The effect of a sulphur bridge on the photochromic properties of indeno-fused naphthopyrans

Article abstract of DOI:10.1016/j.tet.2004.01.034

The synthesis of four new 2,2-diphenyl-2H-naphtho[1,2-b]pyrans with a fused indeno group at the f face and a sulphur junction between the 2,2-phenyl groups is described. The photochromic properties in solution of these novel compounds were investigated under continuous irradiation. Compared to known indeno-fused naphthopyrans, these new compounds showed a significant bathochromic shift in the spectra of the open forms, faster ring closure kinetics and an expected decrease in the colourabilities.

Full text of DOI:10.1016/j.tet.2004.01.034

Tetrahedron 60 (2004) 2593–2599
The effect of a sulphur bridge on the photochromic properties
of indeno-fused naphthopyrans
*
Paulo J. Coelho, Maria A. Salvador, M. Manuel Oliveira and Luis M. Carvalho
´ ´
Centro de Quımica-Vila Real, Universidade de Tras-os-Montes e Alto Douro, Quinta dos Prados, 5001-911 Vila Real, Portugal
Received 5 October 2003; revised 7 January 2004; accepted 14 January 2004
Abstract—The synthesis of four new 2,2-diphenyl-2H-naphtho[1,2-b]pyrans with a fused indeno group at the f face and a sulphur junction
between the 2,2-phenyl groups is described. The photochromic properties in solution of these novel compounds were investigated under
continuous irradiation. Compared to known indeno-fused naphthopyrans, these new compounds showed a significant bathochromic shift in
the spectra of the open forms, faster ring closure kinetics and an expected decrease in the colourabilities.
q 2004 Elsevier Ltd. All rights reserved.
1. Introduction
hindrance between the two phenyl groups. In recent studies
it was showed that in some naphthopyrans the linkage of the
two phenyl sp3-substituents through a sulphur bridge results
in the increase of the maximum wavelength of absorption
and in a very significant increase of the discolouration rate. 9
In order to study this effect on indeno-fused naphthopyrans
we decided to prepare some new indeno-fused spiro[thio-
xanthene-naphthopyrans]. In this paper, we report the
synthesis and photochromic behaviour of these novel
compounds.
Naphthopyrans are one of the most studied classes of
photochromic compounds due to their use in plastic lenses.
When exposed to sunlight, in solution or in polymer
matrices, these molecules exhibit colours from orange to
blue/gray. 1 When the irradiation ceases the solution returns
to its original colourless state, normally via a thermal
electrocyclic ring closure. The change in the visible
absorption spectrum of these compounds is due to the
photoinduced reversible opening of the pyran ring leading to
the formation of an ‘open form’ with an extensively
conjugated p system (Scheme 1). The photochromic
2. Results and discussion
2.1. Synthesis
properties of naphthopyrans are strongly dependent on
1–3
structural features.
The fusion of an indeno group to
the 5,6 positions (f face) of 2,2-diphenyl-2H-naphtho[1,2-
b]pyrans is a well known strategy to improve the
photochromic properties because it effectively extends the
p-system conjugation and introduces important nonbonding
interactions in the open forms, without affecting the process
that leads to the coloured forms. 1 The net result are readily
obtained coloured forms with an observable bathochromic
shift in the visible spectra and interesting bleaching kinetics
due to the increased instability of the open forms. These
indeno-fused naphthopyrans exhibit a wide range of
colours, a high molar absortivity in the near-UV and
Naphthopyrans are usually prepared in fair to good yield by
reaction of phenols with propynols. This reaction is quite
general and a large variety of substituted or fused naphthols
4–8
interesting discolouration kinetics (Scheme 1).
The set of isomers that constitute the open form of the
2,2-diphenyl-2H-naphtho[1,2-b]pyrans, obtained upon UV
irradiation, are not completely planar, due to the steric
Keywords:
Photochromism;
Naphthopyrans;
Spectrokinetics;
Heterocycles; Spiro[thioxanthene-naphthopyrans].
*
Corresponding author. Tel.: þ351-259-350284; fax: þ351-259-350480;
e-mail address: pcoelho@utad.pt
Scheme 1.
