Mizoroki–Heck reaction of 1,2-disubstituted aryl alkenes: Variables of synthesis, solvent and ligand modulation of reactivity

Article abstract of DOI:10.1080/00397911.2020.1811986

Reaction of aryl iodides with 1,2-disubstituted aryl alkenes in the presence of TBABr/TBACl gave high yields of the Mizoroki–Heck product. Phosphine ligands were used for the modulation of reactivity and stereoselectivity, for the reaction of 4-iodoanisole with cinnamaldehyde. tert-Bu₃P.HBF₄ gave the highest E:Z ratio of 1:0.08. The use of PEG-200 and PEG-400 as solvent could activate the reaction of aryl iodides with various 1,2-disubstituetd aryl alkenes.

Full text of DOI:10.1080/00397911.2020.1811986

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
Chemistry
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/lsyc20
Mizoroki–Heck reaction of 1,2-disubstituted aryl
alkenes: Variables of synthesis, solvent and ligand
modulation of reactivity
Pronnoy G. Bangar , Priyanka R. Jawalkar , Swapnil R. Dumbre , Pallavi K.
Raut , Dharmaraj J. Patil , Neethu Tv , Shana Sudhakaran & Suresh Iyer
To cite this article: Pronnoy G. Bangar , Priyanka R. Jawalkar , Swapnil R. Dumbre , Pallavi K.
Raut , Dharmaraj J. Patil , Neethu Tv , Shana Sudhakaran & Suresh Iyer (2020): Mizoroki–Heck
reaction of 1,2-disubstituted aryl alkenes: Variables of synthesis, solvent and ligand modulation of
reactivity, Synthetic Communications, DOI: 10.1080/00397911.2020.1811986
To link to this article: https://doi.org/10.1080/00397911.2020.1811986
Published online: 27 Aug 2020.
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https://doi.org/10.1080/00397911.2020.1811986
Mizoroki–Heck reaction of 1,2-disubstituted aryl alkenes:
Variables of synthesis, solvent and ligand modulation
of reactivity
Pronnoy G. Bangara,b, Priyanka R. Jawalkara, Swapnil R. Dumbrea, Pallavi K. Rauta,
Dharmaraj J. Patila, Neethu Tva, Shana Sudhakarana, and Suresh Iyera,b
b
aOrganic Chemistry Division, National Chemical Laboratory, Pune, Maharashtra, India; Academy of
Scientific and Innovative Research (AcSIR), New Delhi, India
ABSTRACT
ARTICLE HISTORY
Received 22 May 2020
Reaction of aryl iodides with 1,2-disubstituted aryl alkenes in the
presence of TBABr/TBACl gave high yields of the Mizoroki–Heck
product. Phosphine ligands were used for the modulation of reactiv-
ity and stereoselectivity, for the reaction of 4-iodoanisole with cinna-
maldehyde. tert-Bu3P.HBF4 gave the highest E:Z ratio of 1:0.08. The
use of PEG-200 and PEG-400 as solvent could activate the reaction
of aryl iodides with various 1,2-disubstituetd aryl alkenes.
KEYWORDS
12-Disubstituted aryl
alkenes; ligand effect;
Mizoroki–Heck reaction; PEG
200/400; TBABr
GRAPHICAL ABSTRACT
Introduction
The Mizoroki–Heck is a versatile and fast reaction of monosubstituted alkenes with aryl
iodides, giving E-isomer products in very high yields and regioselectivity.[1–4] 1,1 and
1,2 disubstituted alkenes are difficult substrates requiring long reaction times and special
reagents.[5–13] The resulting 1,1,2-trisubstituted aryl alkene scaffolds have been shown to
be important bioactive molecules and drugs like Tamoxifen also synthesized from
them.[14–18] The 1,1-diaryl substitution pattern is present in several drug molecules like
fenpiprane and tolterodine.[18] The core pi structure of various molecules exhibit OLED
and other properties and has been the subject of platform synthesis.[19–21] The 1,10,2,20,-
pi scaffold is a difficult to construct molecular architecture. A user-friendly reaction is
required for arylation and vinylation of disubstituted alkenes and it is also necessary to
address stereoselectivity in these reactions.
CONTACT Suresh Iyer
s.iyer@ncl.res.in
Organic Chemistry Division, National Chemical Laboratory, Pune,
Maharashtra, India
Supplemental data for this article can be accessed on the publisher’s website.
ß 2020 Taylor & Francis Group, LLC

