Synthesis and electrochemical properties of carbocyclic and heterocyclic diazulenylethenes

Article abstract of DOI:10.1002/ejoc.201300354

An efficient two-step method was developed for the synthesis of 1,2-di(azulen-1-yl)ethenes 15-17, having the double bond included in a five-membered carbocyclic or heterocyclic ring. The method involves preparation of the appropriate diketone precursors through Vilsmeier-Haack or Friedel-Crafts reactions, followed by their McMurry cyclization. Alkenes 16 and 17 were quantitatively converted into the corresponding dehydro derivatives 24 and 25, respectively, by oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). The electrochemical properties of compounds 15-17, 24 and 25 were examined by cyclic voltammetry (CV) and differential pulse voltammetry (DPV), and the relationship between their structure and electrochemical behavior was established. Novel 1,2-di(azulen-1-yl)ethenes, having the double bond included in a five-membered carbocyclic or heterocyclic ring, were conveniently synthesized by McMurry coupling reactions. Their electrochemical properties were examined by cyclic voltammetry (CV) and differential pulse voltammetry (DPV), and the electrochemical behavior-structure relationship was established. Copyright

Full text of DOI:10.1002/ejoc.201300354

Job/Unit: O30354
/KAP1
Date: 26-08-13 10:44:49
Pages: 11
FULL PAPER
DOI: 10.1002/ejoc.201300354
Synthesis and Electrochemical Properties of Carbocyclic and Heterocyclic
Diazulenylethenes
[
a]
[a,b]
[a]
[c]
Eugenia Andreea Dragu, Simona Nica,
Victorita Tecuceanu, Daniela Bala,
[c]
[a]
[a]
Constantin Mihailciuc, Anamaria Hanganu, and Alexandru C. Razus*
Keywords: Heterocycles / Arenes / Fused-ring systems / Electrochemistry / Voltammetry / Acylation
An efficient two-step method was developed for the synthe-
sis of 1,2-di(azulen-1-yl)ethenes 15–17, having the double
bond included in a five-membered carbocyclic or heterocy-
clic ring. The method involves preparation of the appropriate
diketone precursors through Vilsmeier–Haack or Friedel–
Crafts reactions, followed by their McMurry cyclization. Alk-
enes 16 and 17 were quantitatively converted into the corre-
sponding dehydro derivatives 24 and 25, respectively, by
oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone
(DDQ). The electrochemical properties of compounds 15–17,
24 and 25 were examined by cyclic voltammetry (CV) and
differential pulse voltammetry (DPV), and the relationship
between their structure and electrochemical behavior was
established.
Introduction
trochemical properties of these polymers have been re-
ported, and a relatively high conductivity was observed.
[
7]
[8]
Azulene, the non-alternant isomer of naphthalene, has
attracted the interest of many research groups because of its
characteristic blue color and unusual properties. The strong
electron-donating effect of the azulen-1-yl group, coupled
with the peculiarities of its electronic structure when conju-
gated with a double bond, renders compounds with general
formulas I–III an attractive research target from both fun-
In addition, the electrochemically synthesized polyazul-
enes are among the most promising conducting polymers,
and they have found applications as materials with unique
[9]
conducting, ferromagnetic and electrochromic proper-
[10]
ties.
In this paper we provide a detailed account of the
synthesis of several new 1,2-di(azulen-1-yl)ethenes having
the double bond included in a five-membered carbocyclic
or heterocyclic ring. Furthermore, due to increased interest
in the application of azulenic compounds in the field of π-
conjugated materials, we also examined the electrochemical
behavior of these compounds.
[
1]
[2]
damental and technical points of view.
Results and Discussion
In connection with our previous work on the synthesis
and properties of 1-(azulen-1-yl) vinyl compounds III, con-
taining various aromatic and heteroaromatic moieties at the
Synthesis
The envisaged synthetic route to the 1,2-di(azulen-1-yl)-
-position, we recently became interested in the study of ethenes mentioned above involves the preparation of the
[
3]
2
[4,5]
linear and cyclic 1,2-diazulenylethenes.
The low ioniza- appropriate diketone precursors, followed by their
tion energy of azulene derivatives enables their electrochem- McMurry cyclization (Scheme 1). For the preparation of
ical polymerization, leading to the formation of polymers the diketones, the Vilsmeier–Haack and Friedel–Crafts re-
on the electrode surface.[ The magnetic, optical and elec- actions were considered. We now report the peculiarities
and limitations of each step of the proposed synthesis.
6]
[
a] Romanian Academy, Institute of Organic Chemistry “C.D.
Nenitzescu”,
2
02 B Splaiul Independentei, Bucharest 060023, Romania
Synthesis of the Starting Diketones 1–3
E-mail: acrazus@cco.ro
Homepage: http://www.cco.ro/
The key intermediates used in the synthesis of the target
[
[
b] Romanian Academy, “Petru Poni” Institute of Macromolecular
Chemistry,
1,2-di(azulene-1-yl)ethenes are diketones 1–3 (Scheme 2),
4
1 A Grigore-Ghica Voda Alley, Iasi 700847, Romania
which were prepared as described below.
c] Physical Chemistry Department, University of Bucharest,
Faculty of Chemistry,
Vilsmeier–Haack Reaction
We recently reported[5] the preparation of 1,5-di(azulen-
1-yl)pentane-1,5-dione (1a) in 64% yield by microwave-
4
–12 Regina Elisabeta, Bucharest 030018, Romania
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201300354
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1

Job/Unit: O30354
/KAP1
Date: 26-08-13 10:44:49
Pages: 11
A. C. Razus et al.
FULL PAPER
Scheme 1. Retrosynthetic strategy for the synthesis of 1,2-di(azulen-1-yl)ethenes with the double bond included in the carbocyclic or
heterocyclic ring.
