Diazadithia[7]helicenes: Synthetic exploration, solid-state structure, and properties

Article abstract of DOI:10.1002/chem.201300843

Diazadithia[7]helicenes were synthesized from the readily available building block ethyl 7-chloro-8-formylthieno[3,2-f]quinoline-2-carboxylate by a Wittig reaction-photocyclization strategy. The helicene core was functionalized by nucleophilic aromatic substitution with a variety of nucleophiles (e.g., O-, N-, and C-centered) and palladium-catalyzed reactions such as Suzuki coupling and Buchwald-Hartwig amination. Racemization studies confirmed that the enantiopure forms of these [7]helicenes are conformationally stable compared to their lower analogues. The solid-state structures of the novel diazadithia[7]helicenes were determined by single-crystal X-ray diffraction. The crystal structures of these azathia[7]helicenes show columnar stacking in antiparallel fashion. The HOMO-LUMO gaps of the new compounds were determined on the basis of electrochemical and optical measurements.

Full text of DOI:10.1002/chem.201300843

FULL PAPER
Heterahelicenes: Diazadithia[7]heli-
cenes were synthesized from the read-
ily available building block ethyl 7-
Helicenes
D. Waghray, A. Cloet, K. Van Hecke,
S. F. L. Mertens, S. De Feyter,
chloro-8-formylthienoACTHNUGTRNEUNG[3,2-f]quinoline-
2-carboxylate by a Wittig reaction–
photocyclization strategy. The helicene
core was functionalized by nucleophilic
aromatic substitution with a variety of
nucleophiles, Suzuki coupling, and
Buchwald–Hartwig amination. Race-
mization studies confirmed that the
enantiopure forms of these [7]heli-
cenes (see figure) are conformationally
more stable than their lower ana-
logues.
L. Van Meervelt, M. Van der Auweraer,
W. Dehaen* ................... &&&& — &&&&
Diazadithia[7]helicenes: Synthetic
Exploration, Solid-State Structure, and
Properties
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DOI: 10.1002/chem.201300843
Diazadithia[7]helicenes:
Synthetic Exploration, Solid-State Structure, and Properties
Deepali Waghray,[a] Arvid Cloet,[b] Kristof Van Hecke,[c] Stijn F. L. Mertens,[b]
Steven De Feyter,[b] Luc Van Meervelt,[d] Mark Van der Auweraer,[b] and Wim Dehaen*[a]
Abstract: Diazadithia[7]helicenes were
synthesized from the readily available
building block ethyl 7-chloro-8-
as Suzuki coupling and Buchwald–
Hartwig amination. Racemization stud-
ies confirmed that the enantiopure
forms of these [7]helicenes are confor-
mationally stable compared to their
lower analogues. The solid-state struc-
tures of the novel diazadithia[7]heli-
cenes were determined by single-crys-
tal X-ray diffraction. The crystal struc-
tures of these azathia[7]helicenes show
columnar stacking in antiparallel fash-
ion. The HOMO–LUMO gaps of the
new compounds were determined on
the basis of electrochemical and optical
measurements.
formylthienoACHTUNGTRENNUNG[3,2-f]quinoline-2-carboxy-
late by a Wittig reaction–photocycliza-
tion strategy. The helicene core was
functionalized by nucleophilic aromatic
substitution with a variety of nucleo-
philes (e.g., O-, N-, and C-centered)
and palladium-catalyzed reactions such
Keywords: chiral resolution · cycli-
zation · helical structures · heli-
cenes · Wittig reactions
Introduction
eters such as dihedral angles and bond lengths that modify
the configurational stability (e.g., racemization barriers),
and are thus relevant to potential applications of these com-
pounds in materials science. Over the past years, helicenes
have been extensively studied due to their self-assembly in
the solid state, their ability to behave as organic conductors,
and their use in optical resolution and molecular and biomo-
lecular recognition.[3]
Heterahelicenes are a special type of condensed aromatic
molecules, as they consist of ortho-annulated aromatic or
heteroaromatic rings which arrange in a non-planar manner
due to steric strain of the terminal rings, and thus give rise
to helical chirality.[1] Helicenes are an interesting class of
conjugated molecules currently being investigated for opto-
electronic application.[2] These inherently chiral molecules
Aza- and thiahelicenes are a subgroup of heterahelicenes.
Although an overview of the literature over the last decade
highlighted carbohelicenes[4] as dominant helical frame-
works, heterahelicenes[5] such as oxa-, aza-, and thiaheli-
cenes recently emerged as an extremely attractive class of
compounds. The presence of sulfur atoms has been shown to
enhance the electronic and optical properties of thiaheli-
cene-based materials. On the other hand, starting from a
helicene backbone having more than one nitrogen atom, in-
teresting supramolecular complexes can be formed. These
compounds show a tendency toward p–p* stacking and
building of columnar systems, which can form the basis for
optoelectronic applications.[6] Azahelicene derivatives have
been reported to have potential applications in the field of
asymmetric catalysis, self-assembly, and metal coordination
complexes,[7] whereas thiahelicenes are appealing candidates
for chiral NLO materials, chiral catalysts, and asymmetric
inducers and have been used as building blocks for helical
conjugated polymers.[8] Combining the features of aza- and
thiahelicenes would be an interesting aspect to study. We en-
visage that these bifunctional analogues comprising p-rich
thiophene and p-deficient pyridine units would be potential-
ly more valuable. The presence of terminal thiophene units
could lead to regioselective a-functionalization of the ring
system. Pyridine nitrogen atoms in the chiral helicenes can
serve as hydrogen acceptors and metal chelating agents for
combine both electronic and chiroptical properties, which
can be attributed to their extended p-conjugated system and
their peculiar helixlike structure. The synthesis of regiode-
fined heterahelicenes is of significant interest. The presence,
nature, and position of heteroatoms can tune helicity param-
[a] D. Waghray, Prof. Dr. W. Dehaen
Molecular Design and Synthesis
Department of Chemistry, KU Leuven
Celestijnenlaan 200F, 3001 Leuven (Belgium)
Fax : (+32)16327990
E-mail: wim.dehaen@chem.kuleuven.be
[b] A. Cloet, Dr. S. F. L. Mertens, Prof. Dr. S. De Feyter,
Prof. Dr. M. Van der Auweraer
Molecular Imaging and Photonics
Department of Chemistry, KU Leuven
Celestijnenlaan 200F, 3001 Leuven (Belgium)
[c] Prof. Dr. K. Van Hecke
Department of Inorganic and Physical Chemistry, Universiteit Gent
Krijgslaan 281-S3, 9000 Gent (Belgium)
[d] Prof. Dr. L. Van Meervelt
Biomolecular Architecture, Department of Chemistry
KU Leuven, Celestijnenlaan 200F, 3001 Leuven (Belgium)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201300843.
