.3,4,5
The most widely used strategy to synthesise naphthopyrans
applies a one pot multi-step reaction involving the Claisen rear-
rangement of propargylic ethers obtained in situ from the acid
catalysed reaction of naphthols with 1,1-diarylprop-2-yn-1-ols.6
Alternatively, several naphthopyrans substituted in position 1
have been prepared from naphthopyranones derived from
1) RMgBr
2) H2O
1
O
O
O
-H2O
Scheme 1. Synthesis of 1-substituted 3H-naphtho[2,1-b]pyrans.
2-norbornanone through reaction with Grignard reagents followed
by dehydration (Scheme 1).5
In an attempt to prepare some new 3H-naphtho[2,1-b]pyrans
functionalized in position 1, we studied the reaction of naph-
thopyranone 1 with some nucleophiles and obtained two photo-
chromic compounds with an unexpected structure. The
photochromic behaviour of these compounds and the structures of
the photoproducts formed under UV irradiation were characterized
by NMR analysis of UV irradiated solutions of these new molecules.7
2. Results and discussion
2.1. Synthesis
The reaction of naphthopyranone 18 with the silyl enol ether
methyl trimethylsilyl dimethylketene acetal in the presence of an
excess of TiCl4 afforded the diester 2 directly (Scheme 2) that sur-
prisingly showed photochromic properties. The trans configuration
* Corresponding author. Tel.: þ351 259 350284; fax: þ351 259 350480; e-mail
address: pcoelho@utad.pt (P.J. Coelho).
y
Deceased.
0040-4020/$ e see front matter Ó 2010 Published by Elsevier Ltd.
doi:10.1016/j.tet.2010.07.044

8318
C.M. Sousa et al. / Tetrahedron 66 (2010) 8317e8324
of the two ester chains in this compound was deduced from the fact
that in the 1H NMR spectrum, H-5 and H-6 appeared as singlets,
whichpointstoa90ꢀ dihedralangleforthesetwohydrogenatomand
thus to a trans configuration for the ester chains. Instead of the more
usual mode of addition of the ketene acetal to the carbonyl group we
obtained the product resulting from double addition to the naph-
thermal pyran ring opening, followed by enolization, rotation and
acid catalyzed lactone formation (Scheme 4).
2.2. Photochromic behaviour under continuous UV
irradiation of compounds 2 and 6 at 20 ꢀC
In toluene solution (10ꢁ3 M) dihydronaphthopyranone 2 is
nearly colourless with a very strong absorption in the near UV re-
gion (lmax¼314 nm). Continuous UV light irradiation of this solu-
tion at 20 ꢀC, leads to the slow development of an intense yellow
colouration with a maximal absorption at 403 nm (Fig. 1), but the
photostationary state was not achieved even after 40 min of irra-
diation (Figs. 1 and 2).
Ph
OSiMe3
OMe
O
Ph
O
3
1
Ph
10
O
O
Ph
5
6
TiCl4
62%
CO2Me
CO2Me
2
1
1.6
1.4
1.2
1.0
Scheme 2. Synthesis of dihydronaphthopyranone 2.
thalene.9 No product from the addition to the carbonyl group was
detected.
0.8
403
The Reformatsky reaction of 1 with ethyl bromoacetate in the
presence of zinc and iodine gave the alcohol 3 along with a minor
amount of the conjugated dye 4 formed by base-catalysed pyranone
ring opening.4 When the alcohol 3 was treated with HOAc under
refluxtwo compounds were obtained:theconjugatedester 5, formed
by dehydration, and the unexpected photochromic benzocoumarin 6
(Scheme 3). The complete NMR data (1 and 2 D spectra and assign-
ments) of compounds 1e6 are reported in the Supplementary data.
Since the ester 5 was stable in HOAc under reflux, the benzo-
coumarin 6 was probably formed from alcohol 3 by dehydration,
0.6
40 min
0.4
0.2
0.0
300
400
500
600
700
Wavelength (nm)
Figure 1. UVevis absorption spectra of dihydronaphthopyranone 2 (10ꢁ3 M) before
(——) and after (ddd ) UV irradiation.
