N,N-dimethylformamide-mediated sodium reduction of frans-3,3′- benzo[c]thienylidene-1,1′ dithione and frans-3,3′-benzo[c] selenonylidene-1,1′-dithione

Article abstract of DOI:10.1021/ol049205t

(Chemical Equation Presented) The synthesis of stable methylthio-capped biisothianaphthene and biisoselenophene derivatives has been achieved using DMF-mediated sodium reduction of cyclic thiocarbonyl compounds.

Full text of DOI:10.1021/ol049205t

ORGANIC
LETTERS
2
004
Vol. 6, No. 18
039-3041
N,N-Dimethylformamide-Mediated
Sodium Reduction of
3
trans-3,3′-Benzo[c]thienylidene-1,1′-dithione
and
trans-3,3′-Benzo[c]selenonylidene-1,1′-dithione
†
Emad Aqad, M. V. Lakshmikantham, and Michael P. Cava*
Department of Chemistry, UniVersity of Alabama, Tuscaloosa,
Box 870336, Alabama 35487-0336
mcaVa@bama.ua.edu
Received April 29, 2004
ABSTRACT
The synthesis of stable methylthio-capped biisothianaphthene and biisoselenophene derivatives has been achieved using DMF-mediated sodium
reduction of cyclic thiocarbonyl compounds.
5
Very little is known concerning the sulfur and selenium
analogues of cyclic anhydrides. Our laboratory is involved
in the synthesis and studies of this class of heterocycles.
of the stable selenium analogues 5 and 6. Thionation of the
8
known selenophthalic anhydride (7) gave rise to insoluble,
1
-5
dark polymeric materials. Apparently, seleno dithiophthalic
anhydride (8) should have formed and, in analogy to the
trithiophthalic anhydride (2), must have polymerized.5
However, the above cyclic thiocarbonyl compounds are
useful precursors for many interesting transformations. Our
present investigation was concerned with examining the
reduction of the stable dithione derivatives 3 and 6. Elec-
trochemical reduction of thiocarbonyl compounds have
We reported the synthesis of the stable thionothiophthalic
2
anhydride 1 in 1988. In contrast, all of our attempts to bring
about the synthesis of trithiophthalic anhyhdride 2 by
thionation of the carbonyl group in 1, using classical
thionation reagents, gave rise to a black polymeric material
from which trans-3,3′-benzo[c]thienylidene-1,1′-dithione (3)
3
was isolated in very low yield. Compound 3 was obtained
9
in good yield by the reaction of trans-3,3′-bithiophthalide
received only very little attention, probably due to the
limited solubility as well as their stability of in organic
solvents. In general, stable thiones are reduced more easily
(
4) with Lawsson’s reagent.6,7 Recently, we resumed our
interest in this class of compounds and reported the synthesis
*
To whom correspondence should be addressed.
Present address: Department of Chemistry, University of Pennsylvania,
(4) Lakshmikantham, M. V.; Chen, W.; Cava, M. P. J. Org. Chem. 1989
54, 4746.
†
2
31 South 34th Street, Philadelphia, Pennsylvania 19104-6323.
1) Lakshmikantham, M. V.; Carroll, P.; Furst, G.; Levinson, M. I.; Cava,
M. P. J. Am. Chem. Soc. 1984, 104, 6084.
2) Raasch, M. S.; Huang, N. Z.; Lakshmikantham, M. V.; Cava, M. P.
J. Org. Chem. 1988, 53, 891.
3) Cava, M. P.; Lakshmikantham, M. V. Phosphorus, Sulfur, Silicon
989, 43, 95.
(5) Lakshmikantham, M. V.; Aqad, E.; Rajagopal, D.; Cava, M. P.
Phosphorus, Sulfur, Silicon 2004, in press.
(6) Raasch, M. S.; Lakshmikantham, M. V.; Cava, M. P. Unpublished
results.
(7) Paulussen, H.; Haitjema, H.; van Asselt, R.; Mylle, P.; Adriaensens,
P.; Vanderzande, D. Polymer 2000, 41, 3121.
(8) Bergman, J.; Engman, L. Org. Prepr. Proc. Int. 1978, 10, 289.
(
(
(
1
1
0.1021/ol049205t CCC: $27.50 © 2004 American Chemical Society
Published on Web 08/03/2004