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Diazadithia[7]helicenes
FULL PAPER
chirality recognition. In the past few years, various methods
have been described for the synthesis of azathiahelicenes,
which include the classical photochemical procedure by Car-
onna et al.[5a,b] and a versatile synthetic method based on
Bu3SnH-mediated coupling developed by Harrowven and
co-workers.[9] Furthermore, the [2+2+2] cycloisomerization
of triynes[10] and palladium-catalyzed arylation[11] are among
the few reported approaches to helicenes by metal-catalyzed
cyclization.
amidobenzo[b]thiophene-2-carboxylate was in turn prepared
from ethyl 5-aminobenzo[b]thiophene-2-carboxylate accord-
ing to literature procedures.[15] Quinoline building block 1
was converted to ethyl 8-formyl-7-(methylthio)thienoACHTUNGTRENNUNG[3,2-
f]quinoline-2-carboxylate (2) by reaction with NaSMe in
DMF at room temperature for 2 h in 78% yield. Aldehydes
1 and 2 were converted to their corresponding alcohols 3a
and 4a by reduction with NaBH4 in THF/MeOH in 85 and
92% yield, respectively. These alcohols were converted to
bromo derivatives 3b and 4b by reaction with PBr3 at 08C
in THF, which were subsequently converted to their respec-
tive phosphonium salts 3c and 4c by reaction with triphenyl-
phosphine in refluxing toluene for 12–15 h in 86 and 89%
yield, respectively (Scheme 2).
An overview of past and current work is shown in
Scheme 1. In our previous work,[12] we synthesized diversely
functionalized diaza[5]helicenes from a readily available
Scheme 1. Overview of past and current work.
quinoline building block by Wittig reaction and photochemi-
cal cyclization. A resolution strategy based on diastereomer-
ic separation was developed by substituting the dichloro aza-
helicene derivatives with a chiral amine. In the present work
we have extended the above methodology to the synthesis
of diazadithia[7]helicenes from the readily available building
Scheme 2. Synthesis of alcohols and corresponding phosphonium salts.
Wittig olefination of 1 and 2 with phosphonium salts 3c
and 4c, respectively, sodium tert-butoxide as base and THF
as solvent at 08C for 3 h gave the corresponding symmetric
azathiastilbene derivatives 5a and 5c in 58 and 74% yield.
Similarly the reaction of aldehyde 1 with phosphonium salt
4c gave the asymmetric azathiastilbene derivative in 69%
yield (Scheme 3).
Alkenes 5a–c were obtained with a relatively high degree
of Z selectivity, but solubility was still very low in a variety
of solvents. The ortho effect was evident only in the case of
halo substituents on the aldehyde to control the stereochem-
ical outcome of the Wittig reaction,[9] The SMe groups play
a very small role in the cooperative ortho effect which oper-
ates in the course of the Wittig olefination. Due to low solu-
bility of alkenes 5a–c, complete spectroscopic characteriza-
tion was not possible. Therefore, these compounds were
characterized by HRMS. The bis(thienoquinolyl)ethene de-
rivatives 5a–c were subjected to oxidative photocycliza-
tion[12] with iodine as oxidant and toluene as solvent
(1.0 mm). Irradiation of the reaction mixture in a photo-
chemical reactor (l=350 nm) furnished diazadithia[7]heli-
cenes 6a–c in good yields. These helicenes showed good sol-
ubility in a variety of medium-polarity solvents and were
completely characterized by NMR spectroscopy and HRMS.
block ethyl 7-chloro-8-formylthienoACTHNUTRGNEU[GN 3,2-f]quinoline-2-car-
boxylate, which was converted by a Wittig reaction–photo-
cyclization strategy to [7]helicenes. Enantiopure forms of
these [7]helicenes were conformationally very stable and
had a much higher racemization barrier than the previously
synthesized diaza[5]helicenes. Determination of the racemi-
zation barrier reflecting the repulsive interaction between
the terminal aromatic rings is a crucial helicity indicator.
Furthermore, as a proof of concept the helicene skeleton
was substituted by O-, S-, N-, and C-centered nucleophiles
in nucleophilic aromatic substitution reactions and palladi-
um-catalyzed reactions such as Suzuki coupling and Buch-
wald–Hartwig amination.[13]
Results and Discussion
Our approach makes use of the building block ethyl 7-
chloro-8-formylthieno
G
(1),
which was readily prepared from ethyl 5-acetamidoben-
zo[b]thiophene-2-carboxylate by Vilsmeier chloroformyla-
tion with DMF and POCl3 at 808C for 15 h.[14] Quinoline
building block 1 was obtained in 87% yield. Ethyl 5-acet-
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W. Dehaen et al.
cules, is significantly higher
(77.6 and 73.68, respectively) in
comparison with 5,10-diaza[5]-
helicene[16] or functionalized
6,9-dichloro- and 6,9-dime-
thoxy-5,10-diaza[5]helicenes.[12]
In the crystal packing, the aza-
thia[7]helicene molecules are
stacked into columns along the
[010] direction in an antiparallel
fashion, with involvement of
the outer thiophene and ben-
zene rings (Figure 2). Several
intermolecular p–p interactions
are observed, in particular ben-
zene–thiophene and benzene–
benzene stacking interactions.
Scheme 3. Synthesis of bis(thienoquinolyl)ethene derivatives and helicenes 6a–c.
Solid-state structure elucidation: Crystals of 6a were ob-
tained from CHCl3/pentane by slow evaporation. Compound
6a crystallized in the non-centrosymmetric orthorhombic
space group Pca21; the asymmetric unit consists of two aza-
thia[7]helicene molecules (Figure 1; for atom labeling, see
Supporting Information). These two molecules are the same
enantiomer, but differ from each other mainly in the spatial
arrangement of their ethoxyl groups. However, in the com-
plete crystal structure, both enantiomers are present, similar
to the previously reported structure of a 5-aza[5]helicene.[5b]
The distortion of the molecules, defined by the sum of the
three dihedral angles C6-C11-C14-C18, C11-C14-C18-C21,
C14-C18-C21-C25, and C36-C41-C44-C48, C41-C44-C48-
C51, C44-C48-C51-C55 for the two azathia[7]helicene mole-
Figure 2. Packing in the crystal structure of compound 6a along the [100]
direction, showing the columnar, antiparallel stacking involving the outer
thiophene and benzene rings. H atoms are omitted for clarity.
Crystals of compound 6c were also obtained from CHCl3/
pentane by slow evaporation. Compound 6c crystallized in
the centrosymmetric monoclinic space group P21/c, with the
asymmetric unit consisting of one azathia[7]helicene mole-
Figure 3. Asymmetric unit of the crystal structure of compound 6c, show-
ing thermal ellipsoids at 50% probability. The chloroform solvent mole-
cule is omitted.
Figure 1. Asymmetric unit of the crystal structure of compound 6a, show-
ing thermal ellipsoids at 50% probability.