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.01.034

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P. J. Coelho et al. / Tetrahedron 60 (2004) 2593–2599
can be used. Several different aromatic propynols have also
10
been used (Scheme 2).
The reaction of thioxanthone with lithium acetylide gave the
expected products but the purification of the propynol 7
proved to be very difficult since an extended decomposition
is observed upon silica or alumina column chromatography.
However, an almost pure sample of this alcohol was
obtained through silica gel flash chromatography. Although
limited to small amounts the use of this technique allowed
the preparation of several grams of alcohol 7 in approxi-
mately 67% overall yield (Scheme 5).
Scheme 2.
For the synthesis of indeno-fused spiro[thioxantene-
naphthopyrans] we needed indeno-fused naphthols and the
propynol derived from thioxanthone. Indeno-fused naphthol
6 was prepared in five steps from commercially available
1,4-dihydroxy-2-naphthoic acid 1. This acid was converted
into the 1,4-dimethoxy-2-naphthoic acid 2 by methylation
followed by basic hydrolysis. In order to introduce a phenyl
group in position 1 the acid 2 was converted into the 4,5-
dihydrooxazole 3. The activating effect of the 4,5-
dihydrooxazole ring allows the nucleophilic substitution
of the methoxy group by an alkyl/aryl group through
reaction with Grignard reagents at room temperature. 11 The
4,5-dihydrooxazole 4 was then hydrolysed to the corres-
ponding acid and treated for 5 min with concentrated
sulphuric acid affording methoxybenzofluorenone 5.
Finally, heating a solution of methoxybenzofluorenone in
HBr/HOAc gave the naphthol 6 in good yield (Scheme 3).
Scheme 5.
Heating a chloroform solution of naphthol 6 with propynol 7
in the presence of a catalytic amount of PPTS gave
spiro[thioxanthene-naphthopyran] 8 in 62% yield. This
compound is not photochromic (Scheme 6). 13 Treatment of
8 with the Grignard reagents derived from methyliodide,
tert-butylcloride, bromobenzene and 2-bromothiophene
gave, after hydrolysis, the photochromic spiro[thio-
xanthene-naphthopyran] 9a–d in low to good yield (24–
84%).
2.2. Photochromic properties
Diaryl propynols are usually prepared through reaction of
diarylketones with lithium or sodium acetylide (Scheme 4).
The reaction is incomplete and gives a diol as secondary
product. Due to the presence of this by-product and a
significant amount of the unreacted ketone, column
The photochromic behaviour of compounds 9a–d was
studied in toluene solutions under continuous near-UV
irradiation. Three spectrokinetic parameters namely, the
maximum wavelength of absorption of the open form
12
chromatography purification is usually necessary.
Scheme 3.
Scheme 4.

P. J. Coelho et al. / Tetrahedron 60 (2004) 2593–2599
2595
Scheme 6.
(lmax), the thermal bleaching rate, (kD) and the colourability
or absorbance of the solution after reaching photostationary
equilibrium (Aeq) were evaluated. The data are summarised
in Table 1. For comparison purposes the same parameters
were obtained, under identical experimental conditions, for
two known naphthopyrans: the compound without any
substituents 2,2-diphenyl-2H-naphtho[1,2-b]pyran 10 and
the known indeno-fused naphthopyran without the sulphur
bridge, 3,3-diphenyl-13-hydroxy-13-methyl-indeno[2,1-
f]naphtho[1,2-b]pyran 11.
Table 1. Spectrokinetic properties under continuous irradiation: maxima
wavelengths of the coloured form (lmax), colourability (Aeq is the
absorbance after photostationary equilibrium at lmax), thermal bleaching
rate (kD) of compounds 9a–d, and two reference compounds in toluene
solutions: 10 (2,2-diphenyl-2H-naphtho[1,2-b]pyran), 11 (13-hydroxy-13-
methyl-3,3-diphenyl-indeno[2,1-f]naphtho[1,2-b]pyran)
Compound
lmax (nm)
Aeq
kD (s21
)
10
469
0.72
0.0006 (98)
0.0003 (2)
All of the new naphthopyrans, 9a–d, exhibited photo-
chromic behaviour at room temperature in toluene solutions.
