Rhodium-catalyzed cross-coupling of alkenyl halides with arylboron compounds

Article abstract of DOI:10.1002/adsc.201300482

The rhodium(I)-catalyzed reaction between arylboronic esters and excess 1,2-dichloroethene selectively afforded (2-chlorovinyl)arenes. Double arylation yielding 1,2-diarylethenes was observed when 1,2-dibromoethene was reacted with 2.5 equivalents of aryl

Full text of DOI:10.1002/adsc.201300482

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DOI: 10.1002/adsc.201300482
Rhodium-Catalyzed Cross-Coupling of Alkenyl Halides with
Arylboron Compounds
Takanori Matsuda,a,* Kentaro Suzuki,a and Norio Miuraa
a
Department of Applied Chemistry, Tokyo University of Science, 1–3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan
Fax : (+81)-3-5261-4631; e-mail: mtd@rs.tus.ac.jp
Received: June 3, 2013; Revised: September 24, 2013; Published online: November 13, 2013
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201300482.
Abstract: The rhodium(I)-catalyzed reaction be-
tween arylboronic esters and excess 1,2-dichloro-
rhodium(I) complex catalysts. It was found that
[Rh(OH)(cod)]2 (cod=cycloocta-1,5-diene, 3 mol%,
ACHTUNGTRENNUNG
A
6 mol% Rh) and 1,4-bis(diphenylphosphino)butane
(DPPB, 6 mol%), in the presence of K3PO4 (3 equiv.),
catalyzed the cross-coupling reaction between 2-naph-
thylboronic acid pinacol ester (1a) and (E)-1,2-
Double arylation yielding 1,2-diarylethenes was ob-
served when 1,2-dibromoethene was reacted with
2.5 equivalents of arylboronic acid.
dichloroACTHNUGRTNEUNGethene (2, 20 equiv., bp 488C) at 1008C in
Keywords: alkenes; boron; cross-coupling; rhodi-
um; synthetic methods
1,4-dioxane (Table 1, entry 1). 2-(2-Chlorovinyl)naph-
thalene (3a) was isolated in 85% yield with high E se-
lectivity. No formation of dinaphthylethenes by
double arylation of 2 was observed by GC analysis.
As can be seen in entries 1–3, the use of DPPB as the
ligand was essential to obtain good results. The prod-
b-Arylvinyl halides are useful synthetic intermediates uct 3a was prepared on a gram scale in a comparable
for the introduction of b-arylvinyl moieties.[1] Barluen- yield with only 1 mol% of [Rh(OH)
AHCTUNGTRENNUNG
ga et al. developed a simple synthesis of b-arylvinyl fied by recrystallization from hexane (entry 4). Re-
chlorides by palladium-catalyzed cross-coupling of ducing the amount of 2 to 5 equiv. led to a lower
1,2-dichloroethene with arylboronic acids.[1h] Howev- yield, albeit without formation of the double arylation
er, the reaction gave stilbenes (1,2-diarylethenes) as product (entry 5). No reaction occurred in the ab-
by-products through double arylation even with an sence of K3PO4 (entry 6), while K2CO3 worked equal-
excess (4 equiv.) of 1,2-dichloroethene. Nonetheless, ly well (entry 7). The choice of solvent also had an
stilbenes remain an important class of compounds for effect on the efficiency of the reaction; the yield was
various applications.[2]
reduced to 48% when toluene was used as the solvent
Rhodium-catalyzed addition reactions of organo- instead of 1,4-dioxane (entry 8). Use of (Z)-1,2-di-
boron compounds to carbon-carbon multiple bonds chloroethene led to a deterioration in the yield with
have become an immensely useful tool in contempo- predominant formation of the (Z)-isomer (entry 9).
rary organic synthesis.[3] There are also reports of rho- The corresponding boronic acid (1’a) and borate salt
dium-catalyzed substitution reactions with organobor- (1’’a) could be used in the cross-coupling reaction (en-
on compounds that have been achieved by a direct tries 10 and 11).
