Synthesis, electrochemical and photochromic behaviour of a series of (1,4-dithiafulven-6-yl)substituted 3H-naphtho[2,1-b]pyran derivatives

Article abstract of DOI:10.1016/j.tet.2004.10.084

The synthesis and electrochemical and photochromic properties of new 3,3-diphenyl-8-(1,4-dithiafulven-6-yl)-[3H]-naphtho[2,1-b]pyran derivatives containing differently substituted dithiafulvenyl units are described. An example of electrochemical dimerization is shown which gives access to electroactive bichromophoric systems. Such systems could allow the study of the interplay of photochromic and electrochemical properties.

Full text of DOI:10.1016/j.tet.2004.10.084

Tetrahedron 61 (2005) 423–428
Synthesis, electrochemical and photochromic behaviour
of a series of (1,4-dithiafulven-6-yl)substituted
3H-naphtho[2,1-b]pyran derivatives
Aude-Emmanuelle Navarro,a Fabrice Moggia,a Corinne Moustrou,a Arnault Heynderickx,a
a
´ ´
Frederic Fages, Philippe Leriche and Hugues Brisset
b
a,
*
a
´ ´ ´
Groupe de Chimie Organique Materiaux Moleculaires, UMR CNRS 6114, Faculte des Sciences de Luminy, 163 avenue de Luminy,
13288 Marseille Cedex 9, France
Groupe Systemes Conjugues Lineaires, CIMMA UMR CNRS 6200, UFR Sciences d’Angers, 2 Boulevard Lavoisier,
49045 ANGERS Cedex 01, France
b
`
´
´
Received 21 July 2004; revised 22 October 2004; accepted 28 October 2004
Available online 18 November 2004
Abstract—The synthesis and electrochemical and photochromic properties of new 3,3-diphenyl-8-(1,4-dithiafulven-6-yl)-[3H]-
naphtho[2,1-b]pyran derivatives containing differently substituted dithiafulvenyl units are described. An example of electrochemical
dimerization is shown which gives access to electroactive bichromophoric systems. Such systems could allow the study of the interplay of
photochromic and electrochemical properties.
q 2004 Elsevier Ltd. All rights reserved.
1. Introduction
the dication. Then, it was anticipated that such system could
represent a new class of molecular switches in which a
reversible redox change could alter the photochromic
response of the naphthopyran unit (Scheme 1).
Tetrathiafulvalene (TTF) and naphthopyrans have been
widely investigated during the three last decades for the
generation of superconductive charge-transfer salts1 and
photochromic materials,2 respectively.
In this work, the synthesis and the characterizations of new
organic photochromic compounds (2a–d) which combine
3,3-diphenylnaphthopyrans and substituted 1,4-dithiaful-
venes units are presented (Chart 2).
Naphthopyrans belong to an important class of organic
photochromic compounds which exhibit reversible changes
between colorless and colored isomers. The colored isomer
is obtained by UV irradiation while the reverse reaction is
thermally controlled. To obtain the bistability of the two
different forms with the possibility of a binary on/off control
of the interconversion, most of the investigations have
focused on naphthopyrans bearing different pendant
groups.3
The synthesis of 1c by the electrochemical dimerization of
2c was investigated and the preliminary photochromic
results presented.
In this context, we have designed a new molecule (1c)
including naphthopyran and TTF vinylogue units, that
possess both electrochromic and photochromic properties
(Chart 1).
Indeed, the TTF vinylogue unit can be reversibly oxidized to
Keywords: Tetrathiafulvalene; Naphthopyran.
* Corresponding author. Tel.: C33 49 182 9587; fax: C33 49 182 9580;
e-mail: brisset@luminy.univ-mrs.fr
Chart 1.
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.10.084

424
A.-E. Navarro et al. / Tetrahedron 61 (2005) 423–428
Scheme 1.
formyl-[3H]-naphtho[2,1-b]pyran 3 prepared as described
in the literature4 using an appropriately substituted dithio-
lium salts 4b,c or phosphonate anion 5a or phosphonium
salt 6d.
