Redox-active tetrathiafulvalene and dithiolene compounds derived from allylic 1,4-diol rearrangement products of disubstituted 1,3-dithiole derivatives

Article abstract of DOI:10.3762/bjoc.6.113

We present a series of compounds by exploiting the unusual 1,4-aryl shift observed for electron-rich 1,3-dithiole-2-thione and tetrathiafulvalene (TTF) derivatives in the presence of perchloric acid. The mechanistic features of this rearrangement are disc

Full text of DOI:10.3762/bjoc.6.113

Redox-active tetrathiafulvalene and dithiolene com-
pounds derived from allylic 1,4-diol rearrangement
products of disubstituted 1,3-dithiole derivatives
Filipe Vilela1, Peter J. Skabara*1, Christopher R. Mason2,
Thomas D. J. Westgate2, Asun Luquin3, Simon J. Coles4
and Michael B. Hursthouse4
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2010, 6, 1002–1014.
1WestCHEM, Department of Pure and Applied Chemistry, University
of Strathclyde, 295 Cathedral Street, Glasgow, G1 1XL, UK, 2School
of Chemistry, University of Manchester, Oxford Road, Manchester,
M13 9PL, UK, 3Departamento de Química Inorgánica, Instituto de
Ciencia de Materiales de Aragón, Universidad de Zaragoza-C.S.I.C.,
50009, Zaragoza, Spain and 4Department of Chemistry, University of
Southampton, Highfield, Southampton, SO17 1BJ, UK
doi:10.3762/bjoc.6.113
Received: 04 June 2010
Accepted: 05 October 2010
Published: 21 October 2010
Editor-in-Chief: J. Clayden
Email:
© 2010 Vilela et al; licensee Beilstein-Institut.
License and terms: see end of document.
Peter J. Skabara* - peter.skabara@strath.ac.uk
* Corresponding author
Keywords:
aldehydes; metal-coordination; rearrangement; sulfur heterocycles;
tetrathiafulvalene
Abstract
We present a series of compounds by exploiting the unusual 1,4-aryl shift observed for electron-rich 1,3-dithiole-2-thione and
tetrathiafulvalene (TTF) derivatives in the presence of perchloric acid. The mechanistic features of this rearrangement are discussed
since this synthetic strategy provides an alternative route for the synthesis and functionalisation of sulfur rich compounds including
redox active compounds of TTFs, and a Ni dithiolene.
Introduction
The search for novel structures derived from TTF has led to hydroxymethyl)-1,3-dithiole-2-thiones (2) in the presence of
extensive investigations of the chemistry of 1,3-dithiole-2- acid catalysts [4]. As well as the expected dihydrofuran, formed
thione (1, Figure 1) [1,2], since this heterocycle and its deriva- by a nucleophilic ring-closing reaction, other compounds were
tives are frequently used as convenient precursors to TTF com- also produced depending on the nature of the aryl group, the
pounds through phosphite-mediated coupling [3].
nature of the solvent and the acid used (e.g., 3). The extent to
which the aryl groups and their substituents are able to stabilise
Our efforts to prepare triaryl derivatives of compound 1 led to the carbocation, formed by the loss of a protonated hydroxy
the discovery of an unexpected rearrangement of 4,5-bis(2-aryl- group, is key in determining the reaction product. The diverse
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Beilstein J. Org. Chem. 2010, 6, 1002–1014.
LDA and subsequent reaction with aryl carboxaldehydes
affords the corresponding bisalcohol products 2 in good yield
(75–90%). Under ambient conditions, these diols decompose
slowly. However, on treatment with a few drops of perchloric
acid to solutions of 2 in dichloromethane (CH2Cl2), the rate of
decomposition of the starting materials greatly increases and in
all cases the diol is consumed within 24 h. Dihydrofurans, such
as 5 (87% yield), were isolated from the corresponding diols as
mixtures of stereoisomers, whereas the 4-methoxyphenyl
substituted diol gave the rearrangement product 6 in 44% yield.
Figure 1: Chemical structures of compounds 1–3.
range of π-rich structures that can be obtained from the diol The rearrangement products from 2 were all obtained as the
includes ketone, aldehyde and haloalkene functionalities and major product (by tlc). By contrast, when 2 was treated with
these offer further possibilities for the synthetic use of TTF- HBr in CH2Cl2, compound 7 was isolated as a yellow oil via the
based compounds that are well known in conducting materials initially produced dihydrofuran 4 along with compound 8
[5].
(observed only by 1H NMR) [6].
Herein, we report an extended study of these unusual 1,4-aryl The behaviour of 4,5-bis(2-thienylhydroxymethyl)-1,3-dithiole-
rearrangements involving 1,3-dithiole-2-thione and TTF deriva- 2-thione in the presence of perchloric acid is of particular
tives, postulate a likely reaction mechanism and comment on interest. Under these conditions the diol undergoes an intramo-
substituent effects.
lecular rearrangement to form the ring-fused product 3 in good
yield [6].
