On the synthesis and optical properties of sulfur-bridged analogues of triangulenium cations and their precursors

Article abstract of DOI:10.1002/poc.1753

Several sulfur-bridged heterocyclic carbocations of the acridinium and triangulenium family were prepared using 9-(2,6-dimethoxyphenyl)-1,8-dimethoxy- thioxanthenium tetrafluoroborate [7][BF₄] as key synthetic intermediate. Thanks to simple yet

Full text of DOI:10.1002/poc.1753

Research Article
Received: 9 March 2010,
Revised: 28 April 2010,
Accepted: 11 May 2010,
Published online in Wiley Online Library: 29 June 2010
(wileyonlinelibrary.com) DOI 10.1002/poc.1753
On the synthesis and optical properties of
sulfur-bridged analogues of triangulenium
cations and their precursorsy
a
b
a
*
´
´ ˆ
Cyril Nicolas , Gerald Bernardinelli and Jerome Lacour
Several sulfur-bridged heterocyclic carbocations of the acridinium and triangulenium family were prepared using
9-(2,6-dimethoxyphenyl)-1,8-dimethoxy-thioxanthenium tetrafluoroborate [7][BF4] as key synthetic intermediate.
Thanks to simple yet not so facile aromatic nucleophilic substitution reactions, thiachromenoacridinium, azaoxa- and
dioxathiotriangulenium salts (e.g., [8][BF4], [9][BF4], and [10][BF4], respectively) were obtained in moderate to good
yields. Importantly, from the crystal structural analysis of 9-(2,6-dimethoxyphenyl)-1,8-dimethoxy-9H-thioxanthen-
9-ol 16, bond lengths between sulfur and carbon atoms were confirmed to be much longer than that of classical C—O
or C—N in analogous frameworks. This clearly triggers a distortion of the sulfur-containing six-membered ring which
can be invoked to explain the relative lack of stabilization of the resulting carbenium ions. The increased electro-
philicity of the central carbon set off a strongly reduced reactivity towards SNAr reactions. A comparison between
electronic absorption spectra of the sulfur-bridged dyes and their aza analogues was also carried out. A ca. 50 nm shift
towards the low energy region was found to occur upon the insertion of the sulfur atom. Copyright ß 2010 John Wiley
& Sons, Ltd.
Additional supporting information may be found in the online version of this article.
Keywords: angulenium; sulfur; synthesis
hydrochloride (PyrHþClꢀ) as solvent to afford a fully ring-closed
INTRODUCTION
derivative of type 6R. The mechanism of this transformation is
probably an intramolecular ring closure from in situ generated
alkoxide moieties.
Trioxa and triaza triangulenium ions 1R and 2R (Fig. 1) are
highly stabilized carbenium ions which can be obtained in only
two steps from 1,3-dimethoxybenzene.[1,2] These compounds are
formally triphenyl methylium ions rigidified and made planar by
the bridging of all ortho positions of the aromatic rings by oxygen
and nitrogen atoms (Fig. 1).[3] Triangulenium ions and their deri-
vatives have been strongly studied because of a large array of
biological,[4–6] chemical,[5–9] photochemical/photophysical,[10–18]
stereochemical,[19–22] structural,[23–26] supramolecular,[27,28] and
synthetic[29] properties.
These derivatives have interesting properties of their own. For
instance, 4R is an effective photooxidant and derivatives may
present interesting conformations.[30,31] Quinacridinium 5R is a
highly stable carbocation (pKRþꢁ19) and one of the most con-
figurationally stable helicene.[2,32] 5R is also an interesting
platform for the discovery of new reactivity and topology.[33–35]
Compound 6R was used as a platform for the preparation of a
non-racemic diazaoxatricornan derivative.[22]
However, somewhat surprisingly, there was a general lack in
the literature of analogues of compounds 1R to 6R containing
sulfur atoms instead of oxygen or nitrogen atoms at bridging
positions.[36,37] We wondered about the origin of this omission
and about the synthetic availability of such derivatives in particu-
These derivatives are rather trivially prepared. Synthetic routes
involve tris(2,6-dimethoxyphenyl)methylium ion 3R as precursor
and successive ortho SNAr reactions of oxygen and/or nitrogen
nucleophiles. Intermediates of one-, two-, or three-ring(s) closure
can be readily isolated, and compounds 4R to 6R in particular
(Fig. 1).[9]
In fact, reactions of salts of 3R with primary (alkyl) amines lead to
the successive formation of tetramethoxyphenylacridinium 4R and
dimethoxyquinacridinium 5R cations before triazatriangulenium
2R is produced. Interestingly, each introduction of a nitrogen
bridge is more difficult than the previous one.[9] This decrease in
reactivity relies primarily on the fact that nitrogen atoms are much
better electron-donating groups than oxygen atoms thus stabili-
zing ever more strongly the central electron poor carbon upon
substitution. It implies that molecules become less electrophilic
(reactive) and more stable with polyaza substitution. Conseq-
uently, more and more forcing conditions (higher temperatures
and longer reaction times) are required to generate sequentially
4R, 5R and then 2R. Compound 5R reacts also in molten pyridine
*
a
b
y
Correspondence to: J. Lacour, Department of Organic Chemistry, University of
Geneva, 30 Quai Ernest-Ansermet, CH-1211 Geneva 4, Switzerland.