2.2. Electrochemistry of compounds 2a–d and
electrosynthesis of 1
Electrochemical studies of compounds 2a–d were per-
formed by cyclic voltammetry with a platinum disk
electrode (AZ2 mm2) in a 10K3 M acetonitrile solution
containing 0.1 M tetrabutylammonium hexafluorophos-
phate as the supporting electrolyte and an Ag/AgCl
reference electrode. The electrochemical data are collected
in Table 1.
Chart 2.
2. Results and discussion
In all cases the cyclic voltammograms (CV) of compounds
2a–d exhibit one irreversible oxidation wave (Fig. 1).
2.1. Synthesis of compounds 2a–d
The synthesis of compounds 2a–d is depicted in Scheme 2.
As expected the replacement of the electron-withdrawing
methylcarboxylate group in 2d by an electron-donating
group, such as the cyclohexyl substituent, leads to a 0.34 V
The target compounds 2a–d were then obtained in 45–50%
yield from the Wittig–Horner olefination of 3,3-diphenyl-8-
Scheme 2.
Table 1. Electrochemical data for compounds 2a–d vs Ag/AgCl at 25 8C. Ferrocene used as internal standard
Compound
R
Epa/V
Epanew/V
Epcnew/V
2a
2b
2c
2d
(CH2)4
H
(CH]CH)2
COOCH3
0.61
0.68
0.82
0.95
0.38
0.44
0.64
0.80
0.34
0.39
0.60
0.71

A.-E. Navarro et al. / Tetrahedron 61 (2005) 423–428
425
photochromic behaviour of these new TTF naphthopyrans
have been evaluated under continuous irradiation with a
xenon lamp at room temperature using toluene as solvent
(Fig. 3).
Figure 1. Cyclic voltammogram of 2c in CH3CN/n-Bu4NPF6 0.1 M at a
scan rate of 100 mV sK1
.
Figure 3. Electronic absorption spectra of the closed (solid line) and
opened (dotted line) forms of compound 2c (toluene, cZ10K3 mol LK1
20 8C).
negative shift of Epa. In all cases the appearance of a new
reversible redox system at lower potentials, is observed after
the first scan (Fig. 1). Previous works on phenyl substituted
1,4-dithiafulvenes which can be reversibility oxidized in
cation radical have shown that these compounds lead to
the formation of tetrathiafulvalene vinylogues by electro-
chemical dimerization.5
,
Spectrokinetic data are summarized in Table 2 and
compared with those obtained with the unsubstituted
naphthopyran taken as a reference. Three parameters were
considered in order to characterize the colored form: the
maximum wavelength of absorption; the thermal decolor-
ation rate (kD) and the colorability (AN), e.g. the
absorbance measured under steady-state irradiation.
By analogy the new redox system can be attributed to the
dimer formation in the solution. In order to confirm this
hypothesis the electrosynthesis of the dimer of 2c, 1c, was
performed on a preparative scale using a reticulated vitreous
carbon working electrode and 2 mol of electron per mol of
substrate as described in the literature. After reduction the
target dimer was purified classically by chromatography on
silica gel column. The CV of 1c was recorded under the
same experimental conditions as those used for compound
2c and displayed a reversible two-electron oxidation wave
with an anodic peak at 0.63 V and the corresponding
cathodic wave at 0.60 V (Fig. 2) in good accordance with
the electrochemical response observed for TTF vinylogue
substituted derivatives on the vinylogue bonds by phenyl
groups.
When compared to the unsubstituted naphthopyran the
absorption maxima wavelength of the closed form (lmaxCF)
shift bathochromically in the case of 2a and hypsochromi-
cally for 2b–d in accordance with the electro-donating and
the electron-withdrawing groups. This behaviour is again
more pronounced in the opened form. Thus, the absorption
maxima wavelength of the colored opened forms (lmaxOF)
of 2a–c undergo important bathochromic shifts, from 92 to
117 nm when compared to the unsubstituted naphthopyran.
These results reveal that the effect of substituted 1,4-
dithiafulvenes groups on the naphthopyran core is more
important in the opened forms. Moreover, compounds 2a–c
display the same colorability AN as that of the
unsubstituted chromene and present a faster thermal
decoloration. The thermal decoloration rate for 2a–c
increase from 0.038 to 0.051 sK1 in accordance with the
electron-withdrawing effect of the substituent grafting on
the 1,4-dithiafulvenes moiety. On other hand compound 2d
was observed not to display any photochromic properties
under our conditions due to the very strong electron-
withdrawing effect of the ester groups.