Compared to the reference naphthopyran 10 the absorption
wavelength in the visible range obtained after irradiation,
11
9a
9b
9c
530
552
557
558
1.2
0.004 (98)
0.0001 (2)
lmax, show, as expected, substantial bathochromic shifts for
all the new indeno-fused derivatives. From the data
presented in Table 1, it can be observed that the extension
of the p-conjugation is due to not only the indeno moiety
but results also from the presence of the sulphur bridge:
similarly substituted indeno-fused naphthopyrans (9a and
11) exhibit significantly different lmax (þ22 nm) confirming
that the introduction of a sulphur bridge linking the 2,2-
diphenyl groups is an efficient way to increase the
participation of each phenyl nucleus in the p-conjugation
0.66
0.27
0.49
0.047 (90)
,0.0001 (10)
Me OH
S
O
9
of the open forms.
0.047 (90)
,0.0001 (10)
On the other hand, all of the new compounds exhibit
absorption localised at ca. 555 nm indicating that the nature
of the substituents at the indeno sp 3-carbon atom have only
a minor influence in the conjugation of the open forms.
With regard to the ring closure kinetics, the new described
compounds exhibit two phases kinetics with similar
amplitudes. It is apparent that the open forms of the
compounds with the sulphur bridge are thermally less stable
than the reference compounds (rate of ring closure 10–20
times faster than 11). The same was already observed with
spiro[thioxanthene-naphthopyrans] 9 and is probably due to
some strain in the planar open forms promoted by the
sulphur bridge. The first rate constant, 0.047–0.11 s21, is
higher than that observed for the reference compounds with
an amplitude a little lower, around 90%. The second rate
constant is very slow, as for the reference compounds, and is
responsible for the persistence of a residual colour even
after several minutes after the removal of the source of the
0.10 (91)
0.0001 (9)
9d
556
0.44
0.11 (83)
,0.0001 (17)

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P. J. Coelho et al. / Tetrahedron 60 (2004) 2593–2599
Figure 1. Variation of the absorbance at lmax of 11 and 9a (toluene solution, 1£1024 M) under continuous UV irradiation (150 W Xe lamp, 30 min) and then
when the irradiation is stopped (20 8C).
activating light. However, as can be shown in Figure 1, the
spiro[thioxantene-naphthopyran] 9a is much faster (almost
6 times) than 11: naphthopyran 9a reaches one half the
highest absorbance attained in 39 s; 11 takes 246 s to reach
one half of its maximum absorbance. The residual colour of
9a is also significantly lower (0.07 after 30 min in the dark)
than for 11 (0.21 in the same time). The observed kinetics
make the novel compounds more acceptable compounds for
application in variable optical transmission materials.
compound without the sulphur bridge (11). The linkage of
the two C-sp 3 phenyl groups in diphenyl indeno-fused
naphthopyrans through a sulphur bridge increases the
participation of each phenyl nucleus in the p-conjugation
of the open forms and constitutes an effective way to extend
the chromophore and to accelerate the ring closure kinetics.
The nature of the substituents at the C-sp 3 of the indeno
group seems to have little effect on the p-conjugation of the
open forms. Bulky substituents at this atom do not have a
marked effect on the thermal stability of the open forms but
aromatic substituents promote some instability. These
indeno-fused spiro[thioxanthene-naphthopyrans] would
appear to be promising compounds for application in
ophthalmic photochromic lenses.
The presence of an aromatic group at the indeno sp 3-carbon
atom (compounds 9c and 9d) contributes to the instability of
the coloured forms leading to two-fold increase in the first
kinetic rate constant. This does not seem to be a steric effect
as compounds 9a and 9b differ markedly in the size of the
substituent group and exhibit similar rates of ring closure.
The colourabilities of all the new described compounds are
variable and lower than the observed for the reference
compounds. This can be related to the faster thermal fading
rates. Under continuous irradiation at low concentration, the
colourability is proportional to both the quantum yield of
photocolouration and the molar absortivity of the coloured
form, but inversely proportional to the fading-rate constant.