E-mail: jerome.lacour@unige.ch
C. Nicolas, J. Lacour
Department of Organic Chemistry, University of Geneva, 30 Quai Ernes-
t-Ansermet, CH-1211 Geneva 4, Switzerland
G. Bernardinelli
Laboratoire de Cristallographie, University of Geneva, Quai Ernest Ansermet
24, CH-1211 Geneva 4, Switzerland
This article is published in Journal of Physical Organic Chemistry as a special
issue on Twelfth European Symposium on Organic Reactivity, edited by Amnon
¸
Stanger, Zvi Rappoport, and Marie-Francoise Ruasse.
J. Phys. Org. Chem. 2010, 23 1049–1056
Copyright ß 2010 John Wiley & Sons, Ltd.

C. NICOLAS, G. BERNARDINELLI AND J. LACOUR
nium 7R (Fig. 2), the sulfur analogue of acridinium cations 4R, as a
key synthetic target. We hoped that it would be readily prepared
and derivatized by sequential ortho SNAr reactions of the met-
hoxy groups. In this context, the previously reported preparation
of 12 (Fig. 2) by Watanabe et al. in 1989 attracted our attention.[38]
This compound seemed ideally suited for the preparation of 7R
through a simple addition of 2-lithio-1,3-dimethoxybenzene and
a subsequent acidification of the carbinol adduct. It is following
this guideline that the synthesis of 7R was started.
Synthesis of tetramethoxyphenylthioxanthenium 7R
Following reported conditions, 2-methoxybenzoic acid 13 was
reacted with neat thionyl chloride (SOCl2) at 40 8C. In situ
distillation of SOCl2 followed by addition of a solution of diet-
hylamine in dichloromethane at ambient temperature gave
N,N-diethyl-2-methoxybenzamide 14 in excellent yield (ꢁ95%
after two steps). Using Watanabe’s conditions, 14 was deproto-
nated with s-butyllithium at low temperature (ꢀ78 8C). Addition
of powdered sulfur and slow elevation of the temperature to
25 8C yielded N,N-diethyl-2-mercapto-6-methoxybenzamide 15
in 75%. After that, reaction of 15 with a mixture of 1-bromo-2-
methoxybenzene and already lithiated N-isopropylcyclohexy-
lamide (LCI) provided a regioselective and efficient way to access
thioxanthen-9-one 12 (98%). With this compound in hand, the
extension of the chemistry to the triangulenium cations was
attempted. Thioxanthenol 16 was generated in good yield by
simple addition of (2,6-dimethoxyphenyl)lithium to 12 (84%)
using a procedure similar to that reported by Wada et al.[39] Then,
dissolution of 16 in absolute ethanol and sequential addition of
aqueous HBF4 and Et2O afforded, after filtration over a Bu¨chner
funnel, thioxanthenium tetrafluoroborate salt [7][BF4] as a green
precipitate (80%). All steps and compounds are detailed in
Scheme 1.
Figure 1. Triangulenium 1R and 2R, tris(2,6-dimethoxyphenyl)methy-
lium 3R and known nitrogen-containing cationic intermediates or deriva-
tives 4R, 5R, and 6R
lar. Herein, we report that cationic sulfur-incorporating deriva-
tives of type 7R to 10R can be prepared, characterized and
investigated for their photochemical properties. A chiral neutral
azaoxathiatricornan derivative 11 was further synthesized.
RESULTS AND DISCUSSION
Synthetic approach
As just mentioned, nitrogen-bridged derivatives of type 4R, 5R,
and 2R are simply prepared from 3R using primary amines as
nucleophiles and successive ortho SNAr reactions of the methoxy
substituents. By analogy, one could assume that sulfur-bridged
derivatives ought to be straightforwardly prepared using H2S – or
an organic form of it – as nucleophile. However, disappointingly
all attempts in our hands to add hydrogen sulfide, sodium hyd-
rosulfide or thiol/thiolate moieties to 3R and/or advanced
derivatives of type 4R and 5R led to either to a lack of reaction or
to complex mixtures of adducts that could not be easily assessed.
Late-stage introduction of sulfur atoms into carbenium deri-
vatives being a non-functional strategy, we decided to invert the
order of events. We selected a tactic consisting in the earliest
possible introduction of the sulfur atom and a post-assembly of
the oxo/aza rings. We identified tetramethoxyphenylthioxanthe-
Double-bridged derivative 8R
With salt [7][BF4] in hands, we attempted the preparation of
doubly bridged compounds, and aza-closed derivatives in parti-
cular. Following the procedure of Laursen and Krebs, salt [7][BF4]
was dissolved in NMP (25 8C) and excesses of n-propylamine or
n-octylamine (25 equiv.) were added. The green reaction media
became instantaneously colorless even after prolonged stirring.
Color did not reappear upon heating crude mixtures at 110 8C for
Scheme 1. Synthesis of thioxanthenium [7][BF4]; (a) SOCl2, 40 8C, 30 min,
97%; (b) Et2NH, CH2Cl2, 25 8C, 1 h, 95%; (c) (1) s-BuLi, TMEDA, THF, ꢀ78 8C,
1 h (2) S8, 25 8C, 12 h, 75%; (d) (1) LCI, THF, ꢀ20 8C, 10 min (2) 1-bromo-
2-methoxybenzene, 25 8C, 20 h, 98%; (e) (1) 1,3-dimethoxybenzene,
n-BuLi, TMEDA, toluene, 0 8C, 1.5 h (2) 25 8C, 24 h, 84%; (f) HBF4, EtOH,
60 min, 80%
Figure 2. Key sulfur-containing cationic (7R to 10R) and neutral (11–12)
derivatives
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J. Phys. Org. Chem. 2010, 23 1049–1056

SULFUR-BRIDGED ANALOGUES
of salt [8][BF4] (30%) was simply achieved by column
chromatography over silica gel (elution CH2Cl2/MeOH, 96/04).