Results and Discussion
Synthesis
Discussion
Scheme 1 summarises the overall procedure that leads to the The first step in this process is the protonation of one of the
1,4-aryl rearrangements. The lithiation of compound 1 with hydroxy groups (Scheme 2). Subsequent loss of water affords a
Scheme 1: Acid-catalysed behaviour of 4,5-bis(2-arylhydroxymethyl)-1,3-dithiole-2-thiones 2.
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Beilstein J. Org. Chem. 2010, 6, 1002–1014.
Scheme 2: The proposed mechanism for the formation of 3.
carbocation that can be stabilised by resonance of π-electrons ation of the positive charge, which could complicate the pinacol
from either the 1,3-dithiole-2-thione or thienyl groups. This mechanism. Related reactions of allylic alcohols are not
intermediate can then undergo intramolecular nucleophilic ring- unknown: periodic acid has been shown to oxidise one of the
closure by the remaining hydroxy group with the formation of alcohol groups in a 1,4-diol fragment to yield the corres-
the dihydrofuan 4 shown in Scheme 1. Dominating this process ponding aldehyde, without any further change to the remnant
is the competing electrophilic attack of the allylic carbocation at allylic alcohol [10]; a related mechanism has been reported for a
the 3-position of the thiophene ring bearing the carbinol group, self-coupling intermolecular reaction, which involves an inter-
forming a new C–C bond and producing a 6-membered ring. mediate allylic cation generated under acidic conditions from an
Concomitantly, the cationic centre migrates to produce a C=S+ electron-rich thienylmethanol derivative, where no intramolecu-
form, where it is stabilised by π-electron density. The second lar rearrangement took place [11]. Also worth noting, is a recent
hydroxy group is eliminated in a dehydration process. Loss of a study on cationic 1,4-aryl migration observed during reactions
further proton affords the neutral product 3 with a fully aroma- of vinylidenecyclopropanes with electron-rich bis(p-alkoxy-
tised 6-membered ring.
phenyl)methanols [12].
This process bears similarities to other rearrangements that are We have extended our study using a 4-methoxyphenyl substi-
well known in classical organic chemistry [7-9]. The pinacol tuted diol as an example. The proposed decomposition of 13 is
rearrangement, for example, also involves the loss of H2O from described in Scheme 3. It should be noted that the involvement
a protonated diol followed by migration of the cation to yield a of a phenonium intermediate in aryl shifts has been previously
protonated carbonyl group and simultaneous rearrangement of observed [13], and that theoretical studies have also shown that
the C–C skeleton. The principle of intermediate carbocation there is significant stabilisation of the phenonium ion through
stabilisation also involves the breaking of carbon–carbon or back-bonding from the ethylene unit of spirocyclopropyl benze-
carbon–hydrogen bonds followed by formation of new ones via nium species [14].
alkyl, hydride and allylic shifts.
However, as seen in Scheme 3, we propose a methoxy stabilised
However, one cannot assume that the mechanism is pinacol- spirocyclopentyl benzenium intermediate. This mechanism is
like. Saturated 1,4-diols favour the formation of tetrahydro- only valid for the 4-methoxy derivative as the position of the
furan derivatives, whilst allylic cations will involve some electron donating groups is fundamental in producing the dihy-
degree of stabilisation through hyperconjugation and delocalis- drofuran or the 1,4-shift products.
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Beilstein J. Org. Chem. 2010, 6, 1002–1014.
Scheme 3: The proposed mechanism for the decomposition of 13 in the presence of perchloric acid.
It is also unusual that the sole product from the corresponding
2-methoxyphenyl compound leads to a dihydrofuran derivative,
particularly since the electron donating substituent effect should
be identical to that of the 4-methoxy compound, which
rearranges to give the corresponding dihydrofuran. One possible
explanation for this can be derived from the X-ray crystal struc-
ture of the dihydrofuran derivative [4]. The intramolecular close
Figure 2: Generalised structure of diol 17.
contacts between O(2)···S(2) and O(3)···S(3) arise from a three-
centre four-electron interaction [15], which decreases the elec-
tron releasing ability of the methoxy groups towards the of the diol resulted in a mixture of products, however, the TTF
benzene ring, thereby conferring a weaker stabilising effect derivative 20 was isolated by column chromatography in only
upon the phenonium ion. This type of intramolecular inter- 9% overall yield from 18. Since the reaction of tetrathiaful-
action has been observed in the X-ray crystal structures of other valenyllithium with simple aldehydes proceeds to give the
triaryl dithiole-2-thione species [16].
corresponding alcohols in 40–60% yield [18], the rearrange-
ment of 19 to give 20 is estimated to proceed in 25–55% yield.
In order to investigate the limitations of this new rearrangement Cyclic voltammetry (in dichloromethane, vs Ag/AgCl) showed
process, we carried out studies on analogous benzene deriva- two sequential, reversible oxidation steps for compound 20 at
tives (17, Figure 2). In each case, the addition of perchloric acid E1/2 = +0.72 and +1.09 V.
resulted in a complex mixture of products, which could not be
easily separated [4].
