Utilization of Synthetic Calcium-Phyllosilicates as Bifunctional Bases in the Matsuda-Heck Reaction

Article abstract of DOI:10.1002/cctc.201801519

Calcium-phyllosilicates can successfully be used as novel bases in the Matsuda-Heck reaction using methanol as solvent. The new experimental set-up distinguishes itself by higher reactivity and better selectivity compared to other systems.

Full text of DOI:10.1002/cctc.201801519

Accepted Article
Title: Utilization of Synthetic Calcium-Phyllosilicates as Bifunctional
Bases in the Matsuda-Heck Reaction
Authors: Heiko Brunner and Lennart Vedder
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To be cited as: ChemCatChem 10.1002/cctc.201801519
Link to VoR: http://dx.doi.org/10.1002/cctc.201801519
A Journal of
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ChemCatChem
10.1002/cctc.201801519
COMMUNICATION
Utilization of Synthetic Calcium-Phyllosilicates as Bifunctional
Bases in the Matsuda-Heck Reaction
[a]
[a]
Heiko Brunner* and Lennart Vedder
sterically demanding bases that can only act as Brønsted bases and
on the other hand mineralic bases unsoluble in methanol were
employed. Thus, Correia et al. have established the utilization of di-
Abstract: Calcium-Phyllosilicates can successfully be used as novel
bases in the Matsuda-Heck reaction using methanol as solvent. The
new experimental set-up distinguishes itself by higher reactivity and
better selectivity compared to other systems
.
tert.-butyl-4-methyl-pyridine
(DTMP)
for
the
successful
enantioselective synthesis of the alkaloids (-)- codonopsine and (-)-
Aryl diazonium salts represent an important class of reactive
[
5]
codonopsinine.
At the same time Genêt and co-workers
[
1]
intermediates in organic synthesis. Beside the Meerwein arylation
successfully introduced the utilization of calcium carbonate as base
the Matsuda-Heck reaction provides a powerful instrument in the
[
6]
in the Matsuda-Heck reaction. Thereby, the calcium carbonate
could be utilized as added base and/or supporting material for the
immobilized palladium-species. Despite of these auspicious
approaches this rewarding area of research in the Matsuda-Heck
reaction sank into oblivion until the years 2010’s. Thus, the synthesis
of functionalized benzalacetones via Matsuda-Heck reaction could
be achieved by the utilization of calcium carbonate. It could be
demonstrated that the presence and usage of calcium carbonate
was mandatory for the preparation of these important building
[
2]
hand of each organic chemist. Due to the high reactivity of these
electrophiles combined with a sufficient tolerance against a wide
variety of functional groups the Matsuda-Heck reaction paved the
road to the synthesis of a plethora of interesting and rewarding
[
3]
synthetic targets.
However, the especial vulnerability of these electrophiles against
bases in protic solvents like methanol is a significant drawback of
this reaction and represents the other side of the coin concerning the
high reactivity of the aryl diazonium salts. Thus, significant homolytic
decompositions especially in the presence of strong Lewis-bases
[
7]
blocks.
The development of enantioselective Matsuda-Heck
reactions goaded Correia et al. to the development and application
of new bases. In addition to the DTMP Correia and co-workers
successfully established the application of zinc carbonate and
[
4]
can be stated.
Especially, in the cases of acid-vulnerable products and reactants
the scavenging of the perpetually evolving tetrafluoroboric acid
during the catalytic cycle represents a conditio sine qua non for the
successful usage of this reaction.
[
8,9]
Rochelle’s salt.
Furthermore, the development of efficient supported palladium
catalysts is one of the most attractive targets of actual research
activities because of an easier metal recovery combined with a lower
contamination of the products by toxic palladium residues and a high
Accepting this challenge several groups have developped sporadical
synthetic protocols. For solving the contradiction of acid scavenging
without any decomposition of the aryl diazonium salts two starting
points were pursued in the past. On the one hand the utilization of
sterically demanding bases that can only act as Brønsted bases and
on the other hand mineralic bases unsoluble in methanol were
employed. For solving the contradiction of acid scavenging without
any decomposition of the aryl diazonium salts two starting points
were pursued in the past. On the one hand the utillization of
[
10]
reactivity as well as stabililty. For this reason a broad range of
[
11-13]
supporting materials were utilized in the Matsuda-Heck reaction.