Ph Ph
Ph
Ph
O
O
OH
Ph
O
O
O
Ph
OH
BrCH2CO2Et
Zn, I2
O
+
4
24%
1
3
50%
Ph Ph
O
O
Ph
Ph
O
O
O
HOAc
+
5
55%
6
31%
Scheme 3. Synthesis of 2,3-dihydro-1H-naphthopyran 5 and benzocoumarin 6.
Ph Ph
O
OH
O
Ph
Ph
O
O
Ph
Ph
O
O
O
O
O
Dehydration
3
Enolization
Ph Ph
OH
Ph Ph
Ph Ph
O
O
O
O
O
Acid catalyzed
O
Rotation
OH
lactone formation
6
Scheme 4. Mechanism for the formation of benzocoumarin 6 from alcohol 3.

C.M. Sousa et al. / Tetrahedron 66 (2010) 8317e8324
8319
UV light off
a maximal absorption at 432 nm (Fig. 3). As observed for compound
2, the absorbance at the maximal absorption wavelength increases
with time but the photostationary state was not achieved after
10 min of irradiation (Fig. 4). When the UV irradiation was turned off,
the absorbance decreased slowly but this behaviour was not fully
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
Vis light on
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
UV light on
0
50
100
150
200
250
Time (min)
Figure 2. Colour forming and colour bleaching for dihydronaphthopyranone 2 mea-
sured at 403 nm.
When the UV light was turned off, a stable absorbance was
observed underlining the formation of a long-lived coloured com-
pound. Visible irradiation (>420 nm) induces a slow absorption
decrease pointing to a photoreversible process (Fig. 2).
0
20
40
60
80
100
120
140
160
180
Time (min)
Figure 4. UV(10 min)/dark cycles for benzocoumarin 6 measured at 432 nm.
In toluene solution (10ꢁ4 M) benzocoumarin 6 was also uncol-
oured with a very strong absorption in the near UV region
(
lmax¼370) (Fig. 3). Continuous UV light irradiation of this solution at
20 ꢀC, leads to the development of a yellow colouration with
reproducible since the repetition of the UV irradiation (10 min)/dark
cycles showed that the maximum absorbance decreases, which in-
dicates that some degradation photoproducts are being formed.
0.5
0.4
432
2.3. NMR analysis of UV irradiated solutions of compounds
2 and 6
0.3
0.2
0.1
0.0
2.3.1. Photochromic behaviour of dihydronaphthopyranone 2. To
investigate the structure of the products formed upon UV irradia-
tion of compounds 2 and 6, NMR studies were carried out before
and after UV irradiation. Fresh samples of dihydronaphthopyr-
anone 2 and benzocoumarin 6 in degassed toluene-d8 were directly
irradiated in the NMR tube (5 mm) at rt using a 1000 W XeeHg HP
400
500
600
700
filtered (Schott 011FG09, 259<
l
<388 nmþ313 nm interferential
Wavelength (nm)
filter) short-arc lamp (Oriel). After irradiation, the sample was
rapidly transferred into the thermoregulated probe of a Bruker
NMR spectrometer. The 1H NMR spectra were recorded at regular
time intervals to monitor the changes in peak-intensities and thus
Figure 3. UVevis absorption spectra of compound 6 (10ꢁ4 M) before (————) and
after (ddd ) UV irradiation.
Figure 5. Aliphatic part of the 1H NMR spectra of 5,6-dihydronaphthopyranone 2: (a) before hv, (b) after 150 min of 313 nm UV light irradiation and (c) after 15 days of thermal
evolution in the dark.

8320
C.M. Sousa et al. / Tetrahedron 66 (2010) 8317e8324
Figure 6. Time-evolution of the photoproducts of dihydronaphthopyranone 2 under UV, in the dark and under visible irradiation, at room temperature.
obtain information about the formation of photoproducts and the
evolution of their concentration in time.
2D-HMBC map between the quaternary carbon C-3 at 154.5 ppm
and the protons H-2 at 7.00 ppm and H-2’/6’ at 7.27 ppm. The
From the analysis of the 1H NMR spectra of dihydronaph-
thopyranone 2 in solution before and after UV irradiation (Fig. 5)
and the time-evolution of each signal, it is clear that UV irradiation
of this compound results in the formation of four new photo-
products, labelled A, B, B0 and C (Fig. 6). The thermal evolution of
the sample for 15 days in the dark indicates that the photoproduct B
evolves slowly towards C, while A seems to be thermally stable.