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Diazadithia[7]helicenes
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cule (Figure 3; for atom labeling, see Supporting Informa-
tion). Whereas in the structure of compound 6a, the ethoxyl
groups are oriented differently, in the structure of com-
pound 6c they are coplanar with the thiophene ring. The
distortion of the azathia[7]helicene molecule, defined by the
sum of the three dihedral angles C6-C11-C14-C19, C11-C14-
C19-C22, and C14-C19-C22-C27, is comparable (65.98) to
those of 5,10-diaza[5]helicene[16] and functionalized 6,9-di-
chloro- and 6,9-dimethoxy-5,10-diaza[5]helicenes.[12] Similar
to the crystal packing of 6a, the azathia[7]helicene mole-
cules also form columnar stacks, along the [100] direction,
featuring intermolecular p–p interactions inside the columns
between two symmetry-equivalent benzene rings C13-C14/
C16-C19, leading to an anti-parallel stacking between cen-
tral aromatic rings (Figure 4). Additionally, intramolecular
Scheme 4. SNAr and palladium-catalyzed Suzuki coupling and Buchwald–
Hartwig amination.
Table 1. Functionalization by SNAr and palladium-catalyzed Suzuki cou-
pling and Buchwald–Hartwig amination reactions.
Entry Reagents and conditions
Diazadithia- Yield
[7]helicene [%]
1
2
5a, 4-tert-butylphenol, K2CO3,
DMF, 808C, 12 h
5a, p-tolylboronic acid, 5 mol% [Pd-
7a
69
7b
58
AHCTUNGTRENNUNG
3
G
7c
65
[a] BINAP: 2,2’-bis(diphenylphosphino)-1,1’-binaphthyl.
both chloro groups at the 7- and 10-positions of the diazadi-
thia[7]helicene was done by Suzuki cross-coupling. Aryl
groups were introduced on the helicene skeleton by Pd-cata-
lyzed reaction with p-tolylboronic acid, which yielded 58%
of the desired product 7b (Table 1, entry 2). Next, we at-
tempted substitution with aniline under Buchwald–Hartwig
amination conditions. Palladium-catalyzed reaction of 7,10-
dichlorodiazadithia[7]helicene with aniline furnished the de-
sired product 7c in 65% yield (Table 1, entry 3).
Figure 4. Packing in the crystal structure of compound 6c along the [100]
direction, showing the columnar, antiparallel stacking between central ar-
omatic rings. H atoms are omitted for clarity.
p–p interactions are observed between the two thiophene
rings S1/C4–C7 and S4/C26–C29 (3.485(2) ꢁ between the
ring centroids), as well as between thiophene ring S1/C4–C7
and benzene ring C21-C22/C24-C27 (3.987(2) ꢁ between
the ring centroids), which is not the case in the structure of
6a. One CHCl3 solvent molecule could be unambiguously
observed, and is positioned between the column stacks.
Resolution by diastereomer separation: Buchwald–Hartwig
amination of the racemic helicene skeleton with a chiral
amine results in the formation of diastereomers, which then
can easily be separated by column chromatography.[12] Thus,
palladium-mediated amination of 6a with l-(ꢀ)-a-methyl-
benzylamine, Cs2CO3, 5 mol% of PdACTHNUTRGNE(UNG OAc)2 and rac-BINAP
in toluene furnished the desired product 7d in 74% yield as
a 1:1 mixture of diastereomers (M,S,S/P,S,S=1:1; the ratio
of isomers was determined by integration of the NMR spec-
tra; Scheme 5). The diastereomers were readily separated
by chromatography on a silica-gel column and were configu-
rationally very stable at room temperature. The diastereom-
ers were completely characterized by NMR spectroscopy,
HRMS and CD spectroscopy.
Functionalization of diazadithia[7]helicenes: Dichloro diaza-
dithia[7]helicene 6a was synthesized in good yield, and the
presence of chloro groups opened an opportunity for further
functionalization. A variety of O-, S-, N-, and C-centered
nucleophiles can be bound to the diazadithiahelicene plat-
form. As a proof of concept for our previously reported
methodology[12] we attempted to substitute the helicene core
by nucleophilic aromatic substitution, palladium-catalyzed
Suzuki coupling, and Buchwald–Hartwig amination
(Scheme 4).
We first tested the SNAr reaction of an O nucleophile.
The SNAr reaction of 4-tert-butylphenol (2.5 equiv) with
7,10-dichlorodiazadithia[7]helicene furnished product 7a in
69% yield (Table 1, entry 1). Next, we explored the Suzuki
and Buchwald–Hartwig amination reactions. Substitution of
Racemization barrier: Racemization studies were performed
on compound 6c. Enantiopure forms were obtained by
HPLC separation on a ChiralPak IA chiral column at room
temperature and a flow rate of 0.7 mLminꢀ1. The mobile
phase was heptane/ethanol (60:40 v/v) under isocratic condi-
tions. Enantiomerically enriched [7]helicene 6c racemizes in
the solid state with a half-life of (6.5ꢁ0.7) h at 2208C. The
corresponding free-energy barrier of racemization is
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W. Dehaen et al.
The fluorescence decay time of
6c in chloroform, determined
by single-photon timing (see
Supporting Information) was
0.36 ns. This leads to a fluores-
cence rate constant of (6.4ꢁ
0.6)ꢂ107 sꢀ1, which is about ten
times smaller than the value ex-
pected for a completely allowed
Scheme 5. Resolution through diastereomer separation.
transition (f=1). On the other
hand, for the non-radiative
(40.26ꢁ0.14) kcalmolꢀ1 (see Supporting Information).
These values are similar to those reported for all-phenylene
[7]helicene.[17]
decay a rate constant of (2.7ꢁ0.3)ꢂ109 sꢀ1 was obtained.
This value is quite large for a relatively rigid molecule for
which no low-lying np* triplet states are expected.
Figure 6 shows the CD spectrum of enantiomers 6c and
diastereomers 7d in chloroform. The CD spectrum of enan-
tiomer (+)-6c starts with a small negative peak, followed by
several large positive bands (lmax =355 nm) and a series of
UV/Vis absorption spectroscopy, fluorescence spectroscopy,
circular dichroism spectroscopy, and cyclic voltammetry:
The absorption and emission spectra of enantiomers 6c and
the absorption spectrum of diastereomers 7d in chloroform
are shown in Figure 5. The absorption spectrum of 6c shows
Figure 6. CD spectra of enantiomers P-(+)-6c (solid) and M-(ꢀ)-6c
(dotted) and diastereomers P-(+)-7d (dashed) and M-(ꢀ)-7d (dashed-
dotted).
