Photochromic properties of new benzoindene-fused 2H-chromenes

Article abstract of DOI:10.1002/hlca.200390057

The synthesis and the photochromic properties of new photochromic 6,7- and 7,8-benzoindene annellated benzopyrans are described. When compared to parent indeno-fused 2H-chromenes (2H-[1]benzopyrans), compounds 10 and 12 exhibit a significant bathochromic shift of maximum-absorption wavelength, an increase in the colorability, and similar fading rates.

Full text of DOI:10.1002/hlca.200390057

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Helvetica Chimica Acta Vol. 86 (2003)
Photochromic Properties of New Benzoindene-Fused 2H-Chromenes
by Cristina I. Martinsa), Paulo J. Coelho*a), Luis M. Carvalhoa), Ana M.F. Oliveira-Camposb),
Andre¬ Samatc), and Robert Guglielmettic)
a
¬
) Dept. QuÌmica, Universidade de Tras-os-Montes e Alto Douro, P-5001-911 Vila Real
(phone: 351-259350284, fax: 351-259350480, e-mail: pcoelho@utad.pt)
b) Centro de QuÌmica, IBQF, Universidade do Minho, Largo do PaÁo, P-4700-320, Braga.
c
¬
¬
¬
) LCMOM, UMR 6114 CNRS, Universite de la Mediterranee, F-13288 Marseille Cedex 9
The synthesis and the photochromic properties of new photochromic 6,7- and 7,8-benzoindene annellated
benzopyrans are described. When compared to parent indeno-fused 2H-chromenes (2H-[1]benzopyrans),
compounds 10 and 12 exhibit a significant bathochromic shift of maximum-absorption wavelength, an increase
in the colorability, and similar fading rates.
1. Introduction. The great commercial success of photochromic plastic ophthalmic
lenses in the last decade attracted the attention to the search for new organic molecules
that exhibit photochromic behavior in polymeric matrices at room temperature [1].
These systems have the ability to undergo a reversible transformation between two
states with different absorption spectra induced, at least in one direction, by
electromagnetic radiation. If the photo-activated state absorbs in the visible region
of the spectrum, a noticeable reversible change of color occurs as a consequence of the
transformation. This makes these systems particularly useful for the production of
variable-transmission optical materials, namely eyewear that darken under sunlight.
Benzo- and naphthopyrans are two classes of photochromic compounds that have
been extensively studied in the last years [2]. Although most of them generate colors
from yellow to red, recently, the introduction of some substituents allowed attainment
of colors ranging from yellow to blue [3]. Thus, with a mixture of naphthopyrans it is
possible to cover almost the whole visible spectrum. However, it is necessary that all
compounds have similar discoloration rates in order to obtain a homogeneous behavior
in the return to the original uncolored state. These photochromic compounds must also
have a high colorability in order to obtain significant absorption at minimal
concentration.
Benzo- and naphthopyrans undergo a photoinduced ring-opening process to give a
set of stereoisomers with an extended conjugated p system (Scheme 1).
Recent studies have shown that the introduction of heterocycles, such as thiophene,
as substituents [4][5] or the annellation with aromatic or heteroaromatic rings [6 8]
have a great influence on the photochromic properties (discoloration rate, colorability,
maximum absorption wavelength, fatigue resistance). We have recently observed that
indeno-fused benzopyrans exhibit important properties, namely extended absorption in
the visible spectra with two bands (around 430and 50 570nm) and interesting
discoloration rates (0.12 0.91 sÀ1) [8].

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571
Scheme 1
In this paper, we describe the synthesis of new benzoindeno-annellated benzopyr-
ans. The extended conjugation of these compounds should improve their photochromic
properties.
2. Results and Discussion. 2.1. Synthesis. Awidely used method for the synthesis of
benzopyrans involves the acid-catalyzed reaction of phenols with propargylic alcohols
[9][10]. The yields of this one-pot reaction are usually low, but the availability of the
starting materials and the simplicity of the procedure rendered this reaction a suitable
method for the synthesis of a large number of benzo- and naphthopyrans [2].
Besides the low yields that are often obtained, the main difficulty of this method is
the synthesis of the phenolic precursors. The synthesis of some −simple× phenols
requires often several steps [9]. We carried out the synthesis of hydroxybenzofluor-
enones 5a 5d in five steps from dimethoxybenzoic acids 1a,b. To introduce the
naphthyl group, the acids 1a,b were transformed into the corresponding dihydroox-
azoles 2a,b, which are very reactive toward organometallic reagents and allow the
nucleophilic aromatic substitution of the 2-MeO group by aryl groups [11]. The
reaction of dihydrooxazoles with Grignard reagents derived from 1-bromo- and 2-
bromonaphthalene gave the naphthyl-oxazoles 3c and 3a,b, respectively (Scheme 2).
