Direct one-pot synthesis of 2,3-diarylbuta-1,3-diene via self-coupling of acetophenones

Article abstract of DOI:10.1055/S-2008-1078412

A mild and straightforward route to 2,3-diarylbuta-1,3-diene is described here. By treatment with SmI2-Ac20, acetophe-none and its analogues underwent self-coupling reactions and subsequent elimination to give a series of 2,3-diarylbuta-1,3-dienes in moderate to good yields.

Full text of DOI:10.1055/S-2008-1078412

LETTER
1529
Direct One-Pot Synthesis of 2,3-Diarylbuta-1,3-diene via Self-Coupling of
Acetophenones
D
irec
t
O
ne
i
-Pot
S
a
ynthesis of
n
2,3-Diarylbuta-1, 3
L
-diene i, Shaoyu Li, Xueshun Jia*
Department of Chemistry, Shanghai University, Shanghai 200444, P. R. of China
Fax +86(21)66132797; E-mail: xsjia@mail.shu.edu.cn
Received 25 February 2008
Abstract: A mild and straightforward route to 2,3-diarylbuta-1,3-
diene is described here. By treatment with SmI2–Ac2O, acetophe-
none and its analogues underwent self-coupling reactions and sub-
sequent elimination to give a series of 2,3-diarylbuta-1,3-dienes in
moderate to good yields.
O
O
SmI2, Ac2O
THF
+
Key words: 2,3-diarylbuta-1,3-diene, self-coupling, acetophenone
1a
2a
3a
Scheme 1
As an important synthetic intermediate, 2,3-diarylbuta-
1,3-dienes play an important role in organic chemistry.1
Therefore, the efficient synthesis of these compounds
continues to attract the interest of organic chemists. They
can be prepared by palladium-catalyzed intermolecular
coupling reactions of vinyl halides mediated by indium,2
palladium-catalyzed reactions of propargyl carbonates
with organoboron or organotin(IV) reagents,3 dehydration
of 2,3-diarylbutane-2,3-diol,4 and copper(I)-catalyzed re-
actions of 1,4-disubstituted but-2-yne with Grignard re-
agents.5 However, the use of expensive or toxic reagents,
high reaction temperature (180 °C), and time-consuming
multiple steps have limited the utility of these reactions in
some cases.2–4
prepared SmI2 solution in THF was added dropwise to a
suspension of acetophenone under a nitrogen atmosphere.
After the 1a was consumed completely (as detected by
TLC), acetic anhydride was added to the mixture until the
reaction was complete. As showed in Table 1, SmI2 (1
mmol) combined with acetic anhydride (1.2 mmol) in
THF under reflux showed the highest catalytic activity,
giving 2a together with the rearranged ketone 3a (Table 1,
entry 3). When the reaction was conducted in the presence
of 0.05 equivalent or 0.5 equivalent of acetic anhydride,
buta-1,3-diene 2a was isolated in low yield (Table 1, en-
tries 4 and 5). In the absence of acetic anhydride, no cou-
pling product was observed and the pinacol was obtained
exclusively (Table 1, entry 6). Furthermore, the reaction
time was dependent on the reaction temperature (Table 1,
entries 1–3). Accordingly, the process was accelerated
significantly at higher reaction temperatures.
It has been well established that ketones and other carbo-
nyl compounds could act as good starting materials for the
preparation of olefins via McMurry coupling reactions.6
On the other hand, the direct conversion into buta-1,3-
dienes from ketones is rare and still remains a challenging
subject. More recently, Taylor et al. have disclosed an in-
teresting route to buta-1,3-dienes from ketones.7 Howev-
er, this method was not atom-economical as the ketones
must be converted into their corresponding sulfonylhy-
drazones, which were then isolated and used for the next
step. In addition, aromatic ketones only gave 2,3-diaryl-
buta-1,3-dienes in poor yields. As a result, the direct syn-
thesis of 2,3-diarylbuta-1,3-diene from acetophenones is
highly desirable. As a continuation of our interest in the
synthesis of substituted alkenes,8 herein we wish to report
a mild and efficient approach to 2,3-diarylbuta-1,3-diene
from acetophenones (Scheme 1).
We chose a variety of structurally diverse acetophenones
to understand the scope and the generality of the SmI2–
Ac2O-promoted coupling reaction to yield 2,3-diarylbuta-
Table 1 Screening Reaction Parameters for the Synthesis of 2,3-
Diphenylbuta-1,3-dienea
Entry
Ac2O
Temp
Time (h)
Yield (%)b
(equiv)
2a
12
43
78
42
5
3a
1
2
3
4
5
6
1.2
r.t.
20
8
60
50
18
25
15
0
1.2
50 °C
reflux
reflux
reflux
reflux
1.2
3
In an effort to develop a better reaction system, a variety
of reaction parameters were screened for self-coupling of
acetophenone (1a) to yield 2,3-diphenylbuta-1,3-diene
(2a) and the results are presented in Table 1. The readily
0.5
10
48
72
0.05
none
0
a Unless otherwise noted, all reactions were carried out with 1a (1
mmol) in the presence of SmI2 (1 equiv).
b Isolated yields.
SYNLETT 2008, No. 10, pp 1529–1531
Advanced online publication: 16.05.2008
DOI: 10.1055/s-2008-1078412; Art ID: W03108ST
x
x
.x
x
.2
0
0
8
© Georg Thieme Verlag Stuttgart · New York