(cross-coupling) or formal (addition/elimination)
With the optimized reaction conditions, various ar-
manner. Herein, we report the rhodium-catalyzed ylboronates 1 were then subjected to the cross-cou-
substitution reaction of alkenyl halides with arylboron pling reaction with 2 (Table 2). Similar to 1a, 6-me-
compounds. The reaction selectively forms (2-chloro- thoxynaphthylboronate 1b also participated in the
vinyl)arenes via the mono-selective cross-coupling re- rhodium(I)-catalyzed monoarylation of 2 to furnish
action of 1,2-dichloroethene with arylboronic esters. 3b in excellent yield (entry 1). Arylation with phenyl-
Furthermore, double arylation furnishing stilbenes boronate (1c) and 4-methyl-, 4-phenyl-, and 4-vinyl-
has been realized by coupling of 1,2-diboromoethene phenylboronates (1d–f) afforded the corresponding
with arylboronic acids using rhodium catalysts.
(2-chlorovinyl)arenes 3c–f in 56–85% yields with
Our initial investigation focused on the cross-cou- stereoselectivities greater than 10:1 (entries 2–5). The
pling reaction of arylboron compounds with readily highly sterically hindered mesitylboronate 1g could
available alkenyl halides in the presence of also provide the coupling product 3g in 64% yield
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Rhodium-Catalyzed Cross-Coupling of Alkenyl Halides with Arylboron Compounds
Table 1. Rhodium(I)-catalyzed cross-coupling of 2-naphthylboronate 1a and (E)-1,2-dichloroethene (2).[a]
Entry
Variation from the standard conditions
Time [h]
Yield [%][b]
E:Z[c]
1
2
none
without DPPB
PPh3 (12 mol%) instead of DPPB
gram scale with 1 mol% [Rh(OH)
5 equiv. of 2
without K3PO4
K2CO3 instead of K3PO4
toluene instead of 1,4-dioxane
(Z)-1,2-dichloroethene instead of 2
(2-naphthyl)B(OH)2 (1’a) instead of 1a
NaB(2-naphthyl)4 (1’’a) instead of 1a
4.5
14
21
8.5
7
12
3
14
6
85
98:2
E only
–
E only
97:3
-
98:2
99:1
23:77
94:6
97:3
24
3
trace[d]
4[e]
5
(cod)]2
79
70
6
7
8
9
10
11
no reaction
85
48
50
20
3
62
156[f]
[a]
Standard conditions: 1a (0.10 mmol), 2 (2.0 mmol), [Rh(OH)
(0.30 mmol) in 1,4-dioxane (0.5 mL) at 1008C.
Isolated yield.
Determined by H NMR.
Not isolated.
ACHTUNGTRNE(NUNG cod)]2 (3 mmol, 6 mol% Rh), DPPB (6 mmol), and K3PO4
[b]
[c]
[d]
[e]
1
1a (7.0 mmol), 2 (140 mmol), [Rh(OH)ACTHNUTRGNE(UNG cod)]2 (0.07 mmol, 2 mol% Rh), DPPB (0.14 mmol), and K3PO4 (21.0 mmol) in
1,4-dioxane (35 mL) at 1008C.
Yield based on the amount of 1’’a.
[f]
Table 2. Synthesis of 2-(2-chlorovinyl)arenes 3 by rhodium(I)-catalyzed monoarylation of 2.
Entry
Ar (1)
Time [h]
3
Yield [%][a]
E:Z[b]
1
2
3
4
5
6
7
8
9
6-(MeO)naphthalen-2-yl (1b)
Ph (1c)
4-MeC6H4 (1d)
4-biphenyl (1e)
4-vinylC6H4 (1f)
2,4,6-Me3C6H2 (1g)
2-(pent-1-yn-1-yl)C6H4 (1h)
4-MeOC6H4 (1i)
9
3b
3c
3d
3e
3f
3g
3h
3i
90
>50:1
>50:1
15:1
40:1
10:1
>50:1
>50:1
30:1
15
15
8
7
5
7
22
7
76[c]
85[c]
74
56
64
49
36
4-MeO2CC6H4 (1j)
3j
20
10:1
[a]
1
Isolated yield unless otherwise noted.[b] Determined by H NMR.[c] NMR yield.
(entry 6). The reaction of 2-alkynylphenylboronate 1h coupling partner compared with arylboronates. The
with 2 proceeded with the alkyne moiety intact and reaction of 2-naphthylboronic acid (1’a) and
4
formed enyne 3h (entry 7). Unfortunately, arylboro- (10 equiv.) produced 2-(2-bromovinyl)naphthalene (5)
nates 1i and 1j bearing electron-donating (entry 8) in 66% yield with an E:Z ratio of 19:1 (Scheme 1).[4,5]
and electron-withdrawing (entry 9) substituents, re-
spectively, suffered from low yields.