In the case of Pd/CaCO as bifunctional catalyst it has to be stated
3
that the evolving tetrafluoroboric acid is dissolving the calcium
carbonate as consequence of the neutralization reaction. Thus, a
negative impact on the reactivity of the catalytic system as a
consequence of the loss of calcium carbonate as supporting material
has to be considered.
However, for bypassing these issues a novel bifunctional reagent
was necessary. In the new synthetic protocol, an acid scavenger
with bifunctionality had to be added to the system. On the one hand
it should neutralize the resulting tetrafluoroboric acid and on the
other hand it should act as a supporting material. It should therefore
be a basic carrier. Since the acid scavenger must inevitably undergo
a chemical reaction with the resulting acid in order to fulfill its
function, a resulting reaction product formed by the neutralization
[a]
Dr. Heiko Brunner, Lennart Vedder
R&D Organic Chemistry
Atotech Deutschland GmbH
Erasmusstrasse 20, D-10553 Berlin
E-mail: heiko.brunner@atotech.com
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.201801519
COMMUNICATION
should be able to continue to function as the supporting material for
stabilizing the palladium catalyst.
It is well known that silicium dioxide represents an excellent
supporting material for the immobilization of palladium in the
[
14, 15]
Matsuda-Heck reaction.
mind we identified synthetic tobermorite (5 CaO • 6 SiO
and xonotlite (6 CaO • 6 SiO • H O) that are commercially available
Keeping our mandatory prerequisites in
Table 1. Comparison of supporting materials and bases
2
• 5 H O)
2
2
2
®
®
as Circosil and Circolit as auspicious candidates for our
investigations. These minerals represent composite materials
composed of silicium dioxide and calcium oxide.
MeO
+
N BF
COOMe
®
®
2
4
Pd] (1
mol-%)
COOMe
[
It has to be pointed out that Circosil and Circolit as multifunctional
COOMe
1
eq.)
®
MeO
MeO
minerals are frequently used as absorbing reagents (e.g. Catsan ),
(
Additive
in construction chemistry and additives for the paper-, print, lacquer-
OMe
[
16]
and colour industry. These reagents distinguish themselves by the
provision of a local alkaline pH-value in combination with an alkaline
buffering impact that should guarantee a stable pH-value over the
entire reaction time. The degradation product of the neutralization
reaction silicium dioxide stabilizes and immobilizes the occurring
palladium species as supporting material and should provide a more
stable catalytic system including high turn-over-frequencies during
the reaction. Furthermore, the contamination of the reaction products
by residual palladium traces should be reduced by this approach.
Stimulated by these features we decided to investigate the
2a
3
a
1
a
[
[b]
-1 [c]
Entry
1
Additive
Yield [%]
94.2
Ratio 2a:3a
TOF (h )
5 CaO • 6 SiO
2
• 5 H
2
O
98.7 : 1.3
625
®
(
Circosil )
2
6 CaO • 6 SiO
2
®
• H
2
O
92.1
99.6 : 0.4
577
(
Circolit )
CaO
SiO
Al
none
3
4
5
6
2.8
-
-
2
93.7
94.2
90.1
99.7 : 1.3
98.7 : 1.3
98.7 : 1.3
736
638
773
®
®
2 3
O
utilizability of Circosil and Circolit as bases and supporting material
in the Matsuda-Heck reaction.