1530
J. Li et al.
LETTER
R
Table 2 SmI2–Ac2O-Mediated Syntheses of 2,3-Diarylbuta-1,3-
dienes from Acetophenones
R
R
O
O
R
SmI2, Ac2O
THF, reflux
Entry
R
Time (h)
Yield (%)c
+
2
3
R
1a
2a
3a
4a
5a
6a
7a
8b
9b
H
3
2
78
88
69
77
47
37
18
10
16
20
33
10
1
2
3
4-MeO
3-MeO
4-Me
2-Me
4-Cl
Scheme 2
1
1,3-diene under the optimal reaction conditions
(Scheme 2) and the results are summarized in Table 2. We
were pleased to find that the reactions proceeded smooth-
ly to produce the desired buta-1,3-dienes 2 in good yields
(method A). As can be seen, the present conversion was
susceptible to electronic factors. In the presence of an
electron-donating group, the desired products 2 were ob-
tained in higher yields within short time (Table 2, entries
2–4). In contrast, when electron-deficient substrates were
utilized, the reaction became sluggish and resulted in low-
er product yield (Table 2, entry 6). In particular, when the
4-bromo-substituted substrate was used, the correspond-
ing diene could not be isolated and only a complex mix-
ture was obtained even with prolonged reaction time
(Table 2, entry 7). However, this problem could be re-
solved by using method B (Table 2, entries 8 and 9).
Hence, after the reaction of 4-chloro- or 4-bromo-substi-
tuted acetophenone with SmI2 in THF was complete under
the optimized reaction conditions, THF was removed un-
der reduced pressure, then MeCN and Ac2O were added
successively, and the resulting mixture was stirred under
reflux to afford the corresponding diene (method B).
Moreover, it should be noted that the electron-donating
group 2-methyl gave rise to a low yield of the correspond-
ing buta-1,3-diene (47%), which may be attributed to ster-
ic hindrance. According to the above reaction results, the
current optimal conditions were superior for the following
reasons: (1) In all cases, only 1 mmol of samarium diio-
dide was needed. (2) The reaction time was significantly
shortened especially when electron-rich substrates were
used. (3) No formation of McMurry coupling product was
observed and the desired 2,3-diarylbuta-1,3-dienes were
obtained as the major products.
2
5
18
24
20
24
d
d
4-Br
4-Cl
–
–
62
43
14
10
4-Br
a Method A.
b Method B.
c Isolated yields.
d In this case, a very complex mixture was produced.
O–
.
O
R
R
SmI2
self-coupling
R
R
R
R
Ac2O
O
O
–O
O–
O
O
A
B
HOAc
SmI2(OAc)
R
R
R
R
HO
OH
O
O
HOAc
O
O
R
Sm
OAc
It has been well known that samarium diiodide can pro-
mote the coupling reaction of carbonyl compounds effi-
ciently,9 and the formation of pinacol-type coupling
species was also detected during our investigations. Ac-
cordingly, we suggest that the formation of the corre-
sponding buta-1,3-dienes proceeded via the pinacol-type
dianion intermediate A. The reactive dianion is rapidly
captured by acetic anhydride to form a diacetate B, which
undergoes double elimination to give product 2. Although
we are not clear about the exact nature, we believe that the
presence of Sm(III) species play a significant role in this
process. The chelation of the trivalent samarium with ox-
ygen (intermediate C) facilitates the cleavage of the C–O
bond to give the final product. Also, rearrangement of A
gives product 3 in the presence of acetic acid (Scheme 3).
I
I
O
C
– 2 MeCOOH
R
R
R
3
2
Scheme 3
To verify our proposition, further investigations on the re-
action mechanism are underway in our laboratory.
Synlett 2008, No. 10, 1529–1531 © Thieme Stuttgart · New York