To demonstrate the reactivity of the 1,4-shift products and to
assess the degree of steric hindrance by the aromatic units
The 1,4-aryl shift was also attempted on compound 19 to ascer- towards the formyl group, compound 21 [4] was reacted with
tain whether or not this type of rearrangement is accessible to ethylenediamine in the presence of a catalytic amount of acetic
TTF derivatives (Scheme 4). The diol 19 was prepared directly acid (Scheme 5).
from compound 18 [17] and treated with two equivalents of
LDA and 2,4-dimethoxybenzaldehyde, as described above for The Schiff base product 22 was obtained in 62% yield as a pale
compound 1. The addition of perchloric acid to a crude sample brown crystalline solid. Although highly strained and buckled
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Beilstein J. Org. Chem. 2010, 6, 1002–1014.
Scheme 4: Reagents and conditions: (i) LDA (1 equiv), 2,4-dimethoxybenzaldehyde (1 equiv), then repeat, −78 °C, THF; (ii) HClO4, CH2Cl2, rt.
Scheme 5: Reagents and conditions: (i) ethylenediamine, AcOH, MeOH; (ii) P(OEt)3, 120 °C, 3 h.
TTF derivatives have been reported [19], treatment of 22 with strengthen the degree of conjugation between the imine func-
triethyl phosphite did not give the desired self-coupled TTF tionality and the dithiole unit: the torsion angle within
compound 23. The X-ray structure of 22 is shown in Figure 3. C(18)–C(19)–C(21)–N(1) is 173.2(9)° whilst the bond length of
The molecule possesses an inversion centre located at the C(19)–C(21) (1.449(6) Å) is shorter than that of a typical conju-
C(22)–C(22’) bond. A close intramolecular contact is observed gated single C(sp2)–C(sp2) bond (mean 1.455 Å) and substan-
between S(2)···N(1) at 2.936(3) Å. This interaction serves to tially shorter than non-conjugated ones (1.478 Å) [20].
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Beilstein J. Org. Chem. 2010, 6, 1002–1014.
tions. For example, benzyl and thienyl annelated TTF deriva-
tives and analogues have been shown to perform well as semi-
conductor materials in organic field effect transistors (OFETs)
[21,22]. This has been attributed to the enhanced π–π stacking
of the extended aromatic groups, which improves intermolecu-
lar electronic transfer. Annelated aromatic groups also lower the
electron donating ability of TTF, which improves resistance to
oxidative degradation in field effect transistor (FET) devices,
whilst the incorporation of solubilising groups to these systems
offers good processability for the annelated products [23-25].
The thione group in 3 has the potential for several synthetically
useful manipulations (Scheme 6).
Compound 3 was shown to be a synthetically versatile com-
pound. Refluxing of 3 in triethyl phosphite followed by purifi-
cation by filtration through silica gel (eluting with chloroform)
gave a mixture of geometrical (cis- and trans-) isomers of the
TTF derivative 25 in 12% yield. The two isomers could not be
separated either by chromatography or by recrystallisation. It
should be noted, that in the oxidation of 25 the central C=C
Figure 3: Molecular structure and numbering scheme of compound 22
with Hs omitted.
Redox-active derivatives of compound 3
Compound 3 contains a fused thienobenzodithiole-2-thione bond is broken, allowing free rotation and therefore isomerisa-
unit. These three annelated cyclic moieties present an interest- tion. It can be anticipated that the two isomers will not differ
ing and potentially useful structural motif for materials applica- significantly in their electrochemical properties (see below).
Scheme 6: Reagents and conditions: (i) P(OEt)3, reflux; (ii) Hg(OAc)2, CH2Cl2/AcOH; (iii) NaOEt, THF, reflux, then Bu4NBr and NiCl2·6H2O, rt; (iv)
NaOMe, THF, then 1,2-dibromoethane.
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Beilstein J. Org. Chem. 2010, 6, 1002–1014.
Compound 3 was trans-chalcogenated by mercury(II)acetate in C22–C21–C15–C14 and C10–C9–C5–C6 are 133.97(24)° and
a mixture of acetic acid and CH2Cl2 to give the oxo derivative 81.79(60)°, respectively. There is a slight distortion in the
26 in 89% yield. Purification of 26 was achieved by recrystalli- Ni-dithiolene core, which is commonly planar, with an angle of
sation from CH2Cl2 and petroleum ether. Treatment of 26 with 6.45(2)° between the two planes of the component rings. There
methoxide solution (generated in situ) resulted in sequential is some disorder in one of the peripheral thiophene rings, with
nucleophilic addition-elimination at the carbonyl carbon, gener- atoms S4 and C10 occupying common positions with 50%
ating the disodium dithiolate salt 24.
probability.
