One-pot synthesis of stilbenes by dehydrohalogenation-Heck olefination and multicomponent Wittig-Heck reaction

Article abstract of DOI:10.1016/j.tetlet.2010.09.050

A variant of olefination reaction involving in situ generation of styrene by either one-pot dehydrohalogenation-Heck or one-pot multicomponent Wittig-Heck reaction is developed.

Full text of DOI:10.1016/j.tetlet.2010.09.050

Tetrahedron Letters 51 (2010) 6227–6231
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Tetrahedron Letters
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One-pot synthesis of stilbenes by dehydrohalogenation–Heck olefination
and multicomponent Wittig–Heck reaction
⇑
Akeel S. Saiyed, Ashutosh V. Bedekar
Department of Chemistry, Faculty of Science, M.S. University of Baroda, Vadodara 390 002, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A variant of olefination reaction involving in situ generation of styrene by either one-pot dehydrohalo-
genation–Heck or one-pot multicomponent Wittig–Heck reaction is developed.
Ó 2010 Elsevier Ltd. All rights reserved.
Received 2 August 2010
Revised 7 September 2010
Accepted 10 September 2010
Available online 17 September 2010
Keywords:
Heck reaction
In situ generation of styrene
One-pot multicomponent reactions
Dehydrohalogenation–Heck
Wittig–Heck
The concept of performing more than one transformation in a
single vessel, or developing one-pot processes, can generate less
waste, reduce work-up procedures, avoid separation of unstable
intermediates, save time and energy, and increase the efficiency
of the desired conversion.1 Since its discovery the Mizoroki–Heck
reaction,2 which involves palladium catalyzed coupling of aryl ha-
lide and styrene, remains the best method for preparation of stil-
bene derivatives. This method has been a subject of extensive
research, while it has been used for the synthesis of a large number
of natural and artificial molecules.3 In most cases the reaction is
done with suitable aryl halide and a styrene or similar olefin in
the presence of small quantity of Pd-catalyst and stoichiometric
amount of a base. Usually the aryl halide or in some cases aryl tri-
flate4 and aryl diazonium salt5 are easily obtained either from a
commercial source or prepared by known methods. The other com-
ponent is usually a styrene or a derivative of acrylic acid/acryloni-
trile etc. Scheme 1.
Although, the Mizoroki–Heck reaction has proved its effective-
ness, the synthetic utility purely depends on the avaiꢀlability of these
components. Usually ArBr, ArI, ArOTf, and ArN2þX are relatively
easy to prepare or are readily available. On the other hand, in many
casestheothercomponents, alkenes, arenotreadily available; either
they are difficult to prepare or tricky to purify due to their tendency
to polymerize during distillation or storage. Even under usual high
reaction temperature conditions there is a possibility of polymeriza-
tionand hence, itis usedinexcess. Thelatterproblemcanbesolved if
the olefin is somehow synthesized in situ during the Mizoroki–Heck
reaction. There are a few reported examples of one-pot combination
of synthesisof substitutedolefins.6–13 Theseincludesynthesisofole-
fins via Hunsdiecker reaction,6 Knoevenagel-decarboxylation se-
quence,9 Mizoroki–Heck, Wittig reaction,11 or four component
Ugi–Heck sequence.12
In this letter we present two one-pot methods consisting of
olefination processes and the Mizoroki–Heck reaction. The prere-
quisite of planning the one-pot multi-step reactions is the compat-
ibility of the reagent system and reaction conditions. In the present
effort the second reaction, the Mizoroki–Heck is carried out with
Pd-catalyst and a suitable base. Taking this into consideration the
required olefin can be either synthesized by base mediated dehy-
drohalogenation of suitable alkyl halide or by Wittig reaction from
aldehyde and appropriate phosphonium salt. The two approaches
are outlined in Scheme 2 taking the example of the in situ synthe-
sis of styrene 1 and then subjected to Mizoroki–Heck conditions to
form stilbene 2. In the approach A-1 the styrene is prepared by
dehydrohalogenation of (2-bromoethyl)benzene 3, and in A-2 from
(1-bromoethyl)benzene 4 using the same base which also facili-
tates subsequent Mizoroki–Heck reaction. Reaction of 3 may be
more favorable compared to 4 if it follows the E1cB mechanism14
and hence, the availability of styrene will be more for further
Mizoroki–Heck reaction.