Figure 5. Absorption (solid) and emission (dotted) spectra of enantiomers
6c and absorption (dashed) spectrum of diastereomers 7d in chloroform.
alternating negative and positive bands below 340 nm. As
expected, the spectrum for enantiomer (ꢀ)-6c is the mirror
image of this. It is commonly accepted that the sign of the
most intense CD band (b band) is representative of the ab-
solute configuration of the helicene, with a positive (nega-
tive) band corresponding to P (M) helicity.[18b] Thus, we can
attribute P helicity to enantiomer (+)-6c, and vice versa.
As the maxima at 430, 407 and 383 nm were attributed to
a vibronic progression of the S0!S1 transition, one would
expect them to all have the same sign in the CD spectrum;
this is clearly not the case. For helicenes the red edge of the
absorption spectrum is known to consist of two bands,
namely, the p and a bands, which can have opposite signs in
a CD spectrum.[18] This suggests that the maximum at
430 nm is due to the 0–0 transition of the a band (in this
case the S0!S1 transition), while the maxima at 407 and
383 nm must be attributed to the 0–0 and 0–1 transition of
the p band. This yields a vibronic progression of (1530ꢁ
100) cmꢀ1 for the p band. However, since the CD intensity
is much larger for the a band than for the p band,[18] it
three initial absorption peaks, located at 430, 407, and
383 nm and attributed tentatively to the vibronic progres-
sion of the S0!S1 transition, followed by a steep rise attrib-
uted to S0!Sn transitions. The molar extinction coefficient e
is 8500 Lmolꢀ1 cmꢀ1 at 430 nm. The absorption spectrum of
diastereomers 7d is similar to that of enantiomers 6c,
except for a bathochromic shift and broadening of the initial
peaks. Thus, it is difficult to clearly distinguish individual vi-
bronic transitions, but we can still see a maximum at 432 nm
(e=9700 Lmolꢀ1 cmꢀ1) and a shoulder at 451 nm.
The fluorescence spectrum of 6c consists of a single tran-
sition with vibronic progression, of which the first two
maxima are located at 441 and 465 nm. This corresponds to
a vibrational spacing of (1170ꢁ100) cmꢀ1 in the ground
state. The fluorescence quantum yield of 6c in chloroform,
determined by using perylene as reference (lex =404 nm),
was (2.3ꢁ0.2)%. This relatively low value suggests that
non-radiative decay is rather efficient in these helicenes.
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Diazadithia[7]helicenes
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cannot be excluded that the three observed vibrational
maxima must be attributed to the p band and that the nega-
tive CD signal at long wavelengths reflects simply an a band
hidden under the p band. Due to better conjugation, the ab-
sorption spectrum of 6c is situated at much longer wave-
length than those of the corresponding carbon–sulfur heli-
cenes described by Rajca and co-workers, in which only
cross-conjugation is possible. It is also slightly red-shifted
compared to a [7]helicene in which thiophene rings alter-
nate with benzene rings.[18b] The spectra of the diastereomers
are largely similar, but display a bathochromic shift and
have the same sign over the complete band of lowest-energy
transitions, which leads to a disappearance of the initial
small peak of opposite sign. Following the same arguments
used for compound 6c, we can attribute P helicity to diaster-
eomer (+)-7d, and vice versa. The fact that the negative
band at long wavelengths has disappeared suggests that for
7d the 0–0 transition of the p band is now lower in energy
than that of the a band. It is also noteworthy that, from
roughly 300 nm onwards, diastereomers (+)-7d and (ꢀ)-7d
display a difference in intensity on top a mere sign change.
This is likely related to the (ꢀ)-a-methylbenzylamine side
chains, which start to contribute to the spectrum.
tion,[19c] using the electrochemically determined HOMO–
LUMO gap and the empirical relationship EHOMO
(ꢀ1.4E
=
(ox1)ꢀ4.6) eV,[19d] we can also estimate the
HOMO and LUMO energies as ꢀ6.0 and ꢀ3.2 eV, respec-
tively, relative to the vacuum level. The position of the
HOMO will make hole injection from most common hole-
injection electrodes (poly(3,4-ethylenedioxythiophene) or
indium tin oxide) quite difficult. The position of the LUMO,
on the other hand, is below the Fermi energy of Ca and
other electropositive metal electrodes. Furthermore, the
presence of an irreversible oxidation feature suggests that
hole conduction may be accompanied by permanent chemi-
cal changes and premature failure of the device. Therefore,
this compound may be better suited as an electron conduc-
tor when used for possible applications in organic electron-
ics.
Conclusion
We have developed an efficient method for synthesis and
functionalization of a helicene skeleton by SNAr and palladi-
um-catalyzed coupling reactions, and thus expanded the
scope of the methodology to higher helicenes. The chiral
forms obtained as a result of diastereomeric separation were
conformationally very stable at room temperature and were
characterized by NMR and CD spectroscopy. This method-
ology of functionalization and resolution has led to further
exploration of the applications of azathiahelicenes. The role
of diazadithia[7]helicenes as chiral inducers in asymmetric
synthesis will also be investigated. We envisage potential ap-
plications of these helicenes in organic electronics.
Figure 7 shows the cyclic voltammogram for compound
6c in acetonitrile/toluene (3:1) containing 0.1m TBAPF6 as
supporting electrolyte. Within the available potential
window of the chosen supporting electrolyte/solvent system,
a single reversible reduction was observed at a potential of
Experimental Section
General experimental methods: NMR spectra were acquired on commer-
cial instruments (Bruker Avance 300 MHz and Bruker AMX 400 MHz
and 600 MHz) and chemical shifts (d) are reported in parts per million
(ppm) referenced to tetramethylsilane (1H) or the internal (NMR) sol-
vent signal (13C). Mass spectra were run on a HP5989A apparatus (EI,
70 eV ionization energy) with Apollo 300 data system, a Micromass
Quattro II apparatus (ESI) with MASSLYNX data system or a Thermo
Finnigan LCQ Advantage apparatus (ESI/APCI). Exact mass measure-
ments were carried out with a Kratos MS50TC instrument (performed in
EI mode at a resolution of 10000). Melting points (not corrected) were
determined by using a Reichert Thermovar apparatus. UV/Vis absorption
spectra and emission spectra were respectively taken on a PerkinElmer
Lambda 40 spectrophotometer and a Horiba Jobin Yvon Fluorolog-3-22
spectrofluorometer. The fluorescence spectra are corrected for the wave-
length dependence of the sensitivity of the detection part. CD measure-
ments were performed on a Jasco J600 spectropolarimeter. All spectro-
scopic measurements were performed in quartz cuvettes with an optical
path length of 1 cm. For column chromatography, 70–230 mesh silica 60
(E. M. Merck) was used as the stationary phase. Chemicals received
from commercial sources were used without further purification. K2CO3
(anhydrous, granulated) was finely ground (with mortar and pestle) prior
to use. All solvents were used as received from commercial sources and
not explicitly dried prior to use (ꢂ0.1% H2O). All photochemical reac-
tions were performed in the Rayonet photochemical reactor equipped
with interchangeable light sources (250, 300, and 350 nm lamps).