2
P. G. BANGAR ET AL.
Scheme 1. TBABr additive for the PdOAc2 catalyzed Mizoroki–Heck reaction of 1,2 disubstituted
aryl alkenes.
There are a few standard protocols for the arylation of disubstituted alkenes, though lim-
ited in the generality of application; they typically are sluggish reactions and requiring long
reaction times, special bases, reagents or ligands.[5–13] Ciufolini and coworkers describe the
reactions to be limited to electron rich aryl iodides, specifically 4-iodo anisole and 4-N, N-
dimethyl amino iodo benzene.[22,23] Other reactions require the use of Ionic Liquids.[24–26]
Monteiro and coworkers have reported the Mizoroki–Heck reaction of aryl bromides with
stilbenes, requiring 48 h for completion.[27] The silver sequestration of halides has been used
in the asymmetric Mizoroki–Heck reaction and vinylation of allyl alcohols.[28–33]
Stoichiometric Ag2CO3 has been used for the Pd catalyzed arylation of fluoro acrylates.[34]
Chen et al have reported AgOAc mediated disubstitution of mono-substituted alkenes, ethyl
acrylate and styrene.[35] More recently the arylation of aryl vinyl MIDA boronates followed
by Suzuki coupling for the synthesis of triarylethylene units have been described.[36] We have
communicated the silver sequestration of aryl iodides for reaction with various 1,1 and 1,2
disubstituted aryl alkenes, providing 1,1,2- trisubstituted aryl alkenes in very high yields in
short reaction times.[37] Ligands and reagents ramp up the magical activity of the catalyst
marvel, Pd. Stoichiometric silver salts being expensive, we investigated ligand alternatives for
silver as well as solvent variations. We now report in this article the studies conducted on the
silver free arylation of various 1,2-disubstituted alkenes.
Results and discussion
In a preliminary communication, we described the Pd catalyzed arylation of diphenylethene,
ethyl atropate, itaconate and several 1,2-disubstituted aryl alkenes in very high yields, using
stoichiometric AgOAc.[37] We report here a silver free, user-friendly protocol for the high
yielding arylation of 1,2-disubstituted aryl alkenes (Schemes 1 and 2). This is thus an easy
entry into drug molecules like Tamoxifen, Fenpiprane, and Tolterodine. While the original
Mizoroki–Heck reaction is E-selective, 1,2-disubstituted aryl alkenes give E: Z mixtures.
The use of silver salts being stoichiometric and expensive, the search for inexpensive
alternatives was essential. Molten TBABr has been used as a solvent for the arylation of
ethyl cinnamate.[5] N-Phenyl urea as ligand promotes the Pd catalyzed reaction of various
1, 2-disubstituted alkenes but limited to 4-iodo anisole and 4-N,N-dimethyl amino iodo
benzene.[22,23] Jeffery Tuyet has reported the first use of TBACl and TBABr for the
Mizoroki–Heck reaction of mono-substituted alkenes giving high yields and reactions at
RT.[38] The use of Ionic liquids, TBAA and TBABr demonstrates enhanced reactivity for

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3
Scheme 2. [Pd] (Cat) Mizoroki–Heck reaction of disubstituted alkenes in PEG-200 and PEG-400.
1,2-disubstituted alkenes.[24–26] In this study, reaction of 1,2-disubstituted aryl alkenes in
DMF as solvent and TBABr as additive, gave reasonably fast reactions and high yields
without the addition of silver salts (Scheme 1; Table 1). TLC monitoring of these reactions
was difficult due to the close Rf value of the product and starting materials. Repeated elu-
tions of the TLC gave visible separations and thus reactions could be concluded.
Having established the reactivity of 4-iodoanisole with cinnamaldehyde, we explored ran-
domly the reactivities of several aryl iodides with various 1,2-disubstituted alkenes using
OTP, BINAP and acetophenone oxime as ligands in conjunction with Pd(OAc)2 as catalyst
(Scheme 1; Table 1). Exceptionally good yields were obtained with several aryl iodides and
alkenes compared to the results of Ciufolini where only electron-rich aryl iodides were pro-
ductive. 4-FC6H4I reacted with ethyl cinnamate to give 86% yield and a E:Z ratio of 9: 1.
In several publications, the use of TBABr and TBACl as an additive has been shown
to be conducive for high yields in the Mizoroki–Heck reactions and also for some
examples with 1,2-disubstituted alkenes.[8] This effect along with variations in ligands in
the reaction of different aryl iodides and several 1,2-disubstituted alkenes was explored
(Scheme 1; Table 1). Very good yields were obtained but low E:Z ratios. Reactions were
comparable with the use of additives like AgOAc and AgBF4.
Search for increased reactivity and inexpensive silver alternatives led us to examine solv-
ent variations. The Mizoroki–Heck reaction has been shown to be especially facile in PEG-
400.[39] PEG has also been shown to be a good solvent for the Mizoroki–Heck reaction
with various other catalysts.[40–47] The reaction of disubstituted aryl alkenes in PEG-400/
200 catalyzed by PdCl2(C6H5CN)2, with an inorganic base and in the absence of Ag salts
was explored (Scheme 2; Table 1). To our delight, most of these reactions were very high
yielding with moderate reaction times of 2.1 ꢀ 34 h, but mixtures of E:Z isomers.
Ligands conjure the magical wizardry associated with Pd catalysis. So the reaction of
4-iodo anisole with E-cinnamaldehyde for the effect of various ligands on reactivity,
yields and stereoselectivity was investigated (Scheme 3; Table 2). All the ligands studied
gave high yields of the substituted alkenes. Best result was obtained with tert-
Bu3P.HBF4 with a yield of 96%, reaction time of 5 h and E:Z ratio of 1:0.08.[48] PCy3
was second with a yield of 90% in 3 h and E:Z ratio of 1: 0.24. Nonphosphine ligands—
acetophenone oxime, ThCOOH and proline gave good yields in 16 ꢀ 24 h, but low E:Z
ratios. Palladacycle catalysts also gave high yields in 20 ꢀ 24 h, but low E:Z ratios.
The effect of OTP was then studied for the reaction of substituted aryl iodides with
1,2-disubstituted aryl alkenes in DMF solvent with TBABr additive and NaOAc as base.

