Alkynyl Fischer carbene complex as a traceless directing group for the regioselective cycloaddition of dithiolethiones to arylacetylene: Synthesis of E-dithiafulvene thione and dithioesters

Article abstract of DOI:10.1039/b715857b

A phenylethynyl Fischer carbene complex was used as a traceless directing group for the regioselective cycloaddition of dithiolethiones to arylacetylene, which constitutes the first synthesis of E-dithiafulvene thione or dithioesters. The Royal Society of Chemistry.

Full text of DOI:10.1039/b715857b

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Alkynyl Fischer carbene complex as a traceless directing group for the
regioselective cycloaddition of dithiolethiones to arylacetylene:
synthesis of E-dithiafulvene thione and dithioesters{{
Alejandro M. Granados,*a Alejandro M. Fracaroli,a Rita H. de Rossi,a Pedro Fuertesb and Toma´s Torroba*b
Received (in Cambridge, UK) 15th October 2007, Accepted 5th November 2007
First published as an Advance Article on the web 14th November 2007
DOI: 10.1039/b715857b
cases.9 A few other heterocycloaddition reactions involving alkynyl
A phenylethynyl Fischer carbene complex was used as a
Fischer carbene complexes and nitrogen-containing reagents are
known10 as well as addition of sulfur nucleophiles to alkynyl
Fischer carbene complexes,11 but cycloadditions involving sulfur-
containing reagents are not reported. We have previously reported
that 3H-1,2-dithiole-3-thione derivatives reacted with aryl Fischer
carbene complexes, giving 1,3-dithiin dithioortho esters through
insertion of the carbonic carbon into the S–S bond next to the
thiocarbonyl function of the substrate.12 In this communication we
report the fully regioselective cycloaddition of dithiolethiones to
alkynyl Fischer carbene complexes followed by stepwise elimina-
tion of methanol and chromium hexacarbonyl, which constitutes
the first regioselective synthesis of E-dithiafulvene thiones and
dithioesters.
traceless directing group for the regioselective cycloaddition of
dithiolethiones to arylacetylene, which constitutes the first
synthesis of E-dithiafulvene thione or dithioesters.
The dithiafulvene unit (1,3-dithiole-2-ylidene group) is a good
electron donor currently used in the design and synthesis of new
organic materials, especially in the search for extended tetra-
thiafulvalene derivatives.1 The design of hybrid extended tetra-
thiafulvalene oligomers, in which a conjugated p-quinodimethane2
or vinylogous3 spacer separates two or more dithiafulvene units or
incorporates some metal–dithiolate fused units,4 is an emerging
and important area of investigation with exciting prospects which
has already afforded materials with a large variety of electronic
properties and structural flexibility for specific applications.1,4b The
dithiafulvene unit is also found as part of push–pull donor–
acceptor dyads and cruciforms with unprecedented non-linear
optical and redox-controlled characteristics.5 A common method
for the synthesis of dithiafulvene functionalized units is the
cycloaddition of 3H-1,2-dithiole-3-thiones to electrophilic alkynes
such as acetylenedicarboxylate or acetylenedicarbaldehyde.6 Aryl
acetylenes and alkyl phenylpropiolates are less reactive and
mixtures of regioisomers are obtained.6c Notwithstanding, the
preparation of non-symmetrically substituted dithiafulvene inter-
mediates may be a significant first step in the way to the
preparation of geometrically pure extended bis-substituted tetra-
thiafulvalene derivatives. Currently, mixtures of isomers are used
in rotaxanes,7a nanovalves,7b sensors and nanodevices.7c We
recalled that the Fischer carbene moiety acts as an electron
withdrawing group that enhances the electrophilic character of the
alkyne group, acting as a Michael acceptor and dipolarophile in
thermal cycloadditions between alkynyl Fischer carbenes and 1,3-
dipoles.8 Nitrones and diazoalkanes are particularly well studied
Thus, we added 5-cyclopentylthio-3H-1,2-dithiole-3-thione 1a
(1 equiv) to a solution of [pentacarbonyl(phenylethynylmethoxy)]-
chromium(0) 2 in dry ether at 240 uC and the mixture was stirred
under nitrogen for 30 min, until complete disappearance of 1a as
evidenced by thin layer chromatography. Work-up and
flash column chromatography (silica, hexane–dichloromethane
80 : 20 v/v) afforded product 3a as black crystals characterized by
the usual spectroscopic and analytical techniques (Scheme 1).
