A new route to extended tetrathiafulvalenes from α-acetyl ketene-S,S-acetals

Article abstract of DOI:10.1016/j.tetlet.2006.02.128

A new route to extended tetrathiafulvalenes was described. The extended TTFs with hexa-2,4-diyne-1,6-diylidene spacer between the two 1,3-dithiole rings were prepared simply from the easily available α-acetyl ketene-(S,S)-acetals in good yields under mild

Full text of DOI:10.1016/j.tetlet.2006.02.128

Tetrahedron Letters 47 (2006) 3157–3159
A new route to extended tetrathiafulvalenes from
a-acetyl ketene-S,S-acetals
Yu-Long Zhao,* Wei Zhang, Ji-Qing Zhang and Qun Liu*
Department of Chemistry, Northeast Normal University, Changchun 130024, China
Received 10 December 2005; revised 21 February 2006; accepted 22 February 2006
Available online 20 March 2006
Abstract—A new route to extended tetrathiafulvalenes was described. The extended TTFs with hexa-2,4-diyne-1,6-diylidene spacer
between the two 1,3-dithiole rings were prepared simply from the easily available a-acetyl ketene-(S,S)-acetals in good yields under
mild conditions.
ꢀ 2006 Elsevier Ltd. All rights reserved.
Since the first synthesis of tetrathiafulvalene (TTF) was
reported by Wudl et al.,1 TTF and its derivatives (TTFs)
have been widely explored in both materials and supra-
molecular chemistry.2 The extended TTFs, in which a
p-conjugated spacer is incorporated between the two
dithiole rings, exhibit enhanced p-donor properties and
stabilization of the dication state3 and thus represent a
topic of great interest in the field of molecular conduc-
tors, small band gap molecular semi-conductors, and
nonlinear optics.4 To date, a considerable number of
olefinic and aromatic spacers have been introduced with
the aim to tune the redox properties of the p-electron
system.3,5 However, there are few reports of the alkyne-
spaced TTFs.
prepared in high yields via a consecutive Vilsmeier–
Haack and dehydrochlorination reaction starting from
the corresponding a-acetyl ketene-(S,S)-acetals under
CO2Me
CO2Me
S
MeO2CC CCO2Me
S
Bu3P
B
Bu3P
CS
2
P +
Bu3
S
- 65 oC
S
A
C
O
CO2Me
CO2Me
S
Bu3P
BF
HBF4
n-BuLi
+
R
4 H
S
SiR1
3
E
D
MeO2C
MeO2C
R
S
S
i) K2CO3
ii) CuCl
TMEAD
In the context of alkyne-spaced TTFs, Gorgues and
co-workers. reported the synthesis of substituted
1,4-bis(1,3-dithiol-2-ylidene)but-2-ynes.6 The acetylenic
TTF dications were isolated by Yoshida and co-work-
ers.7 Recently, some di- and poly-yne acetylenic TTFs
and their derivatives were described by Diederich and
co-workers8 and Nielsen et al.,9 respectively. In the
research mentioned above, a synthetic route, as described
in Scheme 1, is commonly used.6–9 As part of our
research on the synthetic applications of a-acetyl
ketene-(S,S)-acetals,10,11 recently, a series of a-ethynyl
ketene-(S,S)-acetals 3 (Scheme 2) and analogues were
Me
O C
2
R
S
S
MeO2C
CO2Me
CO2Me
S
SiR1
3
S
R
F
G
Scheme 1.
R2
S
S
O
Cl
R2
R2
S
R2
i
ii
iii
S
S
S
S
S
S
S
R2
Keywords: a-Acetyl ketene-S,S-acetals; Acetylenic dithiafulvenes;
Extended tetrathiafulvalene; Acetylenic tetrathiafulvalene; Coupling
reaction.
1
2
3
4
Scheme 2. Reagents and conditions: (i) POCl3–DMF, 0 ꢁC; (ii) NaOH
(1.0 equiv), CH3OH, 20 ꢁC; (iii) Ni(PPh3)2Cl2, PdCl2, CuI,
N(CH2CH3)3, THF, 20 ꢁC.
*
Corresponding authors. Tel.: +86 431 509 9759; fax: +86 431 509
8966 (Y.-L.Z.); e-mail: zhaoyl351@nenu.edu.cn
0040-4039/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2006.02.128