Ar
Ar
+
R
R
Y
Y = halogen/OTf/N2+X-
R = aryl, CN, COOR' etc
⇑
Corresponding author. Tel.: +91 0265 2795552.
E-mail address: avbedekar@yahoo.co.in (A.V. Bedekar).
Scheme 1. Disconnection approach for stilbene or similar molecules.
0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.09.050

6228
A. S. Saiyed, A. V. Bedekar / Tetrahedron Letters 51 (2010) 6227–6231
H
Br
Ph
Ph
O
3
A-1
B-1
B-2
5
Ph3PCH3I
HCHO
dehydrohalogenation
Wittig
Ph
Heck
Ph
1
Br
A-2
Ph X
Pd-L
Ph
PPh3Br
Ph
6
4
Ph
2
Scheme 2. Proposed routes of in situ synthesis of styrene for subsequent one-pot Heck reaction.
Alternatively the intermediate styrene may be prepared by
Wittig reaction of an aldehyde and suitable phosphonium salt
(approach B of Scheme 2). Since the Wittig reaction involves two
components, that is, an aldehyde and a phosphonium salt, synthe-
sis of styrene can be achieved either by approach B-1 using benz-
aldehyde 5 and phosphonium salt obtained from methyl iodide or
Table 1
Synthesis of stilbenes with one-pot two component procedure of dehydrohalogenation-Heck reaction
Entry
1
Alkyl halide (1.0 equiv)
Aryl halide (1.2 equiv)
Olefin obtained
Yielda (%)
3
Iodobenzene (13)
trans-Stilbene (14)
80
(66)b
(54)c
67
2
3
4
5
4
3
3
3
Iodobenzene (13)
4-Iodoanisole (15)
1-Bromo-4-nitrobenzene (17)
1-Bromo-3-nitrobenzene (19)
trans-Stilbene (14)
trans-4-Methoxystilbene (16)
trans-4-Nitrostilbene (18)
trans-3-Nitrostilbene (20)
54
67
78
Ph
6
3
Br
69
(21)
(22)
OMe
OMe
I
I
Ph
Ph
7
3
74
MeO
(23)
MeO
(24)
8
9
4
4
4-Iodoanisole (15)
1-Bromo-4-nitrobenzene (17)
trans-4-Methoxystilbene (16)
trans-4-Nitrostilbene (18)
84
80
Ar
10
11
12
11
11
11
Iodobenzene (13)
64
86
54
(25, Ar = C6H5)
Ar
4-Iodoanisole (15)
4-Iodoacetanilide (27)
(26, Ar = 4-MeOC6H4)
Ar
(28, Ar = 4-AcNHC6H4)
Ar
13
11
4-Bromo chlorobenzene (29)
88
(30, Ar = 4-ClC6H4
14
15
12
12
Iodobenzene (13)
4-Iodo anisole (15)
trans-4-Nitrostilbene (18)
trans-1-(4-Methoxystyryl)-4-nitrobenzene (31)
76
77
All reactions run with aryl halide (1 equiv), alkyl halide (1.2 equiv), K2CO3 (3 equiv), Pd(OAc)2 (0.5%), 7 or 8 (0.55%) in DMA at 140 °C for 40 h. For entry 7:3 (3 equiv), K2CO3
(4 equiv), Pd (1.0%)-8 (2.5%).
a
Isolated Yield.
With L-10.
With L-9.
b
c

A. S. Saiyed, A. V. Bedekar / Tetrahedron Letters 51 (2010) 6227–6231
6229
O
O
OHC
CHO
1 eq.
CHO
2 eq.
O
PPh2
N
N
50
5
N
H2C PPh3
2 eq.