Scheme 2
The removal of the dihydrooxazole activating group is usually carried out under
acidic conditions [11], but, with dihydrooxazoles 3a 3c, only degradation products

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Helvetica Chimica Acta Vol. 86 (2003)
were obtained. The removal of the dihydrooxazole group was finally achieved by
treating 3a 3c with an excess of MeI, followed by the basic hydrolysis of the
oxazolinium salt to yield the corresponding benzoic acids. Treatment with polyphos-
phoric acid (PPA) afforded ketones 4a 4d (Scheme 3).
Scheme 3
While the PPA cyclization of dihydrooxazoles 3a,b gave only one product, the
cyclization of the dihydrooxazole 3c gave a mixture of methoxy-benzofluorenone 4c
and methoxy-benzo-anthracenone 4d. The intramolecular FriedelÀCrafts cyclization of
dihydrooxazole 3c (SOCl2/AlCl3) at À108 was more selective, giving only the methoxy-
benzanthrenone 4d. Finally, treatment of 4a 4d with HBr/AcOH converted the
methoxy ketones to the corresponding phenols in acceptable yield (37 74%).
The condensation of phenols 5a 5d with 1,1-diphenylprop-2-yn-1-ol under
pyridinium toluene-4-sulfonate (PPTS) catalysis gave 2H-chromenes (ˆ2H-[1]benzo-
pyrans) 6 9, respectively, in moderate yields. The reaction of hydroxybenzofluor-
enones 5a,c gave only the linear isomers 6 and 8, respectively. These compounds were
not photochromic at room temperature.

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573
As observed with the corresponding pyranofluorenones, the photochromic
behavior of compounds 6 8 is strongly dependent on the presence of an sp3-C-atom
between the 2,2-diphenyl-2H-chromene and the naphthalene moieties [9].
Converting the CˆO group to an alcohol allowed the production of products that
exhibited photochromism at room temperature. Treatment of 6 8 with an ethereal
solution of MeMgI gave, after hydrolysis, pyranofluorenols 10 12, respectively, that
exhibit photochromic behavior in toluene solutions at room temperature. For
pyranobenzo-anthracenone 9, this reaction gave only degradation products. The
reaction of MeLi with 9 proceeded via 1,4 addition, followed by aromatization, and
provided 2H-chromene 13. No 1,2-addition to the CˆO group was detected.
2.2. Photochromic Properties. The photochromic characteristics of the new
compounds 10 12 were quantified by the flash-irradiation technique coupled to a
rapid spectrophotometer (for details, c.f. Exper. Part). The photochromic behavior of
the compounds described can be evaluated through the data listed in the Table, where
the corresponding pyranofluorenols (Ref 1, Ref 2) and a naphthopyran (Ref 3) were
also included for comparison.
All compounds exhibit two absorption bands, the first one between 444 and 463 nm
and the second one in the region of 538 620nm. The colorability is higher at the first
band and, for compounds 10 and 12, it reaches a high value (2.7 and 4.0). All
compounds exhibit two phases of fading kinetics, which are probably due to different
isomers present in the mixture obtained after irradiation. The second kinetic constant,
although less important (2 20%), is 5 50 times lower than the first. As a consequence,
after irradiation, rapid decay of the coloration was observed, followed by slow decay,
which is probably responsible for the persistence of a residual color during several
minutes after irradiation. This may be also due to colored photodegradation products.
When compared to the parent indeno-fused 2H-chromenes (Ref 1) compounds 10
and 12 exhibit a significant bathochromic shift of maximum-absorption wavelength
(18 27 nm for the first band and 33 39 nm for the second), as expected. The

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Helvetica Chimica Acta Vol. 86 (2003)
Table. Spectrokinetic Properties: Maxima Wavelengths of the Colored Form (l1, l2), Colorability (A01, A02 are
the absorbances just after the flash at l1 and l2, resp.), and Thermal Bleaching Rate (kD ) of 2H-Chromenes
10 12, and Three Reference Compounds in Toluene Solutions (2.5  10À5 m at 258); Ref 1 ˆ 6-hydroxy-6-methyl-
2,2-diphenyl-2H-pyrano[5,6-b]fluorene, Ref 2 ˆ 7-hydroxy-7-methyl-2,2-diphenyl-2H-pyrano[5,6-c]fluorene,
Ref 3 ˆ 3,3-diphenyl-3H-naphtho[2,1-b]pyran.
Compound
Structure
Annellation
l1
A01
l2
A02
kD (amplitude)
[sÀ1] ([%])
[nm]
[nm]
10
6,7
457
4.0
538
0.99
0.091 (80)
0.017 (20)
12
6,7
6,7
7,8
463
2.7
544
0.68
0.63
0.24
0.11 (75)
0.022 (25)
Ref 1
439
444
1.4
505
620
0.120 (82)
0.011 (18)
11
0.94
0.88 (98)
0.014 (2)
Ref 2
7,8
432
432
0.57
0.84
573
0.15
0.91 (92)
0.110 (8)
Ref 3
5,6
0.090
colorability of both compounds is also higher in particular at the first absorption band.
The fading rates are very similar with a slight increase of the lowest constant.