®
The initial point of our investigation was an examination of Circosil
®
[a] final catalyst loading: 3.15 wt.-%. [b] diarylated product determined by HPLC [c]
TOFmax.
and Circolit as bases and supporting materials. For this reason we
investigated the conversion of 4-methoxybenzenediazonium
tetrafluoroborate 1 with methyl acrylate using a combination of
®
®
2
Pd(OAc) as pre-catalyst in the presence of Circosil and Circolit
without any pre-reduction of the Pd(II). For classifying the reactivity
and selectivity patterns the new systems were compared with the
single components of these composite materials calcium oxide and
8
2 3
silica (Table 1). Furthermore, the recently introduced Al O and a
[
12]
base and carrier-free system were investigated.
6
Circosil
Circolit
CaO
Regarding the results depicted in Table 1 with exemption of calcium
oxide (entry 3) with all systems high yields, high selectivities and
high turnover frequencies could be achieved. However, in the case
of calcium oxide no significant reaction could be observed.
4
2
0
In the case of calcium oxide in particular, in addition to the low yield,
the significantly delayed reaction start is noticeable. In addition to the
development of gases, the course of the reaction is reflected above
0
20
500 520 540 560 580 600 620 640
time [min]
all in the heat flow T
r j
-T of a reaction to be observed (Figure 1).
While the reaction starts within 2 to 3 minutes with high exothermia
Figure 1. Comparison of the evolved heat tone
®
®
when using the phyllosilicates Circolit and Cirsosil , in the case of
calcium oxide this only occurs after approx. 550 minutes.
Furthermore, a significantly lower heat tone could be observed, that
can be reconciled with the low yield.
Based on these results, the scope of the new synthetic protocol was
explored with a variety of diazonium salts. In order to better evaluate
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ChemCatChem
10.1002/cctc.201801519
COMMUNICATION
the performance with regard to good chemoselectivity, this study
In addition to the synthesis of economically valuable cinnamic esters,
the applicability of the new catalytic systems for the preparation of
benzalacetones was to be investigated. Previous investigations have
shown the necessity of using calcium carbonate as acid scavenger
®
was performed with the more reactive Circosil (Table 2).
®
Table 2. Scope of the catalytic system using Circosil
[
7]
in the preparation of benzalacetones via Matsuda-Heck reaction.
Furthermore, it could be demonstrated that the utilization of a
supporting material like charcoal was beneficial for the outcome of
this reaction. Thus, by using charcoal as supporting material the
agglomerization of catalytically active Pd-clusters and therefore the
formation of catalytically inactive Pd-black could be diminished. As
can be seen from Table 1, high catalytic activity is obtained in both
N BF
COOMe
2
4
(1
mol-%)
Pd(OAc)
2
COOMe
1
eq.)
•
R
(
R
•
5 H
5
CaO 6 SiO
2
2
O
1
2
]
Entry
R
Product
2a
Yield [%]
1
2
3
4
5
6
7
8
9
4-OMe
94
83
93
87
89
89
85
91
84
97
®
®
Circosil and Circolit . In general a stable catalytic system is
required to achieve the highest possible yields with a low catalyst
loading. It is obvious that an efficient catalytic system should not
have a high turn-over-frequency (TOF) in one range, but also the
highest and most stable turn-over-frequencies possible over the
entire course of reaction. However, one must be aware that the turn-
over-frequency (TOF) as a measure of the catalytic activity strongly
4-NO
2-NO
4-Cl
3-Cl
4-Br
4-I
2
2b
2
2c
2d
2e
2f
[
17]
depends on the course and the progress of the reaction. The TOF
changes with the concentration of the reactants and reaction
products as well as with the deactivation of the utilized catalytic
system. In order to investigate the influence of the concentration of
the reactants and the products on the catalytic activity and a
possible agglomeration of the Pd-clusters during the reaction in
more detail, the course of TOF of our previous test reaction (Table 1)
was studied in dependence of the converted diazonium salt (Figure
2g
H
2h
4-COOMe
4-Me
2i
10
2j
As depicted in Table 2, all products were obtained in good to
excellent yields. As mentioned above, the scavenging of the
tetrafluoroboric acid released during the Matsuda-Heck reaction is
one of the main challenges in the synthesis of acid sensitive
substrates. Thus, Beller et al. have described a transesterification in
the Matsuda-Heck reaction for the preparation of the economically
2). These kinetic results should enable an optimization of the
reaction by selecting the most stable catalyst.
