Rhodium-catalyzed Mizoroki-Heck-type arylation of alkenes with aroyl chlorides under phosphane- and base-free conditions

Article abstract of DOI:10.1002/anie.200351905

Simple but effective! Even without the addition of any phosphane ligand and base, alkenes efficiently undergo Mizoroki-Heck-type arylation upon treatment with aroyl chlorides in the presence of a rhodium catalyst (see scheme). The products were isolated by a very simple procedure.

Full text of DOI:10.1002/anie.200351905

Communications
C-C Coupling Reactions
Rhodium-Catalyzed Mizoroki–Heck-Type
Arylation of Alkenes with Aroyl Chlorides under
Phosphane- and Base-Free Conditions
Toru Sugihara, Tetsuya Satoh, Masahiro Miura,* and
Masakatsu Nomura
The arylation of alkenes with aryl halides (ArX) is well-
known as the Mizoroki–Heck reaction and is now recognized
to be of genuine synthetic utility for preparing aromatic fine
chemicals.[1] Besides the halides, various synthetic equiva-
lents, including ArOTf and ArCOX can also be employed as
the arylating reagents.One of the substantial problems in the
reaction comes from an acidic by-product (HX), which
requires the addition of stoichiometric amounts of base.
Recently, the use of aromatic carboxylic acid anhydrides[2]
and aryl esters[3] allowed the reaction to be conducted under
base-free conditions.Although these methods are useful,
additional workup procedures such as fractional distillation
and acid–base extraction are required to obtain pure coupling
products owing to the corresponding organic by-products.
Aryl and aroyl halides are also capable of undergoing
oxidative addition toward certain rhodium(i) complexes to
form aryl rhodium(iii) species, and a number of useful
catalytic processes involving this step have been devel-
oped.[4,5] We previously demonstrated that aroyl chlorides
efficiently react with terminal and internal alkynes in the
presence of a rhodium–phosphane catalyst to produce the
corresponding vinyl chloride and indenone derivatives,
accompanied by decarbonylation and dehydrochlorination,
respectively.[5a] The coupling with alkenes in place of alkynes
was successful when norbornenes were used in the presence
of a disilane, giving aroylarylation products.[5b] Herein we
report our new findings that styrene and acrylate ester can
also be arylated by using an appropriate phosphane-free
rhodium catalyst.[6] Thus, the alkenes efficiently undergo
Mizoroki–Heck-type coupling with aroyl chlorides in the
absence of any base and phosphane ligand; the by-products
(CO and HCl) are readily removed.[7] The simple conditions
make the product-isolation procedure significantly simple, as
described below.
In an initial attempt, benzoyl chloride (1a) was treated
with styrene (2; 1 equiv) in a batch reactor with an N2 balloon
under conditions similar to those employed for the reaction
with internal alkynes.In the presence of [{RhCl(cod)}
]
2
(1 mol%), PPh3 (2 mol%), and Na2CO3 (1 equiv) in refluxing
o-xylene for 24 h,[5a] (E)-stilbene (3a) was formed in only 7%
[*] Prof. Dr. M. Miura, T. Sugihara, Dr. T. Satoh, Prof. Dr. M. Nomura
Department of Applied Chemistry
Faculty of Engineering, Osaka University
Suita, Osaka 565-0871 (Japan)
Fax : (+81)6-6879-7362
E-mail: miura@chem.eng.osaka-u.ac.jp
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
4672
ꢀ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/anie.200351905
Angew. Chem. Int. Ed. 2003, 42, 4672 –4674