assisted Vilsmeier–Haack acylation of azulene with
N,N,NЈ,NЈ-tetraethylglutaramide (TEGA) and POCl3 at
100 °C for 45 min, followed by alkaline work-up with 10%
aqueous KOH (Scheme 3); a small amount (4%) of
monoacylation product was also obtained. To our surprise,
however, when the same reaction conditions were applied
to 4,6,8-trimethylazulene or guaiazulene, the expected di-
ketones 1b,c were not formed, even in trace amounts. In-
stead, their enamine precursors 5b,c were isolated in good
yields along with small amounts of 6b,c (Scheme 3). In con-
trast, enamine 5a was rapidly hydrolyzed to 1a during work-
up and, thus, could not be isolated. Similar observations
[
11]
were also reported by Hafner and Bangert in the Vilsme-
ier–Haack acetylation of azulenes with N,N-dimethylacet-
amide and POCl . Thus, whereas alkaline hydrolysis of 7b
3
to 1-acetyl-4,6,8-trimethylazulene required 3 h for quantita-
tive conversion, the less hindered enamine 7a could not be
Scheme 2. Key intermediates.
3
Scheme 3. Reaction of azulenes 4a–c with TEGA and POCl .
2
www.eurjoc.org
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 0000, 0–0

Job/Unit: O30354
/KAP1
Date: 26-08-13 10:44:49
Pages: 11
Carbocyclic and Heterocyclic Diazulenylethenes
isolated under alkaline conditions, but, rather, was immedi-
Diketone 2 was obtained, albeit in only 16% yield, by
ately hydrolyzed to 1-acetyl-azulene. Taking into account the Vilsmeier–Haack acylation of azulene with 2,2Ј-oxyb-
these considerations, we assume that diketones 1b,c were is(N,N-diethylacetamide) and POCl under the conditions
3
not obtained because the alkaline hydrolysis of their en- used for the synthesis of 1a (Scheme 4). On the other hand,
amine precursors 5b,c was sterically suppressed by the all attempts to prepare compound 3 by using this approach
methyl radicals at the 8Ј-positions, as well as by the N,N- were unsuccessful and resulted only in the formation of
diethylamino groups (see Scheme 3 for numbering).
complex mixtures. Nevertheless, a very good yield of 3 was
The stereochemistry of enamines 5b and 5c was assigned obtained by heating to reflux for 1.5 h an ethanol/water
on the basis of NMR spectroscopic analysis. For example, (11:1) solution of 1-chloroacetyl-azulene with sodium
as can be seen in Figure 1, the proton spectrum of 5b dis- sulfide (Scheme 4). To our delight, when this same reaction
plays two sets of signals with the same integration for both was carried out in water under sealed-vessel microwave
the five-membered ring protons of azulene as well as for its heating at 125 °C for 10 min, compound 3 was obtained
methyl substituents. Additionally, the NMR signals of all in nearly quantitative yield. Notably, 1-chloroacetyl-azulene
the other protons and most carbon atoms (see the Support- was obtained with an almost fourfold higher yield than pre-
[
12]
ing Information) are also doubled. Based on these observa- vious methods
by microwave-assisted Vilsmeier–Haack
tions, it can be concluded that “compound” 5b was formed acylation of azulene with 2-chloro-N,N-diethylacetamide
either as an equimolar mixture of chromatographically in- and POCl3.
separable (E,E) and (Z,Z) stereoisomers or exclusively as
the (E,Z) isomer. For the latter, the H-2 and H-4 protons
Friedel–Crafts Acylation
are nonequivalent and, thus, the signal of H-3 protons
should consist of two doublets. However, when the two H- Haack acylation prompted us to choose an alternative route
and H-4 protons are identical, as in the case of (E,E) for their synthesis involving the Friedel–Crafts reaction of
The failure to obtain diketones 1b and 1c by Vilsmeier–
2
and (Z,Z) isomers, the H-3 protons should be triplets. The 4,6,8-trimethylazulene and guaiazulene, respectively, with
presence of two triplets at δ = 2.66 and 2.64 ppm for the H- glutaroyl dichloride in the presence of SnCl . The reactions
4
3
3
protons, both with J = 7.2 Hz, suggests therefore that proceeded at 0 °C within 1.5 h and afforded diketones 1b
enamine 5b was obtained as an equimolar mixture of (E,E) and 1c in 59 and 25% yields, respectively, together with keto
and (Z,Z) stereoisomers. Similar considerations can also be acids 10b and 10c in 16 and 29% yields (Scheme 5 and
applied to enamine 5c.
Table 1, entries 2 and 3).
1
Figure 1. H NMR spectrum of 5b (400 MHz, C
6
D
6
, room temperature).
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3

Job/Unit: O30354
/KAP1
Date: 26-08-13 10:44:49
Pages: 11
A. C. Razus et al.
FULL PAPER
Scheme 4. Synthesis of diketones 2 and 3.
Scheme 5. Proposed mechanism for the Friedel–Crafts acylation of azulenes 4a–c with glutaryl dichloride.
4
www.eurjoc.org
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 0000, 0–0

Job/Unit: O30354
/KAP1
Date: 26-08-13 10:44:49
Pages: 11
Carbocyclic and Heterocyclic Diazulenylethenes
Table 1. Friedel–Crafts acylation of azulenes 4a–c with glutaroyl McMurry Coupling Reaction of Diketones 1–3
dichloride.