Figure 3. Structure of thioxanthene 17 and leuco product 18
(R ¼ n-propyl, n-octyl)
Equation 1. Synthesis of dimethoxythiachromenoacridinium
cation 8R.
1 h. Upon precipitation of the adducts by addition of Et2O, only
thioxanthene 17 and large amounts of leuco products of type
18 were afforded (Fig. 3);[40] the chemical nature of 17 being
independently confirmed by direct reduction of [7][BF4] with
[Bu4N][BH4] in methylene chloride. In no instances could we
observe products resulting from the SNAr displacement of MeO
substituents by amine residues.
To our knowledge, this reaction is the first example of a
nucleophilic insertion of an aniline moiety at the second stage of
a 1,13-dimethoxychromenoacridinium derivative formation; this
being of course possible due to the higher electrophilicity of
cation 7R.[42] Most probably, the molecular framework of cation
8
R is that of a cationic [4]helicene.[43–51] Finally evaporation of the
etherate phase yielded, to our surprise, thioxanthene 17 in almost
60% yield. The reason for this surprising formation of 17 under a
controlled atmosphere and in the absence of readily oxidized
amines is still under evaluation.
In fact, the driving force towards SNAr reactions originates in
a delicate balance between the electron-poor nature of the
substrates thanks to the presence of the positive charge and a
lack of electrophilicity of the central carbon ensured by steric and
electronic factors. Obviously and unfortunately, the introduction
of a sulfur atom modifies the chemical nature of the carbenium
substrate profoundly. Its electrophilicity and electron-reducing
ability is greatly enhanced by the heteroatom.[37,41] Conseq-
uently, the ortho MeO positions are not submitted to nucleophilic
substitution anymore but the central carbon center is preferen-
tially attacked instead. Consequently, when excesses of amines
are added to salt [7][BF4] at an ambient temperature, neutral
unreactive leuco adducts are formed immediately. However,
unlike in case of acridinium ions 4R, this addition step is not
reversible.[9] Concerning 17, we assume that its formation is
primarily the consequence of an aerobic photooxidation of
primary n-propyl and n-octylamine to n-propyl and n-octylimine,
respectively.[30]
Longer reaction times and/or addition of benzoic acid as
to reduce the nucleophilic character of the alkylamines or as to
protonate the in situ generated 18 and allow a dissociation to
take place did not change the outcome of the reaction. The
reactions were also carried out under dinitrogen atmosphere as
to decrease potentially the formation of 17 but the outcome
was the same. Finally, when we tried to carry the reaction under
strongly elevated temperatures, degradation products were
obtained.
Triple-bridged derivatives 9R and 10R
With that result in hand, it was then decided to synthesize fully
ring-closed triangulenium derivatives that would contain the
sulfur atom and N/O residues (derivatives 9R and 10R, Figs. 2
and 4). Preparation of [9][BF4] was achieved by heating a mixture
of aniline and [7][BF4] to higher temperature (190 8C). In this case,
the addition of benzoic acid was not necessary as the very high
temperature allowed the spontaneous dissociation of the leuco
product. Obviously, cation 8R is obtained as an intermediate
which reacts further by in situ ring closure to give 9R. To afford
analytically pure salt [9][BF4], the Et2O precipitate from the crude
mixture was dissolved in a 1:2 mixture of CH3CN/EtOH. Selective
crystallization by slow evaporation afforded the resulting purple
dye in moderate yield (30%).
[7][BF4] was also converted into the fully ring-closed dioxat-
hiotriangulenium [10][BF4] in excellent yield (73%) upon (i) heat-
ing salt [7][BF4] in molten pyridine hydrochloride as solvent
(200 8C, 4 h), (ii) dissolution of the crude in CH2Cl2, and (iii) a
treatment with aq. HBF4.
Azaoxathiatricornan derivative 11
At this stage, with unsymmetrically substituted salt [9][BF4] in
hands, we decided to test the feasibility of the addition of an
With these results in hands, trying to prevent the formation of
compounds of type 17 and 18, we turned our attention towards
the addition of primary amines that would be (i) devoid of hyd-
rogen atom(s) on the carbon a to the nitrogen and (ii) weaker
nucleophiles respectively. Aromatic amines appeared to be good
candidates and aniline in particular. As such, salt [7][BF4] was
added to a mixture of 3 equiv. of benzoic acid and aniline used as
solvent under a dinitrogen atmosphere (Eqn 1). The solution
became immediately colorless meaning that the formation of the
leuco derivative was still operating. However, after being heated
at 110 8C for several minutes, the reaction turned green and it was
stirred for 22 h at that temperature. Then, at room temperature,
precipitation of a dark green material was afforded by addition of
Et2O to the reaction crude. A mixture of dimethoxythiachrome-
noacridinium 8R and traces of asymmetrically substituted
azaoxathiotriangulenium 9R was detected upon by electrospray
Figure 4. Synthesis of S-containing triangulenium cations [9][BF4] and
[10][BF4]
1
mass spectrometry and H-NMR spectroscopy analysis. Isolation
J. Phys. Org. Chem. 2010, 23 1049–1056
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C. NICOLAS, G. BERNARDINELLI AND J. LACOUR
organometallic reagent to the carbocationic center;[23–26] the
resulting azaoxathiatricornan being most probably another
example of a chiral bowl-shaped molecule.[22] MeLi (1.6 equiv.)
was added to a solution of salt [9][BF4] in THF at 0 8C. The reaction
medium lost quasi instantaneously its purple color. After 4 h of
reaction (0–25 8C), a traditional work-up and a purification by
column chromatography of the crude mixture (Al2O3, elution
CH2Cl2/pentane, 80/20), the desired compound 11 was afforded
in 55% isolated yield (Eqn 2). This modest yield does not seem to
be due to a post-degradation of 11 as no formation of colorful
adducts was observed during the chromatographic purification.