Single crystal X-ray diffraction analysis confirmed the structure of
3a§ as the Z-isomer (Fig. 1).
aInstituto de Investigaciones en Fisicoqu´ımica de Co´rdoba (INFIQC),
Departamento de Qu´ımica Orga´nica, Facultad de Ciencias Qu´ımicas,
Universidad Nacional de Co´rdoba, X5000HUA Co´rdoba, Argentina.
E-mail: ale@dqo.fcq.unc.edu.ar; Fax: +54 351 4333030;
Tel: +54 351 4334170
bQu´ımica Orga´nica, Facultad de Ciencias, Universidad de Burgos, 09001
Burgos, Spain. E-mail: ttorroba@ubu.es; Fax: +34 947 258831;
Tel: +34 947 258088
{ The HTML version of this article has been enhanced with colour
images.
{ Electronic supplementary information (ESI) available: Crystallographic
details for 3a, 4a, and 4d and the complex between 1d and chromium
pentacarbonyl. Complete description of the experimental procedures.
Physical and spectral data of all new products. 1H and 13C NMR spectra
of 3a–e and 4a–d. See DOI: 10.1039/b715857b
Scheme 1 Reaction of 1,2-dithiole-3-thiones 1a–c and alkynyl Fischer
carbene complex 2.
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Chem. Commun., 2008, 483–485 | 483

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Scheme 2 Mechanism of reaction of dithiolethiones 1a–e and 2.
As expected,13 compound 1e reacted only by the dithiolethiono
moiety, and 5-cyclopentylthio-1,2-dithiole-3-one did not react with
2 under the same conditions.
In our case, also the complex between 1d and chromium
pentacarbonyl§ did not react with 2, showing that the free
thione group was necessary for the reaction. The demetalation–
decarboxylation step has no direct precedent but a lateral
elimination of methanol from a (2-oxacyclopentylidene)pentacar-
bonylchromium(0) complex by treatment with basic aluminium
oxide in ether14 as well as the formal substitution of an
(allyloxy)carbene metal unit for hydrogen in a l-(allyloxy)-3-(4-
methylphenyl)prop-2-yn-l-ylidenepentacarbonylchromium(0) deri-
vative under treatment with silica, that promoted retro-Fischer
reactions, are known,15 therefore a elimination of methanol by
hydrolysis on alumina, followed by elimination of chromium
hexacarbonyl by a retro-Fischer reaction similar to Do¨tz’s
example, should appropriately give rise to 4a–d.
Fig. 1 Single crystal X-ray diffraction structure of 3a.
Fig. 2 Single crystal X-ray diffraction structure of 4a.
Compounds 3a–e and 4a–d were stable in the solid state but
they slowly isomerized in deuterated chloroform solution during
Treatment of 3a in dichloromethane with neutral aluminium
oxide followed by flash chromatography (neutral aluminium
oxide, hexane–dichloromethane 80 : 20 v/v) gave quantitatively
product 4a (Scheme 1) as orange crystals characterized by the
usual spectroscopic and analytical techniques. Single crystal
diffraction analysis confirmed the structure of 4a§ as the
E-isomer (Fig. 2).
1
the NMR spectra acquisition. The H NMR spectra showed a
small signal of the E or Z isomer respectively, that increased with
time until reaching an equilibrium concentration. The 13C NMR
spectra showed an important amount of the corresponding
geometric isomer due to the longer acquisition time required (see
ESI{). This fact was intriguing and the reason could be that these
types of products have never before been described as pure
regioisomers. To be sure that interconversion did not occur in the
reaction mixture, we acquired 1H NMR data (d 4.8–8.2) of a crude
ethereal reaction mixture of 3d (0.5 mL) dissolved in CDCl3
(0.5 mL) and compared the corresponding peaks to pure authentic
samples of 1d and 3d dissolved in 1 : 1 Et2O–CDCl3 mixtures.