H2C PPh3
2 eq.
i.
i.
C-1
C-2
PPh2
NHR
7, R = H
8, R = CH2Ph
ii.
10 (dppp)
9
ii.
Br
I
2 eq.
49 %
89 %
Br
1 eq.
Figure 1. Ligands investigated for the present study.
51
13
by B-2 using formaldehyde and phosphonium salt 6 obtained from
benzyl bromide and triphenylphosphine.
52
Several ligands were chosen for the present Mizoroki–Heck
reaction as shown in Figure 1. There is considerable interest in
screening phosphine free ligands for Pd mediated Mizoroki–Heck
reaction,15 whereas 7 and 8 were synthesized as per the reported
procedures.16
In order to demonstrate the generality of this approach (A), a
series of alkyl bromides are prepared to access a variety of stilb-
enes and are listed in Figure 2. The mixture of suitable aryl halide,
an alkyl halide, an excess of K2CO3, catalytic quantity of Pd(OAc)2-
ligand in dry DMA was heated at 140 °C. Careful TLC analysis indi-
cated the formation of corresponding stilbene, which was isolated
and characterized. The results are presented in Table 1.
In most of the cases the isolated yields of olefin are good with
just 1.2 equiv of alkyl halide. As expected the formation of trans-
stilbene 14 from alkyl halide 3 was more favored than from alkyl
halide 4, due to the more facile elimination process. However, it
will be more logical and practical to use alkyl halides of the type
4 and 11, as they are more readily accessed from ethyl aryls by
benzylic bromination condition [NBS-Bz2O2-light], as we did.
Scheme 3. One-pot five-component approach for 1,4-distyryl benzene 52.
The second approach involves the in situ synthesis of styrenes by
the classical Wittig olefination.17 Reaction of aromatic aldehyde
with phosphonium salts undergoes Wittig reaction even with weak
base like potassium carbonate,18 a typical base for Mizoroki–Heck
reaction. Hence an equimolar amount of benzaldehyde, Ph3P+CH3Iꢀ,
iodobenzene, excess of K2CO3, catalytic quantity of Pd(OAc)2ꢁoxaz-
olinyl ligand 7 or 8, TBAB as PTC was heated in DMF and we found
the formation of trans-stilbene in good yield. Further experimenta-
tion demonstrated that this concept is clearly reproducible for a
number of aldehydes, three representative phosphonium salts,
and another set of aryl halides (Table 2). One carbon aldehyde unit
was accessed by employing para-formaldehyde (0.34 equiv) in the
reaction and hence, the same number of variations was available
for the facile generation of substituted stilbenes. Utilizing the well
established, transition metal free, high yielding Wittig reaction for
Br
Br
Br
Br
O2N
3
4
11
12
Figure 2. Alkyl halides used for in situ generation of olefins by dehydrohalogenation for Mizoroki–Heck reaction.