Finally, irradiation of this sample with visible light converts A into
the initial 5,6-dihydronaphthopyranone 2, whereas, the concen-
trations of B and C remain constant.
Both 1D and 2D NMR experiments were carried out to identify
the structures of the four photoproducts (Scheme 5) (see
Supplementary data). The photoreversible compound A results
from the opening of the pyran ring followed by a hydrogen mi-
gration from the 3-methylene group towards the oxygen atom thus
generating the enol function. The opening of the initial structure
was identified from 1He13C long-range correlations observed in the
highly deshielded chemical shift of OH (
d
¼16.8 ppm) is in agree-
ment with the H-bonding between OH and C]O. The OH function
was located at carbon C-1 at 175.6 ppm as indicated by the cross
peaks between C-1 and H-2 and OH. The ketone function was lo-
cated through the correlation of the signal at 198.2 ppm (C-4a) and
the signals at 3.19 ppm (H-5 and H-6).
A second and parallel irreversible process converts compound 2
to side-products B and B0, resulting from a Norrish type 1 reaction
with breaking of the pyranone ring. Structure B presents a phenol
function, characterized by a singlet signal at 13.9 ppm. The car-
boxylic acid proton was clearly observed as a broad signal at
12 ppm at low temperature.1,1-Diphenylethylene B0 was evidenced
by the singlet signal at 5.38 ppm (integration¼2H) assigned to the
alkene protons in position 2 (Scheme 5). 1He13C long-range cor-
relations were observed in 2D-HMBC between the C-3 quaternary
carbon (150.3 ppm) and the methylene protons (5.38 ppm) and the
aromatic protons H-2’/6’¼H-200/600 (7.31 ppm).
2'
3
Ph
1'
1"
O
6'
hv 313 nm
3
1
OH
Ph
2
10
1
O
10
A
4a
O
10b
5
hv visible
4a
6
5
6
CO2Me
CO2Me
CO2Me
CO2Me
2
hv 313 nm
HO
O
1
10
10
10b
2' 2"
OH
O
5
10b
4a
4a
3
2
+
5
6
6
6'
-CO2
6"
CO2Me
CO2Me
CO2Me
CO2Me
B '
C
B
Scheme 5. Photochemical transformations of compound 2 under UV (313 nm) irradiation.

C.M. Sousa et al. / Tetrahedron 66 (2010) 8317e8324
8321
Figure 7. 1H NMR spectra of benzocoumarin 6 (a) before hv and (b) after 10 min of UV irradiation at room temperature.
Finally, the thermal evolution of B to C was observed. This reaction
results from the loss of CO2 as proved by the disappearance of the
carboxyl proton resonance and the appearance of two doublet signals
at 3.48 and 3.33 ppm (2J¼22 Hz), characterizing a diastereotopic
methylene group at C-10b. Besides, 1He13C correlations were ob-
served between protons H-10b (3.48 and 3.33 ppm), H-5 (2.91 ppm),
H-6 (3.61 ppm) and the carbonyl function C-4a (208 ppm).
and H-400 at 7.58 ppm. Compound D was therefore identified as
a lactone derivative formed by a stilbene-type electrocyclization
followed by an oxidation reaction (Scheme 6). The absorbance
decrease observed in Figure 4 after the UV light was turned off is
therefore due to degradation of the original compound and not to
the return to the uncoloured initial form.
To prevent the oxidation reaction and therefore the formation of
D, the experiment was repeated with a degassed solution of 6. Under
these conditions a new compound F was detected, which reverts
photochemically to benzocoumarin 6 (Scheme 6, Figs. 8 and 9).
As expected, F corresponds to the electrocyclised structure of
the benzocoumarin 6 that upon oxidation is transformed to D. The
formation of the cyclisation product F was evidenced by two dou-
blet signals in 1H NMR spectrum at 3.23 and 3.84 ppm (3J¼22 Hz),
assigned to H-3 and H-600, respectively. A 1He1H COSY experiment
established the connectivity between H-3/H-600 at 3.84 ppm, H-600/
H-500 at 6.61 ppm, H-500/H-400 at 5.90 ppm, H-400/H-300 at 6.02 ppm
and H-300/H-200 at 6.30 ppm.
