Synthesis of photochromic dyes based on annulated coumarin systems

Article abstract of DOI:10.1002/1522-2675(200202)85:2<442::AID-HLCA442>3.0.CO;2-9

Novel 2H-chromenes derived from hydroxycoumarins were synthesized, and their photochromic behaviour was studied under flash-photolysis conditions, showing a wide absorption range in the visible region. All the compounds exhibit low fluorescence, which apparently has no negative effect on their photochromic properties.

Full text of DOI:10.1002/1522-2675(200202)85:2<442::AID-HLCA442>3.0.CO;2-9

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Helvetica Chimica Acta Vol. 85 (2002)
Synthesis of Photochromic Dyes Based on Annulated Coumarin Systems
by Nuno M. F. S. A. Cerqueiraa), Ana M. F. Oliveira-Campos*a), Paulo J. Coelhob),
LuÌs H. Melo de Carvalhob), Andre¬ Samatc), and Robert Guglielmettic)
a) Centro de QuÌmica, IBQF, Universidade do Minho, Largo do PaÁo, 4700-320 Braga, Portugal
(amcampos@quimica.uminho.pt)
b
c
¬
) Departamento de QuÌmica, Univ. Tras-os-Montes e Alto Douro, Quinta de Prados, 5000 Vila Real, Portugal
¬
¬
¬
) Faculte des Sciences de Luminy, Universite de la Mediterranee, UMR CNRS 6114, 13288 Marseille Cedex 9,
France
Novel 2H-chromenes derived from hydroxycoumarins were synthesized, and their photochromic behaviour
was studied under flash-photolysis conditions, showing a wide absorption range in the visible region. All the
compounds exhibit low fluorescence, which apparently has no negative effect on their photochromic properties.
1. Introduction. Photochromic systems have the ability to undergo a reversible
transformation between two states giving rise to different absorption spectra, induced,
at least in one direction, by electromagnetic radiation [1]. If one of the states absorbs in
the visible region under appropriate conditions, a noticeable, reversible change of color
occurs as a consequence of the transformation. Such phototransformations open a wide
field of potential applications based upon the reversible color change or upon
reversible changes in physical or chemical properties as a consequence of the structural
modification accompanying such transformations [2].
In the last two decades, the commercial success of plastic ophthalmic lenses that
darken in sunlight, increased the interest in the search for new matrix-compatible
organic molecules that allow the development of photochromic systems with enhanced
properties. In the field of these variable-transmission optical materials, the main
characteristics strived for, are i) the ability to be activated by sunlight (heliochromism)
and bleached through a thermal process, ii) extended absorption in the visible region
to provide a neutral colour upon irradiation, iii) a suitable fading rate (which is related
to the stability of the coloured state), iv) high efficiency of coloration upon irradia-
tion (−colorability×), and v) a high resistance to photodegradation (−fatigue resistance×)
[3].
Together with spiro-pyrans and spiro-oxazines, the 2H-chromenes (2H-[1]benzo-
pyrans) have been extensively studied. These colorless molecules undergo, upon near-
UV irradiation, a photo-induced reversible cleavage of the C(2)ÀO bond, followed by
isomerization, leading to a (quasi-planar) colored open form that returns to the starting
material by heating or by irradiation with visible light (Scheme 1).
In the activated state, these molecules display a yellow-orange color (400 500 nm)
making them very attractive to be incorporated into lenses together with spiro-
oxazines. The latter are excellent photochromic compounds, but they exhibit relatively
narrow absorption bands, usually in the 560 630 nm range, making it difficult to obtain

Helvetica Chimica Acta Vol. 85 (2002)
443
Scheme 1
a neutral colour in systems with a single photochromic pigment. The use of mixtures of
compounds with complementary absorption spectra seems to be an obvious way to
overcome this difficulty; however, the problem of matching the kinetics of the
photochromic responses of different families of compounds remains [4].
During our research of new photochromic molecules [5 7], we decided to study
new 2H-chromenes (including a coumarin nucleus) and to investigate their photo-
chromic and spectrokinetic behaviour as reported in this paper.
2. Results and Discussion. 2.1. Synthesis. 2H-Chromenes can be easily prepared
from phenolic precursors. The cyclization may be achieved either by thermal reaction
of propynyl naphthyl ethers, first reported by Iwai and Ide [8] (see also [9])
(Method A), or by condensation of naphthols with a,b-unsaturated carbonyl
compounds (Method B) [5][10] (Scheme 2).