The dimer compound, 1c, was observed to display a weak
photochromic behaviour (Fig. 4).
Figure 2. Cyclic voltammogram of 1c in CH3CN/n-Bu4NPF6 0.1 M at a
scan rate of 100 mV sK1
Very little absorbance was observed for the opened form of
compound 1c which indicate a quasi disappearance of the
photochromic properties due to a very stable closed form or
a faster thermally reverse reaction. On the basis of the
literature the neutral compound 1c is probably non planar.5
In this context the stability of the closed or/and opened
forms could be altered by steric hindrances. Moreover, the
absorption maximum wavelength of the closed and opened
.
2.3. Optical properties
Upon UV irradiation, the compounds 2a–d were shown to
undergo a thermally reversible color change due to an
electrocyclic rearrangement of the pyrane moiety. The

426
A.-E. Navarro et al. / Tetrahedron 61 (2005) 423–428
Table 2. Photochromic parameters obtained under continuous irradiation in toluene solutions (150 W xenon lamp, 25 8C) for compounds 2a–d
Compound
R
lmaxCF
lmaxOF
AN
KD (sK1
)
Naphthopyran
—
(CH2)4
H
(CH]CH)2
COOCH3
345
369
342
336
327
432
549
532
524
—
0.17
0.17
0.17
0.17
—
0.060
0.038
0.042
0.051
—
2a
2b
2c
2d
Instrumentation. Melting points are uncorrected and were
1
obtained from an Electrothermal 9100 apparatus. H NMR
and 13C NMR spectra were recorded on Bruker AC 250 at,
respectively, 250 MHz and 62.5 MHz. UV spectra were
obtained on Varian Cary 50. FAB mass spectra were
obtained with a JEOL FX 102 Mass spectrometer
(Laboratoire de Mesures Physiques, USTL, Montpellier,
France). The bulk electrolysis and the cyclic voltammetry
(CV) were performed with computer-based Bioanalytical
instrument (BAS 100) electrochemical workstation. The
bulk electrolysis was made in a divided cell with reticulated
vitreous carbon working electrode, platinium counter
electrode and reference electrode, Ag/AgCl. The CV data
were acquired using a with 1.6 mm diameter platinium
working electrode; platinium counter electrode; reference
electrode, Ag/AgCl.
Figure 4. Electronic absorption spectra of the closed (solid line) and
opened (dotted line) forms of compound 1c (tetrahydrofurane, cZ
10K5 mol LK1, 20 8C).
For compounds 2a–d the photochromic measurements were
performed in toluene solutions of spectrometric grade at
20 8C (0.28), at a concentration of 5!10K3 mol LK1. For
compound 1c the photochromic measurements were
performed in tetrahydrofurane solution of spectrometric
forms were recorded at 333 and about 511 nm, respectively,
corresponding to hypsochromic shifts relative to the
naphthopyran precursor 2c. More detailed investigations
are currently underway especially to determine the influence
of the TTF vinylogue moiety redox state on the photo-
chromic properties of 1c.
grade at 20 8C (0.28), at a concentration of 5!10K5 mol LK1
.
The irradiation flux in each case was 4 W mK2. The analysis
cell (optical pathlength 10 mm) was placed in a thermostated
copper block inside the sample chamber of a Varian Cary 50
spectrometer. An Oriel 150 W high pressure Xe lamp was
used for irradiation.
3. Conclusion
The synthesis of new substituted 3,3-diphenyl-8-(1,4-
dithiafulven-6-yl)-[3H]-naphtho[2,1-b]pyrans has been per-
formed. These compounds display interesting photochromic
properties. The spectroscopic data show that the shift of the
absorption maximum and the thermal decoloration rate
correlate with the electro-donating or electron-withdrawing
effect of the substituent groups. Future work is directed of
the improvement of the photochromic properties of
naphthopyran derivatives incorporating a TTF vinylogue
unit and the investigation of synergistical coupling between
optical and electrochemical properties.