4
P. G. BANGAR ET AL.
Table 1. TBABr/TBACl additive
& solvent (PEG-200, PEG-400) effects for the Pd-catalyzed
Mizoroki–Heck reaction of 1,2 disubstituted aryl alkenes with aryl iodides.
Product
Time, h Yield % (E:Z Ratio)
S. No
Aryl Halide
C6H5I
4-CH3OC6H4I
4-CH3C6H4I
4-CH3OC6H4I
4-FC6H4I
4-CH3OC6H4I
4-CH3OC6H4I
4-FC6H4I
4-CH3OC6H4I
4-CH3OC6H4I
4-CH3OC6H4I
4-CH3OC6H4I
C6H5I
4-CH3OC6H4I
4-CH3OC6H4I
4-CH3OC6H4I
2-CH3C6H4I
4-CH3C6H4I
C6H5I
4-CH3O.C6H4I Ethyl Cinnamate (E)
4-CH3C6H4I
2-CH3C6H4I
Alkene
Ligand/Reagent/Solvent
Catalyst
1
2
3
4
5
6
7
8
PhCH ¼ CH.CHO (E)
PhCH ¼ CH.CHO (E)
PhCH ¼ CH.CHO (E)
PhCH ¼ CH.COOEt (E)
PhCH ¼ CH.COOEt (E)
PhCH ¼ CH.COOEt (E)
PhCH ¼ CH.COOEt (E)
PhCH ¼ CH.COOEt (E)
PhCH ¼ CH.COOEt (E)
PhCH ¼ CH.COOEt (E)
PhCH ¼ CH.COCH3 (E)
Chalcone (E)
Acetophenone Oxime
Acetophenone Oxime
OTP
Acetophenone Oxime
OTP
OTP
BINAP (R)
OTP
AgOAc
AgBF4
OTP
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
24
24
24
39
25
24
26
24
10
3
16
21
44
48
4.5
2.15
7.5
18
15
9.5
2.1
17.1
32
34
5
99
93
91
64
86
83
60
99
68
99
87
94
41
49
83
83
95
92
83
73
99
Traces
79
82
74
99
79
75
53
89
78
73
69
—
1.5:1
1.3:1
2.4:1
9:1
2.4:1
1.8:1
1.1:1
2:1
2.1:1
1.1:1
2.8:1
–
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
OTP
Stilbene (E)
Stilbene (E)
Acetophenone oxime
Acetophenone oxime
2:1
C6H5CH ¼ CH.COC6H5 (E) TBABr, no ligand
1:0.37
1:0.34
1: 0.17
1:1
–
2:1
2:1
–
2:1
3:1
2:1
1:1
1.5:1
–
2:1
1:1
3:1
1.5:1
2:1
C6H5CH ¼ CH.COCH3 (E) TBABr, no ligand
C6H5CH ¼ CH.CHO (E)
PhCH ¼ CH.COCH3 (E)
Cinnamaldehyde (E)
TBACl, no ligand
TBACl, no ligand
PEG-400
PEG-400
PEG-400
PEG-400
PEG-400
PEG-400
PEG-400
PEG-400
PEG-400
PEG-200
PEG-200
PEG-200
PEG-200
PEG-200
PEG-200
Pd(OAc)2
Pd(OAc)2
PdCl2(PhCN)2
PdCl2(PhCN)2
PdCl2(PhCN)2
PdCl2(PhCN)2
PdCl2(PhCN)2
PdCl2(PhCN)2
PdCl2(PhCN)2
PdCl2(PhCN)2
PdCl2(PhCN)2
PdCl2(PhCN)2
PdCl2(PhCN)2
PdCl2(PhCN)2
PdCl2(PhCN)2
PdCl2(PhCN)2
PdCl2(PhCN)2
Cinnamaldehyde (E)
Stilbene (E)
4-CH3O.C6H4I Stilbene (E)
4-CH3O.C6H4I Chalcone (E)
4-CH3CO.C6H4I Chalcone (E)
4-CH3C6H4I
4-CH3O.C6H4I Cinnamaldehyde (E)
Benzalacetone (E)
2 h
16
12
5
4.2
10
14
8
C6H5I
Cinnamaldehyde (E)
4-CH3O.C6H4I Ethyl Cinnamate (E)
4-CH3C6H4I
2-CH3C6H4I
4-CH3O.C6H4I Cinnamaldehyde (E)
4-CH3CO.C6H4I Chalcone (E)
Benzalacetone (E)
Cinnamaldehyde (E)
Scheme 3. Ligand effect on the Mizoroki–Heck reaction of aryl iodides with 1,2-disubstituted
aryl alkenes.
Extremely high yields were obtained in 16 ꢀ 24 h reaction time. But the products were
obtained as E:Z mixtures with only 4-FC6H4I giving a moderately high ratio of 9: 1.
The enhanced reactivity of the catalyst systems described could be attributed to the
formation of Pd nano particles. TBABr addition stabilizes such nanoparticles.[5,8,28,49]
PEG is also known to stabilize Pd NPs which explains the enhanced reactivity in PEG-