Faster bleaching kinetics are normally accompanied by
lower colourabilities due to the lower concentration of
coloured products at the photostationary state (Fig. 1).
4. Experimental
4.1. Spectrokinetic studies under continuous irradiation
For measurements of lmax, Aeq and kD under continuous
irradiation, 1£1024 M toluene solutions were used.
Irradiation experiments were made using a CARY 50
Varian spectrometer coupled to a 150 W Ozone free Xenon
lamp (6255 Oriel Instruments). The light from the UV lamp
was filtered using a water filter (61945 Oriel Instruments)
and then carried to the spectrophotometer holder at the right
angle to the monitoring beam using a fiber-optic system
(77654 Oriel Instruments). A light flux of 40 W m22
,
3. Conclusion
measured with a Goldilux Photometer with a UV-A probe
was used. A thermostated (20 8C) 10 mm quartz cell,
containing the sample solution (3.5 ml), equipped with
magnetic stirring was used. In a preliminary experiment, the
visible absorption spectrum of the closed form 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
with the time was monitored. The rate constants were
calculated using a multi exponential model.
Four new photochromic indeno-fused naphthopyrans were
synthesised in good yield. Spiro[thioxanthene-naphtho-
pyrans] 9a–d showed a general significant bathochromic
shift in the spectra of the open forms, higher ring closure
rates and an expected decrease in the colourabilities when
compared to a similar known indeno-fused naphthopyran
(11). Although all compounds showed a residual colour
even after several minutes in the dark, the absorbance is
considerably lower than that observed for the reference

P. J. Coelho et al. / Tetrahedron 60 (2004) 2593–2599
2597
4.2. General remarks
concentrated and the product purified by column chromato-
graphy (0–20% ethyl acetate/light petroleum) to give pure
4,5-dihydrooxazole 3 (1.027 g, 3.60 mmol) as a yellow oil.
15 Yield: 84%. IR: 2961, 1650, 1370, 1261, 1106; 1H NMR:
8.21 (m, 2H), 7.56 (m, 2H), 7.14 (s, 1H), 4.19 (s, 2H,
CH2O), 4.03 (s, 3H, OCH3), 3.95 (s, 3H, OCH3), 1.45 (s, 6H,
2£CH3). MS: m/z (%): 285 (45), 232 (48), 215 (100), 149
(75), 58 (90). Exact mass for C17H19O3N: 285.1365. Found
285.1354.
1H spectra were recorded in CDCl3 on a Varian Unity Plus
at 300 MHz. 13C spectra were recorded in CDCl3 on a
Varian Unity Plus at 75.4 MHz. IR spectra were recorded on
a Perkin–Elmer FTIR 1600 spectrometer, wave numbers in
cm21. Mass spectra were measured on an AutoSpecE
spectrometer. Melting points are uncorrected. Column
chromatography was performed on silica gel 60 (70–230
mesh). All new compounds were determined to be .95%
pure by 1H NMR spectroscopy. Compounds 10 and 11 were
prepared from 1-naphthol and 5-hydroxy-7H-benzo[c]
fluoren-7-one, respectively, using standard procedures.1,4
The melting points of photochromic naphthopyrans 9a–d
were not measured because thermochromism was observed
at high temperatures.
4.2.3. 2-(10-Phenyl-40-methoxynaphth-2-yl)-4,4-
dimethyl-4,5-dihydrooxazole 4. A solution of phenyl-
magnesium bromide (prepared from bromobenzene (2.84 g,
18.1 mmol) and magnesium (0.435 g, 18.1 mmol) in 20 ml
of dry ethyl ether) was slowly added to a solution of 4,5-
dihydrooxazole 3 (1.00 g, 3.02 mmol) in ethyl ether (15 ml).
After stirring at room temperature for 24 h, the solution was
quenched in aq. sat. NH4Cl, extracted with Et2O (3£40 ml),
dried (Na2SO4) and concentrated under reduced pressure.