Table 2
Synthesis of stilbenes by one-pot three component procedure of Wittig–Heck reaction
Entry
Aldehyde (1 equiv)
Phosphonium salt
(1 equiv)
Aryl halide (1 equiv)
Olefin
Yielda (%)
1
2
3
4
5
Benzaldehyde (5)
Ph3P+CH3 Iꢀ
Ph3P+CH3 Iꢀ
Ph3P+CH3 Iꢀ
Ph3P+CH3 Iꢀ
Ph3P+CH3 Iꢀ
Iodobenzene (13)
Iodobenzene (13)
Iodobenzene (13)
Iodobenzene (13)
Iodobenzene (13)
trans-Stilbene (14)
trans-4-Nitrostilbene (18)
trans-4-Chlorostilbene (34)
trans-4-Methoxystilbene (16)
trans-4-(N,N-Dimethylamino) –stilbene (37)
91b
4-Nitrobenzaldehyde (32)
4-Chloro benzaldehyde (33)
4-Anisaldehyde (35)
4-N,N-Dimethylamino
benzaldehyde (36)
4-Methyl benzaldehyde (38)
3-Pyridine carboxaldehyde (40)
Piperonal (42)
94 (85)c
90
88
83
6
7
8
Ph3P+CH3 Iꢀ
Ph3P+CH3 Iꢀ
Ph3P+CH3 Iꢀ
Iodobenzene (13)
Iodobenzene (13)
Iodobenzene (13)
trans-4-Methylstilbene (39)
trans-3-Styrylpyridine (41)
97
90
92
trans-1-(3,4-Methylenedioxyphenyl)-
2-phenylethene (43)
trans-1-(4-Chlorostyryl)-4-methoxybenzene (44)
trans-1-(4-Methoxystyryl)-4-nitrobenzene (31)
trans-2-Styrylfuran (46)
trans-Stilbene (14)
trans-1-(4-Bromostyryl)-4-methoxybenzene (48)
trans-1-(4-Bromostyryl)-4-nitro benzene (59)
9
10
11
12
13
14
4-Chloro benzaldehyde (33)
4-Anisaldehyde (35)
2-Furaldehyde (45)
Paraformaldehyde (47)
Paraformaldehyde (47)
Paraformaldehyde (47)
Ph3P+CH3 Iꢀ
4-Iodoanisole (15)
1-Bromo-4-nitrobenzene (17)
Iodobenzene (13)
Iodobenzene (13)
4-Iodoanisole (15)
82
82
82
88
56
67
Ph3P+CH3 Iꢀ
Ph3P+CH3 Iꢀ
PhCH2P+Ph3 Clꢀ
4-BrC6H4CH2P+Ph3 Brꢀ
4-BrC6H4CH2P+Ph3 Brꢀ
1-Bromo-4-nitrobenzene (17)
All reactions were run in DMA, with Pd(OAc)2 (0.5 mol %), ligand 7 or 8 (1.0 mol %), K2CO3 (3.5 equiv), TBAB (20%) at 130–140 °C for 40 h.
a
Isolated yield.
With L-10.
With L-9.
b
c

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A. S. Saiyed, A. V. Bedekar / Tetrahedron Letters 51 (2010) 6227–6231
Table 3
One-pot multi component Wittig–Heck approach for distyryl benzenea
No
1
Conditions
Approach (scheme-5)
Distyryl benzene
Yield (%)
49
50 (1.0 equiv), 13 (2 equiv), Pd (1.0%), 7 (2%)
C-1
52
52
52
2
3
51 (1.0 equiv), 5 (2.0 equiv), Pd (1.0%), dppp 10 (2.0%)
51 (1.0 equiv), 5 (2.0 equiv), Pd (1.0%), 7 (2.0%)
C-2
C-2
89
85
NO2
O2N
4
51 (1.0 equiv), 32 (2.0 equiv), Pd (1.0%), 7 (2.0%)
C-2
63
53
5
54 (1.0 equiv), 5 (2.0 equiv), Pd (1.0%), 7 (2.0%)
C-2
77
55
a
With H2C@PPh3 (2.0 equiv), TBAB (40%), K2CO3 (7 equiv), 140 °C, 48 h. 54 = 1,2-dibromobenzene.
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the in situ olefination is an attractive option. It is notable that good
yields of olefins are obtained from equimolar mixture of three re-
agents, compared to the normal Mizoroki–Heck reaction protocol
which often requires excess olefin.
The molecules with alternate double bonds and aromatic rings
have received substantial attention.19,20 Our new strategy can be
further extended to the synthesis of distyryl benzenes from easily
available stable starting materials. The approach involves simulta-
neous formation of two double bonds between three aromatic rings
via a combination of Wittig and Mizoroki–Heck reaction between
five reactant molecules in a single step process. This one-pot five-
component process can be done in two ways. The 1,4-divinyl ben-
zene was prepared in situ by the reaction of terephthalaldehyde
50 and 2 equiv of Wittig reagent and subsequently subjected into
the Pd catalyzed Heck reaction with 2 equiv of iodobenzene (ap-
proach C-1, Scheme 3) or by making twofold excess of styrene with
1,4-dibromo benzene 51 (approach C-2, Scheme 3). The combined
yield of the reactions conducted in a single pot was very good, either
with ligand 7 or with ligand 8 and with dppp, 10, Table 3.