2.3.2. Photochromic behaviour of benzocoumarin 6. At room tem-
perature, UV irradiation of benzocoumarin 6 (10ꢁ2 M, toluene)
leads to the development of a yellow colouration. 1H NMR spectra
analysis before and after UV irradiation (Fig. 7) and the time-evo-
lution of each signal indicate that the UV irradiation of benzocou-
marin 6 results in the formation of one major and thermally stable
photoproduct, labelled D, as well as hydrogen peroxide (singlet
signal at 6.30 ppm). Signals of an additional form, labelled E, are
also observed, but they were not identified due to the very low
concentration of this product.
To elucidate the structure of D (Scheme 6), 1 and 2D NMR ex-
periments were carried out. More particularly, 1He1H long-range
scalar correlations were measured in TOCSY-1D experiment, from
H-500 at 10.38 ppm up to H-200 at 7.97 ppm, via H-400 at 7.58 ppm and
H-300 at 7.31 ppm. The two quaternary carbons C-3 and C-600
resulting from a cyclization product were evidenced at 115.8 ppm
and 132.8 ppm, respectively, from a 2D HMBC experiment. Carbon
C-3 was long-range correlated with H-500 at 10.38 ppm and H-a at
8.39 ppm, while carbon C-600 was correlated with H-200 at 7.97 ppm
3. Conclusion
Two new unexpected photochromic compounds were obtained
from naphtho[2,1-b]pyran-1-one and their behaviour studied by
NMR techniques. UV irradiation of dihydronaphthopyranone 2 lead
to the opening of the pyranone cycle with formation of the very
stable yellow enol A that returned to the initial closed form under
visible irradiation. Both transformations are slow and the
3''
2''
3''
2''
2''
b
4''
4''
b
4
b
4
hv-UV
hv-vis
6''
H
a
a
6"
a
5''
5''
+ H2O2
6''
3
H
3
4
3
O2
4a
2
2
O
O
2
O
10a
O
O
O
9
9
10
10
9
10
D
6
F
Scheme 6. Photochemical transformations of benzocoumarin 6 under UV (313 nm) irradiation.

8322
C.M. Sousa et al. / Tetrahedron 66 (2010) 8317e8324
Figure 8. 1H NMR spectra of benzocoumarin 6 in degassed toluene solution at room temperature: (a) before hv, (b) after UV irradiation and (c) after visible irradiation.
gel 60 (70e230 mesh). The new compounds were determined to be
>95% pure by 1H NMR spectroscopy. The 1H and 13C NMR spectra in
CDCl3 were recorded at 298 K in CDCl3 using a Bruker ARX400
spectrometer (at 400.13 and 100.62 MHz). Chemical shifts (d) are
reported in parts per million UVevis spectra were recorded on
a CARY 50 Varian spectrophotometer. IR spectra were obtained on
a PerkineElmer FTIR 1600 spectrometer using KBr disks (wave-
numbers in cmꢁ1).
4.2. Spectrokinetic studies under continuous irradiation
UVevis irradiation experiments were made using a CARY 50
Varian spectrometer coupled to a 150 W Ozone free Xenon lamp
(6255 Oriel Instruments), equipped with a filter Schott 011FG09
(259<l<388 nm with lmax¼330 nm and T¼79%). The light from the
UV lamp was filtered using a water filter (61,945 Oriel Instruments)
and then carried to the spectrophotometer holder at a right angle to
the monitoring beam using an optical fibre system (77,654 Oriel
Instruments). 40 W mꢁ2 light flux was used (Goldilux Photometer
with UV-A probe). Visible irradiation experiments were performed
using a long-pass filter, Schott GG 420 (Oriel 59,480). A thermostated
(20 ꢀC) 10 mm quartz cell (3.5 mL sample solution) equipped with
magnetic stirring was used. In a preliminary experiment, the UVevis
absorption spectra of the closed and open forms and the lmax of the
open form were determined. In a second experiment the absorbance
at photostationary equilibrium, Aeq, was measured at lmax and then
the decrease in the absorbance vs time was monitored.