Scheme 2
Ph
Ph
HO
O
Ph
Ph
Ph
R
Ph
OH
H+
O
R
R
Ti(OEt3)
O
(EtO)4Ti
O
H
R
Ph
Ph
Our strategy required the preparation of the hydroxycoumarins 1a d. Since only 7-
hydroxycoumarin (1c) is commercially available, the synthesis of 5-, 6- and 8-
hydroxycoumarin (1a, 1b, 1d) was carried out by Wittig reaction [11][12] of 2-
hydroxybenzaldehydes with ethyl (triphenylphosphoranylidene)acetate (Scheme 3).
The 6- and 8-hydroxycoumarins (1b, 1d) were prepared in one step from 2,5- and 2,3-
dihydroxybenzaldehyde, respectively. Formylation [13] of 3-methoxyphenol followed
by Wittig reaction led to 5-methoxycoumarin, which was demethylated with BBr3 [14]
to provide 1a (Scheme 3).

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Helvetica Chimica Acta Vol. 85 (2002)
Scheme 3
R2
CHO
OH
R2
(Ph)3PCHCO2Et
1b R1 = H, R2 = OH
1d R1 = OH, R2 = H
O
O
N,N-Diethylaniline
R1
R1
OMe
OMe
BuLi
OR
(Ph)3PCHCO2Et
CHO
OH
DMF
N,N-Diethylaniline
OH
O
1e R = Me
1a R = H
O
BBr3, CH2Cl2
The condensation of 1a c with 1,1-diphenylprop-2-yn-1-ol catalyzed by p-
tolylsulfonic acid (PTS) or pyridinium p-tolylsulfonate (PPTS) (Method A) provided
the 2H-chromenes 2 5 in low yields. Thereby, slightly higher yields were obtained with
PTS (Table 1). Three different solvents were used, depending on the solubility of the
starting material. Compound 2 was obtained from 1a after refluxing for 24 h with the
highest yield in this series (26%). The reaction of 6-hydroxycoumarin (1b) with 1,1-
diphenylprop-2-yn-1-ol was completely regioselective, providing the angular chromene
3. However, the cyclization of 7-hydroxycoumarin (1c) led to a mixture of linear 4 and
angular 5, respectively. Under these conditions, no reaction was observed with 8-
hydroxycoumarin (1d). When treated with (EtO)4Ti and 3,3-diphenylprop-2-enal
(Method B), the chromene 6 was obtained in trace amounts.
2.2. Fluorescence Properties of the Chromenes 2 5. The absorption and fluores-
cence spectra of the 2H-chromenes were recorded as shown in Figs. 1 and 2. The
excitation and emission data are listed in Table 2. Thereby, compound 4 was the most
Ph
Ph
O
Ph
8
1
10
Ph
1
5
4
6
10
O
4
Ph
Ph
6
O
1
O
O
O
4
O
8
O
O
8
10
6
4
3
2
4
6
6
8
4
O
O
1
O
O
10
O
Ph
O
10
1
8
Ph
Ph Ph
5
6

Helvetica Chimica Acta Vol. 85 (2002)
445
Table 1. Synthesis of the 2H-Chromenes 2 5 from the OH-Substituted Coumarins 1 by Method A
Coumarin
Conditions
Chromene (%)
Conditions
Chromene (%)
PTS-catalyzeda)
PPTS-catalyzedb)
1a
1b
1c
1d
5-OH
6-OH
7-OH
8-OH
PhMe, 24 h
MeCN, 40 h
PhMe, 48 h
2 (26)
3 (20)
4/5 (14 vs. 4)
6 (no reaction)
MeCN, 30 h
CH2Cl2, 36 h
)
3 (16)
4/5 (10 vs. 2)
6 (no reaction)
c
c
)
a) p-Tolylsulfonic acid. b) Pyridinium p-tolylsulfonate. c) Traces obtained by Method B.
Fig. 1. Absorption spectra of the chromenes 2
5
Table 2. Spectroscopic Data of the Chromenes 2 5 in MeOH
Chromene
Excitation
Emission
lexcitation [nm]
f
lemission [nm]
2
3
4
5
290
300
290
340
0.002
0.009
0.156
0.018
500
459
396
437
fluorescent within this series. The quantum yields f were calculated using 9,10-
diphenylanthracene in MeOH as the standard (f ˆ 0.95) [15].