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Table 2. Ligand–catalyst effects for the Mizoroki–Heck reaction of aryl iodides with 1,2-disubstituted
aryl alkenes.
Product
(E:Z Ratio)
S. no
1
Ligand/catalyst
ArI
Alkene
Time, h
4
Yield %
86
Triphenylphosphine
(2 mol %)—Pd(OAc)2
Tri(o-tolyl)phosphine
(4 mol %)—Pd(OAc)2
Dppe—Pd(OAc)2
Dppf—Pd(OAc)2
Johnphos
4-CH3OꢁC6H4I
Cinnamaldehyde (E)
1:0.6
2
4-CH3OꢁC6H4I
Cinnamaldehyde (E)
24
99
1.7:1
3
4
5
4-CH3OꢁC6H4I
4-CH3OꢁC6H4I
4-CH3OC6H4I
Cinnamaldehyde (E)
Cinnamaldehyde (E)
Cinnamaldehyde (E)
20
20
21
85
72
65
1.61:1
1.6:1
1.37:1
(4 mol %)—Pd(OAc)2
Xphos—Pd(OAc)2
Sphos—Pd(OAc)2
BINAP (R)—Pd(OAc)2
Xantphos
(2.1 mol %)—Pd(OAc)2
Acetophenone oxime
(2.5 mol %)—Pd(OAc)2
Proline (l)
(2 mol %)—Pd(OAc)2
2-Thiophene carboxylic acid
(2 mol %)—Pd(OAc)2
PCy3 (2 mol %)—Pd(OAc)2
Tert-Bu3P.HBF4—Pd(OAc)2
Acetophenone oxime
palladacycle
6
7
8
9
4-CH3OꢁC6H4I
4-CH3OꢁC6H4I
4-CH3OꢁC6H4I
4-CH3OꢁC6H4I
Cinnamaldehyde (E)
Cinnamaldehyde (E)
Cinnamaldehyde (E)
Cinnamaldehyde (E)
20
20
24
19
71
81
60
91
1.6:1
1.5:1
1.8:1
1.5:1
10
11
12
4-CH3OꢁC6H4I
4-CH3OꢁC6H4I
4-CH3OꢁC6H4I
Cinnamaldehyde (E)
Cinnamaldehyde (E)
Cinnamaldehyde (E)
24
16
19
93
64
71
1.5:1
1:0.86
1:0.26
13
14
15
4-CH3OꢁC6H4I
4-CH3OꢁC6H4I
4-CH3OꢁC6H4I
Cinnamaldehyde (E)
Cinnamaldehyde (E)
Cinnamaldehyde (E)
3
5
23
90
96
66
1:0.24
1:0.08
1.6:1
16
17
Herrmann–Beller palladacycle
Tris(2,4-di-tert-
butylphenyl)phosphite
palladacycle
4-CH3OꢁC6H4I
4-CH3OꢁC6H4I
Cinnamaldehyde (E)
Cinnamaldehyde (E)
22
24
79
92
1.6:1
2:1
18
19
20
21
22
OTP
OTP
OTP
OTP
4-CH3ꢁC6H4I
4-CH3OꢁC6H4I
4-FꢁC6H4I
Cinnamaldehyde (E)
Ethyl cinnamate (E)
Ethyl cinnamate (E)
Benzalacetone (E)
Chalcone (E)
24
24
24
16
21
91
83
86
87
94
1.3:1
2.4:1
9:1
1.1:1
2.8:1
4-CH3OꢁC6H4I
4-CH3OꢁC6H4I
OTP
Reaction conditions: Aryliodide (1.2 mmol), 1,2-Disubstituted alkene (1 mmol), NaOAc (1.5 mmol), TBABr (1 mmol),
Pd(OAc)2/Cat (1 mol %), Ligand (2–4 mol %), DMF (10 ml), Argon, 140–150 ꢂC.
200 and PEG-400.[39,46,51,52] DMF solvent and base—NaOAc used, also shows the simi-
lar activity as described by Chakraborti and coworkers.[50] Pd (II) is readily converte-
d–reduced to Pd(0) which enhances the oxidative addition to aryl halides and then
readily adds to the 1,2-disubstituted alkenes. Ligands especially, tert-Bu3P.HBF4 and
PCy3 demonstrated high reactivity and also stereoselectivity which could be due to Pd
NPs stabilized by the ligands described. High reaction temperatures used might be the
cause of NPs formation, E: Z isomerization and formation of mixtures as noted earlier.
Experimental procedure
General procedure for Mizoroki–Heck reaction of 1,2-disubstituted aryl alkenes in
PEG-200 or PEG-400
The aryl halide (1.2 mmol), alkene (1 mmol), NaOAc (1.5 mmol), PdCl2(PhCN)2
(2.5 mol%), n-Bu4NBr or n-Bu4NCl (1 mmol) and solvent (PEG-400 or PEG-200), 3 ml
were added to an oven-dried 25 ml single neck round bottom flask which was then
sealed with reflux condenser and two-way stopcock above it. The mixture was purged