The dianion was subsequently ring-closed by two SN2 reac-
tions with 1,2-dibromoethane in THF to yield 27(56% yield)
after purification by column chromatography (eluting with 1:1
(v/v) CH2Cl2:petroleum ether). Dithiolate 24 was also gener-
ated from the analogous reaction with 3. On this occasion, treat-
ment of 24 with excess nickel(II)chloride and tetrabutylammo-
nium bromide afforded the nickel(II)dithiolato complex 28
(40% yield) after purification by recrystallisation from CH2Cl2
and hexane. Dithiolenes represent an important and well-studied
class of molecular conductors [26] and we have previously
studied thiophene-containing analogues as precursors to highly
electroactive polythiophenes [27,28]. We were interested in the
self-assembly of compound 28 in the solid state to assess
whether or not this material would be suitable as a semicon-
ductor in OFETs [29]. Single crystals of compound 28 were
Figure 4: Molecular structure of 28 with the tetrabutylammonium
cation omitted.
grown from a dichloromethane/hexane solution. X-ray crystal- The packing diagram in Figure 5 highlights the intermolecular
lographic data confirmed that the isolated nickel dithiolene was interactions that exist in the bulk, which in turn would support
monoanionic and that only one of the two possible isomers of semiconductor behaviour. Firstly, there are sulfur–sulfur close
this product was isolated by the recrystallisation method (both contacts between adjacent S7 atoms (3.2479(8) Å), and these
non-fused thiophenes are on the same side of the fused frame- interactions are restricted to dimers. Secondly, the six-
work). The molecular structure of the compound is shown in membered ring comprising–C1–C2–C3–C4–C5–C6– and the
Figure 4 and the packing diagram is shown in Figure 5. The adjacent thiophene (–S3–C7–C8–C4–C3–) form π–π interac-
peripheral, non-fused thiophenes are significantly distorted tions with a neighbouring molecule, such that the overlap
from the plane of the fused skeleton, leaving them weakly between the corresponding molecules is restricted to one minor
conjugated to the main π-framework. The torsion angles for portion of the molecule. The centroid–centroid distance
Figure 5: Packing diagram of 28 identifying close intermolecular contacts.
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Beilstein J. Org. Chem. 2010, 6, 1002–1014.
between the benzene and thiophene rings is 3.74 Å and this The electrochemistry of 3, 25, 27 and 28 was investigated by
interaction is also constrained to dimers. Although in Figure 5 cyclic voltammetry. Solutions of the compounds (0.1 mM) were
the cations have been omitted for clarity, the diagram shows prepared in anhydrous CH2Cl2 with 0.1 M tetrabutylammo-
where the tetrabutylammonium molecules reside to block nium hexafluorophosphate as the supporting electrolyte. Glassy
further close π–π interactions. These interactions ultimately lead carbon, platinum wire, and Ag/AgCl electrodes were used as
to orbital overlap in one dimension, albeit through a combina- the working, counter and reference electrodes, respectively. The
tion of chalcogen–chalcogen and π–π contacts.
cyclic voltammograms are shown in Figure 7, and the potential
values of the redox processes are collated in Table 1.
The UV–visible electronic absorption spectra of compounds 3,
25, 27 and 28 were recorded in CH2Cl2 solution and are shown
in Figure 6. The spectra of thione 3 and ethylenedithio-bridged
derivative 27 show similar features. Each shows a peak at 376
nm and one around 275 nm. The intensities of these peaks are
reversed in each case, however. In 27 the 376 nm peak is far
less prominent compared to the 275 nm peak than in the thione.
The spectrum of 27 also shows a shoulder at around 310 nm.
These two bands are also present in TTF derivative 25 and the
nickel complex 28.
Figure 7: Cyclic voltammograms of compounds 3, 25, 27, and 28.
Glassy carbon working electrode, using Pt wire counter and Ag/AgCl
reference electrodes, in CH2Cl2 (substrate ca. 10−3 M), Bu4NPF6
supporting electrolyte (0.1 M), with a scan rate of 100 mV s−1.
In compounds 3 and 27 an irreversible single electron oxidation
wave is seen at +1170 mV and +900 mV, respectively. Further
oxidation processes of these materials do not occur within the
electrochemical window of the solvent. The electron with-
drawing effect of the thione causes the oxidation to occur at a
higher potential in 3 than in 27. In TTF derivative 25 the two
characteristic reversible single electron redox waves, arising
from the step-wise formation of the TTF radical cation and
dication, are seen at +260 mV and +720 mV, respectively. The
formation of the TTF dication hinders subsequent removal of an
electron from the thiophene units, so further oxidations are
beyond the electrochemical window of the solvent. Compound
28 is reversibly oxidised to 28+· at −740 mV, within the range
seen in other nickel dithiolene complexes. A second single-elec-
tron oxidation is seen at around +110 mV, and appears to be re-
versible.
Figure 6: UV–visible spectra of 3, 25, 27 and 28 in CH2Cl2 solution.
The band at 376 nm in 3 and 27 appears at 382 nm in 25 and is
seen as a shoulder at approximately 372 nm in 28. The higher
energy band at around 275 nm in 3 and 27 is shifted in 25 and
28 to lower energy (313 nm in 25, 324 nm in 28). The spectrum
of 28 also shows a broad feature at around 900 nm, corres-
ponding to the π–π * transition of the highly delocalised nickel
dithiolene unit.