2.3. Photochromic Properties. The photochromic characteristics of the new
compounds were determined using a flash-irradiation apparatus coupled to a rapid
spectrometer. Details of the procedure are described in the experimental section. The
results are summarised in Table 3 including the data of two parent naphthopyrans (Ref1
and Ref2) for comparison [8].
Photochromic parameters which have been taken into account include absorption
wavelengths l of the open forms, rate constants (kD) of thermal bleaching and

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Helvetica Chimica Acta Vol. 85 (2002)
Fig. 2. Fluorescent spectra of the chromenes 2
5
−colourability× (measured by the absorbance Ao immediately after the irradiation flash)
[3][17], expressed by: Ao ˆ eOF ¥ Fcol ¥ k ¥ [CF]o (at low concentration), where k depends
on experimental conditions; eOF is the molar absorptivity of the open form at lmax, Fcol
is the photocoloration quantum yield, and [CF]o is the initial concentration of the
closed form.
From a general point of view, two features can be observed for all the compounds.
Two phases in the kinetics of the fading rate occur, and two wide absorption bands are
displayed (except for compound 3). Regarding the absorption of the colored forms, the
occurrence of two wide bands (except for 3), similar to 2H-chromenes fused to five-
membered heterocycles [17], is very interesting, because almost the whole visible range
can be covered with a single dye. Instead of only one kinetic phase, as observed for the
reference compounds, two phases in the kinetics of fading were observed, probably
corresponding to two different isomers with different thermal stabilities in the open
form. Taking into account the results of a recent NMR study performed on a
structurally related naphthopyran [18], these isomers most likely possess two different
configurations at the double bond attached to the naphthalene (or benzopyran) ring as
shown in Scheme 4 for a 5,6-annellated system. The fast fading-rate phase can be
attributed to the transoid (t) tZ-isomer, which is usually of higher amplitude. This can
be observed for both compounds 3 and 5, but not for compounds 2 and 4, for which the
amplitudes of the two kinetic phases are similar.
Compounds 3 and 5, both 5,6-annellated, but with reversed geometry, exhibit
different photochromic behaviours. The open form of 3 displays only one absorption

Helvetica Chimica Acta Vol. 85 (2002)
447
Table 3. Spectrokinetic Properties of 2 5 under Flash-Irradiation Conditions (25 mm in toluene at 258)
Compound
Type of
l1 [nm]
A01
l2 [nm]
A02
kD (amplitude)
(sÀ1) (%)
annellationa)
2
3
4
7,8
420
491
0.90
1.05
512
0.41
0.17 (44)
0.014 (56)
2.20 (69)
0.02 (31)
5,6
6,7432
5,6
0.95
563
0.45
4.50 (53)
0.11
0.03 (47)
20.00 (91)
0.03 (9)
0.09
5
429
0.26
562
b
Ref1
Ref2
)
)
5,6
7,8
429
403
0.84
1.08
c
481
1.62
0.002
a) With respect to the pyranone ring fused to the [1]benzopyrane moiety. b) 3,3-Diphenyl-3H-benzo[f][1]ben-
zopyran. c) 2,2-Diphenyl-2H-benzo[h][1]benzopyran.
band centred at 491 nm, while that of compound 5 interestingly exhibits two extended
absorption bands. The colorabilities observed for the open form of 5, however, are
modest, a fact that can be related to the fast rate of thermal bleaching, hindering the
formation of colored species with a reasonable yield. The presence of the oxygen atom
O(1) in the benzopyranone moiety of 5 (Scheme 4) seems to lead to an appreciable
thermal instability of the open form.
By comparing the two 7,8-annellated compounds2 with Ref2, it can be inferred that
replacing an annellated benzo group by a six-membered lactone modifies lmax, the
colorability as well as the thermal stability of the open form, whose major isomer after
flash-irradiation is considerably more unstable.
The reference compound, to which 4 should be compared, is 2,2-diphenyl-2H-
benzo[g][1]benzopyran, which is photochromic only at very low temperatures [19][20]
as a result of the loss of aromaticity in the naphthalene part upon irradiation. As it can
be observed, 4 displays photochromic behaviour already at room temperature with an
interesting coloration efficiency, although with fast bleaching, indicating that the open
form is not particularly stable.