Figure 6. UV/VIS spectra of [7][BF4], [8][BF4], [9][BF4] and [10][BF4]
recorded in CH3CN (c 3.1–8.4 ꢂ 10ꢀ5 mol Lꢀ1
)
Equation 2. Azaoxathiatricornan 11.
X-ray structural analysis
To confirm this possibility, many efforts were directed towards
growing monocrystals of 11 and of salts [7][BF4], [8][BF4], [9][BF4],
and [10][BF4]. Unfortunately, high quality crystals were never
obtained for these derivatives. Only in the case of thioxanthenol
16 we could obtain colorless crystals of sufficient quality for X-ray
structural analysis be grown from a chloroform solution. As
shown in Fig. 5, the torsion angle between the 2,6-dimethoxy-
phenyl moiety and the thioxanthene skeleton was found to be
close to 908. This perpendicular arrangement of the two ring
systems can be attributed to the steric bulk of the methoxy
substituents but also to a promoted an intramolecular hydrogen
bond interaction between hydrogen H01 and oxygen O5
˚
(dH01–05 ¼ 2.03(3), dO1–O5 ¼ 2.620(3) A, angleO1-H01–O5 ¼ 136(3)8,
see atom numbering on Fig. 5). As expected, bond lengths
between sulfur and carbon atoms (mean S—C distance ¼
˚
1.750 A) were found to be much longer than carbon–carbon of
˚
the thioxanthene central ring (mean C—C distance ¼ 1.468 A).
This trend triggers a significant distortion of the central six-
membered ring of the thioxanthene system. Most probably, it is
Figure 5. Ortep view of the crystal structure of carbinol 16
Figure 7. Electronic absorption spectra. Nitrogen versus sulfur substitution
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SULFUR-BRIDGED ANALOGUES
conserved in all the subsequent derivatives and cation 7R in
particular. It leads, along with electronic effects,[42] to the obser-
ved loss of carbocation stability and increase of electrophilic
reactivity of the central carbon.[43–51]
energy region was found to occur upon the insertion of the sulfur
atom.
EXPERIMENTAL
Materials and measurements
Photochemical properties
Otherwise stated solvents and chemicals were purchased and
used as received. NMR spectra were recorded on an AMX-300
and 400 MHz apparatus at 298K. Assignments have been achi-
As briefly mentioned, novel salts [7][BF4], [8][BF4], [9][BF4], and
[10][BF4] are colorful dyes and their electronic absorption
spectra were recorded and are presented in Fig. 6 (CH3CN, c
3.1–8.4 ꢂ 10ꢀ5 mol Lꢀ1). All derivatives are characterized by
moderately strong absorptions in the visible region (4120 < e <
11720 Mꢀ1 cmꢀ1), which are separated from the somewhat
intense UV transitions that start to emerge below 360 nm.
Thioxanthenium [7][BF4] displays a maximum absorption band
(lmax) at relatively high energy and a moderate maximum ext-
inction coefficient (emax) (lmax ¼ 462 nm; emax ꢁ 4750), the salt
absorbing however essentially continuously up to 660 nm. The
absorption spectrum of [8][BF4] was found to be essentially
identical (lmax ¼ 483 nm; emax ꢁ 4120) to that of [7][BF4] (see
Fig. 6). This was somewhat surprising at first as we expected
the insertion of the electron donating N-atom to increase
resonance and thus entail batho- and hyperchromic effects. One
possible explanation for this lack of change is structural given
the potentially distorted helical conformation of the cationic [4]
helicene induced by the sulfur atom. Compounds [9][BF4] and
[10][BF4] behave rather differently; lmax and emax values being at
lower energies and of higher intensities, respectively.
Finally, the influence of sulfur versus nitrogen was monitored in
two-by-two comparisons of compounds 7R, 8R, and 9R with the
previously reported analogues 4R, 5R, and 6R.[9] The spectral
comparisons are detailed in Fig. 7. Globally, a ꢁ50 nm lmax shifts
towards the low energy region can be observed on average for all
(single-, double-, and triple-bridged) compounds upon a replace-
ment of a nitrogen by a sulfur atom. However, whereas single-
and triple-bridged N-/S-systems displayed absorptions with
rather similar e values, a dramatic difference between extinction
coefficients was detected in the double-bridged series (e ꢁ 18360
and 4120 for compounds 5R[22] and 8R, respectively).