We previously reported that the reductive coupling of 1-
Entry
Substrate
Product (yield [%])
acetylazulene with TiCl /Zn in tetrahydrofuran (THF) at
4
1
2
3
4a
4b
4c
1a (13)
1b (59)
1c (25)
10a (8)
10b (16)
10c (29)
14 (55)
–
–
0
°C gave 2,3-di(azulen-1-yl)butan-2,3-diol in 89% yield,
along with trace amounts of its pinacol rearrangement
[
4]
product. On the other hand, the intramolecular McMurry
coupling of 1a, carried out under the same reaction condi-
tions (Scheme 6), afforded only alkene 15a and ketone 18a
Intriguingly, however, when the same reaction was per- in 77 and 22% yields, respectively, without any trace of diol
[
5]
formed with azulene, a new compound, 14, was obtained in 21a (Table 2, entry 1). The addition of pyridine to the re-
over 50% yield, whereas the expected acylation products 1a action mixture enhanced the alkene/ketone ratio from 3.5
and 10a were isolated in only 13 and 8% yields, respectively to 8.8 (Table 2, entry 6).
(Table 1, entry 1). A plausible mechanism for the formation
In line with this earlier work, we first decided to confirm
of the interesting unsaturated acid 14 is shown in Scheme 5. the intermediacy of titanapinacolate [I] in the McMurry
The first step involves cyclization of δ-keto acid chloride 9a coupling reaction of 1a by isolating its hydrolysis product,
to the protonated δ-lactone 11a, which reacts with azulene diol 21a (Route a, Scheme 7). Indeed, when the reaction
to produce δ,δ-diazulenyl-δ-lactone 12. Subsequently, hy- was performed at –45 °C for 30 min, diol 21a was obtained
drolysis of 12 to δ,δ-diazulenyl-δ-hydroxy acid 13 followed in 9% yield, together with 15a in 18% yield (Table 2, en-
by dehydration leads to the formation of unsaturated acid try 11). The formation of alkene 15a under these mild con-
14. Alternatively, the latter can also be obtained directly ditions, albeit in low yield, was most surprising because the
from 12 through ring-chain tautomerism. Notably, however, McMurry alkene syntheses generally require high tempera-
lactonic tautomer 12 could not be detected in the product tures and long reaction times. For instance, the McMurry
mixture, presumably due to the higher steric interference coupling of 1,5-diphenyl-1,5-pentanedione with TiCl3/
between the two geminal azulenyl moieties when attached LiAlH in THF afforded 1,2-diphenylcyclopentene in 62%
4
3
2
[14]
to a saturated (sp ) carbon in 12 than to a sp -hybridized yield only after 6 d heating to reflux.
However, the
carbon in 14, which shifts the equilibrium towards the lat- reasons for this remarkable reactivity of 1a toward
ter. A similar reaction pathway has previously been pro- McMurry cyclization are not yet clear and require further
posed for the Friedel–Crafts reaction of thiophenes with investigation.
succinyl dichloride in the presence of SnCl4.[13] It is also
By analogy to the previously reported mechanism for the
[
4]
worth noting that the alkyl-substituted azulenes 4b,c did McMurry coupling of 1-acetylazulene, titanapinacolate
not furnish any unsaturated acid, which can be attributed intermediate [I] should also be responsible for the formation
to steric hindrance by the alkyl groups, preventing the of the other coupling products. Thus, as shown in
carbocation intermediates 11b,c from reacting further with Scheme 7, the deoxigenation of this intermediate would
4b,c.
provide alkene 15a (Route b), whereas its pinacol rearrange-
Scheme 6. The McMurry coupling reaction of diketones 1–3.
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
5

Job/Unit: O30354
/KAP1
Date: 26-08-13 10:44:49
Pages: 11
A. C. Razus et al.
FULL PAPER
Table 2. McMurry coupling reaction of diketones 1a–c, 2 and 3 using (a) TiCl
4
/Zn; (b) TiCl
4
/Zn/pyridine, or (c) TiCl
4
/Zn/pyridine/cate-
chol.
Entry
Diketone McMurry reagent
Conditions
Product (yield [%])
Temp. [°C] Time [h]
Alchene
Ketone
Diol
Overall yield
1[a]
2
1a
1b
1c
2
(a)
(a)
(a)
(a)
(a)
(b)
(b)
(b)
(b)
(b)
(b)
(b)
(b)
(c)
(c)
(c)
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
15a (77)
15b (87)
15c (93)
16 (47)
17 (25)
15a (88)
15b (87)
15c (95)
16 (86)
17 (48)
15a (18)
16 (8)
18a (22)
–
–
–
99
87
93
81
80
98
87
95
98
75
27
21
36
61
83
86
–
3
–
[
[
[
b]
c]
a]
4
5
6
7
8
9
1
1
1
1
1
1
1
19 (34)
22 (Ͻ1)
23 (5)
–
–
–
22 (3)
23 (19)
21a (9)
22 (13)
23 (30)
–
3
20 (50)
1a
1b
1c
2
18a (10)
–
–
[
b]
19 (9)
20 (8)
–
–
–
–
0[c]
1
3
0
1
1a
2
–45
–45
–45
0
0
0
0.5
0.5
0.5
1
1
1
2
3
3
17 (6)
4
5
6
1a
2
15a (61)
16 (35)
17 (27)
[
[
b]
c]
19 (3)
20 (6)
22 (45)
23 (53)
3
[
a] Previously reported results.[5] [b] Trace amounts of furan 24 were also obtained. [c] Trace amounts of thiophene 25 were also obtained.
alkenes 15b and 15c in 87 and 95% yields, respectively,
without any pinacol rearrangement side-products (Table 2,
entries 2 and 3). The same results were obtained when pyr-
idine was added to the reaction mixture (Table 2, entries 7
and 8). Similar to the Friedel–Crafts acylation of azulenes
4a–c with glutaroyl dichloride discussed above, the products
of pinacol rearrangement having geminal azulenyl moieties
substituted with bulky alkyl groups were not obtained in
the McMurry cyclization of diketones 1b and 1c.