Angewandte
Chemie
Table 2: Reaction of aroyl chlorides with styrene or n-butyl acrylate.[a]
yield (Table 1, entry 1).Fortunately, it was found that an
ethylene complex [{RhCl(C2H4)2}2] exhibits significantly
higher activity than [{RhCl(cod)}2].Thus, the yield of 3a
was improved to 69%; a minor amount of 1,1-diphenyl-
ethylene (4a) was detected, as was the case in the palladium-
catalyzed Mizoroki–Heck reaction (Table 1, entry 2).[2,3]
Interestingly, the reaction proceeded much more smoothly
in the absence of the phosphane ligand and base.As a result,
3a was obtained in 82% yield within 4 h (Table 1, entry 4).
Under the same conditions, [{Rh(acac)(cod)}2] and
[{RhCl(nbd)}2] showed lower activities (Table 1, entries 5
and 6).In the latter case, however, prolonged reaction time
led to a satisfactory product yield (Table 1, entry 7).Although
a decrease in the amount of [{RhCl(C2H4)2}2] to 0.25 mol%
resulted in a slight decrease in the product yield (Table 1,
entry 8), 3a was obtained in 87% yield within 2 h when
1.2 equivalents of 2 was used (Table 1, entry 9).
Entry
1
Ar
[mmol] Alkene [mmol] t [h] Product Yield [%][b]
1
2
3
4
5
6
7
8
a
b
c
d
e
f
g
h
i
Ph 10
4-MeC6H4 10
2
2
2
2
2
2
2
2
2
5
15
15
6
7
4
6
6
3a
3b
3c
3d
3e
86
79
51
81
73
75
75
83
4-MeOC6H4
4-BrC6H4 10
4-NCC6H4
4-O2NC6H4 10
1
1.2
15
1.5
15
1.5
1.2
1.2
1.2
1
10 3 f
24 3g
3
12 3i
7
4-MeO2CC6H4
2-naphthyl
2-AQ[c]
1
1
1
1
3h
9
69
10[d]
a
Ph
6
(73)[e]
(95:5)[f]
(81) (93:7)[f]
(98) (96:4)[f]
72 (93:7)[f]
11[d,g]
12[d,h]
13[h]
a
a
a
Ph
Ph
Ph 10
1
1
5
5
5
1.2
1.2
12
9
9
48
6
6
6
Table 1: Reaction of benzoyl chloride (1a) with styrene (2).[a]
[a] Unless noted, the reaction was carried out with [{RhCl(C2H4)2}2] (2.5 mmol) in
refluxing o-xylene (5 mL) under a slow stream of N2. [b] Yield of isolated product
based on the amount of 1 used. Value in parenthesis is determined by GC. [c] 2-AQ-
COCl=Anthraquinone-2-carbonyl chloride. [d] With [{RhCl(C2H4)2}2] (0.01 mmol).
[e] No increase in the yield after 24 h. [f] E/Z ratio. [g] With Me(nC8H17)3NCl
(0.04 mmol). [h] With LiCl (0.04 mmol).
Entry
Rh cat. (mol%)
Time [h]
Yield [%][b]
3a
4a
1[c]
2[c]
3
4
5
[{RhCl(cod)}2] (1)/PPh3 (2)
[{RhCl(C2H4)2}2] (1)/PPh3 (2)
[{RhCl(C2H4)2}2] (1)/PPh3 (2)
[{RhCl(C2H4)2}2] (1)
[{Rh(acac)(cod)}2] (1)
[{RhCl(nbd)}2] (1)
24
23
23
4
26
4
18
4
2
7
69
69
82
36
33
88
72
87
75
[ArCORhIIICl2], which then undergoes decarbonylation to
give [ArRhIIICl2] as the key intermediate.[5,10] The subsequent
insertion of the alkene and b-hydride elimination as in the
Mizoroki–Heck reaction affords the coupling product and
RhIII(H)Cl2.The latter may release HCl, regenerating Rh ICl.
Dienes such as cod and nbd on the catalyst precursors may
retard the reaction by their stronger coordination ability
relative to that of the alkene substrates.The success with the
bromide 1d seems to be due to the fact that oxidative addition
of aryl halides under the present conditions is difficult to take
place.Notably, the addition of a chloride source such as an
alkylammonium chloride or lithium chloride considerably
improved the reaction efficiency with the acrylate ester
(Table 2, entry 10 vs.entries 11 and 12), whereas no positive
effect was observed in the case of styrene (Table 1, entry 10).
Thus, it is possible that the enhancement is due to the
generation of anionic rhodium species by the coordination of
chloride.The electron-poor alkene may preferably interact
with the metal center.