Figure 9. Time-evolution of the photoproducts of benzocoumarin 6 in degassed tol-
uene solution under UV and visible irradiation, at room temperature.
irreversible transformation of 2 into three degradation products, B,
B0 and C, was also observed. UV irradiation of a degassed solution of
benzocoumarin 6, formed by a multi-step reaction in the acidic
treatment of alcohol 3, lead to the formation of a yellow and stable
photoproduct F, formed by an electrocyclic stilbene-type electro-
cyclisation reaction that under visible irradiation reverts to the
original form 6. In the presence of oxygen, the photoproduct F was
irreversibly converted to the uncoloured lactone D.
4.3. NMR studies
For NMR investigations, samples in toluene-d8 were irradiated
directly in the NMR tube (5 mm), thermo-regulated, using a 1000 W
XeeHgHPfilteredshort-arc lamp(Oriel)equipped withafilterfor UV
4. Experimental
4.1. General methods
irradiation (Schott 011FG09, 259<
filter) and a filter for visible irradiation (Schott SCFIKG1503:
295< >400 nm). After irradiation had been
l
<388 nmþ313 nm interferential
The reactions were monitored by thin-layer chromatography on
aluminium plates precoated with Merck silica gel 60 F254
(0.25 mm). Column chromatography (CC) was performed on silica
l
<800 nmþoriel 3e74,
l
stopped, thesamples weretransferred tothe thermoregulated probe,
QNP (1He13Ce19Fe31P) or TXI (1He13Ce15N), of a Bruker Avance-500

C.M. Sousa et al. / Tetrahedron 66 (2010) 8317e8324
8323
spectrometer
470 MHz).
(
n0 (1H)¼500 MHz, n0
(
13C)¼125 MHz, n0
(
19F)¼
4.4.1. 1-(Ethoxycarbonylmethyl)-1,2-dihydro-3,3-diphenyl-3H-naph-
tho[2,1-b]pyran-1-ol 3. Mp 106e108. IR: 3472, 3056, 2973, 2936,
1692, 1619, 1442, 1390, 1343, 1229, 1192, 979. 1H NMR: 8.61 (d,
J¼8.8 Hz, 1H), 7.75 (m, 2H), 7.54 (m, 2H), 7.43 (m, 3H), 7.39e7.10 (m,
8H), 4.08 (m, 2H, OCH2CH3), 3.65 (s, 1H, OH), 3.45 (d, J¼14.5 Hz, 1H)
and 3.35 (d, J¼14.5 Hz, 1H) AB system (CH2), 3.38 (d, J¼16.6 Hz, 1H)
and 2.25 (d, J¼16.7 Hz, 1H) AB system (CH2), 1.15 (t, J¼7.1 Hz, 3H,
OCH2CH3). 13C NMR: 172.18 (C]O), 151.53, 144.59, 143.29, 131.87,
131.06, 130.31, 128.83, 128.49, 128.38, 127.41, 127.24, 126.58, 126.21,
125.73, 125.53, 123.32, 119.43, 117.18, 80.93 (CPh2), 69.11 (CeO),
60.48 (CeO), 46.72, 43.78, 14.02 (CH3). MS (TOF): m/z (%): 438 (2),
420 (11), 374 (17), 350 (33), 333 (42), 273 (85), 212 (25), 180 (92),
170 (100), 165 (86). HRMS: calculated for C29H26O4: 438.1831;
found: 438.1825.