4 6
Figure 1. CV of compound 3 in DMF, Bu NBF (0.1 M), Pt
working electrode, SCE reference electrode, 100 mV/s scan rate.
different scanning rates and was established by the separation
of 50-60 mV between cathodic (Epc) and anodic (Epa) peak
potentials. This observation indicates the stability of the
generated anion radical and dianion under the CV experi-
mental conditions. Formally, both the anion radical and the
dianion derived from compounds 3 or 6 can be presented in
more than one mesomeric structure. However, mesomeric
forms 3′, 6′, 3′′, and 6′′, incorporating heteroaromatic
o-quinonoid structures, describe better the nature of bonding
of the partially and fully reduced species. In separate CV
experiments, an excess of the strongly alkylating methyl
iodide was added to the electrochemical cell. In this case,
the reversibility of the two reduction processes vanished and
a new oxidation wave was observed. Apparently, the
generated dianion (3′′ or 6′′) was trapped (alkylated) with
methyl iodide and the observed new oxidation wave corre-
sponds to the S-methylated products 9 or 10 (Scheme 1).
than the corresponding carbonyl structures, and stable
aromatic thioketones, such as thiobenzophenone, upon one-
electron reduction, produce a highly stable anion radical,
which has been demonstrated to play the role of a nucleophile
toward a variety of alkylating agents.9
The electron-accepting properties of the stable thiocarbonyl
derivatives 3 and 6 were studied by cyclic voltammetry (CV).
The voltammograms of DMF solutions of 3 and 6 exhibit
two reversible one-electron reduction waves corresponding
to the generation of the anion radical and the dianion,
respectively (Scheme 1). A representative voltammogram is
Scheme 1
a
Table 1. Electrochemical Behavior of Dithioketone
Derivatives 3 and 6
compd Epc1 (V) Epc2 (V) Epa1 (V) Epa2 (V) ∆E1 (mV) ∆E2 (mV)
3
6
-0.22 -0.55 -0.28 -0.61
-0.29 -0.60 -0.34 -0.66
55
50
60
59
a
CVs experimental conditions: in DMF, Bu4NBF6 (0.1 M), Pt working
electrode, SCE reference electrode, 100 mV/s scan rate.
The solution electrochemical properties of 3 and 6 directed
our attention to the possibility of bringing about the same
reduction chemically. In particular, the metal reduction of
compounds 3 and 6 was especially attractive. For this
purpose, we noted that the well-known reduction of carbon
disulfide was best achieved in DMF mediated by sodium.10
Not surprisingly, the same reduction medium proved to work
very well for our present purpose. In a typical experiment,
shown in Figure 1. Judging from the first reduction potential
(Epc1, Table 1), the all sulfur derivative 3 exhibits slightly
stronger accepting ability than the selenium analogue 6. The
reversibility of the two reduction processes was observed at
(9) (a) Simonet, J. In The chemistry of Functional Groups, Supplement
S: The Chemistry of Sulfur-Containing Functional Groups; Patai, S.,
Rappaport, Z., Eds.; John Wiley & Sons Ltd.: New York, 1993; Chapter
1
0, p 439. (b) Yasui, S.; Nakamora, K.; Ohno, A.; Oka, S. Bull Chem. Soc.
(10) Steimecke, G.; Sieler, H.-J.; Kirms, R.; Hoyer, E. Phosphorus,
Sulfur, Silicon 1979, 7, 49.
Jpn., 1982, 55, 1981.
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Org. Lett., Vol. 6, No. 18, 2004