Table 1: Redox potentials of compounds 3, 25, 27 and 28 (half-wave potentials except where irreversible).
3
25
27
28
E½ 1 (mV)
E½ 2 (mV)
+1170 (irreversible)
—
+260
+720
+900 (irreversible)
—
−740
+110
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Beilstein J. Org. Chem. 2010, 6, 1002–1014.
Attempts to electro-polymerise compounds 3, 25, 27 and 28 properties of the dithiolate anion, as shown in compound 28,
were unsuccessful. The primary reason for this may be the present a potentially rich avenue for further investigation by
inability to oxidise the fused thiophene ring, ruling out coupling variation of the metal cation. This dianion could also be reacted
through the 2-position of this unit. Electro-oxidative coupling of with a variety of dihaloalkanes to create a family of compounds
3 and 27 is therefore only accessible through the pendant group with alkyl bridges of different lengths. Finally, this reaction is
making a dimer the only possible product. Compounds 25 and important for understanding the stabilising effects of
28 have two oxidisable pendant thiophene groups, so polymeri- substituents upon the allylic cation and, independently, the
sation could theoretically proceed through the coupling of these phenonium intermediate, as well as providing an alternative
units. However, repeated cycling over the oxidative electroac- strategy towards the functionalisation of benzylated 1,3-dithiol-
tive range of 25 and 28 did not produce the sequential increase 2-thione and TTF derivatives.
of current characteristic of the formation of a polymer film on
Experimental
the working electrode. Furthermore, no deposited material was
observed on the working electrode surface. Coupling of 25 and X-ray crystallography
28 through the pendant thiophenes may be sterically Table 2 provides all the data collected and the refinement para-
demanding, but the formation of short oligomers cannot be meters for the structures of 22 and 28. All data were collected at
ruled out in this mechanism.
150 K, on a Nonius KappaCCD area detector diffractometer, at
the window of a Nonius FR591 rotating anode (λ MoKα =
0.7106 Å). A correction was applied to account for absorption
Conclusion
We have shown that the unusual 1,4-aryl shift observed in the effects by means of comparing equivalent reflections, using the
presence of perchloric acid for electron-rich 1,3-dithiole-2- program SORTAV [32,33]. A solution was obtained via direct
thione and TTF derivatives can be exploited to further expand methods and refined [34] by full-matrix least-squares on F2,
this family of compounds. For example, previous work has with hydrogens included in idealised positions. There is rota-
shown that the electron-donating ability of terthiophenes can be tional disorder of a thiophene moiety in 28, where C10 and S4
tailored by this approach [30,31]. Also, the metal-coordination occupy the same position in the ring with a site occupancy of
Table 2: Data collection and refinement parameters for structures 22 and 28.
22
28
Empirical formula
C44H44N2O8S6
921.17
C40H48NNiS8
857.98
Molecular mass
Crystal system
P21/c
P-1
Space group
Monoclinic
12.185(2)
10.904(2)
17.597(3)
90
Triclinic
a/Å
9.9368(2)
10.0005(2)
22.5310(3)
95.050(2)
93.054(2)
114.388(2)
2021.34(4)
2
b/Å
c/Å
α/°
β/°
106.87(3)
90
γ/°
V/Å3
2237.3(8)
2
Z
Dcalcd./g cm−3
µ/mm–1
1.367
1.410
0.360
0.924
Crystal size/mm3
θ range
0.25 × 0.25 × 0.20
3.04–25.01
15332
0.38 × 0.04 × 0.01
3.01–27.50
55561
Measured reflections
Independent reflections [I > 2σ(I)]
Rint
3918
8113
0.0672
0.0408
R indices [F2 > 2σF2]
R indices [all data]
Goodness of fit
ρmax/ρmin/e Å−3
0.0664/0.1768
0.0865/0.1954
1.009
0.0383/0.0976
0.0454/0.1018
1.039
0.877/−0.497
0.714/−0.555
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Beilstein J. Org. Chem. 2010, 6, 1002–1014.
50%. Supplementary data for 22 and 28 have been deposited temperature. The residue was washed with saturated NaHCO3
with the CCDC; deposition numbers = CCDC 216240 and (100 cm3) and re-extracted with dichloromethane or ethyl
778197, respectively. These data can be obtained free of charge acetate (3 × 100 cm3). The combined extracts were dried over
at www.ccdc.cam.ac.uk/conts/retrieving.html (or from the magnesium sulfate and the solvent removed under reduced pres-
Cambridge Crystallographic Data Centre, 12, Union Road, sure. All compounds were purified by column chromatography
Cambridge CB2 1EZ, UK; fax: (internat.) +44-1223/336-033; (silica).
E-mail: deposit@ccdc.cam.ac.uk).