4.3.1. 1,2-Dihydro-3,3-diphenyl-3H-naphtho[2,1-b]pyran-1-one 1. A
suspension of 2-hydroxy-1-acetonaphthone (1.05 g, 5.6 mmol),
benzophenone (4.0 g, 22 mmol), sodium (1.0 g, 43 mmol) and tert-
butanol (5.0 mL, 52 mmol) in 30 mL of benzene was heated under
reflux for 2 h. During the heating the suspension became pro-
gressively orange. After cooling to room temperature, the solution
was quenched with water (100 mL), extracted with ethyl acetate
(3ꢂ50 mL) and the combined organic layers dried (Na2SO4) and
concentrated under reduced pressure. To the residue was added
CH3COOH (5 mL) and HCl concn (1 mL) and the solution was heated
under reflux for 1 h. The solution was quenched with water (100 mL)
and extracted with ethyl acetate (3x50 mL). The combined organic
layers were dried (Na2SO4) and the solvent evaporated under re-
duced pressure leaving a brown oil residue that was purified by CC
(3e4% EtOAc/petroleum ether) to give pure 1 as white crystals
(656 mg, 33% yield). Mp 160e161. IR: 3081, 3050, 2998, 1664, 1616,
1592, 1565, 1509, 1432, 1371, 1230, 1216, 1205, 1120, 1000, 975, 823,
750, 698. 1H NMR (toluene-d8): 9.83 (d, J¼8.7 Hz, 1H), 7.39 (d,
J¼9.1 Hz, 1H), 7.35 (d, J¼8.4 Hz, 4H), 7.33 (t, J¼6.8 Hz, 1H), 7.30 (d,
J¼8.2 Hz, 1H), 7.06 (t, J¼6.8 Hz, 1H), 7.02e6.96 (m, 5H), 6.89 (t,
J¼7.2 Hz, 2H), 3.27 (s, 2H). 13C NMR (toluene-d8): 190.7, 160.9, 142.8,
136.9, 131.3, 129.3, 129.1, 128.1, 127.9, 127.4, 126.2, 126.0, 124.4, 118.9,
113.0, 85.8, 49.6. MS (TOF): m/z (%): 350 (28), 322 (24), 273 (100),180
(80), 170 (55), 165 (49), 142 (16), 114 (19).
4.4.2. 1-(1-Oxo-3,3-diphenylprop-2-enyl)-2-naphthol 4. IR: 3488,
3053, 3026, 1727, 1617, 1556, 1501, 1315, 1237, 1182. 1H NMR: 12.82
(s, OH), 8.45 (d, J¼8.5 Hz, 1H), 7.87 (d, J¼8.9 Hz, 1H), 7.77 (d,
J¼8.1 Hz, 1H), 7.52 (t, J¼7.0 Hz, 1H), 7.45e7.25 (m, 11H), 7.15 (s, 1H),
7.12 (d, J¼8.9 Hz,1H). 13C NMR: 196.2,163.8,154.1,141.1,139.0,137.0,
131.7, 129.7, 129.5, 129.0, 128.9, 128.5, 128.4, 128.1, 128.0, 127.7,
124.2, 123.9, 119.4, 115.3. MS (TOF): m/z (%): 350 (24), 322 (19), 273
(100), 180 (64), 170 (50), 165 (46). HRMS: calculated for C25H18O2:
350.1307; found: 350.1310.
4.5. Reaction of alcohol 3 with acetic acid
A solution of naphthopyran-1-ol 3 (110 mg, 0.25 mmol) in gla-
cial HOAc (5 mL) was heated under reflux for 2 h. The solution was
quenched with water (50 mL) and extracted with EtOAc (3ꢂ20 mL).
The combined organic layers were dried (Na2SO4), concentrated
under reduced pressure and the residue purified by CC (2e20%
EtOAc/petroleum ether) to give the ester 5 (58 mg, 55%yield) and
the more polar benzocoumarin 6 (29 mg, 31% yield).