The results obtained for the McMurry coupling reaction
of diketones 2 and 3 containing oxygen and sulfur, respec-
tively, in the alkyl chain linking the azulene moieties are
also summarized in Table 2 and reveal several interesting
features. When TiCl /Zn was employed as coupling reagent
4
at 0 °C, the alkene/ketone product ratio decreased from 3.5
in the case of 1a to 1.38 for 2, and 0.5 for 3. Rather unex-
pectedly, even at this “high” temperature, small amounts of
the corresponding pinacols 22 and 23 were also obtained
(Table 2, entries 4 and 5). As in the case of substrate 1a, the
Scheme 7. Proposed mechanism for the McMurry coupling of di-
ketone 1a.
addition of pyridine to the low-valent titanium reagent led
to an increase in the alkene/ketone ratios and, furthermore,
slightly improved the yields of the pinacols (Table 2, en-
tries 9 and 10). Lowering the reaction temperature to
ment would yield ketone 18a (Route c). Presumably, titana-
pinacolate [I] is particularly prone to rearrangement due to
the efficient stabilization of the positive charge in intermedi-
–45 °C significantly decreased the levels of conversion to
ate [II] by delocalization toward the seven-membered ring less than 50% but, on the other hand, further increased the
of the azulene moiety. To the best of our knowledge, only yields of pinacols 22 and 23 to 13 and 30% yields, respec-
three other examples of McMurry coupling reactions in- tively (Table 2, entries 12 and 13).
[
16]
volving the formation of pinacol rearrangement side-prod-
In previous work by Banerji et al., the addition of cat-
ucts have been reported.[
15]
echol to the TiCl /Mg system was shown to arrest the re-
3
The substrate scope of this coupling reaction was then ductive dimerization of acetophenone at the intermediate
investigated by substituting the azulene moieties of the pinacol stage, even under reflux conditions. With this infor-
starting diketone 1a with alkyl groups, as well as by intro- mation in hand, we attempted to improve the synthetic ac-
ducing a heteroatom in its alkyl chain. As can be seen from cessibility of pinacols 22 and 23 by conducting the
Table 2, alkyl substituents at the azulene moieties signifi- McMurry coupling reactions of 2 and 3, respectively, in the
cantly changed the outcome of the reaction. Thus, whereas presence of the TiCl /Zn/pyridine reagent modified by cate-
4
the McMurry coupling of 1a gave a mixture of 15a and chol. Under these conditions, pinacols 22 and 23 were in-
18a, diketones 1b and 1c afforded solely the corresponding deed obtained in good 45 and 53% yields, respectively,
6
www.eurjoc.org
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 0000, 0–0

Job/Unit: O30354
/KAP1
Date: 26-08-13 10:44:49
Pages: 11
Carbocyclic and Heterocyclic Diazulenylethenes
along with modest yields of the corresponding alkenes as quasi-reference electrode. The CV experiments were per-
35% for 16 and 27% for 17) and only trace amounts of formed at scan rates of 25, 50, 100, 150, and 200 mV/s. Un-
pinacol rearrangement products (Table 2, entries 15 and less otherwise stated, the cyclic voltammograms reported in
6). Notably, however, when starting from 1a, alkene 15a this paper were recorded at 200 mV/s. The DPV studies
was obtained as the sole product in 61% yield, with no were performed in the anodic direction, with step potential
trace of pinacol 21a (Table 2, entry 14). of 10 mV and modulation amplitude of 50 mV. The main
(
1
With alkenes 16 and 17 in hand, we finally turned our redox potentials obtained from CV and DPV are summa-
attention to the synthesis of their dehydro derivatives 24 rized in Table 4.
and 25, respectively, by oxidation with 2,3-dichloro-5,6-di-
cyano-1,4-benzoquinone (DDQ). To our delight, quantita-
tive yields were obtained within only 5 min at room tem-
perature, rendering this approach particularly attractive for Entry Compd. CV [V]
Table 4. Main redox potentials of compounds 15a–c, 16, 17, 24 and
2
5 obtained by CV and DPV techniques.
DPV [V]
the efficient preparation of 3,4-diazulenyl furans and thio-
phenes, which are not easily accessible by other means.
