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
Angew. Chem. Int. Ed. 2003, 42, 4672 –4674
ꢀ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4673