Fluorescence is a competing relaxation process that can negatively affect the
photochromic performance of dyes. In the above compounds, the excited state,
Scheme 4
Ph
Ph
O
O
O
Ph
Ph
Ph
Ph
(tE)-Isomer
(tZ)-Isomer

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Helvetica Chimica Acta Vol. 85 (2002)
normally leading to CÀO cleavage, can be deactivated by fluorescence [21][22]. All
the described compounds however exhibit a modest to low fluorescence except for 4,
which shows a relevant emission band centred at 396 nm (Fig. 1) for excitation in the
near-UV (340 nm). Under the experimental conditions of irradiation, fluorescence can
be activated simultaneously during ring opening. Consequently, we would expect a
negative influence on the photochromic behaviour of this compound. However, under
the experimental conditions no clear effect was observed as reported for some
fluorescent 2H-chromenes [23].
3. Conclusions. Five novel 2H-chromenes incorporating a fused pyranone moiety
have been synthesized. Compounds 2, 4, and 5 displayed photochromic behaviour in
solution at ambient temperature, absorbing throughout the visible range. These
compounds may be interesting for applications such as photochromic ophthalmic
lenses. The presence of the endocyclic O-atom in the coumarin system promotes a
significant thermal instability of the open form upon irradiation. Compound 4, despite
of fast bleaching, exhibited an interesting coloration efficiency. Apparently, the
fluorescence characteristics of these compounds have no negative effect on their
photochromic behaviour in contrast to related chromenes [23].
Experimental Part
1. General. Petroleum ether: b.p. 40 608. Column chromatography (CC): Silica Gel 60 (70 230 mesh).
M.p.: uncorrected. UV-Spectra: in MeOH on a JASCO 7850; lmax (log e [dm3 molÀ1 cmÀ1]. Fluorescence
spectra: in MeOH on a SPEX FLUOLOG-2 analyzer, with a double monochromator and an emission xenon
lamp (450 W). FT-IR Spectra: Bomen, MB Series; in cmÀ1. 1H-NMR Spectra: in CDCl3 (if not stated otherwise)
on a Varian Unity Plus (300 MHz); d in ppm rel. to Me4Si (ˆ0 ppm), J in Hz. 1H-NMR assignments were based
on irradiation experiments. 13C-NMR Spectra: in CDCl3 on a Varian Unity Plus (75.4 MHz). MS: AutoSpecE
Spectrometer; m/z (%). Elemental analyses: LECO 932 CHNS Analyser.
2. Spectrokinetic Measurements. For the determination at 258 of l1, l2, A01, A02, and kD, 25 mm of 1 5 in
toluene were used. The flash-photolysis apparatus was coupled to a Warner and Swasey rapid spectrometer, to
allow recording of absorption spectra of the coloured forms in the visible 400 700 nm range (acquisition time:
1 ms, repetitivity: 1.25 ms) [3][16]. Flashes (duration: 50 ms) were generated by two xenon tubes with a quartz
envelope. The energy of the flashes was 60 J for the whole polychromatic emission spectrum. For measurements,
thermostated (258C) 100 mm cells were used. The light from the analysis lamp (50 W, quartz-iodide) was filtered
using a Schott GG400 high-pass filter. In a preliminary experiment, both the visible absorption spectrum and l1
and l2 of the open form were determined. In a second experiment, the initial absorbances A01 and A02 were
measured, followed by the decrease in absorbance with time. The rate constants were calculated using a bi-
exponential model.
3. Syntheses. 2-Hydroxy-6-methoxybenzaldehyde: A soln. of 3-methoxyphenol (1.8 ml, 16.11 mmol) in
CH2Cl2 (40 ml) was added dropwise to a soln. of BuLi in hexanes (1.6m, 40 ml, 64.12 mmol) at 08 under stirring.