1
eved using COSY and/or INVIET experiments. H-NMR: chemical
shifts are given in ppm relative to Me4Si with the solvent res-
onance used as the internal standard (CD3CN d ¼ 1.94 ppm;
CD2Cl2 d ¼ 5.30 ppm; CDCl3 d ¼ 7.26 ppm). Data were reported
as follows: chemical shift (d) in ppm on the d scale, multiplicity
(s ¼ singlet, d ¼ doublet, t ¼ triplet, and m ¼ multiplet), coupling
constant (Hz), and integration. 13C-NMR (100 and 75 MHz):
chemical shifts were given in ppm relative to Me4Si, with the
solvent resonance used as the internal standard (CD3CN d ¼ 1.32
and 118.26 ppm; CD2Cl2 d ¼ 53.52 ppm; CDCl3 ¼ 77.16 ppm). For
19F NMR, chemical shifts were given in ppm using C6F6 as
reference. IR spectra were recorded with a Perkin-Elmer 1650
FT-IR spectrometer using a diamond ATR Golden Gate sampling
and are reported in wavenumbers (cmꢀ1). Melting points (Mp)
were measured in open capillary tubes on a Stuart Scientific
SMP3 melting point apparatus and were uncorrected. UV spectra
were measured with a 1.0 cm quartz cell; lmax are given in nm and
molar absorption coefficient e in cmꢀ1 dm3 molꢀ1. Mass deter-
mination was recorded with a Finnigan SSQ 7000 Electrospray
mass spectrometer (ESI-MS). Accurate mass measurements were
performed on a quadrupole-time of flight instrument (QStar XL,
AB/MDS Sciex) using electrospray positive mode ionization. The
analytes were infused at typically 5–10 mL/min using a Haward
syringe pump. The instrument was optimized in such a way that
up-front collision induced dissociation was minimized and the
resolution was of about 10000. Crystal structure analysis of 16 is
contained in the CIF file provided as supporting information.
Synthetic procedures
9-(2,6-Dimethoxyphenyl)-1,8-dimethoxy-9H-thioxanthen-9-ol 16
CONCLUSION
The reaction was carried out under a dinitrogen atmosphere by
means of an inert gas/vacuum double manifold line and standard
Schlenk techniques. Toluene and TMEDA was dried and distilled
prior to use. To a solution mixture of 1,3-dimethoxybenzene
(1.04 mL, 8.05 mmol) and TMEDA (302 mL, 2.00 mmol) in toluene
(35 mL) at 0 8C was added n-BuLi in hexane (4.60 mL, c ¼ 1.60 M,
7.38 mmol). The resulting yellow solution was stirred an addi-
tional 30 min at 0 8C and allowed to reach room temperature
(ꢁ20 8C) over a period of 15 min. The mixture was further stirred
at the same temperature during 1 h 30 min and added via
cannula to a suspension of 1,8-dimethoxy-9H-thioxanthen-9-one
12 (1.82 g, 6.67 mmol) in toluene (60 mL) in a 250 mL two necked
round bottom flask surrounded by a reflux condenser. The reac-
tion mixture became instantaneously brown. After 24 h at 50 8C
the black reaction was cooled down and evaporated in vacuo as
to give 2.38 g of a yellow precipitate. The titled compound was
suspended in Et2O (100 mL), collected by filtration over Bu¨chner
funnel and further purified by addition of Et2O (ꢁ200 mL)
affording 16 as a light yellow precipitate (2.30 g, 5.60 mmol, 84%).
1H NMR (CD2Cl2, 300 MHz): d ¼ 7.58 (s, 1H), 7.15–6.95 (m, 3H), 6.78
A series of novel sulfur-bridged heterocyclic carbocations of the
acridinium and triangulenium family was prepared using 9-(2,6-
dimethoxyphenyl)-1,8-dimethoxy-thioxanthenium tetrafluorobo-
rate [7][BF4] as key synthetic intermediate. Thanks to simple yet
not so facile aromatic nucleophilic substitution reactions, thia-
chromenoacridinium, azaoxa- and dioxathiotriangulenium salts
[8][BF4], [9][BF4], and [10][BF4] were obtained in moderate to
good yields. From the crystal structural analysis of carbinol 16,
bond lengths between sulfur and carbon atoms were confirmed
to be much longer than that of classical C—O or C—N in ana-
logous frameworks. This clearly triggers a distortion of the
sulfur-containing six-membered ring which can be invoked to
explain the relative lack of stabilization of the resulting carbe-
nium ions; the lower p-electron-donating ability of sulfur versus
oxygen being also responsible for this effect.[42] The increased
electrophilicity of the central carbon set off a strongly reduced
reactivity towards SNAr reactions. A comparison between elect-
ronic absorption spectra of the sulfur-bridged dyes and their aza
analogues was also carried out. A 50 nm shift towards the low
J. Phys. Org. Chem. 2010, 23 1049–1056
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C. NICOLAS, G. BERNARDINELLI AND J. LACOUR
(d, J ¼ 7.82 Hz, 2H), 6.62 (d, J ¼ 8.01 Hz, 2H), 6.62 (s, br, 1H), 6.35 (s,
br, 1H), 4.08 (s, br, 3H), 3.53 (s, 6H), 3.17 (s, br, 3H); 13C NMR (CD2Cl2,
75 MHz): d ¼ 158.6 (C), 129.7 (C), 127.9 (C), 127.1 (CH), 126.9 (CH),
125.5 (C), 116.4 (CH), 110.1 (CH), 74.1 (C), 56.6 (OCH3), 55.9 (OCH3);
UV/VIS (CH2Cl2, 4.63 ꢂ 10ꢀ5 M, lmax (log e)): 259 (1.38), 274 (3.60),
279 (2.43), 303 (8.94); IR (neat): n ¼ 3495, 2989, 2931, 2896, 2833,
1584, 1564, 1473, 1455, 1429, 1374, 1307, 1270, 1249, 1155, 1114,
1082, 1049, 1018, 949, 916, 864, 853, 783, 773, 743, 702, 603,
582 cmꢀ1; MS (ESI, m/z): 393.3 (Mþ, 100%); 347.3 (53%); 301.3
(22%); 257.3 (57%); 241.3 (58%); HRMS (EI, m/z): Calcd for
C23H22O5S [Mþ]: 410.118796. Found: 410.118350; Mp: >285 8C
(decomposition).