For cross-coupling with 1,2-dibromoethene (4, curred at both the C Br bonds of 4 to yield symmetri-
E:Z=30:70), arylboronic acids were the preferred cal (E)-stilbenes 6 (Table 3). A range of arylboronic
When 4 was treated with 2.5 equiv. of arylboronic
acids under identical conditions, cross-coupling oc-
À
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Takanori Matsuda et al.
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Scheme 1. Monoarylation of 1,2-dibromoethene (4) with 1’a.
Table 3. Synthesis of (E)-stilbene derivatives 6 by rho- through double arylation (entries 7 and 8). Further-
ACHTUNGTRENNUNGdium(I)-catalyzed double arylation of 4.
more, the method was successfully applied to the
preparation of diphenylhexatriene 6o by reaction of
(E)-b-styrylboronic acid (1’o) (entry 9).
To gain information on the arylation reaction, a-
bromostyrene (7) was subjected to coupling with 1’c,
and the reaction gave an 88:12 mixture of 1,1-diphe-
nylethene (8) and (E)-stilbene (6c) in a 46% com-
bined yield (Scheme 2). The formation of the latter
product would support that the arylation proceeded
at least partially through a mechanism similar to that
of the rhodium-catalyzed cine-substitution reactions
of alkenyl sulfones[6] and alkenyl acetates,[7] where ad-
dition/b-elimination mechanisms were proposed for
the transformation.
McNeil et al. reported that the rhodium(I)-phos-
phine-catalyzed dechlorination of 1,2-dichloroethene
with Et3SiH proceeds via addition/b-chlorine elimina-
tion, and both syn- and anti-elimination can occur for
the rhodium(I)-based pathway.[8] Therefore, it would
be possible to assume that the present rhodium(I)-cat-
alyzed arylation of alkenyl halides proceeds via a se-
quence of syn addition of an arylrhodium(I) species
(ArRh) across a C=C bond followed by b-halogen
elimination in an anti fashion (Scheme 3).[9] In this
mechanism, (E)- and (Z)-1,2-dihaloethenes lead to
(E)- and (Z)-(2-halovinyl)arenes, respectively, via anti
b-halogen elimination. Likewise, (E)- and (Z)-(2-
Entry
Ar (1’)
6[a]
Yield [%][b]
1
2
3
4
5
6
7
8
9
Ph (1’c)
6c
6d
6i
6k
6l
6m
6a
6n
6o
75
78
60
64
65
72[c]
57
85
58
4-MeC6H4 (1’d)
4-MeOC6H4 (1’i)
4-FC6H4 (1’k)
3-MeC6H4 (1’l)
3-AcC6H4 (1’m)
2-naphthyl (1’a)
3-thienyl (1’n)
(E)-b-styryl (1’o)
[a]
Virtually, only the (E)-isomers were obtained.
Isolated yield.
Isolated as a 70:30 mixture with the biaryl by-product.
[b]
[c]
haloACTHNUTRGNEvNUG inyl)arenes follow this mechanism to deliver
(E)- and (Z)-stilbenes, respectively. Exclusive forma-
tion of (E)-stilbenes, irrespective of the stereochemis-
try of 4, can be accounted for by considering an iso-
Scheme 2. Reaction of a-bromostyrene (7) with 1’c.
acids 1’ participated in the double arylation of 4 to merization of (Z)-stilbenes to the corresponding ther-
afford stilbene derivatives 6 in moderate to good modynamically stable (E)-isomers under the reaction
yields (entries 1–6). 1,2-Di(2-naphthyl)ethene (6a) conditions. This has been confirmed by an independ-
and 1,2-di(3-thienyl)ethene (6n) were also synthesized ent experiment.[10]
Scheme 3. Proposed mechanism for rhodium(I)-catalyzed arylation of 1,2-dihaloethenes involving anti b-halogen elimina-
tion.
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Rhodium-Catalyzed Cross-Coupling of Alkenyl Halides with Arylboron Compounds
could synthesize several other (2,2-dichlorovinyl)-
arenes 12 by the C-2 selective arylation (entries 2–6).