4.1.1. 8-(4,5-Cyclohexeno-1,3-benzodithiol-2-ylidene)-
3,3-diphenyl-[3H]-naphtho[2,1-b]pyrane 2a. Into a flask
of 50 mL, 181 mg (0.68 mmol) of phosphonate 5a prepared
as describe in literature,6 and 7 mL of anhydrous THF were
cooling to K78 8C under argon. 0.27 mL (0.68 mmol) of
nBuLi (solution 2.5 M in hexane) are added drop by drop
and 120 mg (0.45 mmol) of chromene carbaldehyde 3 was
added. The mixture is let return at ambient temperature.
Water was added and the mixture is extracted with
methylene chloride. The combined organic phases were
washed with water, dried (MgSO4), and evaporated in
vacuo. The crude product was purified on a silica gel
column and eluting with ethyl acetate–cyclohexane mixture
(5/95). The desired fractions were pooled and concentrated
to afford 0.10 g (44%) of pale yellow solid: Mp 192–194 8C;
1H NMR (400 MHz, pyridine-d5) d: 1.74–1.82 (m, 4H);
2.22–2.32 (m, 4H); 6.24 (d, JZ9.9 Hz, 1H); 6.54 (s, 1H);
7.16 (d, JZ8.8 Hz, 1H); 7.20–7.33 (m, 7H); 7.36 (dd, JZ
1.7, 8.9 Hz, 1H); 7.44–7.50 (m, 4H); 7.55 (br s, 1H); 7.62 (d,
JZ8.8 Hz, 1H); 7.86 (d, JZ8.9 Hz, 1H). 13C NMR
(100 MHz, pyridine-d5) d: 82.64 (C); 22.63 (–CH2–);
22.67 (–CH2–); 25.06 (–CH2–); 25.68 (–CH2–); 112.08
(–CH]); 114.09 (C); 118.67 (–CH]); 119.63 (–CH]);
121.44 (–CH]); 123.98 (C); 124.30 (C); 125.08 (–CH]);
4. Experimental
4.1. General
Materials. Cyclohexane, methylenechloride, diethylether,
tetrahydrofurane (THF), chloroform, hexane, ethylacetate
were purchased from CarloErba. Anhydrous acetonitrile
(analytical grade) was purchased from CarloErba and used
as received. Tetrabutylammonium hexafluorophosphate was
purchased from Fluka. Silica gel (240–400 mesh) from
Merck. Triethylphosphite, butyllithium in hexane, were
purchased from Sigma-Aldrich.

A.-E. Navarro et al. / Tetrahedron 61 (2005) 423–428
427
126.85 (–CH]); 127.11 (4!–CH]); 127.60 (2!–CH]);
127.87 (–CH]); 128.18 (4!–CH] and C); 129.63 (C);
129.85 (–CH]); 132.72 (C); 134.32 (C); 144.97 (2!C);
150.40 (C). IR (KBr) 3059, 3019, 2935, 2925, 2857, 1634,
1587, 1579, 1543, 1492, 1469, 1447, 1372, 1246, 1210,
1094, 1083, 1010, 954, 857, 837, 806, 764, 729, 701, 636,
606. MS (EI) 502 (MC, 5), 307 (30); HRMS for C33H26OS2
calcd 502.1425, found 502.1432.
1H); 7.69 (d, JZ8.8 Hz, 1H); 7.95 (d, JZ8.7 Hz, 1H). 13C
NMR (100 MHz, pyridine-d5) d: 82.70 (C); 114.08 (C); 114,
65 (–CH]); 118.84 (–CH]); 119.49 (–CH]); 121.01
(–CH]); 121.61 (–CH]); 121.78 (–CH]);125.66 (–CH]);
125.95 (–CH]); 126.02 (–CH]); 126.69 (–CH]); 127.08
(4!–CH]); 127.60 (2!–CH]); 127.95 (–CH]); 128.10
(C); 128.17 (4!–CH]); 129.47 (C); 129.93 (–CH]);
132.17(2!C);134.87(C);136.41(C);144.90(2!C);150.71
(C).UV(toluene) (log 3): 346 (4.33); 369 (4.30);415 (3.64). IR
(KBr) 3059, 3032, 2925, 2852, 1632, 1587, 1572, 1556, 1510,
1491, 1460, 1448, 1381, 1245, 1221, 1091, 1009, 841, 809,
765,753,743,734,699,614.MS(EI)498(M$C, 22), 421(12),
347 (8); HRMS for C33H22OS2 calcd 498.1112, found
498.1152.