3158
Y.-L. Zhao et al. / Tetrahedron Letters 47 (2006) 3157–3159
mild conditions.12 Most recently, through sequential
oxidative coupling of a,a-diethynyl ketene-(S,S)-acetal,
we successfully prepared the first heteroatom-substi-
tuted expanded 1,3-dithiolan[5]radialene with the basic
structural characters of the alkyne-extended tetra-
thiafulvalenes.13 These experimental results prompted
us to explore a direct synthetic route to acetylenic TTFs
starting from the readily available a-acetyl ketene-(S,S)-
acetals. In the letter, we wish to report our preliminary
results of this research.
Table 2. Synthesis of compounds 6 and 7
Entry
R3
Product and yielda (%)
6
Yield
7
Yield
1
2
3
4
COOC2H5
4-Cl–PhNHCO
COCH3
6a
6b
6c
6d
87
76
55
83
7a
7b
7c
7d
52
45
43
40
CN
a Isolated yields.
Although the route in Scheme 1 is efficient for the prep-
aration of acetylenic TTFs, a five-step procedure and
time consuming or expensive starting materials are nor-
mally required. With the consideration that a-ethynyl
ketene-(S,S)-acetals 3 are a kind of acetylenic dihydro-
dithiafulvenes and could be served as the building
blocks of alkyne-extended tetrahydro-TTFs, we first
focused our attention on the self-coupling reaction of
3. It was found that compounds 3 underwent the
homo-coupling reaction very easily and the correspond-
ing extended tetrahydro-TTFs 4 were formed in high to
excellent yields when 3 (1.0 equiv) was added to the
mixture of 2.0 mol % of Ni(PPh3)2Cl2, 2.0 mol % of
PdCl2, 5.0 mol % of CuI, and 1.5 equiv of triethylamine
in THF and stirred for 5–6 h at room temperature
(Scheme 2 and Table 1).
Figure 1. Crystal structure of the acetylenic TTFs 7a. Hydrogen atoms
are omitted for clarity.
the two 1,3-dithiole rings, were finally synthesized in
good yields under the similar conditions as the synthesis
of 4 except the dehydrochlorination and the dehydro-
bromination of 6 and the followed oxidative coupling
steps were combined (Scheme 3 and Table 2) to simplify
the experimental procedures. Compared with the route
of Scheme 1, this new route had following advantages:
(1) the readily available starting materials and cheap
reagents; (2) a procedure proceeded smoothly under mild
conditions. Therefore, our preliminary results presented
a simpler procedure for the synthesis of extended TTFs.
With the successful synthesis of extended tetrahydro-
TTFs 4, we then focused on the preparation of acetyl-
ene-spaced TTFs based on the three-step procedure as
described in Scheme 2. Starting from the activated meth-
ylene compounds and 1,2,3-tribromopropane, the corre-
sponding a-acetyl ketene-(S,S)-acetals 5 (Scheme 3),
which possessed the skeleton structure and unsaturated
degree as required for acetylene-spaced TTFs, were syn-
thesized region-specifically in 87–94% yields according
to the known method.10–13 Subsequently, the a-chloro-
vinyl ketene-(S,S)-acetals 6 were produced through the
Vilsmeier–Haack reaction of compounds 5 in good
yields (Table 2). Similarly, compounds 7,14 the extended
TTFs with hexa-2,4-diyne-1,6-diylidene spacers between
According to the 1H NMR spectra of compounds 6 and
7, it was indicated that these compounds were produced
as a mixture of isomers (with methyl substitute at the
4(40)- or 5(50)-position of the corresponding 1,3-dithiol-
ane or 1,3-dithiole moiety). During the crystallization
of 7a from the mixed solvents of diethyl ether–hexane
(1:1, v/v), one isomer of 7a was isolated and the single
crystal structure revealed that two fulvene double bonds
in this isomer adopted the s-trans conformation with
respect to the connecting buta-1,3-diynediyl moiety and
the two dithiafulvene units lay on the same plane
(Fig. 1).15
Table 1. Preparation of alkyne-extended tetrahydro-TTFs 4
Entry Substrate R2
Time Product Yielda
(h)
(%)
In conclusion, we have described a novel method for the
synthesis of acetylene-spaced TTFs, by which a series of
tetrahydro acetylenic TTFs and acetylene-spaced TTFs
with laterally appended function groups were obtained
with the readily available a-acetyl ketene-(S,S)-acetals
involving only the Vilsmeier–Haack reaction, dehydro-
halogenation and the oxidative coupling steps. Further
research on expanding the application of this new route
is in progress.
1
2
3
3a
3b
3c
COOCH3
4-Cl–PhNHCO
H
6
6
5
4a
4b
4c
97
91
75
a Isolated yields.
R3
S
S
H3C
Cl
S
O
R3
R3
ii
i
iii
S
S
S
S
S
CH2Br
CH2Br
CH3
Acknowledgments
R3
5
6
7
Financial supports of this research by the Key Grant
Project of Chinese Ministry of Education (10412) and
SFYTNNU (111494020) are gratefully appreciated.
Scheme 3. Reagents and conditions: (i) POCl3–DMF, 0 ꢁC, 8–10 h; (ii)
NaOH (2.0 equiv), C2H5OH, 60–70 ꢁC, 3–4 h; (iii) Ni(PPh3)2Cl2,
PdCl2, CuI, THF, N(CH2CH3)3, 20 ꢁC, 15–20 min.