However, it is worth noting that several other types of thi-
enylazulene derivatives have recently been synthesized and
Epa
Epc E1/2
ΔEp
Epa
W1/2
1
2
3
4
5
6
7
15a
15b
15c
0.75
0.59 0.67
0.67 0.76
0.16
0.18
0.62
0.72
0.083
0.083
0.85
0.59
1.23
0.40 0.50
1.13 1.18
0.19
0.10
0.53
1.14
0.091
–
their electronic properties investigated by UV/Vis absorp-
tion spectroscopy and cyclic voltammetry.[3b,17]
For the characterization of compounds 15a–c, 16, 17, 24
and 25 various spectroscopic techniques were used, as de-
tailed in the Supporting Information. The UV/Vis spectro-
scopic data summarized in Table 3 shows that substitution
of the azulene moieties of 15a with alkyl groups, as in com-
pounds 15b and 15c, produces a slight hypsochromic shift
of the longest wavelength band (Table 3, entry 1 vs. entries 2
and 3). This effect can be attributed to the decrease in con-
jugation between the azulenyl groups and the central
double bond in these latter compounds due to loss in copla-
narity induced by the presence of alkyl groups. On the other
hand, the insertion of oxygen or sulfur in the cyclopentene
0.57
1.00
0.50 0.54
0.86 0.93
0.07
0.14
0.51
0.92
0.100
0.081
16
0.87
0.67 0.77
0.81 0.89
0.20
0.16
0.75
0.89
0.081
0.086
0.97
17[a]
0.84
0.98
0.68 0.76
0.92 0.95
0.16
0.06
0.77
0.94
0.072
–
24
25
0.93
–
–
–
–
–
–
0.92
1.46
0.071
–
1.54
0.89
1.59
–
–
–
–
–
–
0.88
1.52
0.081
0.100
group produces no significant shifts in the absorption [a] A broad peak was also observed at 1.75 V by CV (1.61 V by
bands, except for a hypsochromic shift of 11 nm of the long- DPV).
est wavelength band of 17 compared with that of 15a
The CV curves of 15a, at scan rates from 25 to 200 mV/
(Table 3, entry 1 vs. entries 4 and 5). In the case of com-
s, are shown in Figure 2. At 200 mV/s scan rate, two redox
couples with anodic peaks at 0.75 and 0.85 V (correspond-
ing to 0.62 and 0.72 V by DPV), and cathodic peaks at 0.59
and 0.67 V were observed (Table 4, entry 1). The very slow
increase of the potential separations between the anodic
pounds 24 and 25, an additional band arising from the het-
erocyclic moiety appears at around 300 nm, whereas the
longest wavelength bands are shifted hypsochromically by
11 nm relative to 15a (Table 3, entry 1 vs. entries 6 and 7).
Table 3. Absorption maxima [nm] and coefficients (logε) of com-
pounds 15a–c, 16, 17, 24 and 25 in hexane.
Entry Compd.
λmax (logε)
1[5]
2
3
4
5
15a
15b
15c
16
232 (4.71), 277 (4.94), 321 sh (4.16), 379 (4.08)
244 (4.80), 288 (4.91), 368 (4.11)
246 (4.55), 286 (4.71), 308 sh (4.44), 373 (4.08)
232 (4.65), 278 (4.89), 321 sh (4.36), 379 (4.05)
233 (4.71), 279 (4.91), 368 (4.04)
238 (4.51), 284 (4.64), 298 sh (4.61), 368 (3.67)
240 (4.54), 285 (4.62), 301 sh (4.58), 368 (3.97)
17
6
7
24
25
Electrochemical Investigations
The electrochemical properties of compounds 15a–c, 16,
17, 24 and 25 were investigated by means of cyclic voltam-
metry (CV) and differential pulse voltammetry (DPV). The
measurements were carried out in acetonitrile solution con-
taining 0.1 m Bu NClO as the supporting electrolyte, with
4
4
platinum disk working and counter electrodes, and Ag wire Figure 2. CV curves of 15a at different scan rates.
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
7

Job/Unit: O30354
/KAP1
Date: 26-08-13 10:44:49
Pages: 11
A. C. Razus et al.
FULL PAPER
and cathodic peaks (ΔE ) with the scan rate seems to indi- ure S36) and 17 (Figure S37), and the results are summa-
p
cate that both couples are quasireversible. In addition, the rized in Table 4. For both compounds, the first two oxi-
width-at-half-height of both DPV peaks (W1/2 = 83 mV; dation processes involve single-electron transfers and, ap-
Table 4, entry 1) is close to the theoretical value of 90 mV, parently, are quasireversible, with peak separations (ΔEp)
corresponding to the transfer of one electron.[ Thus, it very slowly increasing with scan rate. Similarly, as in the
can be concluded that the electrochemical oxidation of 15a case of compound 15a, these oxidation processes can be
occurs by two successive one-electron transfers, giving the ascribed to the successive formation of the corresponding
18]
[
1b,5]
corresponding radical-cation and dication, respectively.
radical-cations and dications, respectively. Comparison of
To assess the effect induced by alkyl substitution of the the cyclic voltammograms of 15a, 16 and 17 (Figure 4)
azulene moieties upon the oxidation proclivity of 15a, we shows that replacement of one methylene group of the cy-
also investigated the electrochemical behavior of cycloalk- clopentene ring with oxygen or sulfur shifts the peak poten-
enes 15b and 15c (see the Supporting Information, Fig- tials and half-wave potentials to higher values (Table 4, en-
ures S34 and S35). By comparing the CV curves of cyclo- try 1 vs. entries 4 and 5), most probably due their inductive
alkenes 15a–c (Figure 3), it can be seen that the substitution electron-attracting effect.
of azulene moieties with alkyl groups induces a decrease in
the first oxidation potential and an increase in the second.
Electrochemical investigations of furan 24 (see the Sup-
porting Information, Figure S38) and tiophene 25 (Fig-
Figure 3. Overlapped CV curves of 15a (black), 15b (red), and 15c
(blue) at 200 mV/s scan rate.
Figure 5. Overlapped CV curves of 16 (solid line) and 24 (dashed
line) at 200 mV/s scan rate.
CV and DPV measurements were also performed for
compounds 16 (see the Supporting Information, Fig-
Figure 4. Overlapped CV curves of 15a (black), 16 (red) and 17
blue) at 200 mV/s scan rate.