In summary, we have demonstrated that the Mizoroki–
Heck-type arylation of alkenes can be performed using
benzoyl chlorides in the presence of a rhodium catalyst
without the addition of any phosphane ligand and base.Not
only does the reaction proceed efficiently, but also the workup
procedure is significantly simple.Thus, this protocol seems to
provide a new, convenient route to vinyl-substituted aromatic
compounds.
8
7
8
3
2
6
10
9
6
7
8
[{RhCl(nbd)}2] (1)
[{RhCl(C2H4)2}2] (0.25)
[{RhCl(C2H4)2}2] (0.25)
[{RhCl(C2H4)2}2] (0.25)
9[d]
10[d,e]
8
7
[a] Unless noted, the reaction of 1a (1 mmol) with 2 (1 mmol) was
conducted in refluxing o-xylene (5 mL) under N2 (balloon). [b] Yield
determined by GC based on the amount of 1a used. [c] With Na2CO3
(1 mmol). [d] 2 (1.2 mmol) was used. [e] With LiCl (0.04 mmol).
Table 2 summarizes the results for the syntheses of
stilbenes 3a–i and cinnamate 6 by the reactions of 4-
substituted benzoyl chlorides 1a–g, 2-naphthoyl chloride
(1h), or anthraquinone-2-carbonyl chloride (1i) with 2 and
of 1a with n-butyl acrylate (5).The reactions were carried out
under a slow stream of N2 to effectively remove HCl and CO
evolved.It can be seen from Table 2 that various functional
groups are tolerated under the present conditions.[8] It should
be emphasized that essentially pure stilbenes 3 were isolated
after a simple workup procedure, that is, only filtration,
evaporation, and washing with an appropriate solvent such as
methanol (see Experimental Section).The cinnamate 6 was
isolated by Kugelrohr distillation.[9] The reactions in Table 2,
entries 1, 2, 4, 6, and 13 were carried with use of 10 mmol of 1.
Even on a relatively larger scale and with a higher substrate/
catalyst ratio (1/Rh = 2000), the products were obtained with
good yields after reasonable reaction times.
Experimental Section
Typical procedure: A mixture of 1a (10 mmol, 1.41 g), 2 (15 mmol,
1.56 g), and [{RhCl(C2H4)2}2] (2.5 mmol, 1 mg) in refluxing o-xylene
(5 mL) was stirred under N2 flow (in a draft chamber).The effluent
The initial step of the present reaction appears to involve
oxidative addition of 1 to a RhICl species to generate
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Communications
gas was led to water during the reaction, so that HCl could be
recovered as hydrochloric acid.After 6 h, the mixture was cooled to
room temperature, Et2O (30 mL) was added, and a small amount of
insoluble material was removed by filtration through filter paper.
After evaporation of the solvents under vacuum, MeOH (10 mL) was
added, and the resulting mixture was filtered to give white crystals of
3a (1.54 g, 86%). Characterization data of products are summarized
in the Supporting Information.
Received: May 15, 2003 [Z51905]
À
Keywords: aromaticsubstitution · C C coupling ·
Heck reaction · homogeneous catalysis · rhodium
.
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[7] We also reported that the iridium-catalyzed coupling of aroyl
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[8] The reaction of 1a with N-tert-butylacrylamide, however, was
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[9] In the reaction with 5, only a trace amount of a-phenylated
product was detected by GC-MS.
[10] For an example of a Mizoroki–Heck-type reaction involving an
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4674
ꢀ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
Angew. Chem. Int. Ed. 2003, 42, 4672 –4674