20 min after the preparation of the crude reaction mixture less than
4% of the minor isomer 3d could be detected by NMR, somewhat
less than the amount of minor isomer observed by NMR in a
solution of pure 3d 18 min after the preparation of the sample.
Taking into account the uncertainty of the method, the
regioselectivity of the reaction can be considered higher than
98% (see ESI{).
Similarly, reactions of 1b–e and 2 afforded, respectively,
products 3b–e and 4b–e in variable yields (4e was not obtained).
It is remarkable that we never obtained even traces of the product
from the insertion of the carbene moiety into the S–S bond and
some attempts of reacting 1a–b and 2 under the insertion
conditions12 (dioxane, 40 uC, 3 h) gave only traces of 3a–b in
addition to a complex mixture of unstable products from which
the insertion product could not be found. The reaction of the
simple 5-methyl-1,2-dithiole-3-thione 1d and Fischer carbene 2
afforded, after aluminium oxide treatment, E-dithiafulvene thione
4d as orange crystals suitable for single crystal X-ray diffraction,
which again confirmed the structure of 4d§ as the E-isomer (Fig. 3).
A plausible mechanism should consist of a very asynchronous9
cycloaddition oriented from the thiono group of 1a–e to the
b-position of the Fischer carbene 2 as in 5 to give 3a–e (Scheme 2).
In summary, we have shown the use of an alkynyl Fischer
carbene complex as a traceless directing group for the regioselective
cycloaddition of dithiolethiones to arylacetylene, which constituted
a safe synthesis of E-dithiafulvene thione or dithioesters that are
stable in the solid state but slowly interconvert in CDCl3 solution
to Z–E-mixtures.
We gratefully acknowledge financial support from the Direccio´n
General de Investigacio´n of Spain (Project ref. CTQ2006-15456-
C04-04BQU), Junta de Castilla y Leo´n, Consejer´ıa de Educacio´n y
Cultura, y Fondo Social Europeo (Project ref. BU013A06),
Consejo Nacional de Investigaciones Cient´ıficas y Te´cnicas
Fig. 3 Single crystal X-ray diffraction structure of 4d.
484 | Chem. Commun., 2008, 483–485
(CONICET-Argentina),
Fundacio´n
Antorchas,
Agencia
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and M. Gross, J. Mater. Chem., 2005, 15, 2599; (b) R. Andreu,
J. Aramburo, M. A. Cerda´n, J. Gar´ın, J. Ordun˜a and B. Villacampa,
Tetrahedron Lett., 2006, 47, 661; (c) J. K. Sørensen, M. Vestergaard,
A. Kadziola, K. Kilsa˚ and M. B. Nielsen, Org. Lett., 2006, 8, 1173; (d)
Nacional de Promocio´n Cient´ıfica y Te´cnica (FONCYT), and
Universidad Nacional de Co´rdoba, Argentina. AMF is a grateful
recipient of a fellowship from CONICET. We thank SCAI of the
University of Burgos for solving structures by single-crystal X-ray
diffraction.
˚
M. A. Petersen, L. Zhu, S. H. Jensen, A. S. Andersson, A. Kadziola,
K. Kilsa˚ and M. B. Nielsen, Adv. Funct. Mater., 2007, 17, 797.
6 Several examples in: (a) V. A. Ogurtsov, O. A. Rakitin, C. W. Rees,
A. A. Smolentsev, P. A. Belyakov, D. G. Golovanov and
K. A. Lyssenko, Org. Lett., 2005, 7, 791; (b) M. Garc´ıa-Valverde and
T. Torroba, Eur. J. Org. Chem., 2006, 849; For a dedicated review see:
(c) A. Gorgues, P. Hudhomme and M. Salle´, Chem. Rev., 2004, 104,
5151.
7 (a) X. Guo, Y. Zhou, M. Feng, Y. Xu, D. Zhang, H. Gao, Q. Fan and
D. Zhu, Adv. Funct. Mater., 2007, 17, 763; (b) S. Saha, K. C.-F. Leung,
T. D. Nguyen, J. F. Stoddart and J. I. Zink, Adv. Funct. Mater., 2007,
17, 685; (c) I. Willner, B. Basnar and B. Willner, Adv. Funct. Mater.,
2007, 17, 702.