Figure 6. Overlapped CV curves of 17 (solid line) and 25 (dashed
line) at 200 mV/s scan rate.
(
8
www.eurjoc.org
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 0000, 0–0

Job/Unit: O30354
/KAP1
Date: 26-08-13 10:44:49
Pages: 11
Carbocyclic and Heterocyclic Diazulenylethenes
ure S39) afforded the results shown in Table 4. The more with distilled water and then sonicated in double-distilled water for
1
min.
positive oxidation potentials of these latter compounds
compared with those of 16 and 17 (Figure 5 and Figure 6)
Vilsmeier–Haack Reaction of Azulenes 4b and 4c with N,N,NЈ,NЈ-
are attributable to their aromaticity, which leads to in- Tetraethylglutaramide (TEGA) and POCl : A 2–5 mL microwave
3
creased stability and, consequently, improved oxidation re- reaction vessel equipped with a stir bar was charged under an inert
atmosphere with TEGA (265 mg, 1.1 mmol) and POCl
3
(0.3 mL,
sistance.
3.3 mmol). The resulting mixture was stirred at room temperature
for 45 min, then a solution of azulenes 4b,c (2.4 mmol) in anhy-
drous 1,4-dioxane (4.6 mL) was added. The reaction vessel was se-
aled, shaken vigorously by hand until the mixture became homo-
geneous, and then irradiated for 45 min (fixed hold time) at 100 °C
by applying the “high” absorption level. After cooling to room
temperature, the reaction mixture was poured into ice-cooled water
Conclusions
An efficient, two-step method was developed for the syn-
thesis of 1,2-di(azulen-1-yl)ethenes 15–17 having the double
bond included in a five-membered carbocyclic or heterocy-
clic ring. The method involves preparation of the appropri-
(
100 mL), filtered with suction, and the insoluble residue was
washed thoroughly with water. The combined washings and filtrate
ate diketone precursors through Vilsmeier–Haack or Frie- were washed with toluene (2ϫ 15 mL), cooled in an ice bath, and
del–Crafts reactions, followed by their McMurry cycliza- then made slightly basic with 10% KOH aqueous solution. The
tion. Furthermore, alkenes 16 and 17 were quantitatively whole was extracted with diethyl ether (4ϫ 50 mL) and the ethereal
extracts were washed with water (3ϫ 100 mL), dried with anhy-
drous Na SO , and the solvent was removed in vacuo. The residue
2 4
converted into their respective dehydro derivatives 24 and
25, by oxidation with DDQ. The electrochemical properties
was purified by alumina column chromatography using ether/Et
(
3
N
of compounds 15–17, 24 and 25 were examined by CV and
DPV, and the relationship between their structure and elec-
trochemical behavior was established. In line with this
work, we are currently investigating the solid-state photo-
physical properties and electrochemical polymerization of
these compounds. Furthermore, work is in progress to syn-
thesize analogues of 15a by varying the size of the central
cycloalkene from a three- to six-membered ring.
100:1) as eluent to afford enamines 5b,c and 6b,c[ with the yields
19]
reported in Scheme 3.
Friedel–Crafts Acylation of Azulenes 4a–c with Glutaroyl Dichloride
Catalyzed by SnCl : To the ice-cooled solution of azulenes 4a–c
4.4 mmol) and glutaroyl dichloride (338 mg, 2 mmol) in anhydrous
carbon tetrachloride (15 mL) under an inert atmosphere, SnCl
0.56 mL, 4.8 mmol) was added dropwise. The resulting mixture
4
(
4
(
was stirred for 1.5 h at 0 °C and then the reaction was quenched
by the addition of water (100 mL). Work-up details are described
for each case in the Supporting Information and the results are
shown in Table 1.
Experimental Section
General Procedure for the McMurry Reaction of Diketones 1a–c, 2
and 3: To an ice-cooled suspension of active zinc dust (295 mg,
General Remarks: All reagents were purchased from commercial
suppliers and used without further purification, unless otherwise
noted. Tetrahydrofuran (THF) and 1,4-dioxane were distilled under
4
.5 mmol) in anhydrous THF (5 mL for 1a–c and 3, 20 mL for 2)
under an inert atmosphere, freshly distilled TiCl (0.25 mL,
.25 mmol) was added dropwise. The mixture was warmed to room
4
an inert atmosphere from LiAlH
sieves. Dichloromethane (CH Cl
tilled from fresh CaH . Microwave reactions were performed in se-
4
and stored over 4 Å molecular
2
2
2
) was heated to reflux and dis-
temperature and then heated at reflux for 2 h to yield a dark-brown
slurry of low-valent titanium reagent. When pyridine (0.365 mL,
2
aled glass vessels with a Biotage Initiator 2.0 reactor. Melting
points were determined with a Koehler Automatic Melting Point
Range Apparatus (K90190). HPLC was performed with an
AGILENT 1100/1200 system equipped with a quaternary pump
and Multiple Wavelength Detectors (MWD). Elemental analyses
were carried out with a Perkin–Elmer CHN 240B analyzer. FTIR
spectra were acquired with a Bruker Vertex 70 Spectrometer, with
a horizontal device for attenuated reflectance and diamond crystal,
4.5 mmol) and catechol (495 mg, 4.5 mmol) were used, they were
added successively to the low-valent titanium slurry at 0 °C and the
resulting mixture was stirred at this temperature for 15 min and 1 h,
respectively. A solution of the appropriate diketone (0.45 mmol) in
THF (5 mL for 1a, 20 mL for 1b and 1c, 45 mL for 3, 2 was added
as solid) was added in one portion and the reaction mixture was
stirred for the time and at the temperature indicated in Table 2.