4.3.2. trans-5,6-Di[(1-methyl-1-methoxycarbonyl)ethyl]-3,3-di-
phenyl-1,2,5,6-tetrahydro-3H-naphtho[2,1-b]pyran-1-one
(215 l, 2.03 mmol) was added to a solution of naphtho[2,1-b]pyr-
anone 1 (200 mg, 0.677 mmol) and methyl trimethylsilyl dime-
thylketene acetal (411
l, 2.03 mmol) in CH2Cl2 (2 mL) at 0 ꢀC. After
1 h, another equivalent of TiCl4 was added (70 l, 0.677 mmol) and
2. TiCl4
m
m
m
the solution kept at 0 ꢀC for 30 min more. The solution was then
quenched with water (20 mL) and extracted with ethyl acetate
(3ꢂ20 mL). The combined organic phases were dried (Na2SO4) and
the solvent evaporated under reduced pressure leaving a residue
that was purified by CC (10% EtOAc/petroleum ether) to give 2 as
a white solid (230 mg, 62 %). Mp 67e69. IR: 3066, 2977, 2946, 2940,
1728, 1665, 1593, 1452, 1395, 1255, 1130. 1H NMR: 8.34 (d, J¼8.0 Hz,
1H), 7.48 (d, J¼7.4 Hz, 2H), 7.40e7.20 (m, 8H), 7.23 (t, J¼7.6 Hz, 1H),
7.08 (t, J¼7.6 Hz, 1H), 6.97 (d, J¼7.5 Hz, 1H), 3.69 (s, CH3O), 3.45 (s,
CH3O), 3.34 (d, J¼16.4 Hz,1H) and 3.44 (d, J¼16.4 Hz,1H) AB system
(COCH2), 3.17 (s, 1H), 2.79 (s, 1H), 1.17 (s, CH3), 1.06 (s, CH3), 0.75 (s,
CH3), 0.48 (s, CH3). 13C NMR: 189.9, 177.7, 176.6, 170.5, 144.4, 142.0,
131.7,130.8, 130.7,128.9, 128.7, 128.0, 127.8,126.6,126.3, 126.1,113.6,
87.9, 52.4, 52.1, 48.6, 48.4 (two signals), 48.0, 47.2, 25.1, 24.0, 23.8,
20.6. MS (TOF): m/z (%): 522 (10), 451 (5), 419 (22), 271 (50), 239
(81), 211 (100), 179 (23), 165 (23). HRMS: calculated for C35H36O6:
552.2512; found: 552.2507.
4.5.1. 1-(Ethoxycarbonylmethylidene)-1,2-dihydro-3,3-diphenyl-3H-
naphtho[2,1-b]pyran 5. White solid. Mp 124e126. IR: 3030, 2956,
2920, 2848, 1707, 1629, 1447, 1338, 1229, 1172, 1155. 1H NMR: 8.34
(d, J¼8.8 Hz, 1H), 7.81 (m, 2H), 7.59 (d, J¼7.3 Hz, 4H), 7.51 (t,
J¼7.1 Hz, 1H), 7.42e7.22 (m, 8H), 6.38 (s, 1H), 4.37 (s, 2H, CH2), 4.28
(q, J¼7.1 Hz, 2H, OCH2CH3), 1.36 (t, J¼7.1 Hz, 3H, OCH2CH3). 13C
NMR: 167.1, 153.3, 145.7, 143.6, 132.0, 130.2, 128.8, 128.2, 127.3 and
127.3, 125.9, 123.8 (two signals) 123.8, 123.7, 118.8,118.6,115.4, 84.2,
58.9, 35.3, 14.4. MS (TOF): m/z (%): 420 (56), 374 (18), 346 (17), 333
(42), 269 (47), 167 (54). HRMS: calculated for C29H24O3: 420.1725;
found: 420.1734.
4.5.2. 1-(2,2-Diphenylethenyl)-3H-naphtho[2,1-b]pyran-3-one
6. Pale yellow solid. Mp 181e185. IR: 3056, 3019, 1724, 1620, 1541,
1512, 1441, 1338, 1207, 997. 1H NMR: 8.95 (d, J¼8.0 Hz, 1H), 8.04 (d,
J¼8.9 Hz, 1H), 7.97 (d, J¼7.3, 1H), 7.59 (m, 2H), 7.51 (d, J¼8.9 Hz, 1H),
7.49e7.42 (m, 5H), 7.33e7.20 (m, 6H), 6.08 (s, 1H). 13C NMR: 160.5,
154.3, 153.3, 145.7, 141.3, 138.2, 133.6, 131.1, 130.1, 130.0, 129.4, 128.6,
128.5, 128.4, 126.8, 125.8, 125.7, 125.3, 117.7, 116.6, 113.9. MS (TOF):
m/z (%): 374 (100), 357 (44), 346 (47), 329 (33), 297 (24), 269 (23),
239 (41). HRMS: calculated for C27H18O2: 374.1307; found: 374.1303.