1574, 1499, 1477, 1455, 1435, 1422, 1346, 1285, 1266, 1237, 1196,
1182, 1174, 1095, 1035, 982, 858, 788, 772, 730, 704, 987, 663, 652,
631, 599, 571, 534 cmꢀ1; MS (ESI, m/z): 422.5 (Mþ, 88.3%), 376.3
(100%); HRMS (ESI-TOF, m/z): Calcd for C27H20NO2Sþ [Mþ]:
422.1209. Found: 422.1203; Mp: 308 8C (decomposition).
4-Phenyl-4-aza-8-oxa-12-thiotriangulenium tetrafluoroborate
[9][BF4]
[7][BF4] (100 mg, 2.08 mmol) and aniline (3.5 mL, 380 mmol) were
inserted in a 10 mL round bottom flask under dinitrogen
atmosphere. The initially colorless reaction mixture was heated
at 190 8C for 22 h and allowed to cool to room temperature.
Unreacted aniline was distilled off under reduced pressure (90 8C,
10ꢀ1 mbar). The residual oil was thoroughly washed with 200 mL
of Et2O affording the titled compound as a purple precipitate.
Further purification was carried out by dissolution of the pre-
cipitate in a minimum of CH3CN, addition of EtOH (twice the
CH3CN volume) and slow evaporation under vacuum condenser
9-(2,6-Dimethoxyphenyl)-1,8-dimethoxy-thioxanthenium
tetrafluoroborate [7][BF4]
Aqueous HBF4 (7 mL, 50%) was added to a solution of
9-(2,6-dimethoxyphenyl)-1,8-dimethoxy-9H-thioxanthen-9-ol 16
(0.60 g, 1.46 mmol) in absolute ethanol (15 mL). After stirring
further 60 min, diethyl ether was added (50 mL). The dark-green
precipitate formed was collected by filtration and thoroughly
washed with additional Et2O, yielding [7][BF4] (0.56 g, 1.17 mmol,
80%) as a green solid. 1H NMR (CD3CN, 400 MHz): d ¼ 8.19 (t,
J ¼ 8.34 Hz, 2H), 8.04 (d, J ¼ 8.34 Hz, 2H), 7.47 (t, J ¼ 8.34 Hz, 1H),
7.29 (d, J ¼ 8.34 Hz, 2H), 6.79 (d, J ¼ 8.34 Hz, 2H), 3.57 (s, 6H), 3.56
(s, 6H); 13C NMR (CD3CN, 100 MHz): d ¼ 169.4 (C), 165.6 (C), 156.7
(C), 147.0 (C), 141.0 (CH), 131.2 (CH), 124.2 (C), 121.2 (C), 119.6
(CH), 112.2 (CH), 104.8 (CH), 58.3 (OCH3), 56.8 (OCH3); 19F NMR
(CD3CN, 282 MHz): d ¼ ꢀ151.78 (20%); ꢀ153.84 (80%); UV/VIS
(CH3CN, 4.2 ꢂ 10ꢀ5 M, lmax (log e)): 353 (1.60), 462 (4.75), 632
(2.42); IR (neat): n ¼ 3006, 2949, 2845, 1587, 1548, 1477, 1457,
1436, 1420, 1383, 1298, 1283, 1244, 1195, 1146, 1107, 1048, 1030,
869, 854, 795, 774, 739, 701, 667, 641, 624, 597, 571, 519,
504 cmꢀ1; MS (ESI, m/z): 393.3 (Mþ, 100%); 347.3 (79%); 301.3
(47%); 257.3 (68%); 241.3 (79%); 226.3 (32%); HRMS (ESI-TOF, m/z):
Calcd for C23H21O4Sþ [Mþ]: 393.1155. Found: 393.1160; Mp:
246 8C.
1
yielding [9][BF4] as purple needles (29 mg, 0.06 mmol, 30%). H
NMR (CD3CN, 300 MHz): d ¼ 8.06 (t, J ¼ 8.58 Hz, 1H), 7.99 (t,
J ¼ 8.20 Hz, 1H), 7.96–7.81 (m, 4H), 7.77 (d, J ¼ 7.63 Hz, 1H), 7.68 (d,
J ¼ 8.20 Hz, 1H), 7.59–7.41 (m, 4H), 6.97 (d, J ¼ 8.76 Hz, 1H), 6.82 (d,
J ¼ 8.76 Hz, 1H); 13C NMR (CD3CN, 75 MHz): d ¼ 155.7 (C), 153.0 (C),
145.9 (C), 145.3 (C), 142.5 (C), 140.6 (CH), 138.4 (CH), 138.3 (C),
138.1 (CH), 137.4 (C), 137.1 (C), 133.1 (CHPh), 132.3 (CH), 128.8
(CHPh), 122.1 (CH), 120.9 (CH), 115.8 (CH), 115.4 (CH), 115.3 (C),
113.0 (C), 112.2 (C), 112.1 (CH), 110.2 (CH); 19F NMR (CD3CN,
282 MHz): d ¼ ꢀ151.80 (20%); ꢀ151.85 (80%); UV/VIS (CH3CN,
8.42 ꢂ 10ꢀ5 M, lmax (log e)): 493 (6.46), 555 (8.27), 596 (11.72); IR
(neat): n ¼ 3082, 1629, 1583, 1569, 1548, 1521, 1497, 1476, 1452,
1434, 1383, 1349, 1277, 1262, 1232, 1185, 1158, 1054, 1022, 958,
906, 884, 848, 815, 751, 739, 702, 648, 636, 624, 611, 585,
548 cmꢀ1; MS (ESI, m/z): 376.3 (Mþ, 100%); 299.3 (6.6%); 245.5
(10%); HRMS (ESI-TOF, m/z): Calcd for C25H14NOSþ [Mþ]: 376.0790.