4,6-Diphenyl-4,6-dihydro-[1,3]dithiolo[4,5-c]furan-2-
General
thione (5)
Unless, otherwise stated all reactions were performed under an From the corresponding diol (0.93 g, 2.7 mmol) compound 5, a
inert atmosphere of dry nitrogen using standard Schlenk tech- brown solid, was isolated as a mixture of diastereomers (0.77 g,
niques. All glassware was flame dried under vacuum prior to 87%). mp 153–155 °C; found: C, 61.76; H, 3.86; S, 28.68%.
use. All solvents and reagents were purchased from the Sigma- C17H12O1S3 requires C, 62.16; H, 3.68; S, 29.28%; m/z (CI)
Aldrich chemical company and used as received. 1H, and 13C 329 (M+); δH (CDCl3) 7.40–7.20 (10H, m) and 6.10 (2H, s);
NMR spectra were recorded on a Bruker AC300 FTNMR 7.40–7.20 (10H, m) and 6.21 (2H, s); δC (CDCl3) 217.6, 141.3,
instrument operating at room temperature (300 MHz for 1H, 75 140.8, 137.8, 128.9, 126.4 and 84.9; νmax (KBr)/cm−1 1453,
MHz for 13C). Mass spectra were recorded on a Kratos concept 1273, 1124, 1056, 1009, 749, 699 and 478.
1S instrument. Infrared spectra were recorded on a Specac
single reflectance ATR instrument (4000–400 cm−1, resolution 5-[Bis(4-methoxyphenyl)methyl]-2-thioxo-
4 cm−1). Elemental analysis was performed by the University of [1,3]dithiole-4-carbaldehyde (6)
Manchester micro-analytical laboratory. Melting points were From the corresponding diol (1.45 g, 3.6 mmol) compound 6
recorded on a Gallenkamp melting point apparatus and are was obtained as a yellow flocculent solid (0.50 g, 36%). mp
uncorrected. Cyclic voltammetry was performed with a CH 60–62 °C; found: C, 58.66; H, 3.87; S, 25.20%. C19H16O3S3
instruments voltammetric analyser with iR compensation, in an- requires C, 58.74; H, 4.15; S, 24.76%; m/z (CI) 389 (M+); δH
hydrous dichloromethane, with aqueous Ag/AgCl as the refer- (CDCl3) 9.61 (1H, s), 7.14 (4H, dd, J 6.7 and 1.9), 6.90 (4H, dd,
ence electrode and platinum wire and gold disk as the counter J 6.7 and 2.2), 6.05 (1H, s) and 3.81 (6H, s); δC (CDCl3) 209.5,
and working electrodes, respectively. The solution was 178.1, 166.2, 159.3, 139.4, 132.3, 129.5, 114.5, 55.3 and 49.6;
degassed (N2) and contained the substrate in a concentration of νmax (KBr)/cm−1 1664, 1608, 1511, 1249, 1178, 1077, 1031,
ca. 10−3 M together with Bu4NPF6 (0.1 M) as the supporting 829 and 582.
electrolyte.
5-[Bis(2,4-dimethoxyphenyl)methyl]-4',5'-bis-methyl-
General procedure for compounds 5–6 and 20
sulfanyl-[2,2']bi{[1,3]dithiolylidene}-4-carbaldehyde
To a solution of vinylene trithiocarbonate or compound 15 in (20)
dry tetrahydrofuran (20–80 ml) at −78 °C under nitrogen, was From the corresponding diol (0.75 g, 1.2 mmol) compound 20
added lithium diisopropylamide mono(tetrahydrofuran) (1.5 M was obtained as a red oil (68 mg, 9%), m/z (EI) 610.0100 (M+,
in hexanes, 1.1 equiv). The mixture was stirred under dry C26H26O5S6 requires 610.0104); δH (CDCl3) 9.60 (1H, s), 7.02
nitrogen for 20 min. The relevant aldehyde was then added and, (2H, d, J 8.4), 6.43 (4H, m), 6.36 (1H, s), 3.86 (6H, s), 3.83
after stirring for 5 min, a second portion of LDA was added (1.1 (6H, s), 2.46 (3H, s) and 2.43 (3H, s); δC (CDCl3) 180.0, 164.9,
equiv). The mixture was stirred for a further 15 min followed by 160.8, 157.9, 132.3, 129.7, 128.4, 127.2, 121.7, 109.4, 104.4,
the addition of another portion of aldehyde and stirred for a 98.9, 56.0, 55.7, 37.1 and 19.5; νmax (KBr)/cm−1 1650, 1610,
another 5 min. The reaction was then allowed to warm to room 1503, 1294, 1208 and 1033.
temperature and poured into saturated NaHCO3 solution
(20–100 ml). The organic layer was separated and the aqueous N,N’-Bis{5-[bis(2,4-dimethoxyphenyl)methyl]-2-
phase extracted with CH2Cl2 (3 × 50 ml). The combined thioxo-[1,3]dithiole-4-ylmethylene}ethan-1,2-di-
organic extracts were dried (MgSO4) and evaporated under amine (22)
reduced pressure. The product was used in the next step without Compound 21 (0.50 g, 1.12 mmol) was dissolved in methanol
further purification.