Y.-L. Zhao et al. / Tetrahedron Letters 47 (2006) 3157–3159
3159
Boudon, C.; Jensen, F.; Nielsen, S. B.; Nielsen, M. B.
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Supplementary data
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.tetlet.
2006.02.128.
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14. General procedure for 7a: To a solution of compound 6a
(2.00 mmol, 687 mg) and NaOH (4.00 mmol, 160 mg) in
EtOH–H2O (4:1; v/v, 30 mL) was heated at 60–70 ꢁC for
3–4 h. The reaction mixture was poured into cold water
(50 mL), extracted with diethyl ether (3 · 10 mL), and
dried over anhydrous MgSO4. This extract combined was
`
5. (a) Frere, P.; Skabara, P. J. Chem. Soc. Rev. 2005, 34, 69;
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(b) Sarhan, A. A. O. Tetrahedron 2005, 61, 3889; (c)
Boulle, C.; Desmars, O.; Gautier, N.; Hudhomme, P.;
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(0.040 mmol, 26.16 mg), PdCl2 (0.040 mmol, 7.08 mg),
CuI (0.10 mmol, 19.00 mg), and triethylamine (3.00 mmol,
0.42 mL) in THF (30 mL). After the reaction solution was
stirred for 15–20 min at room temperature, the solvent was
removed under reduced pressure, and the residue was
purified by silica gel chromatography (diethyl ether–
hexane = 1/1, v/v) to give the pure 7a (234 mg, 52% yield).
Compound 7a: red crystal; mp 192–194 ꢁC; 1H NMR
(CDCl3, 400 MHz) one isomer d: 1.35 (t, J = 8.0 Hz, 6H),
2.29 (s, 6H), 4.31 (q, J = 8.0 Hz, 4H), 6.49 (s, 2H); the other
d: 1.35 (t, J = 8.0 Hz, 6H), 2.28 (s, 6H), 4.28 (q, J = 8.0 Hz,
4H), 6.43 (s, 2H); IR (KBr, cmꢀ1): 3445, 3065, 2982, 2121,
1668, 1473, 1373, 1285, 1235, 1172, 1029, 933, 761; MS (EI)
m/z 451 [(M+1)]+; calcd (found) for C20H18O4S4: C, 53.31
(53.52); H, 4.03 (4.10).
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¨
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15. Crystal data for 7a: C20H18O4S4, dark red crystal,
˚
M = 450.58, monoclinic, P2(1)/n, a = 10.7902(8) A, b =
˚
˚
9. (a) Nielsen, M. B.; Petersen, J. C.; Thorup, N.; Jessing,
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(b) Qvortrup, K.; Jakobsen, M. T.; Gisselbrecht, J.-P.;
7.4372(10) A, c = 13.6358(14) A, a = 90ꢁ, b = 102.762(2)ꢁ,
3
˚
c = 90ꢁ, V = 1067.2(2) A , Z = 2, T = 293(2), F000 = 468,
R1 = 0.0762, wR2 = 0.2400. The CCDC deposition num-
ber: 246076.