6
P. G. BANGAR ET AL.
with argon and heated at 140 ꢀ 150 ꢂC for 2 ꢀ 34 h. When the starting materials were
completely consumed as determined by TLC, the reaction mixture was allowed to cool
to room temperature, diluted with EtOAc and washed three times with water. The
organic layer was dried over Na2SO4, filtered and concentrated under vacuum to give
the crude product. Purification by column chromatography afforded the analytically
pure product.
1
Ethene-1,1,2-triyltribenzene (3a) (2 h, 74%) CAS Registry Number 58-72-0 H NMR
(200 MHz, CDCl3, d)—7.39–7.23 (m, 10H), 7.19 ꢀ 7.05 (m, 5H), 7.02 (s, 1H) 13C NMR
(200 MHz, CDCl3, d)—143.4, 142.6, 140.3, 137.4, 130.4, 129.5, 128.6, 128.2, 127.9, 127.6,
127.5, 127.4, 126.7, 116.5, 87.5, 83.1, 68.8, 65.1, 64.6 IR (cmꢀ1)—3023, 2402, 1597, 1522,
1428, 1216, 1028, 928, 768, 671 HRMS-ESI: [MþþH]þ calcd for C20H17 [MþþH]þ
257.1325, found: 257.1326
Conclusions
Inexpensive silver free protocols were developed for the Mizoroki–Heck reaction of 1,2-
disubstituted alkenes. Use of TBABr or n-Bu4NCl in DMF, ramped up the
Mizoroki–Heck reaction of aryl iodides with various 1,2-disubstituted aryl alkenes. PEG
200/400 as solvent conjured magically, high yields of the Mizoroki–Heck product in
short reaction times. Several phosphine ligands also gave excellent results, with various
1,2-disubstituted alkenes and aryl iodides, though the E:Z ratios were low. Preliminary
studies with tertBu3PꢁHBF4 as ligand show high reactivity and E-isomer selectivity.
Further studies with such ligand variations are expected to show the desired modulation
of reactivity.
Supplementary information associated with this article can be found online.
Acknowledgments
Financial support is gratefully acknowledged from the CSIR Network Project, ORIGIN – under
the XII Five year plan CSC 0108 and PGB thanks the UGC for a SRF.
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