Figure 7. Cyclic voltammogram of 6c in acetonitrile/toluene (3:1) at a
nominal concentration of 0.8 mm (solid gray). Supporting electrolyte:
0.1m TBAPF6; scan rate: 200 mVsꢀ1. The black dashed trace shows the
base electrolyte response.
E
G
E
A shallow peak at about ꢀ0.7 V, indicated by an asterisk,
may be related to adsorption of a reaction product. From
the redox potentials of 6c, a HOMO–LUMO gap of (2.96ꢁ
0.05) eV can be estimated under the stated experimental
conditions. This gap is only slightly larger than the optical
band gap of 2.85 eV determined from the intersection of the
normalized absorption and emission spectra, and therefore
these values are more similar than is typically observed.[19a,b]
Assuming in the simplest case that these energy levels are
indeed responsible for the observed oxidation and reduc-
Chem. Eur. J. 2013, 00, 0 – 0
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www.chemeurj.org
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W. Dehaen et al.
Single-photon timing (SPT): Fluorescence decay times were determined
by SPT measurements and the setup has been described in detail previ-
ously.[20] A time-correlated single-photon counting PC module (SPC 830,
Becker & Hickl) was used to obtain the fluorescence decay histogram in
4096 channels. The decays were recorded with 10000 counts in the peak
channel in time windows of 6.6 ns corresponding to 1.6 ps per channel
and analyzed with time-resolved fluorescence analysis software (FAST)
based on iterative reconvolution with a Goldin algorithm. The full width
at half-maximum (FWHM) of the instrument response function was typi-
cally on the order of 40 ps. The quality of the fits was judged by the
random distribution of the residuals and by the value of the reduced chi-
squared parameter (c2 <1.1).[21] All measurements were performed in
quartz cuvettes with an optical path length of 1 cm at an optical density
of ca. 0.1 at the excitation wavelength of 430 nm.
Synthesis of ethyl 7-chloro-8-(hydroxymethyl)thienoACHTNGUTERNNU[G 3,2-f]quinoline-2-
carboxylate (3a): general procedure: Sodium borohydride (0.065 g,
1.72 mmol) was added to a stirred solution of aldehyde 1 (0.500 g,
1.56 mmol) in THF (50 mL) and MeOH (10 mL), and the reaction mix-
ture stirred at 08C for 30 min. The reaction mixture was quenched with
water and diluted with Et2O, and the organic layer was separated,
washed with brine, dried over anhydrous MgSO4, and evaporated to dry-
ness to give 3a (0.425 g, 85%) as a white solid. The product was used
without further purification. M.p. 225–2278C; MS (EI): m/z: 322 [M+H];
HRMS (EI) calcd for C15H12ClNO3S: 321.0226; found: m/z 321.0039;
1H NMR (300 MHz, [D6]DMSO): d=9.06 (s, 1H, ArH), 8.90 (s, 1H,
ArH), 8.36 (d, 1H, J=9.2 Hz, ArH), 7.97 (d, 1H, J=9.0 Hz, ArH), 5.70
(t, 1H, J=5.6 Hz, OH), 4.75 (d, 2H, J=5.2 Hz, CH2OH), 4.42 (q, 2H,
J=7.1 Hz, OCH2), 1.38 ppm (t, 3H, J=7.1 Hz, CH3); 13C NMR (75 MHz,
CDCl3, 258C, TMS): d=161.7, 148.1, 144.8, 140.5, 134.8, 134.5, 132.7,
128.6, 127.2, 125.2, 123.8 (C, CH), 61.6, 60.2, 14.1 ppm (CH2, CH3).
Cyclic voltammetry: Acetonitrile (ꢃ 99.8%, H2O <0.001%, Sigma-Al-
drich) and toluene (HPLC grade, Sigma-Aldrich) were used as received,
whereas tetra-n-butylammonium hexafluorophosphate (TBAPF6, electro-
chemical grade, Fluka) was dried overnight in vacuo at 1108C. For solu-
bility reasons, the electroactive substance (rac-diazadithia[7]helicene 6c)
was dissolved in acetonitrile/toluene (3:1). Electrochemical measure-
ments were carried out in a custom-made single-compartment three-elec-
trode cell with a working volume of 1 cm3, containing a Pt coil counter-
electrode. The reference electrode was a laboratory-built non-aqueous
AgjAg+ electrode, contacted to the cell through a porous glass dia-
phragm, and was calibrated versus ferrocene after the measurements. All
potentials are given with reference to the ferrocene equilibrium potential.
The working electrode (WE) was a polycrystalline Pt bead, polished to
mirror finish, exposing a geometric surface area of 0.032 cm2 in hanging-
meniscus configuration. The WE was annealed with a butane flame
before every measurement and cooled in a stream of high-purity Ar. The
Synthesis of ethyl 8-(hydroxymethyl)-7-(methylthio)thienoACTHNUTRGNEUGN[3,2-f]quino-
line-2-carboxylate (4a): Synthesis according to general procedure leading
to 3a (see the Supporting Information).
Synthesis of ethyl 8-(bromomethyl)-7-chlorothienoACTHNUGRTNEUNG[3,2-f]quinoline-2-car-
boxylate (3b): general procedure: Phosphorus tribromide (0.149 mL,
1.58 mmol) was added to a solution of compound 3a (0.425 g, 1.32 mmol)
in THF (50 mL) and the reaction mixture cooled to 08C. The reaction
mixture was stirred at room temperature for 5 h and then quenched with
water. The organic layer was separated, washed with brine, dried over an-
hydrous MgSO4, evaporated to dryness, and purified by column chroma-
tography with EtOAc/petroleum ether (20:80) as eluent to furnish com-
pound 3b (0.301 g, 59%) as a white solid. M.p. 192–1938C; MS (EI): m/
z: 383 [M+H]; HRMS (EI) calcd for C15H11ClBrNO2S: 382.9382; found:
m/z 382.9364; 1H NMR (300 MHz, [D6]DMSO): d=9.49 (s, 1H, ArH),
8.95 (s, 1H, ArH), 8.45 (d, 1H, J=9.0 Hz, ArH), 8.01 (d, 1H, J=9.0 Hz,
ArH), 4.90 (s, 2H, CH2Br), 4.41 (q, 2H, J=7.1 Hz, OCH2), 1.38 ppm (t,
3H, J=7.1 Hz, CH3); 13C NMR (75 MHz, CDCl3, 258C, TMS): d=161.6,
140.9, 136.2, 135.1, 134.7, 132.6, 128.7, 127.1, 126.6, 123.7 (C, CH), 61.7,
14.1 ppm (CH2, CH3).
potentiostat was
a software-controlled Autolab PGSTAT101 system
(Metrohm Autolab BV, The Netherlands). In all cases, the WE was
brought into contact with the electrolyte under potential control at a po-
tential within the stability range of the studied compound. Before and
during the measurements, solutions were kept under a solvent-saturated
Ar (purity 5.0, Praxair) atmosphere.