Found: 376.0799; Mp: 388 8C.
4,8-Dioxa-12-thiotriangulenium tetrafluoroborate [10][BF4]
1,13-Dimethoxy-9-phenyl-thiachromenoacridinium
tetrafluoroborate [8][BF4]
[7][BF4] (174.5 mg, 0.36 mmol) was added to molten pyridine
hydrochloride (9.30 g) and the reaction mixture heated to
approximately 200 8C for 4 h. The reaction was allowed to reach
room temperature and aqueous HBF4 (130 mL, 15.6%) was added.
The aqueous phase was extracted with CH2Cl2 (2 ꢂ 70 mL). The
combined organic extracts were washed further with aqueous
HBF4 (120 mL, 50%), dried under Na2SO4, and evaporated in
vacuo. The titled compound was suspended into CHCl3 (20 mL),
collected by filtration over Bu¨chner funnel and thoroughly
washed with CHCl3 (20 mL) which afforded [10][BF4] as a dark
Benzoic acid (40 mg, 32.8 mmol) and aniline (3.06 g, 328 mmol)
were added to [7][BF4] salt (53 mg, 11.0 mmol) in a 50 mL round
bottom flask. The reaction mixture was heated at 110 8C for 22 h
and allowed to cool to room temperature. Addition of Et2O
(50 mL) afforded a green precipitate, which was filtered over
Bu¨chner funnel washed with additional Et2O (50 mL) and coll-
ected. The titled compound was further purified by chromatog-
raphy over silica gel (CH2Cl2/MeOH, 96/04, L ¼ 13.6 cm, Ø ¼ 1 cm,
Rf ¼ 0.23) yielding [8][BF4] as a green solid (17.0 mg, 0.033 mmol,
1
pink solid (102 mg, 0.26 mmol, 73%). H NMR (CD2Cl2, 300 MHz):
1
30%). H NMR (CD2Cl2, 300 MHz): d ¼ 7.95–7.78 (m, 6H), 7.70 (t,
d ¼ 8.36 (t, br, J ¼ 8.19 Hz, 1H), 8.25 (t, br, J ¼ 8.20 Hz, 2H), 7.97 (d,
J ¼ 8.20 Hz, 2H), 7.77 (d, J ¼ 8.39 Hz, 2H), 7.66 (d, J ¼ 8.47 Hz, 2H);
13C NMR (CD2Cl2, 75 MHz): d ¼ 157.0 (C), 153.7 (C), 143.5 (CH),
141.0 (CH), 139.8 (C), 123.0 (CH), 116.2 (CH), 113.0 (CH); 19F NMR
(CD2Cl2, 282 MHz): d ¼ ꢀ151.7 (20%); ꢀ151.8 (80%); UV/VIS
(CH3CN, 3.1 ꢂ 10ꢀ5 M, lmax (log e)): 489 (5.67), 535 (5.64), 570
(7.06); IR (neat): n ¼ 1640, 1592, 1574, 1509, 1435, 1350, 1322,
1275, 1251, 1225, 1192, 1164, 1091, 1033, 966, 890, 815, 783, 737,
695, 656, 606, 572; MS (ESI, m/z): 301.3 (Mþ, 100%); HRMS (ESI-TOF,
m/z): Calcd for C19H9O2Sþ [Mþ]: 301.0317. Found: 301.0319; Mp:
347 8C.
J ¼ 8.10 Hz, 1H), 7.60–7.48 (m, 1H), 7.46–7.35 (m, 2H), 7.12 (d,
J ¼ 8.10 Hz, 1H), 7.20–6.90 (m, 2H), 6.79 (d, J ¼ 8.95 Hz, 1H), 3.78 (s,
3H), 3.68 (s, 3H); 13C NMR (CD2Cl2, 75 MHz): d ¼ 160.3 (C), 159.5 (C),
148.5 (C), 143.5 (C), 141.5 (C), 139.5 (C), 139.4 (CH), 137.3 (C), 135.6
(CH), 134.7 (C), 134.5 (CH), 132.3 (CH), 131.6 (CH), 131.4 (CH), 128.7
(CH), 127.5 (CH), 123.2 (C), 120.3 (CH), 120.1 (C), 118.5 (CH), 117.5
(C), 114.2 (CH), 110.1 (CH), 108.5 (CH), 104.2 (CH), 56.2 (OCH3), 55.7
(OCH3); 19F NMR (CD2Cl2, 282 MHz): d ¼ ꢀ153.27 (20%); ꢀ153.32
(80%); UV/VIS (CH3CN, 3.9 ꢂ 10ꢀ5 M, lmax (log e)): 304 (14.2), 368
(2.57), 483 (4.12), 600 (3.75), 632 (3.50); IR (neat): n ¼ 1726, 1613,
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J. Phys. Org. Chem. 2010, 23 1049–1056

SULFUR-BRIDGED ANALOGUES
12c-Methyl-12-phenyl-8-aza-4-oxa-12-thia-tricornan 11
[3] Compounds 1 and 2 are 4,8,12-trioxadibenzo[cd,mn]pyrene and
4,8,12-trialkyl-8,12-dihydro-4H-benzo[1,8][2,7]naphthyridino[3,4,5,6-
klmn]acridine cations respectively.