A rhodium(I) catalyst prepared from [RhCl(cod)]2
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
and 1,3-bis(diphenylphosphino)propane was reported
to catalyze the cross-coupling of arylboronic acids
with aryl halides; however, the detailed mechanism
was not provided.[14] Indeed, arylboronic acid 1’a cou-
pled with bromobenzene under our optimized reac-
tion conditions (1008C, 9 h, 58% yield of 2-phenyl-
naphthalene) but not with chlorobenzene. The reac-
tion with the aryl halide appears to proceed via
a mechanism that does not necessitate the addition/
elimination process. In consideration of the results,
elucidation of the precise mechanism by which aryla-
tion of alkenyl halides proceeds would require more
experimentation.
Scheme 4. Rhodium(I)-catalyzed arylation of 2,3-dichloro-
propene (7) with 1a (1a:9=1.5:1).
We applied the rhodium(I)-catalyzed cross-coupling
method to other alkenyl halides. 2,3-Dichloropropene
In summary, we have demonstrated that 1,2-di
AHCTUNGTREGeNNUN thenes are simple, yet valuable, precursors for the
ACHTUNGTRENNUNGhalo-
(9) reacted with 1a to afford 2-(2-chloroallyl)naphtha- synthesis of b-arylvinyl halides and 1,2-diarylethenes
lene (10) in 32% yield (Scheme 4), while (E)-1,3-di- by rhodium(I)-catalyzed arylation using arylboron
chloropropene failed to undergo cross-coupling with compounds.
1a. If the addition/elimination mechanism operates,
the formation of 10 can be explained by intermediate
A.
The reaction of trichloroethene (11) with 1a selec-
Experimental Section
À
tively occurred at the C(2) Cl bond of 9, giving 2- General Procedure for Monoarylation (Table 2)
(2,2-dichlorovinyl)naphthalene (12a) in 47% yield
A
Schlenk tube was charged with arylboronic ester
(Table 4, entry 1).[11,12] This selectivity is in stark con-
trast to palladium-catalyzed cross-coupling of tribro-
moethene with phenylboronic acid,[1g,13] where the
1
(0.10 mmol), [Rh(OH)ACTHUNGTRENNU(G cod)]2 (3.0 mmol), DPPB
(6.0 mmol), and K3PO4 (0.30 mmol). The tube was evacuated
and backfilled with nitrogen. 1,4-Dioxane (0.50 mL) and 1,2-
dichloroethene (2, 2.0 mmol) were added via syringe
through the septum. The mixture was stirred at 1008C for
the indicated period of time. The reaction mixture was fil-
tered through a plug of Florisilꢁ washing with hexane-
AcOEt (10:1), and the filtrate was concentrated. The resi-
due was purified by preparative TLC on silica gel to afford
(2-chlorovinyl)arene 3. The product could be obtained by
recrystallization from hexane when the reaction was per-
formed on gram-scale.
À
trans C(1) Br bond selectively reacted to afford (Z)-
(1,2-dibromovinyl)benzene. Based upon the mecha-
nism depicted in Scheme 3, it is conceivable that the
reaction proceeded by way of intermediate B. We
Table 4. Synthesis of (2,2-dichlorovinyl)arenes 12 by rho-
ACHTUNGTRENNUNGdium(I)-catalyzed arylation of 11 (1:11=1:5).
General Procesure for Double Arylation (Table 3)
A Schlenk tube was charged with arylboronic acid 1’
(0.25 mmol), [Rh(OH)ACHTNUGTRNEUNG(cod)]2 (3.0 mmol), DPPB (6.0 mmol),
and K3PO4 (0.30 mmol). The tube was evacuated and back-
filled with nitrogen. 1,4-Dioxane (0.50 mL) and 1,2-dibro-
moethene (0.10 mmol) were added via syringe through the
septum. The mixture was stirred at 1008C for 3 h. The reac-
tion mixture was filtered through a plug of Florisilꢁ washing
with hexane-AcOEt (10:1), and the filtrate was concentrat-
ed. The residue was purified by preparative TLC on silica
gel to afford 1,2-diarylethene 6.
Entry
Ar (1)
12
Yield [%][a]
1
2
3
4
5
6
2-naphthyl (1a)
6-(MeO)naphthalen-2-yl (1b)
4-biphenyl (1e)
1-naphthyl (1p)
2-methylnaphthalen-1-yl (1q)
4-(tBu)C6H4 (1r)
12a
12b
12e
12p
12q
12r
47
59
42
54
59
45
Acknowledgements
[a]
Isolated yield.
We thank Manac Inc. for financial support.
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Takanori Matsuda et al.
COMMUNICATIONS
References
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[11] The structure of 10a was proved by its independent
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