Synthesis of ethyl 8-(bromomethyl)-7-(methylthio)thienoACTHNUTRGNEU[GN 3,2-f]quinoline-
2-carboxylate (4b): Synthesis according to procedure leading to 3b (see
Supporting Information).
Synthesis of ethyl 7-chloro-8-formylthienoACHTNUGTRNEUNG[3,2-f]quinoline-2-carboxylate
(1): POCl3 (13.9 mL, 151.9 mmol) was added dropwise over a period of
15 min to dimethylformamide (DMF) (3.8 mL, 53.17 mmol) at 08C. The
resulting Vilsmeier salt was stirred for 10 min at 08C, and then ethyl 5-
acetamidobenzo[b]thiophene-2-carboxylate (4.0 g, 15.19 mmol) was
added and reaction mixture heated to 808C. After 15 h, reaction mixture
was quenched with ice water and extracted with CH2Cl2. The organic
layer was separated, washed with brine, dried over anhydrous MgSO4,
and evaporated to dryness to furnish compound 1 (4.25 g, 87%) as
yellow powder. M.p. 209–2118C; MS (EI): m/z 320 [M+H]+; HRMS (EI)
calcd for C15H10NO3ClS: 319.0070; found: m/z 319.0098; 1H NMR
(300 MHz, CDCl3): d=10.62 (s, 1H, CHO), 9.18 (s, 1H, ArH), 8.69 (s,
1H, ArH), 8.24 (d, 1H, J=9.0 Hz, ArH), 8.05 (d, 1H, J=9.06 Hz, ArH),
4.47 (q, 2H, J=7.1 Hz, OCH2), 1.47 ppm (t, 3H, J=7.1 Hz, CH3);
13C NMR (75 MHz, CDCl3, 258C, TMS): d=189.1 (CHO), 162.1, 150.2,
149.1, 141.7, 137.1, 135.8, 135.1, 128.4, 127.5, 127.4, 126.4, 123.6 (C, CH),
62.2, 14.4 ppm (CH2, CH3).
Synthesis
of
ethyl
8-[(bromotriphenylphosphoranyl)methyl]-7-
chlorothienoAHCTUNETGRG[NNUN 3,2-f]quinoline-2-carboxylate 3c: general procedure: Tri-
phenylphosphine (0.616 g, 2.35 mmol) was added to a solution of com-
pound 3b (0.301 g, 0.78 mmol) in toluene, the reaction mixture heated to
reflux for 12 h and cooled to room temperature, and the resulting solid
isolated by filtration, washed with pentane, and dried under vacuum to
furnish phosphonium salt 3c (0.434 g, 86%) as a white solid. M.p. 239–
2418C; MS (EI): m/z: 646 [M+H] (observed [MꢀBr]=566); HRMS (EI)
calcd for C33H26ClBrNO2SP 645.0294; found: m/z 566.1106 [MꢀBr];
1H NMR (300 MHz, CDCl3): d=8.29 (d, 1H, J=8.4 Hz, ArH), 8.05 (d,
1H, J=9.2 Hz, ArH), 7.89–7.79 (m, 10H, ArH), 7.71–7.64 (m, 7H, ArH),
6.10–6.05 (m, 2H, CH2P), 4.46 (q, 2H, J=7.1 Hz, OCH2), 1.48 ppm (t,
3H, J=7.1 Hz, CH3); 13C NMR (75 MHz, CDCl3, 258C, TMS): d=162.2,
135.6, 134.7, 134.6, 134.5, 130.6, 130.5, 117.8, 116.7 (C, CH), 62.0,
14.5 ppm (CH2, CH3).
Synthesis
of
ethyl
8-[(bromotriphenylphosphoranyl)methyl]-7-
Synthesis of ethyl 8-formyl-7-(methylthio)thienoACTHNUGRTNEUNG[3,2-f]quinoline-2-car-
(methylthio)thienoACHTUNGTERNN[GUN 3,2-f]quinoline-2-carboxylate (4c): See Supporting In-
boxylate (2): NaSMe (0.438 g, 6.25 mmol) was added to a solution of
compound 1 (1.0 g, 3.12 mmol) in DMF, and the reaction mixture stirred
at room temperature for 2 h, quenched with water, and extracted with
CH2Cl2. The organic layer was separated, washed with brine, dried over
anhydrous MgSO4, and evaporated to dryness to furnish compound 2
(0.805 g, 78%) as a yellow powder. M.p. 202–2048C; MS (EI): m/z: 332
[M+H]; HRMS (EI) calcd for C16H13NO3S2 331.0337; found: m/z
331.0338; 1H NMR (300 MHz, CDCl3): d=10.43 (s, 1H, CHO), 8.90 (s,
1H, ArH), 8.63 (s, 1H, ArH), 8.14 (d, 1H, J=9.0 Hz, ArH), 7.99 (d, 1H,
J=9.0 Hz, ArH), 4.46 (q, 2H, J=7.1 Hz, OCH2), 2.75 (s, 3H, SCH3),
1.46 ppm (t, 3H, J=7.1 Hz, CH3); 13C NMR (75 MHz, CDCl3, 258C,
TMS): d=189.8 (CHO), 162.4, 159.9, 149.0, 140.3, 136.7, 136.3, 135.8,
127.9, 127.5, 127.4, 127.1, 121.1 (C, CH), 62.1, 14.4, 13.2 ppm (CH2, CH3).
formation.
Synthesis of diethyl 8,8’-(ethene-1,2-diyl)bis(7-chlorothieno
line-2-carboxylate) 5a: general procedure: solution of 7-chloro-8-
formylthieno[3,2-f]quinoline-2-carboxylate (1; 0.155 g, 0.49 mmol) was
ACHTUNGTREN[NUNG 3,2-f]quino-
A
AHCTUNGTRENNUNG
added dropwise to a stirred solution of phosphonium salt 3c (0.350 g,
0.54 mmol) and potassium tert-butoxide (0.082 g, 0.73 mmol) in THF at
08C, after which the reaction mixture was stirred for 6 h. The solvent was
removed under reduced pressure and a mixture of CH2Cl2 and MeOH
was added to give a precipitate, which was collected by filtration and
dried in vacuo to give 5a (0.170 g, 58%) as a yellow solid. Compound 5a
was difficult to characterize by NMR spectroscopy due to its poor solu-
bility. M.p. 189–1908C; MS (EI): m/z: 607 [M+H]; HRMS (EI) calcd for
C30H20Cl2N2O4S2: 606.0242; found: m/z 607.0302 [M+H].