4.1.2. 8-(Bis(1,3-dithiol-2-ylidene)-3,3-diphenyl-[3H]-
naphtho[2,1-b]pyrane 2b. In a round-bottomed flask
equipped with a dropping funnel and argon inlet were
introduced dithiolium salt 4b7 (0.20 g, 0.8 mmol), triethyl
phosphite (0.14 mL, 0.8 mmol) and NaI (0.12 g, 0.8 mmol)
in 4 mL of acetonitrile. After 2 h stirring at room temp.,
evaporation of the solvent and excess of triethyl
phosphite left the phosphonate as an oil. Dry THF
(4 mL) and chromene carbaldehyde 3 (0.29 g, 0.8 mmol)
were then added and the mixture cooled to 0 8C. n-
Butyllithium (0.5 mL, 0.8 mmol) (1.6 M in hexanes) was
added dropwise, and the mixture stirred for 2 h at room
temp. Upon addition of methanol a red precipitate and
was formed which is filtered, washed with methanol–
diethyl ether and dried. Yield 0.19 g (54%): Mp 1H
NMR (400 MHz, pyridine-d5) d: 6.26 (dd, JZ1.2,
6.7 Hz, 1H); 6.35 (d, JZ6.7 Hz, 1H); 6.63 (br s, 1H);
7.18 (d, JZ8.8 Hz, 1H); 7.22–7.34 (m, 6H); 7.26
(superimposed d, JZ9.9 Hz, 1H); 7.37 (dd, JZ1.8,
8.8 Hz, 1H); 7.44–7.50 (m, 4H); 7.57 (d, JZ1.8 Hz,
1H); 7.63 (d, JZ8.8 Hz, 1H); 7.89 (d, JZ8.8 Hz, 1H).
13C NMR (100 MHz, pyridine-d5) d: 82.65 (C); 112.73
(–CH]); 114.09 (C); 117.42 (–CH]); 117.50 (–CH]);
118.76 (–CH]); 119.56 (–CH]); 121.54 (–CH]);
124.99 (–CH]); 126.61 (–CH]); 127.09 (4!–CH]);
127.61 (2!–CH]); 127.78 (C); 127.92 (–CH]);
128.18 (4!–CH]); 129.54 (C); 129.85 (–CH]);
132.46 (C); 136.01 (–C]); 144.92 (2!C); 150 50 (C). IR
(neat) 3062, 3027, 1688, 1633, 1600, 1566, 1508, 1493, 1447,
1264, 1245, 1222, 1160, 1092, 1007, 879, 809, 762, 737, 700,
646.
4.1.4. 8-(4,5-Bis(methoxycarbonyl)-1,3-dithiol-2-yli-
dene)-3,3-diphenyl-[3H]-naphtho[2,1-b]pyrane 2d. Into
a flask of 50 mL, 421 mg (0.8 mmol) of [4,5-Bis(methoxy-
carbonyl)-1,3-dithiol-2-yl]tributyl-phosphonium tetra-
fluoroborate 6d9 are introduced in 5 mL of THF. The
reactional mixture is brought to 0 8C under argon. 200 mg
(0.55 mmol) of carboxaldehyde chromene 3 and 0.38 mL
(0.61 mmol) of nBuLi (solution 1.6 M in hexane) are added
drop by drop without the temperature exceeding 5 8C. The
addition of methanol leads to the precipitation of the
compound 2d. After filtration, 204 mg (66%) of product are
obtained in the form of a orange solid: Mp 196–197 8C; 1H
NMR (400 MHz, pyridine-d5) d: 3.87 (s, 3H); 3.89 (s, 3H);
6.31 (d, JZ9.9 Hz, 1H); 6.56 (br s, 1H); 7.23 (d, JZ8.8 Hz,
1H); 7.25–7.40 (m, 8H); 7.51 (d, JZ7.5 Hz, 4H); 7.53 (br s,
1H); 7.67 (d, JZ8.9 Hz, 1H); 7.93 (d, JZ8.8 Hz, 1H).