The route involving in situ synthesis of 1,4-divinyl benzene
from terephthalaldehyde (route C-1, Scheme 3) was less effective
because of its tendency of cross linking polymerization.
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A.; Santi, R. J. Org. Chem. 1993, 58, 7421; (c) Albert, K.; Gisdakis, P.; Rosch, N.
Organometallics 1998, 17, 1608; (d) Buchmeiser, M. R.; Wurst, K. J. Am. Chem.
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Organomet. Chem. 2003, 687, 229; (g) Grasa, G. A.; Singh, R.; Stevens, E. D.;
Nolan, S. P. J. Organomet. Chem. 2003, 687, 269; (h) Farina, V. Adv. Synth. Catal.
2004, 346, 1553; (i) Botella, L.; Najera, C. J. Org. Chem. 2005, 70, 4360; (j)
Decken, A.; Gossage, R. A.; Yadav, P. N. Can. J. Chem. 2005, 83, 1185; (k) Mino,
T.; Shire, Y.; Sasai, Y.; Sakemoto, M.; Fujita, T. J. Org. Chem. 2006, 71, 6834; (l)
Chen, W.; Xi, C.; Yang, K. Appl. Organomet. Chem. 2007, 21, 641; (m) Yoo, K. S.;
Park, C. P.; Yoon, C. H.; Sakaguchi, S.; O’Nell, J.; Jung, K. W. Org. Lett. 2007, 9,
3933; (n) Montaya, V.; Pons, J.; Branchadell, V.; Garcia-Anton, J.; Solans, X.;
Font-Bardia, M.; Ros, J. Organometallics 2008, 27, 1084.
16. (a) Gajare, A. S.; Shaikh, N. S.; Jnaneshwara, G. K.; Deshpande, V. H.;
Ravindranathan, T.; Bedekar, A. V. J. Chem. Soc., Perkin Trans. 1 2000, 999; (b)
Berg, D. J. Can. J. Chem. 2005, 83, 449.
17. Kormos, C. M.; Leadbeater, N. E. J. Org. Chem. 2008, 73, 3854.
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Chem. Soc. 1967, 89, 6273.
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A. C.; Holmes, A. B. Angew. Chem., Int. Ed. 1998, 37, 402; (c) Hoeben, F. J. M.;
Jonkheijm, P.; Meijer, E. W.; Schenning, A. P. H. J. Chem. Rev. 2005, 105, 1491;
(d) Schenning, A. P. H. J.; Meijer, E. W. Chem. Commun. 2005, 3245; (e)
Ajayaghosh, A.; Praveen, V. K. Acc. Chem. Res. 2007, 40, 644.
The two one-pot multi-step procedures developed herein21
have the advantage of using reduced number of work-up and puri-
fication steps, adequate chemical yield, and avoiding waste due to
polymerization of intermediates.
Acknowledgments
We wish to thank the Gujarat Narmada Fertilizer Corporation
(GNFC, Bharuch, India) for the financial assistance for this work.
We are grateful to Professor B.V. Kamath and Professor S. Devi
for their help and encouragement during this study. We wish to
thank Mr. S. P. Sahoo of Sun Pharmaceutical Advanced Research
Center and RSIC Chandigarh for recording some of the NMR spectra
for this work.
20. (a) Li, C.-L.; Shieh, S.-J.; Lin, S.-C.; Liu, R.-S. Org. Lett. 2003, 5, 1131; (b) Nielsen,
C. B.; Johnsen, M.; Arnbjerg, J.; Pittelkow, M.; McIlroy, S. P.; Ogilby, P. R.;
Jørgensen, M. J. Org. Chem. 2005, 70, 7065; (c) Lin, H.-C.; Tsai, C.-M.; Huang, G.-
H.; Tao, Y.-T. Macromolecules 2006, 39, 557; (d) He, J.; Xu, B.; Chen, F.; Xia, H.;
Li, K.; Ye, L.; Tian, W. J. Phys. Chem. 2009, 113, 9892.