The reaction was conducted under dinitrogen atmosphere. To a
suspension of 4-Phenyl-4-aza-8-oxa-12-thiotriangulenium tetra-
fluoroborate [9][BF4] (47.6 mg, 0.10 mmol) in THF (4 mL) at 0 8C
was added an excess of MeLi in ether (100 mL, 0.16 mmol). The
purple suspension turned to a colorless solution. The reaction
mixture was allowed to reach room temperature (2 h) and further
stirred during 2 h. The reaction was quenched by addition of
two drops of ethanol, and ether (60 mL). The organic layer was
washed with water (3 ꢂ 60 mL), dried over Na2SO4 and con-
centrated under reduced pressure. The titled compound was
purified by flash chromatography over basic alumina (CH2Cl2/
pentane, 80/20, L ¼ 9 cm, Ø ¼ 2.3 cm, Rf ¼ 0.47) yielding 11 as a
colorless viscous residue (22.0 mg, 0.056 mmol, 55%). 1H NMR
(CD2Cl2, 400 MHz): d ¼ 7.64 (t, J ¼ 7.83 Hz, 2H), 7.53 (t, J ¼ 7.08 Hz,
1H), 7.33 (d, J ¼ 7.84 Hz, 2H), 7.21 (t, J ¼ 7.33 Hz, 1H), 7.06 (d,
J ¼ 7.83 Hz, 1H), 7.00–6.82 (m, 4H), 6.68 (d, J ¼ 8.09 Hz, 1H), 6.12 (d,
J ¼ 8.33 Hz, 1H), 5.96 (d, J ¼ 8.34 Hz, 1H), 1.56 (s, 3H); 13C NMR
(CDCl3, 100 MHz): d ¼ 151.6 (C), 151.6 (C), 141.6 (C), 141.5 (C), 140.7
(C), 131.5 (C), 131.2 (C), 131.1 (CH), 128.8 (CH), 128.0 (CH), 127.8
(CH), 127.2 (CH), 124.0 (C), 121.7 (C), 120.3 (CH), 118.4 (CH), 114.4
(CH), 112.7 (CH), 111.2 (C), 108.8 (CH), 108.5 (CH), 32.16 (C), 27.9
(CH3); IR (film): n ¼ 3060, 2953, 2923, 2853, 1617, 1604, 1584, 1496,
1471, 1443, 1357, 1333, 1306, 1255, 1221, 1181, 1144, 1095, 1070,
1044, 1003, 973, 935, 870, 834, 769, 732, 700, 662, 637, 616, 589,
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.
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9-(2,6-Dimethoxyphenyl)-1,8-dimethoxy-9H-thioxanthene 17
To a solution of [7][BF4] (22.0 mg, 0.045 mmol) in CH2Cl2 (4 mL)
was added tetrabutylammonium borohydride nBu4NBH4 (12.80 mg,
0.05 mmol) at room temperature. The green solution became
spontaneously colorless. The reaction mixture was stirred for 30 s
and was concentrated under reduced pressure. The white residue
was purified by chromatography over silica gel (CH2Cl2/pentane,
50/50, L ¼ 8.7 cm, Ø ¼ 2.3 cm, Rf ¼ 0.36) affording the product 17
as a white solid (9.9 mg, 0.025 mmol, 55%). 1H NMR (CD2Cl2,
300 MHz): d ¼ 7.07 (t, J ¼ 8.39 Hz, 1H), 7.06 (t, J ¼ 8.00 Hz, 2H), 6.78
(d, J ¼ 7.91 Hz, 2H), 6.59 (d, J ¼ 8.1 Hz, 2H), 6.52 (d, J ¼ 8.30 Hz, 2H),
6.41 (s, 1H), 3.82 (s, 6H), 3.70 (s, 6H); 13C NMR (CD2Cl2, 75 MHz):
d ¼ 159.0 (C), 158.2 (C), 133.5 (C), 126.9 (2 ꢂ CH), 122.6 (C), 121.9
(C), 117.3 (CH), 107.9 (CH), 104.3 (CH), 55.6 (OCH3), 55.3 (OCH3),
29.5 (CH); IR (neat): n ¼ 3329, 2991, 2930, 2830, 1693, 1646, 1621,
1586, 1558, 1472, 1461, 1430, 1372, 1333, 1308, 1271, 1242, 1213,
1149, 1110, 894, 885, 850, 808, 782, 765, 741, 718, 707, 683, 642,
625, 603, 580 cmꢀ1; HRMS (ESI-TOF, m/z): Calcd for C23H22NaO4Sþ
[Mþ]: 417.1136. Found: 417.1131; Mp: >320 8C (decomposition).
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synthesized. See the next reference.
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[40] As determined by 1H-NMR and electrospray mass spectrometry
analysis.
We are grateful for financial support of this work by the Swiss
National Science Foundation, the State Secretariat for Education
´ ´
´
`
and Research, and the Societe Academique de Geneve.
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p-electron-donating ability of sulfur vs. oxygen (sþ ꢀ0.16 and ꢀ0.65
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J. Phys. Org. Chem. 2010, 23 1049–1056