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Diazadithia[7]helicenes
FULL PAPER
Synthesis of ethyl 7-chloro-8-{2-[2-(ethoxycarbonyl)-7-(methylthio)-
thienoACHTUNGTRENNUNG[3,2-f]quinolin-8-yl]vinyl}thienoACHTUNGTNER[NUGN 3,2-f]quinoline-2-carboxylate 5b:
132.7, 130.5, 129.6, 129.5, 129.4, 128.2, 126.8, 126.7, 124.1, 121.3 (C, CH),
61.4, 21.5, 14.4 ppm (CH2, CH3).
Synthesis according to procedure leading to 5a (see Supporting Informa-
tion)
Buchwald–Hartwig amination: synthesis of 7,10-bis(phenylamino)-6,11-
diaza-3,14-dithia[7]helicene-2,15-bis(carboxylate) (7c): Aniline (7.6 mg,
Synthesis of diethyl 8,8’-(ethene-1,2-diyl)bis[7-(methylthio)thieno
[3,2-
0.08 mmol),
Cs2CO3
(98 mg,
0.3 mmol),
rac-BINAP
(1.0 mg,
f]quinoline-2-carboxylate] 5c: Synthesis according to procedure leading
to 5a (see Supporting Information)
0.0015 mmol), and PdAHCTUNGTRENNUNG
(OAc)2 (0.3 mg, 0.0015 mmol) were added to a sol-
ution of 6a (20 mg, 0.03 mmol) in toluene (10 mL), and the reaction mix-
ture was stirred at 808C for 12 h. Subsequently, the mixture was diluted
with ethyl acetate (20 mL) and washed with distilled water (3ꢂ20 mL).
The organic fraction was dried over MgSO4 and filtered and the solvent
was removed under vacuum. After column chromatographic purification
with EtOAc/petroleum ether (40:60) as eluent, substituted helicene 7c
(15.5 mg, 65%) was obtained as an orange solid. M.p. 325–3278C; MS
(EI): m/z: 719 [M+H]; HRMS (EI) calcd for C42H30N4O4S2: 718.1708;
found: m/z 719.1774 [M+H]; 1H NMR (300 MHz, [D6]DMSO): d=9.75
(s, 2H, NH), 9.04 (s, 2H, ArH), 8.14–8.09 (m, 6H, ArH), 7.92 (d, 2H, J=
8.6 Hz, ArH), 7.49–7.44 (m, 4H, ArH), 7.15–7.10 (m, 2H, ArH), 6.91 (s,
2H, ArH), 4.21–4.02 (m, 4H, OCH2), 1.24–1.20 ppm (m, 6H, CH3);
13C NMR (75 MHz, [D6]DMSO, 258C, TMS): d=161.4, 150.8, 143.2,
141.0, 138.0, 132.9, 131.1, 128.8, 128.5, 127.6, 124.1, 122.5, 122.4, 121.9,
120.9, 117.6 (C, CH), 61.0, 14.1 ppm (CH2, CH3).
Synthesis of 7,10-dichloro-6,11-diaza-3,14-dithia[7]helicene-2,15-bis(car-
boxylate) (6a): general procedure: Iodine (0.073 g, 0.28 mmol) was added
to a solution of compound 5a (0.169 g, 0.26 mmol, mixture of two iso-
mers) in toluene (265 mL). Argon was bubbled through the solution for
30 min, and then an excess of propylene oxide was added to the solution.
The reaction mixture was irradiated in a Rayonet photochemical reactor
(l=350 nm) for 15 h, after which it was washed with aqueous Na2S2O3,
water, and brine, dried over anhydrous MgSO4, and evaporated to afford
a dark yellow residue. Purification by column chromatography with
EtOAc/petroleum ether (20:80) as eluent gave the racemic helicene 6a
(0.090 g, 56%) as a light yellow solid. M.p. 230–2328C; MS (EI): m/z:
605 [M+H]; HRMS (EI) calcd for C30H18Cl2N2O4S2: 604.0085; found: m/
z 605.0305; 1H NMR (300 MHz, CDCl3): d=8.85 (s, 2H, ArH), 8.26 (d,
2H, J = 8.6 Hz, ArH), 8.08 (d, 2H, J = 8.8 Hz, ArH), 6.87 (s, 2H, ArH),
4.26 (m, 2H, OCH2), 4.12 (m, 2H, OCH2), 1.30 ppm (m, 6H, CH3);
13C NMR (75 MHz, CDCl3, 258C, TMS): d=161.6, 150.2, 143.9, 143.8,
142.7, 133.7, 133.1, 129.3, 129.2, 128.9, 128.0, 127.3, 126.8, 125.1, 121.1 (C,
CH), 61.6, 14.4 ppm (CH2, CH3).
Synthesis
of
7,10-bis[(S)-a-(methylbenzylamino)]-6,11-diaza-3,14-di-
thia[7]helicene-2,15-bis(carboxylate) (7d): (S)-a-Methylbenzylamine
(30 mL, 0.268 mmol), Cs2CO3 (348 mg, 1.07 mmol), rac-BINAP (3.3 mg,
0.0053 mmol, 5 mol%) and PdACTHNUTRGNE(NUG OAc)2 (1.2 mg, 0.0053 mmol, 5 mol%)
were added to a solution of 6a (65 mg, 0.107 mmol) in toluene (20 mL),
and the reaction mixture was stirred at 808C for 12 h. Subsequently, the
mixture was diluted with ethyl acetate (20 mL) and washed with distilled
water (3ꢂ20 mL). The organic fraction was dried over MgSO4 and fil-
tered, and the solvent was removed under vacuum. After column chro-
matographic purification with EtOAc/petroleum ether (20:80) as eluent,
helicene 7d (54 mg, 74%, 1:1 mixture of diastereomers) was obtained as
a light yellow solid. M.p. 139–1418C; MS (EI): m/z: 775 [M+H]; HRMS
(EI) calcd for C46H38N4O4S2: 774.2334; found: m/z 775.2413 [M+H];
1H NMR (300 MHz, CDCl3, diastereomer 2): d=8.05 (s, 2H, ArH), 7.89
(d, 2H, J=8.8 Hz, ArH), 7.76 (d, 2H, J=8.8 Hz, ArH), 7.61–7.58(m, 4H,
ArH), 7.40–7.35 (m, 4H, ArH), 7.30–7.27 (m, 2H, ArH), 7.01 (s, 2H,
ArH), 5.87–5.82 (m, 2H, CH), 5.71–5.69 (m, 2H, NH), 4.27–4.08 (m, 4H,
OCH2), 1.85 (d, 6H, J=6.7 Hz, CHCH3), 1.34–1.25 ppm (m, 6H,
CH2CH3).13C NMR (75 MHz, CDCl3, 258C, TMS): d=162.5, 151.8, 144.9,
144.5, 138.4, 133.6, 131.5, 129.8, 129.7, 127.3, 126.7, 123.7, 121.0, 119.9,
117.8 (C, CH), 61.1, 50.9, 22.3, 14.3 ppm (CH2, CH3).