The same behavior is observed for compound 11. The annellation of a benzene ring
to the indene moiety of the molecule led to an increase of the maximum wavelength of
absorption (from 432 and 573 nm in Ref 3 to 444 and 620nm for 11) and the

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575
colorability (from 0.57 at 432 nm for Ref 2 to 0.94 at 444 nm). The first rate constant of
compounds 11 and Ref 2 are very similar, while the second constant is lower for
compound 11.
3. Conclusions. Three new benzoindeno-fused 2H-chromenes were prepared.
These photochromic compounds exhibit improved colorabilities and important bath-
ochromic shifts when compared to the corresponding indeno-fused 2H-chromenes. The
annellation of an additional benzene ring has little effect on the fading rate.
Compounds 10 and 12 exhibit high colorabilities, two bands of absorption, and kD
values that are well-suited for practical applications. Compound 11, although exhibiting
a maximum of absorption located at higher wavelength (620nm), has a rather low
colorability, and its discoloration rate is too high.
Experimental Part
1. General. Column chromatography (CC): silica gel 60 (70 230mesh). M.p.: uncorrected. FT-IR spectra:
Perkin-Elmer FTIR 1600; in cmÀ1 (KBr disc). 1H-NMR Spectra: in CDCl3 (if not stated otherwise) on a Varian
1
Unity Plus (300 MHz); d in ppm relative to Me4Si (ˆ0ppm); J in Hz. H-NMR Assignments were based on
irradiation experiments. 13C-NMR Spectra: in CDCl3 on a Varian Unity Plus (75.4 MHz).
2. Spectrokinetic Measurements. For the determination at 258 of l1 and l2, A01 and A02, and kD, 50 mm of 10
12 in toluene were used. The flash-photolysis apparatus was coupled to a Warner and Swasey rapid
spectrophotometer, to allow recording of absorption spectra of the colored forms in the visible 400 700 nm
range (acquisition time: 1 ms, repetitiveness: 1.25 ms). Flashes (duration: 50 ms) were generated by two Xe
tubes with a quartz envelope. The energy of the flashes was 60J for the whole polychromatic emission spectrum.
Thermostated (258) 100-mm cells were used. The light from the analysis lamp (50 W, quartz-iodide) was filtered
with 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, and the decrease in absorbance with time was monitored. The rate constants were calculated with a
biexponential model.
3. Synthesis. General Procedure for the Synthesis of 2a and 2b. A mixture of dimethoxybenzoic acid (0.182 g,
1.0mmol) in SOCl 2 (10ml) was stirred at r.t., for 24 h. The excess SOCl 2 was removed in vacuo, and the residue
was diluted with CH2Cl2 (10ml). This soln. was added dropwise to a soln. of 2-amino-2-methylpropan-1-ol
(0.178 g, 2.0 mmol) in CH2Cl2 (10ml) kept between À10and 0 8. After stirring for 20h at r.t. the suspension was
filtered, and the filtrate was evaporated to give the amide as a yellow oil. The latter was treated dropwise with
SOCl2 (10ml) and stirred at r.t. for 7 h. The soln. was then poured into dry Et 2O (100 ml), and the
dihydrooxazole hydrochloride precipitated. The salt was filtered and treated with aq. 20% NaOH (50 ml). The
alkaline soln. was extracted with Et2O, dried (Na2SO4) and concentrated in vacuo to give the dihydrooxazole as
a yellow oil.
4,5-Dihydro-2-(2',4'-dimethoxyphenyl)-4,4-dimethyloxazole (2a). Yield 85%. FT-IR: 1641, 1608, 1274.
1H-NMR: 1.36 (s, 2 Me); 3.81 (s, MeO); 3.85 (s, MeO); 4.04 (s, HÀC(5)); 6.46 6.49 (m, HÀC(3'), HÀC(5'));
‡
7.71 (d, J ˆ 9.0, HÀC(6')). MS: 235 (90, M ), 220 (100), 192 (56), 165 (88), 149 (59), 135 (31), 121 (28), 106
(11), 92 (9), 77 (12).
4,5-Dihydro-2-(2',3'-dimethoxyphenyl)-4,4-dimethyloxazole (2b). Yield 84%. FT-IR: 1646, 1577, 1261.
1H-NMR: 1.39 (s, 2 Me); 3.86 (s, MeO); 3.87 (s, MeO); 4.11 (s, HÀC(5)); 7.00 (dd, J ˆ 8.0, 2.0, HÀC(4') or
‡
HÀC(6')); 7.05 (t, J ˆ 8.0, HÀC(5')); 7.30( dd, J ˆ 8.0, 2.0, HÀC(4') or HÀC(6')). MS: 235 (100, M ), 220(48),
206 (44), 192 (31), 178 (28), 163 (96), 149 (72), 135 (43), 121 (42), 106 (19), 92 (19), 77 (26).
General Procedure for the Synthesis of 3a 3c: A soln. of naphthylmagnesium bromide (prepared from
bromonaphthalene (0.621 g, 3.0 mmol) and Mg (0.144 g, 6.0 mmol) in 20 ml of dry THF) was slowly added to a
soln. of 2 (0.235 g, 1.0 mmol) in THF (15 ml). After stirring at r.t. for 24 h, the soln. was quenched in aq. sat.