8 Several examples in reviews: (a) J. Barluenga, J. Santamar´ıa and
M. Toma´s, Chem. Rev., 2004, 104, 2259; (b) J. Barluenga, Pure Appl.
Chem., 2002, 74, 1317; See also: (c) J. Barluenga, M. A. Ferna´ndez-
Rodr´ıguez and E. Aguilar, J. Organomet. Chem., 2005, 690, 539.
9 I. Ferna´ndez, M. A. Sierra and F. P. Coss´ıo, J. Org. Chem., 2006, 71,
6178.
10 Recent examples: 1,4-Diazafulvenes: (a) J. Barluenga, J. Garc´ıa-
Rodr´ıguez, S. Mart´ınez, A. L. Sua´rez-Sobrino and M. Toma´s, Chem.–
Eur. J., 2006, 12, 3201; Pyrazolinones: (b) Z. Zheng, Z. Yu, N. Luo and
X. Han, J. Org. Chem., 2006, 71, 9695.
11 (a) M. A. Sierra, M. J. Manchen˜o, J. C. del Amo, I. Ferna´ndez and
M. Go´mez-Gallego, Chem.–Eur. J., 2003, 9, 4943; (b) H.-P. Wu,
R. Aumann, R. Fro¨hlich, E. Wegelius and P. Saavenketo,
Organometallics, 2000, 19, 2373.
12 A. M. Granados, J. Kreiker, R. H. de Rossi, P. Fuertes and T. Torroba,
J. Org. Chem., 2006, 71, 808.
13 H. Behringer and R. Wiedenmann, Tetrahedron Lett., 1965, 6, 3703.
14 C. P. Casey and W. R. Brunsvold, J. Organomet. Chem., 1975,
102, 175.
Notes and references
§ CCDC 664202 (the complex between 1d and chromium pentacarbonyl),
664203 (3a), 664204 (4a), 664205 (4d). For crystallographic data in CIF or
other electronic format see DOI: 10.1039/b715857b
1 For a dedicated review, see: (a) P. Fre`re and P. J. Skabara, Chem. Soc.
Rev., 2005, 34, 69; Several examples in: (b) M. Bendikov, F. Wudl and
D. F. Perepichka, Chem. Rev., 2004, 104, 4891; A recent example: (c)
H. Gopee, B. M. Petersen, A. D. Bond and J. O. Jeppesen, Chem.
Commun., 2007, 4110.
2 Recent examples are: (a) C. A. Christensen, A. S. Batsanov and
M. R. Bryce, J. Am. Chem. Soc., 2006, 128, 10484; (b) M. C. D´ıaz,
B. M. Illescas, N. Mart´ın, I. F. Perepichka, M. R. Bryce, E. Levillain,
R. Viruela and E. Ort´ı, Chem.–Eur. J., 2006, 12, 2709; (c)
C. A. Christensen, A. S. Batsanov and M. R. Bryce, J. Org. Chem.,
2007, 72, 1301.
3 Selected examples are: (a) M. Guerro, R. Carlier, K. Boubekeur,
D. Lorcy and P. Hapiot, J. Am. Chem. Soc., 2003, 125, 3159; (b)
D. Lorcy, M. Guerro, P. Pellon and R. Carlier, Chem. Commun., 2004,
212; (c) J. Massue, N. Bellec, M. Guerro, J.-F. Bergamini, P. Hapiot
and D. Lorcy, J. Org. Chem., 2007, 72, 4655.
4 A recent example: (a) E. Fujiwara, K. Yamamoto, M. Shimamura,
B. Zhou, A. Kobayashi, K. Takahashi, Y. Okano, H. Cui and
H. Kobayashi, Chem. Mater., 2007, 19, 553; For a dedicated review, see:
(b) A. Kobayashi, E. Fujiwara and H. Kobayashi, Chem. Rev., 2004,
104, 5243.
5 Selected examples are: (a) M. B. Nielsen, J. C. Petersen, N. Thorup,
M. Jessing, A. S. Andersson, A. S. Jepsen, J.-P. Gisselbrecht, C. Boudon
15 J. Christoffers and K. H. Do¨tz, Organometallics, 1994, 13, 4189.
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Chem. Commun., 2008, 483–485 | 485