[
14]
important 2-ethylhexyl (E)-3-(4-methoxyphenyl)acrylate 4. For this
reason we have chosen the preparation of this important compound
that is frequently utilized as UV-absorber and antioxidant in a
plethora of pharmaceuticals, agrochemicals and flagrances as an
object of study (Scheme 1).
800
700
600
500
Circolit
Circosil
O
400
300
200
N
2
BF
4
Et
-
4
C H
Pd(OAc)
2
(2 mol %)
O
9
+
O
C
4
H
9
MeOH
RT
Et
MeO
MeO
O
4
1a
3
with 5 CaO • 6 SiO2
with 6 CaO •6 SiO2
• 5 H O (Circosil) 72%
2
•
H O (Circolit):
73%
100
2
without base and supporting material:
62%
0
Scheme 1
.
Synthesis of 2-ethylhexyl (E)-3-(4-methoxylphenyl)acrylate 4
0
2
4
6
8
10
12
Consumed Diazonium salt [mmol]
As is shown in Scheme
1
the 2-ethylhexyl-(E)-3-(4-
Figure 2. Course of the TOF in dependence of the converted diazonium salt.
methoxyphenyl)acrylate
4
was obtained in good yields when
®
®
Circosil and Circolit were used. It is noteworthy that in both cases
a significantly higher yield was achieved compared to a base- and
carrier-free system.
®
As depicted in Figure 2, the catalytic system using Circolit
distinguishes itself by a more stable developing of TOF-values
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ChemCatChem
10.1002/cctc.201801519
COMMUNICATION
®
compared to the Circosil containing system. Despite significantly
attributed to a minor agglomeration tendency using lower catalyst
[
18]
higher turn-over-frequencies at the beginning of the reaction in the
concentrations.
®
case of Circosil a substantially larger drop in these values can be
Stimulated by these excellent results we decided to embark on
another challenging acid sensitive class of substances. Besides
benzalacetones, cinnamaldehydes are another interesting substance
®
observed after approx. 50% conversion compared to Circolit .
Strikingly, in both cases a gradual decrease of the TOF values can
be observed over the course of the reaction. In light of these results
class as they are used extensively in the food and cosmetic
®
®
[19]
the applicability of the novel bifunctional bases Circosil and Circolit
industries.
In addition, the antifungal, antibiotic and antitermic
[
20]
for the synthesis of 4-methoxy-benzalacetone 5 in comparison to the
preperties have been intensively investigated.
So far, the
established calcium carbonate should be further investigated (Table
preparation of this important substance class by Heck reaction has
only been described sporadically. The disadvantages of using
3).
acrolein to produce cinnamaldehydes are the long reaction times
®
®
Table 3. Impact of Circosil and Circolit on the preparation of 4-methoxy-
benzalacetone
[21]
and sometimes low yields.
Cacchi et al. describe that using 4-
iodanisole under Jeffery conditions the corresponding 4-
methoxycinnamedehyde could only be obtained in a yield of 18%
O
[
21]
N BF
after 96 hours reaction time. Furthermore, the use of acrolein has
only been described in the Matsuda-Heck reaction with sophisticated
arenediazonium o-benzenedisulfonimides as electrophiles and
2
4
(x
mol-%)
Pd(OAc)
2
MeO
MeO
O
(
2 eq.)
Base
1
5
[
22]
sodium formiate as base. The use of acetonitrile as solvent in this
Entry
Base
Catalyst
loading
Yield [%]
Reference
process was imperative, while THF as solvent and calcium
[
22]
[mol-%]
carbonate as base failed. For this reason, the development of a
novel synthetic protocol using methanol as solvent and classical
diazonium salts as electrophiles for the preparation of this important
class of substances is still tempting. In this respect, the synthesis of
1
2
3
4
5
5 CaO •6 SiO
2
• 5 H
2
O
4
86
82
62
89
93
This work
This work
This work
This work
This work
®
(
Circosil )
5 CaO • 6 SiO • 5 H
2
2
O
2
1
2
1
®
(
Circosil )
4-methoxycinnamaldehyde, which has found a broad application as
fragrance, should be further investigated (Table 4). Furthermore, it
could be isolated as a natural substance from the shoots of
5 CaO • 6 SiO • 5 H
2
2
O
®
(
Circosil )
[
23]
Agastache rugosa, the Korean Mint, and shows antiviral effects.