NH4Cl, extracted with Et2O (3 Â 40ml), dried (Na 2SO4), and concentrated in vacuo. The residue was purified
by CC (0 30% AcOEt/light petroleum).
4,5-Dihydro-2-[4'-methoxy-2'-(naphthalen-2''-yl)phenyl]-4,4-dimethyloxazole (3a). Yield 90%. FT-IR:
1
3054, 1648, 1604. H-NMR: 1.29 (s, 2 Me); 3.71 (s, HÀC(5)); 3.88 (s, MeO); 6.94 (dd, J ˆ 8.7, 3.0, HÀC(5'));

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Helvetica Chimica Acta Vol. 86 (2003)
7.00 ( d, J ˆ 2.7, HÀC(3')); 7.49 7.52 (m, 2 H); 7.54 (d, J ˆ 1.8, HÀC(1'')); 7.76 (d, J ˆ 9.0, HÀC(6')); 7.84 7.89
(m , 4 H).
4,5-Dihydro-2-[3'-methoxy-2'-(naphthalen-2''-yl)phenyl]-4,4-dimethyloxazole (3b). Yield 89%. FT-IR:
1
3052, 1658, 1577. H-NMR: 1.15 (s, 2 Me); 3.58 (s, HÀC(5)); 3.78 (s, MeO); 7.09 (dd, J ˆ 7.5, 1.5, HÀC(4') or
HÀC(6')); 7.34 (dd, J ˆ 8.1, 2.1, HÀC(4') or HÀC(6')); 7.39 (t, J ˆ 7.8, HÀC(5')); 7.46 7.49 (m, 2 H); 7.52 (dd,
J ˆ 8.5, 1.5, HÀC(5'') or HÀC(8'')); 7.80 7.88 ( m, 4 H).
4,5-Dihydro-2-[4'-methoxy-2'-(naphthalen-1''-yl)phenyl]-4,4-dimethyloxazole (3c). Yield 90%. FT-IR:
3045, 1644, 1602. 1H-NMR: ((D6)DMSO): 0.69 (s, Me); 0 .86 s(, Me); 3.17, 3.20, 3.44, 3.47 (AB, J ˆ 8.0,
HÀC(5)); 3.83 (s, MeO); 6.92 (d, J ˆ 3.0, HÀC(3')); 7.09 (dd, J ˆ 8.7, 3.0, HÀC(5')); 7.32 7.54 (m, 5 H); 7.75 (d,
J ˆ 8.7, HÀC(6')); 7.87 7.95 (m, HÀC(8''), HÀC(4'')).
General Procedure for the Synthesis of 4a 4d. A soln. of 3a 3c (1.0g) in 6 ml of MeI was stirred at r.t.
overnight, and the excess MeI was removed in vacuo. To the crude MeI salt MeOH (12 ml) and NaOH 20%
(12 ml) were added, and the mixture was heated to reflux for 12 h. The soln. was extracted with Et2O, and the
org. layer was discarded. The aq. layer was acidified with HCl (aq), extracted with Et2O, dried (Na2SO4), and
concentrated to give the corresponding acids. Without further purification, the benzoic acids were added to
polyphosphoric acid (20g; prepared by mixing P 2O5 (13 g) with H3PO4 (7 g)), and the suspension was stirred at
60 70 8 for 8 24 h. The resulting dark-colored soln. was poured into 200 ml of H2O and extracted with Et2O
(3 Â 50ml). The org. layer was dried (Na 2SO4), and the solvent was evaporated under reduced pressure. The
crude ketone was purified by CC (0 30% AcOEt/light petroleum).
8-Methoxybenzo[a]fluoren-11-one (4a). Yield 64% M.p. 148 1508. FT-IR: 1697, 1612, 1218. 1H-NMR: 3.93
(s, MeO); 6.71 (dd, J ˆ 8.1, 2.0, HÀC(9)); 7.04 (d, J ˆ 2.0, HÀC(7)); 7.46 (td, J ˆ 8.0, 1.2, HÀC(3)); 7.56 7.64
(m, HÀC(2), HÀC(10), and HÀC(5) or HÀC(6)); 7.79 (d, J ˆ 8.4, HÀC(4)); 8.0( d, J ˆ 8.4, HÀC(5) or
‡
HÀC(6)); 8.99 (dd, J ˆ 8.4, 0.9, HÀC(1)). MS: 260 (100, M ), 217 (14), 189 (25).