The reaction was then quenched by the addition of 10% aqueous
–
1
1
on a spectral window ranging from 4000 to 400 cm .
H
K
2
(
2
CO
5 mL). The combined organic extracts were washed with water
4ϫ 100 mL), dried with anhydrous Na SO , and the solvent was
3 2 2 3
(10 mL) and extracted with CH Cl /Et N (100:1, 4ϫ
400 MHz) and 1 C NMR (100.56 MHz) spectra were recorded
3
(
with a Bruker Avance DRX4 spectrometer in CDCl with TMS as
3
2
4
an internal standard at room temperature. COSY and HETCOR
correlation experiments were used for the structure assignment.
Mass spectra were recorded with a Varian 1200L Quadrupole MS/
MS spectrometer by direct injection in ESI, positive mode. Cyclic
voltammetric measurements were performed with a potentiostat-
galvanostat system AutoLab PGStat 12, controlled by a GPES
removed in vacuo. When catechol was used, the organic extracts
were additionally washed with 5% aqueous KOH (2ϫ 100 mL) and
then with water (4ϫ 100 mL). Column chromatography was used
for the separation of the resulting products. The conditions used
for the chromatography are indicated in the Supporting Infor-
mation and the obtained compounds together with their yields are
reported in Table 2.
(General Purpose Electrochemical System) electrochemical inter-
face for Windows (version 4.9.007). Three electrodes in a one-com-
partment cell (10 mL) were used in all experiments. Two disk-
shaped platinum electrodes (Metrohm, 3 mm in diameter) were
used as working and counter electrodes, and Ag wire was used as
pseudoreference electrode. The platinum electrode surfaces were
polished with alumina slurry (0.05 μm) on a polishing pad, washed
General Procedure for the Oxidation of Alkenes 16 and 17 with
DDQ: To a stirred solution of the appropriate alkene 16 or 17
(0.05 mmol) in 1,4-dioxane (3 mL), DDQ (11 mg, 0.05 mmol) was
added. The reaction mixture was stirred for 5 min at room tempera-
ture and then passed through a short pad of alumina, eluting with
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
9

Job/Unit: O30354
/KAP1
Date: 26-08-13 10:44:49
Pages: 11
A. C. Razus et al.
FULL PAPER
EtOAc. The solvent was removed under reduced pressure to afford
4 or 25 in quantitative yields.
[7] S. Hayashi, S. Nakajima, K. Kaneto, K. Yoshino, Solid State
Commun. 1986, 60, 545–548.
2
[
8] S. Hino, K. Matsumoto, K. Iwasaki, Synth. Met. 1991, 41,
Supporting Information (see footnote on the first page of this arti-
cle): Work-up procedure for the Friedel–Crafts acylation of azu-
lenes 4a–c, synthesis of diketones 2 and 3, purification procedure
for the McMurry reaction of diketones 1a–c, 2 and 3, general pro-
cedure for the electrochemical experiments, characterization of all
793–796.
[9] a) F. X. Redl, O. Köthe, K. Röckl, W. Bauer, J. Daub, Macro-
mol. Chem. Phys. 2000, 201, 2091–2100; b) B. Meana-Esteban,
C. Lete, C. Kvarnström, A. Ivaska, J. Phys. Chem. B 2006, 110,
2
3343–23350; c) G. Nie, T. Cai, S. Zhang, J. Hou, J. Xu, X.
1
13
Han, Mater. Lett. 2007, 61, 3079–3082.
new compounds, copies of the H and C NMR spectra of com-
pounds 1–3, 14–17, 19, 20, 21a, 22–25, CV and DPV curves of
compounds 15a–c, 16, 17, 24, and 25.
[
10] a) A. Mirlach, M. Feuerer, J. Daub, Adv. Mater. 1993, 5, 450–
453; b) M. Porsch, G. Sigl-Seifert, J. Daub, Adv. Mater. 1997,
9, 635–639; c) J. R. Dias, J. Phys. Org. Chem. 2007, 20, 395–
406; d) G. Nöll, C. Lambert, M. Lynch, M. Porsch, J. Daub,
J. Phys. Chem. C 2008, 112, 2156–2164; e) G. O. Buica, E. M.
Ungureanu, L. Birzan, A. C. Razus, M. R. Bujduveanu, Elec-
trochim. Acta 2011, 56, 5028–5036.
Acknowledgments
The authors thank Professor Klaus Hafner from T. U. Darmstadt
for valuable discussions and helpful comments. This work was par-
tially supported by the European Social Fund “Cristofor I.
Simionescu” Postdoctoral Fellowship Programme for S. N. (ID
POSDRU/89/1.5/S/55216).
[11] K. Hafner, K.-F. Bangert, Justus Liebigs Ann. Chem. 1961, 650,
98–115.
[12] J. Brunken, E.-J. Poppe, Chem. Ber. 1960, 93, 2572–2577.
13] V. I. Smirnov, A. V. Afanas’ev, L. I. Belen’kii, Chem. Hetero-
cycl. Compd. 2011, 46, 1199–2007.
14] A. L. Baumstark, C. J. McCloskey, K. E. Witt, J. Org. Chem.
[
[
1
978, 43, 3609–3611.