21. General Procedure for the Heck reaction using (2-bromoethyl)benzene 3 as styrene
source. Preparation of catalyst solution (in all the cases catalyst is separately
prepared as follows): In a typical procedure a catalyst solution was separately
prepared in an oven dried, N2 flushed two-necked r.b. flask. A solution of
References and notes
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Broadwater, S. J.; Roth, S. L.; Price, K. E.; Kobašlija, M.; Tyler McQuade, D. Org.
Biomol. Chem. 2005, 3, 2899.
2. (a) Heck, R. F.; Nolly, J. P. J. Org. Chem. 1972, 37, 2320; (b) Mizoroki, T.; Mori, K.;
Ozaki, A. Bull. Chem. Soc. Jpn. 1971, 44, 581.
3. (a) Heck, R. F. Org. React. 1982, 27, 345; (b) Overman, L. E. Pure Appl. Chem. 1994,
66, 1423; (c) De Meijere, A.; Meyer, F. E. Angew. Chem., Int. Ed. Engl. 1994, 33,
2379; (d) Cabri, W.; Candiani, I. Acc. Chem. Res. 1995, 28, 2; (e) Crisp, G. T. Chem.
palladium acetate (1.2 mg, 0.0055 mmol, 0.5 mol %) and ligand
0.0137 mmol, 1.25 mol %) was prepared in dry N,N-dimethylacetamide (5 mL),
under N2 atmosphere. The mixture was stirred at room temperature until
7 (2.6 mg,

A. S. Saiyed, A. V. Bedekar / Tetrahedron Letters 51 (2010) 6227–6231
homogeneous (about 15 min) and degassed several times prior to use. 80%) (Table 1, entry 1).
6231
In another dry N2 flushed two-necked round bottomed flask a mixture of
iodobenzene 13 (0.2 g, 0.98 mmol), dry K2CO3 (0.406 g, 2.94 mmol) in dry N,N-
dimethylacetamide (5 mL) was taken and repeatedly degassed by purging with
General Procedure for the one pot Wittig–Heck reaction: Catalyst solution was
prepared in the same way as above. In another dry N2 flushed two-necked r.b.
flask a mixture of iodobenzene 13 (0.5 g, 2.45 mmol), benzaldehyde 5 (0.260 g,
2.45 mmol), triphenylmethylphosphonium iodide (0.995 g, 2.45 mmol), TBAB
(0.158 g, 0.49 mmol), and K2CO3 (1.18 g, 8.57 mmol) in dry N,N-
dimethylacetamide (5 mL) was taken and kept under N2 atmosphere. The
solution was then heated to 100 °C, previously prepared palladium catalyst
solution was added dropwise, and the reaction mixture heated to 140 5 °C for
40 h. The cooled mixture was then poured into water (25 mL)and extracted
with dichloromethane (3 ꢂ 30 mL). The dry solution (Na2SO4) was
concentrated and purified by column chromatography using silica gel and
petroleum ether as eluent to give trans-stilbene 14 as white solid; mp 121–
122 °C (0.401 g, 91%, entry 1 of Table 2)
N2 gas. Then the solution was heated to 60 °C and (2-bromoethyl)benzene 3 or
(1-bromoethyl)benzene 4 (0.217 g, 1.17 mmol) was slowly added. Then the
temperature was increased to 100 °C, previously prepared palladium catalyst
solution was added dropwise, and the reaction mixture was heated to
140 5 °C for 40 h. The cooled mixture was then poured into water (25 mL)
containing 6 N HCl (5 mL) and extracted with dichloromethane (3 ꢂ 30 mL).
The organic layer was washed with water and dried over anhydrous sodium
sulfate. The solution was concentrated under reduced pressure to obtain a
viscous liquid, which was purified by column chromatography using silica gel
and petroleum ether as eluent to give trans-stilbene 14 as white solid (0.140 g,