7-Methoxybenzo[a]fluoren-11-one (4b). Yield 94%. M.p. 121 1238. FT-IR: 1698, 1579, 1272. 1H-NMR:
4.01 (s, MeO); 7.03 (dd, J ˆ 6.6, 2.7, HÀC(8)) or HÀC(10)); 7.21 7.26 (m, 2 H); 7.41 (td, J ˆ 6.6, 1.2, HÀC(2) or
HÀC(3)); 7.57 (td, J ˆ 6.6, 1.2, HÀC(2) or HÀC(3)); 7.77 (d, J ˆ 8.7, HÀC(4)); 7.95 (d, J ˆ 8.4, HÀC(5) or
‡
HÀC(6)); 8.03 (d, J ˆ 8.1, HÀC(5) or HÀC(6)); 8.95 (dd, J ˆ 8.4, 0.6, HÀC(1)). MS: 260 (100, M ), 245 (30),
231 (15), 217 (24), 202 (13), 189 (52), 163 (19), 95 (13), 82 (4).
10-Methoxybenzo[c]fluoren-7-one (4c). Yield 12%. M.p. 148 1508. FT-IR: 1726, 1597, 1290. 1H-NMR: 4.0
(s, MeO); 6.75 (dd, J ˆ 8.0, 2.0, HÀC(9)); 7.59 7.69 (m, 4 H); 7.75, 7.77, 7.82, 7.85 (AB, J ˆ 8.1, HÀC(5),
‡
HÀC(6)); 7.89 (dd, J ˆ 7.8, 1.8, HÀC(1) or HÀC(4)); 8.47 (d, J ˆ 8.4, HÀC(1) or HÀC(4)). MS: 260(8, M ),
167 (51), 149 (100), 113 (22), 83 (8), 70 (33).
10-Methoxybenzo[d,e]anthracen-7-one (4d). Yield 34%. M.p. 158 1608. FT-IR: 3054, 1705, 1609.
1H-NMR: 4.0( s, MeO); 7.12 (dd, J ˆ 9.0, 2.4, HÀC(9)); 7.68 7.82 (m, 3 H); 8.0 4 (d, J ˆ 8.4, HÀC(3)); 8.22
(dd, J ˆ 8.4. 1.2, HÀC(4)); 8.44 (d, J ˆ 6.9, HÀC(1)); 8.51 (d, J ˆ 9.0, HÀC(8)); 8.77 (dd, J ˆ 7.2, 1.2, HÀC(6)).
‡
MS: 260(5, M ), 167 (6), 149 (22), 118 (6), 83 (10), 71 (6), 57 (9).
General Procedure for the Synthesis of 5a 5d. A mixture of 4a 4d (0.260 g, 1.0 mmol), AcOH (2.5 ml),
and HBr 47% (5 ml) was heated under reflux for 6 20h. After cooling, the mixture was poured into 100ml of
H2O and extracted with Et2O (3 Â 50ml). The org. layer was dried (Na 2SO4), and the solvent was evaporated
under reduced pressure. The crude ketone was purified by CC (0 50% AcOEt/light petroleum).
8-Hydroxybenzo[a]fluoren-11-one (5a). Yield 57%. M.p. 235 2378. FT-IR 3442, 3054, 1707, 1612.
1H-NMR: 6.64 (dd, J ˆ 7.8, 2.1, HÀC(9)); 7.00 (d, J ˆ 2.1, HÀC(7)); 7.45 7.63 (m, 4 H); 7.80( d, J ˆ 7.8,
‡
HÀC(4)); 7.99 (d, J ˆ 8.4, HÀC(5) or HÀC(6)); 8.98 (d, J ˆ 8.7, HÀC-(1)). MS: 246 (100, M ), 218 (5), 189
(33), 163 (5), 123 (3), 109 (7), 95 (85).
7-Hydroxybenzo[a]fluoren-11-one (5b). Yield 74%. M.p. 268 2708. FT-IR: 3286, 3059, 1651. 1H-NMR:
6.93 7.12 (m, 3 H); 7.35 (td, J ˆ 8.1, 0.9, HÀC(2) or HÀC(3)); 7.51 (td, J ˆ 8.1, 1.2, HÀC(2) or HÀC(3)); 7.73
(d, J ˆ 8.1, HÀC(4)); 7.89, 7.92, 8.04, 8.07 (AB, J ˆ 8.4, HÀC(5), HÀC(6)); 8.89 (d, J ˆ 8.7, HÀC(1)); 9.38 (s,
‡
OH). MS: 246 (100, M ), 218 (20), 189 (49), 163 (14), 153 (4), 123 (6), 109 (4), 95 (10).
10-Hydroxybenzo[c]fluoren-7-one (5c). Yield 42%. M.p. 198 1998. 1H-NMR: ((D6)DMSO): 6.70( dd, J ˆ
7.9, 2.0, HÀC(9)); 7.50( d, J ˆ 8.4, HÀC(10)); 7.63 7.74 (m, HÀC(2), HÀC(3), HÀC(5), HÀC(11)); 7.95 (d,
J ˆ 8.1, HÀC(1) or HÀC(4)); 8.04 (dd, J ˆ 7.8. 1.8, HÀC(1) or HÀC(4)); 8.51 (d, J ˆ 8.4, HÀC(6)). MS: 246
‡
(100, M ), 218 (10), 189 (34), 163 (10), 149 (19), 123 (4), 109 (8), 95 (8), 71 (4), 57 (5).