Synthesis of 7-chloro, 10-thiomethoxy-6,11-diaza-3,14-dithia[7]helicene-
2,15-bis(carboxylate) 6b: Synthesis according to procedure leading to 6a
(see Supporting Information)
Synthesis of 7,10-bis(thiomethoxy)-6,11-diaza-3,14-dithia[7]helicene-2,15-
bis(carboxylate) 6c: Synthesis according to procedure leading to 6a (see
Supporting Information).
Nucleophilic substitution reaction: synthesis of 7,10-bis(tert-butylphenyl)-
6,11-diaza-3,14-dithia[7]helicene-2,15-bis(carboxylate)
(7a):
K2CO3
(11.3 mg, 0.082 mmol) and tert-butylphenol (12.3 mg, 0.082 mmol) were
added to a solution of 6a (20 mg, 0.03 mmol) in DMF (10 mL), and the
reaction mixture was stirred at 808C for 12 h. Subsequently, the mixture
was diluted with ethyl acetate (20 mL) and washed with distilled water
(3ꢂ20 mL). The organic fraction was dried over MgSO4 and filtered, and
the solvent was removed under vacuum. After column chromatographic
purification with EtOAc/petroleum ether (15:75) as eluent, substituted
helicene 7a (19 mg, 69%) was obtained as a yellow solid. M.p. 327–
3298C; MS (EI): m/z: 833 [M+H]; HRMS (EI) calcd for C50H44N2O6S2:
1
Crystallographic data: For the structures of compounds 6a and 6c, X-ray
intensity data were collected on a SMART 6000 diffractometer equipped
with CCD detector by using CuKa radiation (l=1.54178 ꢁ) and f and w
scans. The images were interpreted and integrated with the program
SAINT from Bruker.[22] Both structures were solved by direct methods
and refined by full-matrix least-squares techniques on F2 by using the
SHELXTL program package.[23] Non-hydrogen atoms were anisotropical-
ly refined and the hydrogen atoms in the riding mode and isotropic tem-
perature factors fixed at 1.2Ueq of the parent atoms (1.5Ueq for methyl
groups). CCDC-925861 (6a) and CCDC-925862 (6c) contain the supple-
mentary crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
832.4621; found: m/z 833.2715 [M+H]; H NMR (300 MHz, CDCl3): d=
8.91 (s, 2H, ArH), 8.00 (d, 2H, J=8.8 Hz, ArH), 7.92 (d, 2H, J=8.6 Hz,
ArH), 7.55 (d, 4H, J=8.2 Hz, ArH), 7.43 (d, 4H, J=8.4 Hz, ArH), 7.00
(s, 2H, ArH), 4.24–4.08 (m, 4H, OCH2), 1.43 (s, 18H, tBu), 1.28–
1.26 ppm (m, 6H, CH3); 13C NMR (75 MHz, CDCl3, 258C, TMS): d=
162.1, 158.4, 151.4, 148.0, 142.2, 140.5, 133.6, 132.2, 130.1, 129.8, 128.1,
126.5, 124.0, 123.8, 122.6, 121.2, 120.0 (C, CH), 61.3, 34.7, 31.7, 14.5 ppm
(CH2, CH3).
Palladium-catalyzed Suzuki coupling: synthesis of 7, 10-bis(4-methyl-
phenyl)-6,11-diaza-3,14-dithia[7]helicene-2,15-bis(carboxylate) (7b): [Pd-
ACHTUNGTRENNUNG(PPh3)4] (3 mg, 5 mol%) was added to a solution of 6a (20 mg,
0.03 mmol) in toluene (20 mL), and to the resulting solution p-tolylbor-
onic acid (13 mg, 0.099 mmol) in aqueous NaHCO3 (10 mg, 0.228 mmol)
and MeOH (0.5 mL) were added. The reaction mixture was heated to
reflux for 12 h. Subsequently, the mixture was washed with distilled water
(3ꢂ20 mL). The organic fraction was dried over MgSO4 and filtered, and
the solvent was removed under vacuum. After column chromatographic
purification with EtOAc/petroleum ether (20:80) as eluent, substituted
helicene 7b (14 mg, 58%) was obtained as a yellow solid. M.p. 255–
2578C; MS (EI): m/z: 717 [M+H]; HRMS (EI) calcd for C44H32N2O4S2:
716.1803; found: m/z 717.1865 [M+H]; 1H NMR (300 MHz, CDCl3): d=
8.41 (d, 2H, J=8.6 Hz, ArH), 8.35 (s, 2H, ArH), 8.07 (d, 2H, J=8.6 Hz,
ArH), 7.79 (d, 2H, J=7.7 Hz, ArH), 7.44 (d, 2H, J=7.7, ArH), 7.07 (s,
2H, ArH), 4.29–4.23 (m, 2H, OCH2), 4.21- 4.08 (m, 2H, OCH2), 2.52 (s,
6H, ArH-CH3), 1.31–1.25 ppm (m, 6H, CH3); 13C NMR (75 MHz,
CDCl3, 258C, TMS): d=162.1, 159.5, 143.7, 142.2, 139.3, 136.4, 133.3,
Crystal data for compound 6a: C30H18Cl2N2O4S2, M=605.50; orthorhom-
bic, Pca21 (No. 29); a=22.657(10), b=12.435(5), c=18.362(3) ꢁ; V=
5173(3) ꢁ3;
T=100(2) K;
Z=8;
1calcd =1.555 gcmꢀ3
;
mACHTUNGTRENNUNG(CuKa)=
4.128 mmꢀ1; F
AHCTUNGTERG(NNNU 000)=2480; crystal size 0.5ꢂ0.2ꢂ0.1 mm; 8772 independ-
ent reflections (Rint =0.1014). Final R=0.0968 for 6981 reflections with
I>2s(I) and wR2=0.2138 for all data. Detection of a pseudo-center of
symmetry suggested the centrosymmetric space group Pbca.[24] However,
refinement of the structure in the latter space group converged to an R
value of 17%, which is about twice that in space group Pca21. Therefore,
Pca21 was kept as the preferred space group.
Crystal data for compound 6c: C33H25Cl3N2O4S4, M=748.18; monoclinic,
P21/c (No. 14); a=7.5328(6), b=28.1374(16), c=15.6203(10) ꢁ; b=
103.576(3)8; V=3218.3(4) ꢁ3; T=100(2) K; Z=4; 1calcd =1.544 gcmꢀ3; m-
Chem. Eur. J. 2013, 00, 0 – 0
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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W. Dehaen et al.
A
E
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Acknowledgements
We thank the FWO (Fund for Scientific Research - Flanders), the K.U.
Leuven through GOA 2011/2, and BELSPO through IAP-VI-27 and VII-
05 for continuing financial support, the Hercules Foundation of the
Flemish Government (Grant No. 20100225-7) for mass spectrometry.
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Received: March 4, 2013
Published online: && &&, 0000
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ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
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These are not the final page numbers!