(50 cm3). Ethylenediamine (0.06 g, 1.12 mmol) was added
along with 1–3 drops of acetic acid with stirring. The solution
The corresponding diol was dissolved in dichloromethane (100 was heated at reflux overnight. The resulting brown precipitate
cm3) and perchloric acid was added dropwise (typically 3–6 was recovered and washed successively with ice-cold methanol
drops). The resulting mixture was stirred overnight at room (50 cm3) and petroleum ether (50 cm3). Recrystallisation from
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Beilstein J. Org. Chem. 2010, 6, 1002–1014.
dichloromethane/hexane gave the product as a pale brown crys- magnesium sulfate and filtered. The solvent was removed under
talline solid (0.32 g, 62%). mp 213–215 °C; found: C, 57.19; H, reduced pressure to yield a straw-coloured solid which was
4.73; N, 3.12 %. C44H44N2O8S6 requires C, 57.43; H, 4.82; N, purified by recrystallisation from dichloromethane and petro-
3.04%; m/z (ES) 921 (M+); δH (CDCl3) 7.95 (2H, s), 6.95 (4H, leum ether 40/60, to give 26 as straw needles, 0.145 g, 89%, mp
d. J 8.5), 6.51 (4H, d, J 2.3), 6.46 (4H, dd, J 8.4 and 2.5), 3.82 118–124 °C; EI+ MS (M+) 306; Accurate mass calculated for
(12H, s), 3.80 (12H, s) and 3.69 (4H, s); νmax (KBr)/cm−1 2935, C13H6S4O 305.9296, found 305.9292; 1H NMR (300 MHz,
1612 and 1059.
CDCl3) δH (ppm): 7.95 (1H, d, J = 0.7 Hz), 7.53 (1H, dd, J =
5.1 and 1.2 Hz), 7.45 (1H, d, J = 5.6 Hz), 7.34 (1H, dd, J = 5.6
2,2’-Bis[(8-(2-thienyl)thieno[2,3-f][1,3]benzodithiolyli- and 0.7 Hz), 7.27 (1H, dd, J = 3.6 and 1.2 Hz), 7.20 (1H, dd, J =
dene)] (25) 5.1 and 3.6 Hz); 13C NMR (75 MHz, CDCl3) δC (ppm): 189.6,
8-(2-Thienyl)thieno[2,3-f][1,3]benzodithiole-2-thione 3 (0.377 138.8, 138.8, 138.6, 131.0, 129.1, 128.5, 127.7, 127.6, 127.3,
g, 1.17 mmol) was suspended in the minimal amount of freshly 125.5, 123.2, 116.5; IR ν (cm−1) 3102, 1651, 1403, 1370, 1068,
distilled triethyl phosphite (<5 ml) under a nitrogen atmosphere. 875, 852, 828, 697; Anal. calculated for C13H6S4O: C, 50.95;
The suspension was placed into an oil bath pre-heated to 110 °C H, 1.97; S, 41.85; found: C, 50.52, H, 1.62; S, 42.66.
and heated under reflux with magnetic stirring for 20 h. A
yellow-brown precipitate was collected on a Hirsch funnel and 5,6-ethylenedithio-4-(thiophen-2-yl)benzo[b]thio-
washed with copious amounts of hexane, then dissolved in chlo- phene (27)
roform and passed through a layer of silica gel eluting with 8-(2-Thienyl)thieno[2,3-f][1,3]benzodithiole-2-one 26 (0.200 g,
chloroform until thin-layer chromatography indicated that the 6.52 × 10−4 mol) was dissolved in anhydrous tetrahydrofuran
filtrate contained none of the product. Removal of solvent under (15 ml) under a nitrogen atmosphere with magnetic stirring.
reduced pressure afforded a bright yellow sparingly soluble Separately, a methanolic solution of sodium methoxide (0.718
solid, shown by 1H NMR to be a mixture of two isomers in the mol·L−1) was prepared by adding sodium (0.428 g, 0.0186 mol)
ratio 1:2.4, 80 mg, 12%, mp > 300 °C (decomp.); MALDI-TOF to anhydrous methanol (15 ml) under a nitrogen atmosphere.
MS: 580; Accurate Mass calculated for C26H12S8 579.8699 2.0 ml of this sodium methoxide solution (2.2 equivalents
found 579.8707; 1H NMR (major isomer, 400 MHz, CDCl3) δH (0.001434 mol) was added by syringe to the THF solution. The
(ppm): 7.71 (1H, d, J = 0.7 Hz), 7.49 (1H, dd, J = 5.1 and 1.1 mixture was stirred at room temperature for 1.5 h, then 1,2-
Hz), 7.34 (1H, d, J = 5.5 Hz), 7.26 (1H, dd, J = 3.5 and 1.1 Hz), dibromoethane (0.058 ml, 0.126 g, 6.700 × 10−4 mol) was
7.23 (1H, dd, J = 5.5 and 0.7 Hz), 7.19 (1H, dd, J = 5.1 and 3.5 added and the reaction stirred at room temperature for 16 h,
Hz); (minor isomer, 400 MHz, CDCl3) δH (ppm): 6.68 (1H, d, J during which time a white precipitate formed. The mixture was
= 0.7 Hz), 7.52 (1H, dd, J = 5.1 and 1.2 Hz), 7.34 (1H, d, J = added to water (50 ml) and extracted with dichloromethane (3 ×
5.5 Hz), 7.29 (1H, dd, J = 3.5 and 1.2 Hz), remaining minor 100 ml). The combined organic extracts were dried over magne-
isomer signals obscured in region 7.3–7.2; IR ν (cm−1) 3088, sium sulfate, filtered, and the solvent was removed under
1402, 1372, 1310, 1198, 1135, 1092, 842, 827, 715, 691; reduced pressure. The resulting yellow solid was purified by
UV–vis, λmax = 382 nm, ε = 2000; Anal. Calculated for column chromatography on silica gel eluting with 1:1 (v/v)
C26H12S8: C, 53.76; H, 2.08; S, 44.16; found C, 53.56; H, 1.82; dichloromethane:petroleum ether 40/60 to yield a bright yellow
S, 44.14.