10-Hydroxybenzo[d,e]anthracen-7-one (5d). Yield 37%. M.p. 282 2838. FT-IR: 3284, 3059, 1644.
1H-NMR: 7.04 (dd, J ˆ 9.0, 2.7, HÀC(9)); 7.78 (t, J ˆ 7.8, HÀC(5)); 7.83 7.88 (m, HÀC(2), HÀC(11));
8.18 8.24 (m, HÀC(4), HÀC(8)); 8.40( dd, J ˆ 8.1, 1.2, HÀC(3)); 8.56 8.59 (m, HÀC(1), HÀC(6)). MS: 246
‡
(100, M ), 218 (18), 189 (35), 163 (5), 149 (5), 109 (9), 95 (7).

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General Procedure for the Synthesis of 2H-Chromenes 6 9. To a mixture of 5a 5d (0.246 g, 1.00 mmol),
1,1-diphenylprop-2-yn-1-ol (0.416 g, 2.0 mmol) and PPTS (10 mg) were added 50 ml of dry CHCl3. The
suspension was refluxed for 2 d under Ar. Solvent evaporation gave a red oil, which was purified by CC (4%
AcOEt/hexane). Recrystallization from hexane/CH2Cl2 gave a crystalline material.
9,9-Diphenyl-9H,13H-benzo[7,8]fluoreno[3,2-b]pyran-13-one (6). Yield 51%. M.p. 232 2338. FT-IR:
3046, 1681, 1224. 1H-NMR: 6.16 (d, J ˆ 9.6, HÀC(10)); 6.64 (d, J ˆ 9.9, HÀC(11); 7.07 (s, HÀC(7) or
HÀC(12)); 7.30 7.46 ( m, 12 H); 7.54 7.58 (m, 2 H); 7.77 (d, J ˆ 8.4, HÀC(4)); 7.90( d, J ˆ 8.1, HÀC(5) or
HÀC(6)); 8.94 (dd, J ˆ 7.5, 0.9, HÀC(1)). DEPT: 84.10(C q); 109.60 (CH); 118.13 (CH); 120.55 (Cq); 122.93
(CH); 123.05 (CH); 124.42 (CH); 126.10 (CH); 126.54 (CH); 127.10 (CH); 127.99 (CH); 128.44 (CH); 128.60
(CH); 129.35 (CH); 130.09 (Cq); 134.62 (Cq); 135.52 (CH); 144.44 (Cq); 144.91 (Cq); 146.23 (Cq); 158.23 (Cq);
‡
194.26 (CO). The signals of two C-atoms are probably buried under other signals. MS: 436 (100, M ), 359 (96),
302 (12), 218 (8), 191 (7), 165 (9), 93 (4), 77 (5).
2,2-Diphenyl-2H,7H-benzo[7,8]fluoreno[4,3-b]pyran-7-one (7). Yield 28%. M.p. 233 2348. FT-IR: 1693,
1
1581, 1230. H-NMR: 6.37 (d, J ˆ 9.9, HÀC(9)); 6.69 (d, J ˆ 9.9, HÀC(10)); 6.92, 6.94, 7.18, 7.20 (AB, J ˆ 7.2,
HÀC(11), HÀC(12)); 7.31 7.60( m, 12 H); 7.78 (d, J ˆ 8.1, HÀC(4)); 7.97, 7.99, 8.13, 8.15 (AB, J ˆ 8.4,
HÀC(5), HÀC(6)); 8.96 (dd, J ˆ 8.7, 1.2, HÀC(1)). DEPT: 83.79 (Cq); 117.53 (CH); 121.99 (CH); 123.37
(CH.); 124.33 (CH); 126.28 (CH); 127.04 (CH); 127.59 (CH); 127.91 (Cq); 128.02 (CH); 128.53 (CH); 128.79
(Cq); 129.33 (CH); 130.19 (Cq); 131.03 (CH); 131.6 (CH.); 132.56 (Cq); 133.86 (Cq); 136.07 (CH); 136.43 (Cq);
‡
144.49 (Cq.); 145.34 (Cq); 147.85 (Cq); 194.3 (CO). MS: 436 (100, M ), 359 (45), 302 (7), 218 (5), 165 (5).
11,11-Diphenyl-7H,11H-benzo[5,6]fluoreno[3,2-b]pyran-7-one (8). Yield 54%. Mp. 210 211 8. FT-IR:
1682, 1594, 1260. 1H-NMR: 6.20( d, J ˆ 9.6, HÀC(10)); 6.66 (d, J ˆ 9.9, HÀC(9)); 7.31 7.41 (m, 8 H); 7.46 7.49
(m, 3 H); 7.59 7.62 (m, 3 H); 7.70, 7.73, 7.76, 7.79 (AB, J ˆ 8.4, HÀC(5), HÀC(6)); 7.79 (dd, J ˆ 7.8, 1.8, HÀC(1)
or HÀC(4)); 8.45 (dd, J ˆ 7.8, 1.5, HÀC(1) or HÀC(4)). DEPT: 82.36 (Cq); 117.36 (CH); 118.47 (Cq); 125.08
(CH); 125.88 (Cq); 126.03 (CH); 126.49 (CH); 126.60 (Cq); 127.11 (CH); 127.82 (CH); 127.90(CH); 128.30
(CH); 129.56 (CH); 129.97 (CH); 130.14 (CH); 130.68 (CH); 132.60 (Cq); 134.74 (CH); 135.74 (Cq); 144.15
(Cq); 144.52 (Cq); 158.10(C q); 182.88 (CO). The signal of one C-atom is probably buried under other signal.