4.4. Reaction of 3H-naphtho[2,1-b]pyranone 1 with ethyl
bromoacetate
A solution of 1 (162 mg, 0.46 mmol) and ethyl bromoacetate
(0.60 mL, 5.4 mmol) in 10 mL of ethyl ether/benzene (1:4) was
slowly added over 1 h to a mixture of zinc (2.0 g, 30 mmol) and
iodine (six small crystals) and heated with stirring under reflux.
After the addition was complete the solution was maintained under
reflux with stirring for one additional hour and then poured into
water. The aqueous phase was extracted with EtOAc (3ꢂ50 mL) and
the combined organic layers dried (Na2SO4) and concentrated un-
der reduced pressure. The residue was purified by CC (8e10%
EtOAc/petroleum ether) to give the alcohol 3 as a white solid
(101 mg, 50%) and the dye 4 as an orange oil (38 mg, 24%).
Acknowledgements
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 and 500 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).

8324
C.M. Sousa et al. / Tetrahedron 66 (2010) 8317e8324
2004, 3, 878e885; (f) Coelho, P. J.; Salvador, M. A.; Oliveira, A. M.; Carvalho, L. A.
Supplementary data
Tetrahedron 2004, 60, 2593e2599.
3. Van Gemert, B. In Organic Photochromic and Thermochromic Compounds. Main
Photochromic Families; Crano, J. C., Guglielmetti, R., Eds.; Plenum: New York, NY,
1998; Vol. 1, p 111.
4. Coelho, P. J.; Carvalho, L. M.; Vermeersch, G. Delbaere S. Tetrahedron 2009, 65,
5369e5376.
5. (a) Tanaka, T.; Imura, S.; Tanaka, K.; Kida, Y. U.S. Patent 5,349,065, 1994. (b)
Tanaka, T.; Okazaki, S. J.P. Patent 4,112,885A, 1992. (c) Tanaka, T.; Imura, S.; Ta-
naka, K.; Kida, Y.; J.P. Patent 2,069,471, 1990.
6. (a) Iwai, I.; Ide, J. Chem. Pharm. Bull. 1963, 11, 1042e1049; (b) Zhao, W. L.; Carreira,
E. M. Org. Lett. 2003, 5, 4153e4154; (c) Jha, A.; Huang, P. J. J. Heterocycl. Chem.
2009, 46, 1098e1106.
7. Delbaere, S.; Vermeersch, G. J. Photochem. Photobiol. C-Photochem. Rev. 2008, 9,
61e80.
8. Cottam, J.; Livingstone, R.; Walshaw, M.; Bartle, K.; Jones, D. J. Chem. Soc. 1965,
5261e5265.
9. (a) Yamamoto, H.; Yanagisawa, A.; Ishihara, K.; Saito, S. Pure Appl. Chem. 1998, 70,
1507e1512; (b) RajanBabu, T. V.; Reddy, G. S.; Fukunaga, T. J. Am. Chem. Soc. 1985,
107, 5473e5483.
Supplementary data for this article can be found in the online
version, at doi:10.1016/j.tet.2010.07.044. These data include MOL
files and InChIKeys of the most important compounds described in
this article.
References and notes
1. Hepworth, J. D.; Heron, B. M. In Functional Dyes; Kim, Sung-Hoon, Ed.; Elsevier:
Amsterdam, 2006; pp 85e135.
2. (a) Ercole, F.; Davis, T. P.; Evans, R. A. Macromolecules 2009, 42, 1500e1511; (b)
Sriprom, W.; Neel, M.; Gabbutt, C. D.; Heron, B. M.; Perrier, S. J. Mater. Chem.
2007, 17, 1885e1893; (c) Berthet, J.; Coelho, P. J.; Carvalho, L. M.; Vermeersch, G.;
Delbaere, S. J. Photochem. Photobiol. A-Chem 2009, 208, 180e185; (d) Alberti, A.;
Teral, Y.; Roubaud, G.; Faure, R.; Campredon, M. Dyes Pigments 2009, 81, 85e90;
(e) Ortica, F.; Smimmo, P.; Favaro, G.; Mazzucato, U.; Delbaere, S.; Venec, D.;
Vermeersch, G.; Frigoli, M.; Corinne, M. C.; Samat, A. Photochem. Photobiol. Sci.