13C NMR (100 MHz, pyridine-d5) d: 53.30 (CH3–); 53.46
(CH3–); 82.76 (C); 114.09 (C); 115.68 (–CH]); 119.01
(–CH]); 119.37 (–CH]); 121.81 (–CH]); 125.95
(–CH]); 126.31 (–CH]); 127.06 (4!–CH]); 127.64
(2!–CH]); 128.06 (–CH]); 128.18 (4!–CH]); 128.31
(C); 129.32 (2!C); 129.68 (C); 129.97 (–CH]); 131.30
(C); 131.49 (C); 144.75 (2!C); 150.94 (C); 159.91
(OC]O); 160.35 (OC]O). IR (KBr) 3060, 3028, 2949,
2928, 1741, 1732, 1701, 1631, 1584, 1553, 1491, 1470,
1448, 1431, 1376, 1247, 1093, 1086, 1054, 1010, 868, 836,
807, 769, 756, 738, 700, 637. HRMS for C33H26OS2 calcd
564.1065, found 564.1057.
4.1.3. 8-(1,3-benzodithiol-2-ylidene)-3,3-diphenyl-[3H]-
naphtho[2,1-b]pyrane 2c. Into a flask of 50 mL, 302 mg
(1 mmol) of 4,5,6,7-tetrahydro-benzo[1,3]dithiol-1-ylium
hexafluorophosphate 4c8 0.171 mg (1 mmol) of triethyl-
phosphite, 149 mg (1 mmol) of sodium iodide and 3 mL of
acetonitrile are successively introduced. The reaction
carried out under inert argon. After 2 h of agitation at
ambient temperature the solvent were remove under vaccuo.
The resulting oil is taken again with 3 mL of anhydrous
THF and the reactional mixture is brought to 0 8C under
argon. 362 mg (1 mmol) of carboxaldehyde chromene 3 and
0.625 mL (1 mmol) of nBuLi (solution 1.6 M in hexane) are
added drop by drop without the temperature exceeding 5 8C.
The mixture is let return at ambient temperature. The
reaction is controlled by CCM with a pentane/diethylic
mixture (50:50). The addition of methanol leads to the
precipitation of the compound 2c. After filtration, 408 mg
(0.441 mmol, 44%) of product are obtained in the form of a
yellow powder: Mp 227–228 8C; 1H NMR (400 MHz,
pyridine-d5) d: 6.30 (d, JZ9.9, 1H); 6.67 (s, 1H); 7.09–7.20
(m, 2H); 7.23 (d, JZ8.8 Hz, 1H); 7.25–7.40 (m; 9H); 7.47
(br s, JZ8.7 Hz, 1H); 7.52 (d, JZ7.6 Hz, 4H); 7.68 (br s,
4.1.5. 3,3-diphenyl-8-8-[Benzo[1,3]dithiol-2-ylidene-
methyl]-[3H]-naphto-[2,1-b]pyrane
1c.
68.3 mg
(0.14 mmol) of 2c was dissolved in 75 mL of acetonitrile
containing 19.35 g (50 mmol) of tetrabutylammonium
hexafluorophosphate The solution is then oxidized under
controlled potential (0.80 V vs Ag/AgCl). The colored
solution is reduced at K0.2 V vs Ag/AgCl without any
treatment (1 mol of electron per mol of substrate). The
solvent was removed under reduce pressure and diethyl-
ether was added to the residue. Tetrabutylammonium
hexafluorophosphate precipitated and was filtered off. The
solvent was evaporated in vacuo and the crude product
was purified on a silica gel column and eluting with
methylene chloride–cyclohexane mixture (1/1). Concen-
tration under reduced pressure affords 57 mg (0.06 mmol,
83%) of yellow powder corresponding to title compound:
Mp 304–305 8C.

428
A.-E. Navarro et al. / Tetrahedron 61 (2005) 423–428
References and notes
1. (a) Bryce, M. R. Chem. Soc. Rev. 1991, 20, 355–390.
(b) Khodorkovsky, V.; Becker, J. Y. In Organic Conductors;
Farges, J.-P., Ed.; Dekker: New York, 1994. (c) Bryce, M. R. J.