2
equiv of finely divided sodium was added to a thoroughly
dried DMF solution of 3 under inert atmosphere. A deep
blue color developed within a few minutes, and the sodium
was consumed completely within 2 h. At that point, methyl
iodide was added, and the mixture was stirred under nitrogen
atmosphere for an additional 15 min. Working up the reaction
mixture gave the expected 3,3′-bis(methylthio)-1,1′-biiso-
thianaphthene 9 in 56% yield.11 Compound 6 reacted under
the same reduction conditions in similar manner, and the
corresponding biisoselenophene 10 was formed in 43%
1
1
yield. Compounds 9 and 10 were found to be very stable
under normal laboratory conditions. Derivatives of bi-
isothianaphthene have received considerable theoretical at-
tention since they present model systems for understanding
the structural and physical properties of higher oligo-
isothianaphthenes.1
2,13
In this regard, it is notable that the
number of chemical approaches and types of biisothianaph-
tene derivatives are rather limited.14 Interestingly enough,
2 2
Figure 2. UV-vis spectrum of 9 in CH Cl .
bismethylthio derivative 10, represents the first example of
a dimeric benzo[c]selenophene.
located at 436 nm and for derivative 10 is located at 445
nm. Theoretical calculations have shown that the lowest
energy transition of model biisothianaphthene originated from
π to π* transition, which primarily involved the excitation
of an electron from the HOMO to the LUMO. Judging from
the different lowest energy absorptions and the difference
in the first oxidation potentials, it appears that the replace-
ment of the sulfur atom on dimeric o-quinonoid heterocycle
The redox properties of the new dimers 9 and 10 were
examined by cyclic voltammetry. On anodic scanning,
compound 9 exhibits an one-electron irreversible oxidation
wave at 0.38 V (SCE reference electrode) (Figure 2). Similar
CV features were observed for the selenium analogue 10.
Compound 10, however, oxidized at 0.30 V under the same
experimental conditions, indicating the enhanced donating
ability of selenium. A similar one-electron irreversible
13
9
by the more polarizable selenium atom fine tunes the
electronic properties of the system.
oxidation process was observed for the known diformyl-
capped biisothianaphthene.14b The optical absorption spectra
of 9 contains three main peaks in the range 200-500 nm,
In conclusion, the synthesis of stable methylthio-capped
biisothianaphthene (9) and biisoselenophene (10) derivatives
has been achieved using DMF-mediated sodium reduction
of cyclic thiocarbonyl compounds. Sulfur and selenium
dimeric o-quinonoid heterocycles appear to possess slightly
different electronic properties. In view of the great interest
in conducting polymers derived from isothianaphthene,
studies aimed at the synthesis and properties of poly-
which is in accordance with the calculated and experimental
1
3
UV-vis spectra of biisothianaphthene model compound.
The longest absorption maxima (λmax) of the derivative 9 is
(
11) Selected spectroscopic data. Compound 8: 1H NMR (360 MHz,
CDCl3, relative to TMS) δ 2.55 (s, 6H), 7.11-7.22 (m, 4H), 7.78-7.82
1
3
(
m, 4H); C NMR (360 MHz, CDCl3, relative to TMS) δ 128.1, 144.0,
1
5
+
isoselenophene are highly desirable.
1
3
3
37.0 132.6, 124.2, 123.1, 123.8, 122; MS m/e 358 (M , 55), 344 (23),
42 (100), 326 (21), 264 (38). Anal. Calcd for C18H14S4: C, 60.29; H,
.94; S, 35.77. Found: C, 60.21; H, 3.84; S, 35.69. Compound 9: 1H NMR
Acknowledgment. This work was supported by a grant
from the National Science Foundation (No. CHE-9910177).
(
7
1
360 MHz, CDCl3, relative to TMS) δ 2.48 (s, 6H), 7.11-7.20 (m, 4H),
13
.78-7.82 (m, 4H); C NMR (360 MHz, CDCl3, relative to TMS) δ 128.1,
44.0, 137.0 132.6, 124.2, 123.1, 123.8, 122. Anal. Calcd for C18H14S2Se2:
C, 47.79; H, 3.12; S, 14.18. Found: C, 47.71; H, 3.14; S, 14.29.
12) Quattrocchi, C.; Lazzaroni, R.; Bredas, J. L.; Kiebooms, R.;
Vanderzande, D.; Gelan, J.; Van. Meervelt, L. J. Phys. Chem. 1995, 99,
932.
Supporting Information Available: Experimental details
and selected NMR and MS spectra. This material is available
free of charge via the Internet at http://pubs.acs.org.
(
3
(13) Kwon, O.; McKee, M. L. J. Phys. Chem, 2000, 104, 7106.
14) To the best of our knowledge, the only known derivatives of
OL049205T
(
biisothianaphthenes are tert-butyldimethylsilyl-capped biisothianaphthene,
which was reported by us: (a) Okuda, Y.; Lakshmikantham, M. V.; Cava,
M. P. J. Org. Chem. 1991, 56, 6024. The formyl-capped biisothianaphthene,
which was reported recently: (b) Shimizu, Y.; Shen, Z.; Ito, S.; Uno, H.;
Daub, J.; Ono, N. Tetrahedron Lett. 2002, 43, 8485.
(15) Interestingly enough, the only patent describing the preparation of
conductive poly-benzo[c]selenophene was reported in 1991 but was not
further examined: Kubota, F. JP application no. 1989-86323; Chem. Abstr.
1991, 115, 2029.
Org. Lett., Vol. 6, No. 18, 2004
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