[
1] a) S. Hünig, B. Ort, Liebigs Ann. Chem. 1984, 1905–1935; b)
M. Nakatsuji, Y. Hata, T. Fujihara, K. Yamamoto, M. Sasaki,
H. Takekuma, M. Yoshihara, T. Minematsu, S. Takekuma, Tet-
rahedron 2004, 60, 5983–6000; c) S. Takekuma, H. Matsuoka,
T. Minematsu, H. Takekuma, Tetrahedron 2010, 66, 3004–3015.
2] a) T. Arai, Y. Hozumi, O. Takahashi, K. Fujimori, J. Pho-
tochem. Photobiol. A 1997, 104, 85–89; b) P. G. Lacroix, I.
[15] a) P. Härter, K. Latzel, M. Spiegler, E. Herdtweck, Polyhedron
1998, 17, 1141–1148; b) T. Yamato, K. Fujita, H. Tsuzuki, J.
Chem. Soc. Perkin Trans. 1 2001, 2089–2097; c) Y. Ortin, J.
Grealis, C. Scully, H. Müller-Bunz, A. R. Manning, M. J.
McGlinchey, J. Organomet. Chem. 2004, 689, 4683–4690.
[16] N. Balu, S. K. Nayak, A. Banerji, J. Am. Chem. Soc. 1996, 118,
5932–5937.
[
Malfant, G. Iftime, A. C. Razus, K. Nakatani, J. A. Delaire, [17] a) T. Shoji, S. Ito, K. Toyota, M. Yasunami, N. Morita, Chem.
Chem. Eur. J. 2000, 6, 2599–2608; c) L. Cristian, I. Sasaki, P. G.
Lacroix, B. Donnadieu, I. Asselberghs, K. Clays, A. C. Razus,
Chem. Mater. 2004, 16, 3543–3551; d) A. Natarajan, J. T.
Mague, K. Venkatesan, T. Arai, V. Ramamurthy, J. Org. Chem.
Eur. J. 2008, 14, 8398–8408; b) A. C. Razus, L. Birzan, V. Tecu-
ceanu, M. Cristea, C. Enache, ARKIVOC 2008, 11, 210–226;
c) T. Shoji, S. Ito, K. Toyota, T. Iwamoto, M. Yasunami, N.
Morita, Eur. J. Org. Chem. 2009, 4307–4315; d) T. Shoji, S. Ito,
K. Toyota, T. Iwamoto, M. Yasunami, N. Morita, Eur. J. Org.
Chem. 2009, 4316–4324; e) T. Shoji, J. Higashi, S. Ito, T. Oku-
jima, N. Morita, Eur. J. Org. Chem. 2011, 584–592; f) T. Oku-
jima, A. Toda, Y. Miyashita, A. Nonoshita, H. Yamada, N.
Ono, H. Uno, Heterocycles 2012, 86, 637–648.
2006, 71, 1055–1059.
[
3] a) A. C. Razus, C. Nitu, S. Carvaci, L. Birzan, S. A. Razus, M.
Pop, L. Tarko, J. Chem. Soc. Perkin Trans. 1 2001, 1227–1233;
b) A. C. Razus, C. Nitu, V. Tecuceanu, V. Cimpeanu, Eur. J.
Org. Chem. 2003, 4601–4610; c) A. C. Razus, L. Birzan, M.
Cristea, V. Tecuceanu, L. Blanariu, C. Enache, Dyes Pigm.
[18] C. M. A. Brett, A. M. Oliveira Brett, in: Electrochemistry. Prin-
ciples, Methods and Applications, Oxford University Press, Ox-
ford, UK, 1993, p. 186–187.
[19] Unfortunately, enamines 6b,c could not be isolated in pure
form due to decomposition upon concentration and, therefore,
were not characterized spectroscopically. However, their struc-
ture was confirmed by MS analysis of their solutions after
chromatography, which showed molecular peaks at m/z = 395
(6b) and 423 (6c) corresponding to the [M + H]+ ions.
Received: March 8, 2013
2009, 80, 337–342; d) A. C. Razus, L. Birzan, M. Cristea, E.-
M. Ungureanu, M.-S. Cretu, Dyes Pigm. 2010, 86, 1–5; e) A. C.
Razus, S. Nica, L. Cristian, M. Raicopol, L. Birzan, A. E.
Dragu, Dyes Pigm. 2011, 91, 55–61.
[
4] A. C. Razus, E. A. Dragu, S. Nica, A. Nicolescu, Tetrahedron
Lett. 2011, 52, 1858–1862.
[
5] E. A. Dragu, S. Nica, M. Raicopol, A. Baran, D.-F. Anghel,
B. Cojocaru, L. Tarko, A. C. Razus, Tetrahedron Lett. 2012,
53, 2611–2614.
[6] R. J. Waltman, J. Bargon, Can. J. Chem. 1986, 64, 76–95.
Published Online: ᭿
10
www.eurjoc.org
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 0000, 0–0

Job/Unit: O30354
/KAP1
Date: 26-08-13 10:44:49
Pages: 11
Carbocyclic and Heterocyclic Diazulenylethenes
Azulene Derivatives
E. A. Dragu, S. Nica, V. Tecuceanu,
D. Bala, C. Mihailciuc, A. Hanganu,
A. C. Razus* ................................... 1–11
Synthesis and Electrochemical Properties
of Carbocyclic and Heterocyclic Diazulen-
ylethenes
Novel 1,2-di(azulen-1-yl)ethenes, having
the double bond included in a five-mem-
bered carbocyclic or heterocyclic ring, were
conveniently synthesized by McMurry
coupling reactions. Their electrochemical
properties were examined by cyclic voltam-
metry (CV) and differential pulse voltam-
metry (DPV), and the electrochemical be-
havior–structure relationship was estab-
lished.
Keywords: Heterocycles / Arenes / Fused-
ring systems / Electrochemistry / Voltam-
metry / Acylation
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
11