The mixture was left at r.t. for 12 h, while colorless crystals separated. Then, a soln. of methyl(phenyl)forma-
mide (2 ml, 16.11 mmol) in Et2O was added dropwise (20 min). The mixture was refluxed for 30 min and
poured into a soln. of 1m aq. H2SO4 at 08. The org. layer was extracted with Et2O, the combined extracts
were dried (MgSO4), and the solvent was removed in vacuo, providing a brown oil, which was purified by
CC (SiO2; petroleum ether/Et2O). Yellow solid (1.5 g, 61%). M.p. 74 768 (Lit. 758 [24]). 1H-NMR: 3.91
(s, MeO); 6.39 (d, J ˆ 8.4, HÀC(3)); 6.54 (d, J ˆ 8.4, HÀC(5), 7.42 (t, J ˆ 8.4, HÀC(4)); 10.35 (s, CHO), 12.0
(s, HO).
General Procedure for the Synthesis of 1b, 1d, and 1e. A mixture of 2-hydroxybenzaldehyde (18.1 mmol)
and ethyl (triphenylphosphoranylidene)acetate (7.6 g, 21.72 mmol) inN,N-diethylaniline (50 ml), was refluxed
under N2 for the length of time indicated below. The reaction mixture was diluted with 5% aq. HCl soln.,
extracted with Et2O, and concentrated in vacuo. The remainder was purified by CC (petroleum ether/Et2O).

Helvetica Chimica Acta Vol. 85 (2002)
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6-Hydroxy[1]benzopyran-2(2H)-one (−6-Hydroxycoumarin×) (1b): 6 h reflux; gray solid (85%). M.p. 252
2548 (Lit. 252 2548 [24]). 1H-NMR ((CD3)2CO): 6.38 (d, J ˆ 9.6, HÀC(3)); 7.04 7.11 (m, HÀC(7)); 7.13
(d, J ˆ 3, HÀC(5)); 7.21 (d, J ˆ 8.7, HÀC(8)); 7.89 (d, J ˆ 9.6, HÀC(4)); 8.6 (s, HO).
8-Hydroxy[1]benzopyran-2(2H)-one (1d): 8 h reflux; gray solid (50%). M.p. 148 1508 (Lit. 1608 [24]).
1H-NMR: 6.13 (s, HO); 6.44 (d, J ˆ 9.6, HÀC(3)); 6.88 7.30 (m, HÀC(5,6,7)); 7.74 (d, J ˆ 9.6, HÀC(4)).
5-Methoxy[1]benzopyran-2(2H)-one (1e): 8 h reflux, yellow solid (31%). M.p. 78 808 (Lit. 78 808 [24]).
1H-NMR: 3.93 (s, MeO); 6.33 (d, J ˆ 9.6, HÀC(3)); 6.71 (d, J ˆ 8, HÀC(6) or HÀC(8)); 6.91 (d, J ˆ 8,
HÀC(8), or HÀC(6)); 7.43 (t, J ˆ 8, HÀC(7)); 8.08 (d, J ˆ 9.6, HÀC(4)).
5-Hydroxy[1]benzopyran-2(2H)-one (1a): Compound 1e (0.4 g, 2.0 mmol) was dissolved in anh. CH2Cl2
under stirring. A soln. of BBr3 (6 ml, 1m in CH2Cl2) was added dropwise at À608. The mixture was stirred at r.t.
under N2 for 24 h. The soln. was treated with H2O (40 ml), extracted with Et2O (3 Â 20 ml), and the organic
layers were combined and dried (Na2SO4). Evaporation gave a red solid which was purified by CC (petroleum
ether/Et2O): 0.23 g (69%). M.p. 231 2328 (Lit. 221 2238 [24]). 1H-NMR: 5.76 (s, HO); 6.37( d, J ˆ 9.9,
HÀC(3)); 6.66 (dd, J ˆ 8.4, 0.6, HÀC(6)); 6.92 (d, J ˆ 8.4, HÀC(8)); 7.34 (t, J ˆ 8.1, HÀC(7)); 8.10 (d, J ˆ 9.6,
HÀC(4)).
General Procedure for the Synthesis of 2 5 (Method A). p-Tolylsulfonic acid (PTS, 0.154 g, 0.80 mmol)
and the corresponding benzopyrane 1 (6.17mmol) were added to a soln. of 1,1-diphenylprop-2-yn-1-ol (2 g,
9.26 mmol) in anh. solvent (50 ml). The suspension was refluxed under Ar and (after cooling) was poured on
H2O. The aq. phase was extracted with CHCl3 (4 Â 30 ml). The combined org. layers were washed with 10% aq.
NaOH soln. (4 Â 30 ml), dried (Na2SO4), and evaporated. The remaining yellow oils were purified by CC
(petroleum ether/Et2O).