waxy solid 0.112 g, 56%, mp 57–61 °C; APCI +ve MS (M + 1)
307; Accurate mass calculated for C14H10S4 305.9660, found
305.9666; 1H NMR (400 MHz, CDCl3) dH (ppm): 7.83 (1H, d,
J = 0.7 Hz), 7.51 (1H, dd, J = 5.1 and 1.2 Hz), 7.29 (1H, d, J =
8-(2-Thienyl)thieno[2,3-f][1,3]benzodithiole-2-one
(26)
8-(2-Thienyl)thieno[2,3-f][1,3]benzodithiole-2-thione, 3 (0.171 5.6 Hz), 7.20 (1H, dd, J = 5.1 and 3.5 Hz), 7.11 (1H, dd, J = 3.5
g, 5.302 × 10−4 mol) was dissolved in a mixture of 3:1 by and 1.2 Hz), 7.02 (1H, dd, J = 5.6 and 0.7 Hz), 3.33 (2H, m),
volume CH2Cl2:glacial acetic acid (100 ml) with magnetic stir- 3.16 (2H, m); 13C NMR (100 MHz, CDCl3) δC (ppm): 139.4,
ring. Mercury (II) acetate (0.236 g, 7.423 × 10−4 mol) was 138.5, 136.9, 131.1, 129.2, 129.0, 127.2, 126.8, 126.4, 123.6,
added which caused an immediate lightening of the yellow 122.7, 114.9, 30.9, 30.7; IR ν (cm−1) 3100, 2916, 1559, 1406,
solution and the formation of a white precipitate. The reaction 1365, 1312, 1288, 1194, 1138, 853, 824. 769, 702; UV–vis,
was stirred at room temperature for 4 h then filtered through a λmax = 376 nm, ε = 8000.
layer of silica gel, washing with dichloromethane until the
filtrate was colourless. The filtrate was concentrated to approxi- Tetrabutylammonium bis[(4-thiophen-2-
mately 100 ml under reduced pressure then washed sequen- yl)benzo[b]thiophene-5,6-bis(thiolato)]nickel(II) (28)
tially with water (75 ml), sodium hydrogen carbonate (satu- To a solution of 8-(2-thienyl)thieno[2,3-f][1,3]benzodithiole-2-
rated aqueous solution, 2 × 50 ml), water (100 ml), dried over thione 3 (0.092 g, 2.85 × 10−4 mol) in dry THF (10 ml) under a
1012

Beilstein J. Org. Chem. 2010, 6, 1002–1014.
14.del Rio, E.; Menédez, M. I.; López, R.; Sordo, T. L. J. Phys. Chem. A
2000, 104, 5568–5571. doi:10.1021/jp994068g
nitrogen atmosphere, was added sodium ethoxide (0.1 M
aqueous solution, 2.85 ml, 2.85 × 10−4 mol) and the mixture
heated under reflux for 1 h. Tetrabutylammonium bromide
(0.097 g, 3.01 × 10−4 mol) and nickel (II) chloride hexahydrate
(0.036 g, 1.51 × 10−4 mol) were then added and the mixture was
stirred magnetically for 18 h then filtered. The filtrate was
concentrated to a few ml under reduced pressure, and addition
of petroleum ether 40/60 afforded a dark green precipitate
which was recrystallised from dichloromethane/hexane, 0.103
g, 40%, mp 215–216 °C; 1H NMR (major isomer, 400 MHz,
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A
(relative integral 2.1, v. broad s), 1.63 (relative integral 6.1,
20.Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen, A. G.;
broad s), 1.32 (relative integral 3.0, broad s), 1.26 (relative inte-
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3417, 3091, 2956. 1618, 1466, 1311, 1286, 851, 822, 699;
UV–vis, λmax = 901 nm, ε = 12000.
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Acknowledgements
We thank the EPSRC for research grant EP/E027431 (F.V.).
22.Mas-Torrent, M.; Masirek, S.; Hadley, P.; Crivillers, N.; Oxtoby, N. S.;
Reuter, P.; Veciana, J.; Rovira, C.; Tracz, A. Org. Electron. 2008, 9,
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