6 CaO • 6 SiO
2
• H
• H
2
O
O
®
(
Circolit )
®
®
Table 4. Impact of Circosil and Circolit on the preparation of 4-methoxy-
cinnamaldehyde
6 CaO • 6 SiO
2
2
®
(
Circolit )
.
O
6
CaCO
CaCO
none
3
2
1
2
1
74
34
58
31
Ref. 7
Ref. 7
N BF
2
4
(x
mol-%)
Pd(OAc)
2
H
H
7
8
9
3
MeO
MeO
O
(
2 eq.)
Base
Ref. 7
1
6
Entry
Base
Catalyst
loading
Temp.
[°C]
Yield [%]
none
This work
[mol-%]
As Table 3 shows, significantly higher yields are obtained with both
1
2
3
4
5
5 CaO •6 SiO • 5 H O
1
50
50
40
50
50
58
63
61
59
40
2
®
2
®
®
(Circosil )
Circosil and Circolit compared to calcium carbonate and base-free
systems (Table 3). In good accordance with our observed TOF-
6 CaO • 6 SiO • H O
1
1
2
1
2
2
®
®
(Circolit )
courses (Figure 2) the best results are obtained with Circolit and
are proof of the good stability and reactivity of the catalyst (Table 3,
entries 4 and 5).
6 CaO • 6 SiO • H O
2
2
®
(
Circolit )
Due to the high stability combined with the high catalytic activity, it
was possible for the first time to reduce the previously required
6 CaO • 6 SiO • H O
2
2
®
(
Circolit )
[
7]
catalyst quantity from 2 mol-% to 1 mol-%. Strikingly, in the case of
none
®
Circolit even higher yields are achieved by using 1 mol-% versus 2
Based on prior investigations with methacrylaldehyde, the above
mol-%. According to prior results by Reetz and de Vries, this can be
[6]
reactions were carried out at 40° and 50°C. As in Table 4 shown
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.201801519
COMMUNICATION
®
®
higher yields were obtained with both Circosil and Circolit
Keywords: Catalysis • Calcium-Phyllosilicates • Matsuda-Heck-
compared to a base-free system (Table 4, entries 1-4 vs. entry 5).
As in the case of the previously described 4-methoxy-benzalacetone,
slightly higher yields are also obtained with the corresponding
reaction • Palladium • Turn-over-frequency
[1]
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®
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®
calcium-phyllosilicates. The calcium-phyllosilicates Circosil and
®
Circolit , whose utilization in organic synthesis has not yet been
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TM
In a 100 mL EasyMax reactor, equipped with a reflux condensor
[9]
2
and a magnetic stirrer methyl acrylate (0,83 g; 10 mmol) and
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®
To this dispersion Circosil (0.73 g, 1 mmol, 0.1 eq.) and palladium
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2
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ChemCatChem
10.1002/cctc.201801519
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ChemCatChem
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Title
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Heiko Brunner*, Lennart Vedder
O
Page No. – Page No.
N BF
2
4
Pd(OAc)
2
(1 mol-%)
Utilization of Synthetic Calcium-
Phyllosilicates as Bifunctional Bases
in the Matsuda-Heck Reaction
MeO
MeO
O
• •
CaO 6 SiO H O
2 2
y
=
93%
6
Calcium-Phyllosilicates can successfully be used as novel bifunctional bases in the
Matsuda-Heck-reaction using methanol as solvent. The new experimental set-up
distinguishes itself by higher reactivity and better selectivity compared to other
systems.
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