The residue was purified by CC (0–30% ethyl acetate/light
petroleum) to give pure 4,5-dihydrooxazole 4 (0.740 g,
2.24 mmol) as a yellow oil. Yield: 75%. IR: 2969, 2877,
1658, 1592, 1457, 1145; 1H NMR: 8.33 (d, J¼8.4 Hz, 1H),
7.62 (d, J¼8.0 Hz, 1H), 7.52 (dt, J¼8.4 Hz, 1.5, 1H), 7.48–
7.30 (m, 6H), 7.11 (s, 1H), 4.10 (s, 3H, OCH3), 3.72
(s, OCH2, 2H), 1.23 (s, 6H, 2£CH3). MS: m/z (%): 331 (55),
330 (100), 316 (25), 245 (24), 189 (24), 77 (14). Exact mass
for C22H21O2N: 331.1572. Found 331.1568.
4.2.1. 1,4-Dimethoxynaphthoic acid 2. A mixture of 1,4-
dihydroxynaphthoic acid (10.0 g, 0.0490 mol), K2CO3
(61 g, 0.44 mol), dimethyl sulphate (14 ml, 0.15 mol) and
acetone (100 ml) was heated for 2 days at reflux under argon
atmosphere. After return to room temperature the mixture
was filtered and the filtrate evaporated to give the crude 1,4-
dimethoxynaphthoic methyl ester. 100 ml of aqueous NaOH
(20%) was added to the crude ester and the solution heated
under reflux for 3 h. After return to room temperature the
aqueous solution was extracted with CH2Cl2 and the organic
phase discarded. The aqueous phase was acidified with HCl
(10%) and extracted with Et2O (3£100 ml). The combined
organic layers were dried (Na2SO4) and concentrated
to give pure 1,4-dimethoxynaphthoic acid 2 (10.80 g,
4.2.4. 5-Methoxy-7H-benzo[c]fluoren-7-one 5. A solution
of 4,5-dihydrooxazole 4 (0.690 g, 2.08 mmol) in MeI
(10 ml) was stirred at room temperature overnight and the
excess of MeI removed under reduced pressure. To the
crude methyl iodide salt, were added methanol (12 ml) and
NaOH 20% (12 ml) and the mixture heated to reflux for
12 h. The solution was extracted with Et2O and the organic
layer discarded. The aqueous layer was acidified with HCl
(aq.), extracted with Et2O, dried (Na2SO4) and concentrated
to give the 4-methoxy-1-phenylnaphthoic acid. Without
further purification, H2SO4 (5 ml) was added. After stirring
for 5 min at room temperature the resulting dark coloured
solution was poured into ice (50 g) and then extracted with
Et2O (3£50 ml). The organic layer was dried (Na2SO4) and
the solvent was evaporated under reduced pressure to give
0.0466 mmol) as a light brown solid. Yield: 95%. Mp
14
68.3–69.2 (lit.
57–59). IR: 3200–2400 broad band,
1675, 1367, 1110; 1H NMR: 11.5 (s, 1H, COOH), 8.32 (m,
1H), 8.11 (m, 1H), 7.66 (m, 2H), 7.39 (s, 1H), 4.13 (s, 2H,
OCH3), 4.06 (s, 2H, OCH3). Exact mass for C13H12O4:
232.0736. Found 232.0735.
4.2.2. 2-(10,40-Dimethoxynaphth-2-yl)-4,4-dimethyl-4,5-
dihydrooxazole 3. A mixture of 1,4-dimethoxynaphthoic
acid (1.00 g, 4.31 mmol), CH2Cl2 (60 ml) and oxalyl
chloride (0.60 ml, 5.6 mmol) was stirred at room tempera-
ture for 24 h. The solvent and the oxalyl chloride excess
were removed by rotary evaporation. 1,2-Dichloroethane
(15 ml) was added followed by additional rotary evapo-
ration in order to remove any residual oxalyl chloride. The
crude acyl chloride was then dissolved in 1,2-dichloro-
ethane (30 ml) and treated successively with triethylamine
(0.80 ml, 5.76 mmol) and 2-amino-2-methyl-1-propanol
(574 mg, 6.44 mmol) at 0 8C and stirred overnight at room
temperature. Aq. sat. NH4Cl (15 ml) and water (15 ml) was
added and then the entire mixture was transferred to a
separatory funnel and extracted with Et2O (3£100 ml). The
combined organic layers were dried (Na2SO4) and con-
centrated to give the crude hydroxy amide which was
redissolved in CH2Cl2 (120 ml) and benzene (20 ml) and
placed at 0 8C. Thionyl chloride (2.0 ml, 27.5 mmol) was
added and the mixture stirred 4 h at room temperature. After
solvent evaporation, ether (260 ml), aq. sat. NaHCO3
(24 ml), water (24 ml) and NaOH (2 N, 24 ml) were
added. The mixture was stirred 30 min and then the organic
layer removed and the aqueous layer re-extracted with ether
(2£100 ml). The combined organic layers were dried,
pure ketone 5 (0.340 g, 1.31 mmol) as a red solid. Yield:
16
63%. Mp 142.0–143.3 (lit.