Mater. Chem. 1995, 5, 1481–1496.
2. Crano, J. C.; Guglielmetti, R. J. In Organic Photochromic and
Thermochromic Compounds, Vols. 1 and 2; Kluwer Academic/
Plenum: New York, 1998.
3. Samat, A.; Lokshin, V.; Chamontin, K.; Levi, D.; Pepe, G.;
Guglielmetti, R. Tetrahedron 2001, 57, 7349–7359 and
references therein.
4. Chamontin, K.; Lokshin, V.; Rossolin, V.; Samat, A.;
Guglielmetti, R. Tetrahedron 1999, 55, 5821–5830.
¨
5. (a) Mayer, R.; Krober, H. J. Prakt. Chem. 1974, 6, 907–912.
`
(b) Frere, P.; Behamed-Gasmi, A.; Roncali, J.; Jubault, M.;
¨
Gorgues, A. J. Chim. Phys. 1995, 92, 863–866. (c) Shoberl, U.;
1H NMR (500 MHz, CDCl3) d: 6.23 (d, JZ9.9 Hz, 2H, H2),
7.05 (m, 2H, H6 ), 7.08 (m, 2H, H5 ), 7.15 (d, JZ8.9 Hz,
00
00
Salbeck, J.; Daub, J. Adv. Mater. 1992, 4, 41–44. (d) Lorcy, D.;
`
Carlier, R.; Robert, A.; Tallec, A.; le Magueres, P.; Ouahab, L.
J. Org. Chem. 1995, 60, 2443–2447. (e) Ohta, A.; Yamashita, Y.
00
00
2H, H5), 7.16 (m, 2H, H4 ), 7.21 (m, 2H, H7 ), 7.23 (d, JZ
0
0
0
9.9 Hz, 2H, H1), 7.23 (m, 4H, H4 ), 7.30 (m, 8H, H3 , H5 ),
0
0
´
Heterocycles 1995, 40, 123–126. (f) Fourmigue, M.; Johansen,
7.46 (m, 8H, H2 , H6 ), 7.61 (d, JZ8.9 Hz, 2H, H6), 7.63 (dd,
JZ8.9;1.8 Hz, 2H, H9), 7.86 (d, JZ9.0 Hz, 2H, H10), 7.91
(d, JZ1.6 Hz, 2H, H7), 13C NMR (270 MHz, CDCl3) d:
82.65 (C3), 114.16 (C1a), 118.70 (C5), 119.60 (C1), 121.39
I.; Boubekeur, K.; Nelson, C.; Batail, P. J. Am. Chem. Soc.
1993, 115, 3752–3759. (g) Yamashita, Y.; Tomura, M.; Badruz
Zaman, M.; Imaeda, K. Chem. Commun. 1998, 1657–1658.
6. Mora, H.; Fabre, J. M.; Giral, L.; Montginoul, C. Bull. Soc.
Chim. Belg. 1992, 101, 137–146.
00
(C4 ), 121.63 (C7 ), 121.87 (C10), 125.50 (C1 ), 125.57
00
(C5 ), 125.75 (C6 ), 125.93 (C9), 126.77 (C7), 127.08 (C2 ),
00
00
00
0
0
127.60 (C4 ), 127.92 (C2), 128.17 (C3 ), 128.79 (C10a),
00
129.41 (C6a), 130.12 (C6), 133.35 (C8), 136.33 (C2 ), 136.47
0
7. Schukat, G.; Fanghanel, E. Sulfur Reports 2003, 24(1–2),
1–190.
00
00
0
(C3 ), 136.56 (C8 ), 144.85 (C1 ), 150.88 (C4a); UV–Vis
(CH2Cl2) lmax nm (log 3); MS (EI) 994 (M$C, 100), 55 (15),
22 (31); HRMS for C66H42O2S4 calcd 994.2068, found
994.2060.
8. (a) Nakayama, J.; Fujiyama, K.; Oshino, M. Chem. Lett. 1975,
1099–1102. (b) Nakayama, J. Synthesis 1975, 38.
9. Sato, M.; Gonella, M. C.; Cava, M. P. J. Org. Chem. 1979, 44,
930–934.