2,8-Dihydro-2,2-diphenylpyrano[2,3-f]benzopyran-8-one (2): 24 h reflux in CH2Cl2; light yellow solid
(26%). M.p. 192 1938. UV: 224 (4.46), 255 (4.19), 264 (4.23), 290 (4.28). FT-IR (Nujol): 1719 (CˆO), 1594,
1493, 1367, 1237, 1173, 1103.1H-NMR: 6.14 (d, J ˆ 10, HÀC(3) or HÀC(4)); 6.55 (d, J ˆ 9.6, HÀC(9)); 6.50
(d, J ˆ 10, HÀC(4) or HÀC(3)); 6.82 (d, J ˆ 8.6, HÀC(6)); 7.18 (d, J ˆ 8.6, HÀC(5)); 7.29 7.42 (m, 10 arom. H,
Ph); 8.15 (d, J ˆ 9.6, HÀC(10)). 13C-NMR: 84.04 (C(2)); 109.04 (d); 115.13 (d); 116.48 (s); 122.35 (d); 126.79
(4d, Ph); 127.65 (s); 127.89 (C(4',4'')); 128.29 (4d, Ph); 129.45 (d); 137.80 (d); 144.03, 148.93, 154.59 (3s); 160.57
‡
(CˆO). The signal of one C-atom was probably buried under another signal. MS: 353 (25, [M ‡ 1] ), 352 (100,
‡
M ), 323 (6), 276 (19), 275 (85), 247 (10), 191 (11), 189 (10), 165 (8). Anal. calc. for C24H16O3 (352): C 81.82,
H 4.54; found: C 81.47, H 4.806.
3,8-Dihydro-8,8-diphenylpyrano[3,2-f][1]benzopyran-3-one (3): 40 h reflux in MeCN; yellow crystals
(20%). M.p. 226 2278 (EtOH). UV: 222 (4.65), 290 (4.27), 302 (4.27). FT-IR (KBr): 1719 (C ˆO), 1565, 1271,
1196, 1119. 1H-NMR: 6.38 (d, J ˆ 10, HÀC(9) or HÀC(10)); 6.41 (d, J ˆ 9.6, HÀC(2)); 6.96 (d, J ˆ 10,
HÀC(10) or HÀC(9)); 7.11/7.14/7.15/7.18 A( B, J ˆ 9, HÀC(5), HÀC(6)); 7.24 7.42 (m, 10 arom. H, Ph); 7.92
(d, J ˆ 9.6, HÀC(1)). 13C-NMR: 82.57(C(8)); 114.41 ( s); 116.79 (d); 117.01 (s); 117.37 (d); 117.81 (d); 120.87
(d); 126.91 (4d, Ph); 127.85 (C(4',4''); 128.24 (4d, Ph); 131.86 (d); 138.41 (d); 143.89, 148.69, 149.01 (3s); 160.58
‡
‡
(CˆO). MS: 353 (18, [M ‡ 1] ), 352 (72, M ), 276 (20), 275 (100), 247 (8), 191 (6), 189 (5), 165 (8). Anal. calc.
for C24H16O3: C 81.82, H 4.54; found: C 81.78, H 4.69.
2,8-Dihydro-2,2-diphenylpyrano[3,2-g][1]benzopyran-8-one (4): 48 h reflux in toluene; yellowish solid
(25%). Recrystallization from CHCl3/petroleum ether yielded colourless crystals (14%). M.p. 190 1938. UV:
222 (4.46), 267(4.40), 339 (4.08), 347(4.10). FT-IR (Nujol): 1740 (C ˆO), 1721, 1650, 1627, 1564, 1366, 1275,
1140. 1H-NMR: 6.23 (d, J ˆ 9.3, HÀC(7)); 6.27 (d, J ˆ 10, HÀC(3) or HÀC(4)); 6.66 (d, J ˆ 10, HÀC(4), or
HÀC(3)); 6.89 (s, HÀC(10)); 7.11 (s, HÀC(5)); 7.26 7.44 (m, 10 arom. H, Ph); 7.57 (d, J ˆ 9.3, HÀC(6)).