155–156). IR: 2930, 1718,
1270, 1122; 1H NMR: 8.43 (d, J¼7.8 Hz, 1H), 8.34
(d, J¼8.1 Hz, 1H), 7.91 (d, J¼7.8 Hz, 1H), 7.70–7.55
(m, 3H), 7.48 (dt, J¼1.2 Hz, 7.5, 1H), 7.22 (dt, J¼1.0 Hz,
7.5, 1H), 7.13 (s, 1H), 4.08 (s, 3H, OCH3). MS: m/z (%): 260
(55), 245 (37), 217 (22), 189 (20), 167 (45), 149 (100).
Exact mass for C18H12O2: 260.0837. Found 260.0827.
4.2.5. 5-Hydroxy-7H-benzo[c]fluoren-7-one 6. A mixture
of ketone 5 (0.340 g, 1.31 mmol), acetic acid (2.5 ml) and
HBr 47% (5 ml) was heated under reflux for 5 h. After
cooling the reaction mixture was poured into 100 ml of
water and extracted with ethyl ether (3£50 ml). The
combined organic layers were extracted 3 times with
NaOH (5%, 20 ml) and the organic phase discarded. The
aqueous phase was acidified with HCl 10%, and extracted
with ether (3£50 ml). The combined organic layers were
dried (Na2SO4) and the solvent evaporated under reduced

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P. J. Coelho et al. / Tetrahedron 60 (2004) 2593–2599
pressure giving the pure hydroxybenzofluorenone 6 (0.212 g,
0.86 mmol) as a red solid. Yield: 66%. Mp 252.2–253.3
solid. Yield: 44%. IR: 3386, 3058, 2950, 1457, 1268, 1112.
UV/Vis (closed form): 372 (1 7800), 392 (1 4700); 1H
NMR: 8.64 (dd, J¼8.4 Hz, 1H), 8.48 (dd, J¼8.4 Hz, 1.0,
1H), 8.15 (d, J¼7.8 Hz, 1H), 7.80–7.72 (m, 2H), 7.67
(dt, J¼8.4 Hz, 1.5, 1H), 7.60 (dd, J¼7.5 Hz, 1.0, 1H), 7.57–
7.50 (m, 2H), 7.44 (dt, J¼7.8 Hz, 1.2, 1H), 7.40–7.20
(m, 7H), 6.30 (d, J¼10.2 Hz, 1H), 1.80 (s, CH3, 3H). 13C
NMR: 151.14, 148.59, 143.96, 139.47, 138.44, 138.32,
130.86, 130.13, 129.69, 129.46, 128.97, 127.64, 127.62,
127.54, 126.99, 126.92, 126.87, 126.44, 126.31, 126.26,
126.18, 125.72, 124.58, 124.08, 123.20, 122.44, 122.12,
122.02, 118.35, 110.88, 80.78, 80.21, 26.59. MS: m/z (%):
482 (50), 464 (33), 449 (100), 221 (35), 197 (46). Exact
mass for C33H22O2S: 482.1341. Found 482.1349.
1
(lit.16 above 235). IR: 3397, 1714, 1579, 1351; H NMR
(acetone-d6): 9.78 (s, 1H, OH), 8.60 (d, J¼8.5 Hz, 1H),
8.36 (d, J¼8.4 Hz, 1H), 8.11 (d, J¼7.8 Hz, 1H), 7.72
(t, J¼7.5 Hz, 1H), 7.64 (t, J¼7.5 Hz, 1H), 7.57 (m, 2H),
7.28 (t, J¼7.5 Hz, 1H), 7.16 (s, 1H). MS: m/z (%): 246
(100), 217 (6), 189 (40), 149 (7), 95 (14). Exact mass for
C17H10O2: 246.0681. Found 246.0680.