LETTER
Direct One-Pot Synthesis of 2,3-Diarylbuta-1,3-diene
1531
(6) (a) McMurry, J. E.; Felming, M. P. J. Am. Chem. Soc. 1974,
96, 4708. (b) Mukaiyama, T.; Sato, T.; Hanna, J. Chem. Lett.
1973, 2, 1041. (c) Fürstner, A.; Bogdanovic, B. Angew.
Chem. Int. Ed. 1996, 35, 2442. (d) McMurry, J. E. Chem.
Rev. 1989, 89, 1513. (e) Lenoir, D. Synthesis 1989, 883.
(f) Duan, X. F.; Zeng, J.; Lu, J. W.; Zhang, Z. B. J. Org.
Chem. 2006, 71, 9873.
(7) Addie, M. S.; Taylor, R. J. K. ARKIVOC 2000, (v), 660.
(8) (a) Li, J.; Xu, X. X.; Zhang, Y. M. Tetrahedron Lett. 2003,
44, 9349. (b) Li, J.; Wang, X. X.; Zhang, Y. M. Tetrahedron
2004, 60, 5793.
In conclusion, we have developed a mild and efficient
method for the construction of 2,3-diarylbuta-1,3-dienes
in moderate to good yields, using SmI2–Ac2O system.10 A
variety of acetophenones were converted directly into the
corresponding 2,3-diarylbuta-1,3-dienes, which makes
this method superior to most existing reports. The simple
operation and mild conditions also add to its attractive-
ness. In this regard, we believe that our method will find
use in organic synthesis.
(9) (a) Namy, J. L.; Kagan, H. B. Tetrahedron Lett. 1983, 24,
765. (b) Molander, G. A.; Etter, J. B.; Harring, L. S.; Thorel,
P. J. J. Am. Chem. Soc. 1991, 113, 8036. (c) Fuchs, J. R.;
Mitchell, M. L.; Shabangi, M.; Flowers, R. A. Tetrahedron
Lett. 1997, 38, 8157. (d) Chiara, J. L.; Cabri, W.; Hanessian,
S. Tetrahedron Lett. 1991, 32, 1125. (e) Uenishi, J.;
Masuda, S.; Wakabayashi, S. Tetrahedron Lett. 1991, 32,
5097.
(10) General Procedure for the Synthesis of 2,3-Diarylbuta-
1,3-dienes (Method A): To the stirred acetophenone or its
analogues 1 (1 mmol) in an oven-dried glassware under a
nitrogen atmosphere, samarium diiodide (1 mmol) in THF
(15 mL) was added dropwise. Generally the reaction
finished within 15 min. After the deep blue color faded,
Ac2O (1.2 mmol) was added to the yellow mixture rapidly.
The reaction mixture was stirred under reflux until reaction
completion. After the usual workup, the crude product was
purified by silica gel column chromatography using EtOAc–
PE (1:20) as eluent to afford the corresponding pure buta-
1,3-diene 2.
Acknowledgment
We thank the National Natural Science Foundation of China (No.
20572068) and the Innovation Fund of Shanghai University for fi-
nancial support.
References and Notes
(1) (a) Boehrner, J.; Grigg, R. Tetrahedron 1999, 55, 13463.
(b) Shimizu, H.; Hatano, T.; Matsuda, T.; Iwamura, T.
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General Procedure for the Synthesis of 2,3-Bis(4-
bromophenyl)buta-1,3-diene and 2,3-Bis(4-chloro-
phenyl)buta-1,3-diene (Method B): To the stirred 4-
chloro- or 4-bromo-substituted acetophenone (1 mmol) in an
oven-dried glassware under a nitrogen atmosphere,
samarium diiodide (1 mmol) in THF (15 mL) was added
dropwise. Generally the reaction finished within 15 min.
After the deep blue color faded, THF was removed under
reduced pressure, then MeCN (3 mL) and Ac2O (3.0 mmol)
were added to the yellow mixture successively, and the
resulting mixture was stirred under reflux until reaction
completion. After the usual workup, the crude product was
purified by silica gel column chromatography using EtOAc–
PE (1:20) as eluent to afford the corresponding diene.
Synlett 2008, No. 10, 1529–1531 © Thieme Stuttgart · New York