13C-NMR: 83.76 (C(2)); 104.69 (d); 113.18 (s); 113.45 (d); 118.38 (d); 121.78 (s); 125.16 (s); 126.87(4 d, Ph);
127.87 (C(4',4'')); 128.27(4 d, Ph); 129.45 (d); 143.15 (d); 143.96 (d); 155.51 (s); 156.09 (d); 160.86 (CˆO). MS:
‡
‡
353 (27, [M ‡ 1] ), 352 (100, M ), 323 (8), 276 (10), 275 (55), 247 (10), 191 (9), 189 (5), 165 (5). Anal. calc. for
C24H16O3: C 81.81, H 4.54; found: C 81.60, H 4.77.
2,8-Dihydro-8,8-diphenylpyrano[2,3-f][1]benzopyran-2-one (5): 48 h reflux in toluene; white solid (4%).
M.p. 229 2308. FT-IR (Nujol): 1731 (CˆO), 1599, 1259, 1111. UV: 237(4.18), 284 (4.00), 292 (4.03), 330 (3.87),
347(3.73). 1H-NMR: 6.23 (d, J ˆ 9, HÀC(3)); 6.29 (d, J ˆ 10, HÀC(9) or HÀC(10)); 6.88 (d, J ˆ 8, HÀC(6));
7.20 (d, J ˆ 10, HÀC(10) or HÀC(9)); 7.24 (d, J ˆ 8, HÀC(5)); 7.25 7.46 (m, 10 arom. H, Ph); 7.58 (d, J ˆ 9,
HÀC(4)). 13C-NMR: 83.66 (C(8)); 109.47( s); 112.97( d); 112.99 (s); 113.59 (d); 116.24 (d); 126.92 (4d, Ph);
127.84 (C(4',4'')); 128.17( d); 128.22 (4d, Ph); 129.13 (d); 143.74 (d); 143.97, 150.15, 155.53 (3s); 160.74 (CˆO).
‡
‡
MS: 353 (16, [M ‡ 1] ), 352 (60, M ), 275 (70), 247 (14), 167 (21), 164 (42), 149 (58), 119 (100). Anal. calc. for
C24H16O3 (352): C 81.81; H 4.54; found: C 82.15, H 4.33.

450
Helvetica Chimica Acta Vol. 85 (2002)
2,9-Dihydro-2,2-diphenylpyrano[3,2-h]benzopyran-2-one (6) (Method B). To a soln. of 1d (0.3 g,
1.54 mmol) in anh. toluene (20 ml) a soln. of (EtO)4Ti (0.3 ml, 1.54 mmol) in anh. toluene (20 ml) was added
over a period of 20 min. After the mixture had been refluxed for 1 h, the EtOH formed was slowly distilled off
and the mixture was cooled to r.t. Then, 3,3-diphenylprop-2-enal (b-phenylcinnamaldehyde) was added (0.32 g,
1.54 mmol), and the mixture was refluxed for 30 h under Ar. After cooling, a 2m soln. of aq. NaOH (50 ml) was
added, the mixture was extracted with CH2Cl2 (4 Â 30 ml), the org. layers were combined, dried (MgSO4), and
concentrated in vacuo. The resulting product was purified by CC to yield an oily brown solid (2 mg). 1H-NMR:
6.15 (d, J ˆ 10, HÀC(3) or HÀC(4)); 6.36 (d, J ˆ 9.6, HÀC(8)); 6.45 (d, J ˆ 10, HÀC(4) or HÀC(3)); 6.82
(d, J ˆ 8.5, HÀC(5) or HÀC(6)); 7.18 (d, J ˆ 8.5, HÀC(6) or HÀC(5)); 7.26 7.50 (m, 10 arom. H,Ph); 8.16
‡
‡
(d, J ˆ 9.6, HÀC(7)). MS: 353 (24, [M ‡ 1] ), 352 (100, M ), 323 (5), 276 (14), 275 (72), 247 (7), 191 (8), 189
‡
(5), 165 (5). HR-MS: 352.1092 (M , C24H16O3; calc. 352.1099).
√
We thank FundaÁaƒo para a Ciencia e Tecnologia, Portugal for financial support (Praxis XXI /P/QUI/10021),
R. Dubest and Dr. J. Aubard (ESA CNRS 7086, University of Paris VII) for the evaluation of spectrokinetic
parameters, E. Pinto for NMR, MS and elemental analyses, and M.R. Pereira and Dr. E. Oliveira for advice
concerning the fluorescence experiments.
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Received August 6, 2001