4.2.6. Spiro[13-oxoindeno[2,1-f]naphtho[1,2-b]pyran-
3,90-thioxanthene] 8. A suspension of thioxanthone
(2.00 g, 9.43 mmol), and lithium acetylide ethylene diamine
complex (3.00 g, 29.4 mmol) in dry THF (250 ml) was
stirred under an argon atmosphere for 24 h. The suspension
was treated with water (200 ml) and the aqueous phase
extracted with ethyl ether (3£100 ml). The organic phase
was dried over anhydrous Na2SO4 and the solvent
evaporated leaving the crude 9-hydroxy-9-ethynyl-9H-
thioxanthene. The crude product was further divided into
four fractions each one was submitted to flash column
chromatography (10% ethyl acetate/hexane) (not more than
30 min) affording almost pure 9-hydroxy-9-ethynyl-9H-
thioxanthene 7 (1.5 g, 67% yield); 17 1H NMR: 8.15 (dd,
J¼7.8 Hz, 2.1, 2H), 7.52 (dd, J¼7.2 Hz, 2.1, 2H), 7.37 (ddd,
J¼7.5 Hz, 7.5, 1.8, 2H), 7.33 (ddd, J¼7.5 Hz, 7.5, 1.8, 2H),
2.94 (s, 2H).
4.3.2. 13-tert-Butyl-13-hydroxy-spiro[indeno[2,1-f]-
naphtho[1,2-b]pyran-3,90-thioxanthene] 9b. Light yellow
solid. Yield: 28%. IR: 3410, 3050, 2982, 1620. UV/Vis
1
(closed form): 366 (1 3500); H NMR: 8.64 (d, J¼8.1 Hz,
1H), 8.48 (d, J¼8.2 Hz, 1H), 8.11 (d, J¼7.9 Hz, 1H), 7.80–
7.78 (m, 1H), 7.73–7.71 (m, 4H), 7.66–7.63 (t, J¼7.5 Hz,
1H), 7.55–7.50 (m, 3H), 7.40–7.38 (t, J¼7.5 Hz, 1H),
7.30–7.20 (m, 4H), 6.20 (d, J¼10.3 Hz, 1H), 0.92 (s, CH3,
9H). MS: m/z (%): 524 (20), 467 (42), 450 (10), 271 (17),
221 (40), 210 (45), 197 (57), 149 (100). Exact mass for
C36H28O2S: 524.1810. Found 524.1827.
4.3.3. 13-Hydroxy-13-phenyl-spiro[indeno[2,1-f]-
naphtho[1,2-b]pyran-3,90-thioxanthene] 9c. Light blue
solid. Yield: 81%. IR: 3457, 3058, 2923, 1457, 1268,
1162. UV/Vis (closed form): 372 (1 12300), 393 (1 7400);
1H NMR: 8.67 (d, J¼8.7 Hz, 1H), 8.43 (d, J¼8.4 Hz, 1H),
8.15 (d, J¼7.8 Hz, 1H), 7.74–7.15 (m, 18H), 6.75
(d, J¼10.2 Hz, 1H), 6.07 (d, J¼10.2 Hz, 1H). MS: m/z
(%): 544 (1), 526 (1), 444 (4), 347 (5), 287 (28), 273 (15),
213 (100), 184 (31), 77 (31). Exact mass for C38H24O2S:
544.1497. Found 544.1498.
A solution of 9-hydroxy-9-ethynyl-9H-thioxanthene 7
(0.800 mg, 3.36 mmol), 5-hydroxy-7H-benzo[c]fluoren-7-
one 6 (0.174 g, 0.707 mmol) p-toluenosulphonic acid
(50 mg) and CHCl3 (60 ml) was refluxed for 4 h under an
argon atmosphere. Solvent evaporation gave a brown oil
which was purified by silica gel column chromatography
(3% ethyl acetate/hexane). Recrystallisation from CHCl3/
pentane gave a crystalline red compound (0.240 g,
0.515 mmol). Yield: 73%. Mp 234–235 8C. IR: 3052,
2921, 1698, 1641, 1270, 1068; 1H NMR: 8.46 (dd,
J¼7.8 Hz, 1.2, 1H), 8.38 (dd, J¼7.8 Hz, 1.2, 1H), 7.95
(d, J¼7.5 Hz, 1H), 7.81 (d, J¼10.2 Hz, 1H), 7.76–7.68
(m, 2H), 7.68–7.46 (m, 6H), 7.36–7.20 (m, 5H), 6.37
(d, J¼10.2 Hz, 1H). 13C NMR 195.70; 148.95; 144.83;
137.52; 135.48; 134.56; 134.45; 129.90; 129.61; 128.16;
128.06; 127.80; 127.64; 127.09; 126.92 (two carbons
overlapped); 126.50; 126.10; 124.80; 124.24; 123.76;
123.53; 122.36; 117.63; 111.56; 80.53. MS: m/z (%): 466
(100), 449 (20), 330 (26), 233 (45), 221 (90), 210 (35).
4.3.4. 13-Hydroxy-13-thiophen-2-yl-spiro[indeno[2,1-f]-
naphtho[1,2-b]pyran-3,90-thioxanthene] 9d. Light brown
solid. Yield: 84%. IR: 3519, 3062, 2915, 1562, 1455, 1365,
1268, 1110. UV/Vis (closed form): 368 (1 11000); 1H NMR:
8.64 (d, J¼8.4 Hz, 1H), 8.45 (d, J¼8.1 Hz, 1H), 8.13
(d, J¼7.5 Hz, 1H), 7.76–7.70 (m, 2H), 7.67 (dt, J¼7.5 Hz,
1.2, 1H), 7.57 (dt, J¼7.5 Hz, 1.2, 1H) 7.54–7.46 (m, 2H),
7.40 (dt, J¼7.5 Hz, 1.2, 1H), 7.30–7.20 (m, 6H), 7.19 (dd,
J¼4.5 Hz, 1.0, 1H), 6.93 (d, J¼10.2 Hz, 1H), 6.83 (dd,
J¼4.5 Hz, 4.8, 1H), 6.68 (dd, J¼4.5 Hz, 1.0, 1H), 6.15
(d, J¼10.2 Hz, 1H). 13C NMR: 150.50; 148.83; 147.00;
142.84; 139.32; 137.77; 137.22; 130.10; 129.87; 129.25;
127.70; 127.65; 127.50; 126.88; 126.84; 126.77; 126.69;
126.61; 126.58; 126.02; 125.27; 124.48, 124.18; 123.74;
123.35; 122.30; 122.01; 119.30; 111.58; 82.59; 80.09. MS:
m/z (%): 550 (98), 532 (82), 466 (42), 449 (43), 221 (55),
197 (100). Exact mass for C36H22O2S2: 550.1061. Found
550.1050.
4.3. Procedure for the reaction of naphthopyran 8 with
Grignard reagents
A solution of the Grignard reagent prepared in ethyl ether
(2.0 ml, 2.0 mmol) was added to a solution of the
naphthopyran 8 (0.100 mg, 0.215 mmol) dissolved in THF
(10 ml) at 0 8C. After stirring at room temperature for 4 h,
the solution was quenched in aq. sat. NH4Cl, extracted with
Et2O (3£40 ml) and the combined organic layers dried
(Na2SO4) and concentrated under reduced pressure. The
residue was purified by CC (3% ethyl acetate/light
petroleum) to give the pure naphthopyrans 9a–d.
Acknowledgements
To FCT (Portugal’s Foundation for Science and Techno-
logy) and FEDER for financial support through project
POCTI/QUI/38771/2001.
4.3.1. 13-Hydroxy-13-methyl-spiro[indeno[2,1-f]-
naphtho[1,2-b]pyran-3,90-thioxanthene] 9a. Light yellow

P. J. Coelho et al. / Tetrahedron 60 (2004) 2593–2599
2599
`
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