‡
MS: 436 (100, M ), 359 (97), 302 (8), 246 (10), 225 (6), 218 (8), 191 (6), 165 (7), 106 (16), 91 (7), 57 (9).
3,3-Diphenyl-3H,7H-benzo[8,9]anthraceno[2,1-b]pyran-7-one (9). Yield 57%. FT-IR: 3058, 1700, 1650.
1H-NMR: 6.33 (d, J ˆ 9.6, HÀC(12)); 7.23 7.40( m, 7 H); 7.55 7.65 (m, 5 H); 7.69 (t, J ˆ 8.0, HÀC(2)); 7.75 (t,
J ˆ 8.0, HÀC(5)); 8.00 (d, J ˆ 8.1, HÀC(1) or HÀC(3)); 8.20( m, HÀC(4), HÀC(1) or HÀC(3)); 8.43 (d, J ˆ
8.4, HÀC(8)); 8.68 (dd, J ˆ 7.5, 1.2, HÀC(6)). DEPT: 84.25 (Cq); 113.07 (CH); 116.68 (CH); 119.76 (Cq); 122.78
(CH); 124.67 (CH); 127.11 (CH); 127.76 (CH); 128.03 (CH); 128.12 (CH.); 128.19 (CH); 128.46 (CH); 128.65
(CH); 129.66 (CH); 130.15 (CH); 132.96 (Cq); 137.79 (Cq); 141.50(C q); 144.38 (Cq); 146.99 (Cq); 158.03 (Cq);
‡
193.12 (CO). The signals of two C-atoms are probably buried under other signals. MS: 436 (100, M ), 359 (83),
329 (7), 300 (6), 254 (6), 218 (4), 179 (7), 165 (17), 106 (3), 77 (74).
General Procedure for the Synthesis of 2H-Chromenes 10 12. A soln. of MeMgI in Et2O (2.0ml, 2.0mmol)
was slowly added to a soln. of 6 9 (0.436 g, 1.0 mmol) in Et2O (10ml) under Ar. After stirring for 1 2 h, the
soln. was treated with a sat. soln. of NH4Cl, extracted with Et2O (3 Â 20ml), and the org. layer was dried
(Na2SO4). Solvent evaporation gave an orange oil, which was purified by CC (0 30% ethyl AcOEt/hexane).
18-Methyl-9,9-diphenyl-9H,13H-benzo[7,8]fluoreno[3,2-b]pyran-13-ol (10). Yield 57%. M.p. 180 182 8.
1
FT-IR: 3534, 1614. H-NMR: 1.89 (s, CH3), 6.22 (d, J ˆ 9.6, HÀC(10)); 6.73 (d, J ˆ 9.6, HÀC(11)); 7.28 7.39
(m, 8 H); 7.48 7.51 (m, 5 H); 7.57 (td, J ˆ 8.4, 1.5, HÀC(2) or HÀC(3)); 7.69 (d, J ˆ 8.1, HÀC(4) or HÀC(1));
7.85 7.92 (m, 2 H); 8.44 (d, J ˆ 8.1, HÀC(4) or HÀC(1)). DEPT: 26.7 (CH3); 81.2 (Cq); 83.1 (Cq); 108.4 (Cq);
118.5 (CH); 121.0(CH); 123.9 (CH); 124.6 (CH); 125.6 (CH); 126.7 (CH); 127.1 (CH); 127.2 (CH); 127.7 (CH);
128.3 (CH); 129.3 (CH); 129.4 (Cq); 130.0 (CH); 134.1 (Cq); 135.8 (Cq); 140.5 (Cq); 144.4 (Cq); 144.6 (Cq); 145.0
‡
(Cq); 145.1 (Cq), 153.7 (Cq). MS: 452 (100, M ), 437 (33), 375 (87), 359 (31), 331 (7), 302 (7), 226 (6), 191 (17),
180(13), 167 (8), 149 (12), 83 (7), 57 (11). HR-MS: 452.179482 (C 33H24O2; calc. 452.177630).
7-Methyl-(2,2)-diphenyl-2H,7H-benzo[7,8]fluoreno[4,3-b]pyran-7-ol (11). Yield 97%. M.p. 191 1928. FT-
IR: 3430, 1615, 1230. 1H-NMR: 1.87 (s, Me3); 6.23 (d, J ˆ 9.6, HÀC(9)); 6.72 (d, J ˆ 9.9, HÀC(10)); 7.01 (d, J ˆ
7.5, 1 H); 7.14 (d, J ˆ .5, 1 H); 7.22 7.59 (m, 12 H); 7.88 7.93 (m, 2 H); 8.36 (d, J ˆ 8.4, 1 H); 8.46 (d, J ˆ 8.4,
1 H). DEPT: 29.81 (Me); 81.65 (Cq); 83.45 (Cq); 115.53 (CH); 121.92 (Cq); 122.21 (CH); 123.67 (CH); 124.46
(CH); 125.35 (CH); 126.38 (CH); 126.50(CH); 127.10(CH); 127.72 (CH); 128.41 (CH); 128.72 (CH); 129.14
(CH); 129.34 (Cq); 130.05 (CH); 133.53 (Cq); 135.11 (Cq); 143.31 (Cq); 145.09 (Cq); 145.26 (Cq); 148.07 (Cq);
‡
153.92 (Cq). MS: 452 (100, M ), 437 (86), 375 (42), 360(24), 331 (10), 302 (9), 259 (4), 219 (21), 191 (23), 165
(12), 91 (5). HR-MS: 452.177304. (C33H24O2; calc. 452.177630).

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Helvetica Chimica Acta Vol. 86 (2003)
7-Methyl-11,11-diphenyl-7H,11H-benzo[5,6]fluoreno[3,2-b]pyran-7-ol (12). Yield 93%. FT-IR: 3442, 1610.
1H-NMR: 1.78 (s, Me); 6.22 (d, J ˆ 9.9, HÀC(10)); 6.71 (d, J ˆ 9.9, HÀC(9)); 7.26 7.39 (m, 7 H); 7.48 7.52 (m,
2 H); 7.59 7.64 (m, 4 H); 7.68, 7.71, 7.84, 7.87 (AB, J ˆ 8.4, HÀC(5), HÀC(6)); 7.80( s, HÀC(8) or HÀC(3));
7.92 (d, J ˆ 8.4, HÀC(1) or HÀC(4)); 8.61 (d, J ˆ 8.1, HÀC(1) or HÀC(4)). DEPT: 29.46 (Me); 77.68 (Cq);
83.10(C q); 111.78 (CH); 119.76 (Cq); 120.99 (CH); 123.65 (CH); 124.09 (CH); 125.71 (CH); 126.94 (CH);
127.18 (CH); 127.64 (CH); 128.27 (CH); 128.62 (CH); 128.87 (CH); 129.34 (CH); 130.95 (CH); 134.61 (Cq);
‡
141.14 (Cq); 144.09 (Cq); 144.81 (Cq); 145.02 (Cq); 149.75 (Cq); 153.40(C q); 167.82 (Cq). MS: 452 (100, M ). 380
(8), 338 (7), 330 (100), 322 (4), 316 (20), 301 (7), 295 (10), 281 (74), 264 (19), 254 (33), 245 (25), 238 (21), 222
(50). HR-MS: 452.176941 (C33H24O2; calc. 452.177630).
8-Methyl-3,3-diphenyl-3H,7H-benzo[8,9]anthraceno[2,1-b]pyran-7-one (13). A soln. of MeLi in hexane
(10.0 ml, 10.0 mmol) was slowly added to a soln. of 9 (0.109 g, 0.25 mmol) in Et2O (10ml) under Ar at 0 8. After
stirring for 24 h at r.t., the soln. was treated with NH4Cl, extracted with Et2O (3 Â 20ml), and the org. layer was
dried (Na2SO4). Solvent evaporation gave an orange oil, which was purified by CC (0 30% AcOEt/hexane) to
1
provide 13 (0.090 g, 20%). FT-IR: 3060, 1695, 1650. H-NMR: 3.05 (s, Me); 6.30( d, J ˆ 9.6, HÀC(12)); 7.23
7.39 (m, 11 H); 7.54 7.57 (m, 2 H); 7.59 7.68 (m, HÀC(2), HÀC(5)); 7.98 (dd, J ˆ 8.4, 1.2, HÀC(1) or
HÀC(3)); 8.07 (d, J ˆ 8.1, HÀC(4)); 8,16 (d, J ˆ 7.5, 0.9, HÀC(1) or HÀC(3)); 8.40( d, J ˆ 8.7, HÀC(8) or
‡
HÀC(9)). MS: 450 (100, M ), 435 (65), 373 (68), 279 (7), 186 (8), 167 (11), 149 (22), 105 (4), 83 (5), 71 (8), 57
(13).
We are grateful to FCT (Portugal×s Foundation for Science and Technology) for financial support through
project Praxis XXI/P/QUI/10021/1998, to E. Pinto for NMR spectra monitoring, and to R. Dubest and J. Aubard
(ESA CNRS 7086 University of Paris VII, France) for their help in the evaluation of spectrokinetic data by flash
photolysis.
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[3] A. Kumar, B. van Gemert, D. B. Knowles, Mol. Cryst. Liq. Cryst. 2000, 344, 217.
¡
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Received October 19, 2002