Palladium-catalyzed dienylation of haloalkynes using 2,3-butadienyl acetates: A facile access to (1Z)-1,2-dihalo-3-vinyl-1,3-dienes

Article abstract of DOI:10.1002/adsc.201100113

A highly efficient and stereoselective method for the synthesis of (1Z)-1,2-dihalo-3-vinyl-1,3-dienes featuring palladium-catalyzed coupling of haloalkynes and 2,3-butadienyl acetates was developed. The resulting products were smoothly converted into cis-1,2-dihalostyrene derivatives using the Diels-Alder/aromatization sequence. Copyright

Full text of DOI:10.1002/adsc.201100113

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DOI: 10.1002/adsc.201100113
Palladium-Catalyzed Dienylation of Haloalkynes using
2,3-Butadienyl Acetates: A Facile Access to (1Z)-1,2-Dihalo-
3-vinyl-1,3-dienes
Dongxu Chen,a Xiaoyi Chen,a Zenghui Lu,a Haiting Cai,a Jinbei Shen,a
and Gangguo Zhua,b,*
a
Department of Chemistry, Zhejiang Normal University, 688 Yingbin Road, Jinhua 321004, Peopleꢀs Republic of China
Fax : (+86)-579-8228-2610; phone: (+86)-579-8228-3702; e-mail: gangguo@zjnu.cn
Zhejiang Key Laboratory for Reactive Chemistry on Solid Surfaces, Zhejiang Normal University, Jinhua 321004, Peopleꢀs
b
Republic of China
Received: February 14, 2011; Revised: April 3, 2011; Published online: June 16, 2011
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/adcs.201100113.
Abstract: A highly efficient and stereoselective
method for the synthesis of (1Z)-1,2-dihalo-3-vinyl-
1,3-dienes featuring palladium-catalyzed coupling of
haloalkynes and 2,3-butadienyl acetates was devel-
oped. The resulting products were smoothly con-
verted into cis-1,2-dihalostyrene derivatives using
the Diels–Alder/aromatization sequence.
droxy, amine, and more recently, carbon nucleophiles
as the capture reagents.
Very recently, we[6] reported a convenient method
for the regio- and stereoselective synthesis of (1Z)- or
(1E)-1,2-dihalo-1,4-dienes with the halopalladation of
haloalkynes as the key step. In a subsequent study of
the haloallylation of alkynyl halides with allyl alcohol,
we found that phenylethynyl bromide (1a) was selec-
tively allylated to give 2a in 81% yield, whereas phe-
nylacetylene was intact under the reaction conditions
(Scheme 1).
À
Keywords: alkynes; C C bond formation; dienes;
halopalladation; palladium
The unique reactivity of haloalkynes under the hal-
opalladation conditions promoted us to examine the
feasibility of trapping the alkenyl-palladium inter-
Transition metal-catalyzed reactions have become mediate with readily accessible substrates, such as 2,3-
powerful tools for the formation of carbon-carbon butadienol and its derivatives, for diversity-oriented
and carbon-heteroatom bonds in organic synthesis.[1] synthesis (DOS).[7] Herein, we report the Pd-cata-
In this regard, the halopalladation reaction of acety- lyzed dienylation reaction of haloalkynes with 2,3-bu-
lenes has attracted considerable attention over the tadienyl acetates as the capture reagents, allowing
past decades, owing to its easy access to highly func- access to (1Z)-1,2-dihalo-3-vinyl-1,3-dienes in a highly
tionalized haloalkenes in a rather efficient and atom- efficient and stereoselective fashion.
economical way.[2–4] Despite the significant progress
In the initial attempts to achieve the dienylation of
that has been achieved along this line, the halopalla- haloalkynes, we found that treatment of phenylethyn-
dation reaction was mainly limited to the addition of yl bromide (1a) and 2,3-butadienol (3a) in the pres-
allyl halides, carbon monoxide and 1,3-dienes. There- ence of 5 mol% of PdACTHNUTRGNEUNG(OAc)2 and 2 equivalents of
fore, an exploration of the trapping of alkenyl-palladi- LiBr in HOAc at 608C gave the desired 1,2-dibromo-
um intermediates resulting from halopalladation of 3-vinyl-1,3-diene 4aa in 58% yield with 82:18 mixture
ꢀ
the C C triple bond with other readily available ma-
terials, such as allyl alcohol or 2,3-butadienol, is still
highly desirable.
In 2006, Jiang and co-workers[4a] disclosed an ele-
gant protocol for the stereoselective approach to 1,4-
dienes through Pd-catalyzed coupling of alkynes with
allyl alcohol. Liꢀs group[5] also implemented a series
of halopalladation-initiated annulation reactions by
the use of intramolecular nucleophiles, such as hy- Scheme 1. Competitive reaction of 1a and phenylacetylene.
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Palladium-Catalyzed Dienylation of Haloalkynes using 2,3-Butadienyl Acetates
Table 1. Optimization of the reaction conditions.[a] Table 2. Pd-catalyzed dienylation of haloalkynes with 3d.[a]
Entry 3/X
PdLn
Solvent Yield
[%][b,c]
Z/E[d]
Entry
1
R/X
4
Yield Z/E[c]
[%][b]
1
2
3
4
5
6
7
8
3a/OH Pd
3b/OBz Pd
3c/Br Pd
3d/OAc Pd
3d/OAc Pd
3d/OAc Pd
3d/OAc Pd
3d/OAc Pd
3d/OAc Pd
3d/OAc PdCl2
3d/OAc PdBr2
3d/OAc Pd
3d/OAc Pd
N
HOAc 58
HOAc 62
HOAc 21
HOAc 78
DMSO trace
82/18
87/13
81/19
84/16
–
1
2
3
4
5
6
7
8
1a
1b
1c
1d
1e
1f
1g
1h
1i
Ph/Br
p-Cl-C6H4/Br
Ph/Cl
(Z)-4aa
(Z)-4ba
(Z)-4ca
(Z)-4da
(Z)-4ea
(Z)-4fa
(Z)-4ga
(Z)-4ha
(Z)-4ia
(Z)-4ja
(Z)-4ka
(Z)-4la
85
73
87
65
81
78
77
71
79
80
82
58
>95/5
>98/2
>98/2
>98/2
>98/2
>98/2
>98/2
>98/2
>98/2
>98/2
>98/2
>98/2
>98/2
>98/2
>98/2
>98/2
>98/2
p-F-C6H4/Cl
p-Cl-C6H4/Cl
p-Br-C6H4/Cl
o-Br-C6H4/Cl
p-Me-C6H4/Cl
p-MeO-C6H4/Cl
m-MeO-C6H4/Cl
o-MeO-C6H4/Cl
2-furan/Cl
DMF
THF
trace
82
–
90/10
91/9
dioxane 86
9
CH3CN 90(85)[c] >95/5
9
10
11
12
13
CH3CN 79
CH3CN 80
91/9
93/7
92/8
91/9
10
11
12
13
14
15
16
17
1j
1k
1l
1m 2-thiophene/Cl
(Z)-4ma 67
(Z)-4na
(Z)-4oa
1n
1o
1p
1q
2-naphthalene/Cl
80
72
67
82
[a]
Reaction conditions: 1a (0.5 mmol), 3 (0.75 mmol), LiBr
(1.0 mmol) and Pd catalyst (0.025 mmol) in 2 mL of sol-
vent at 608C for 5 h.
GC yield, with naphthalene as the internal standard.
Isolated yield.
CH3A(CH2)4/Cl
CTHUNGTRENNUNG
TBSOCH2CH2/Cl (Z)-4pa
BnOCH2/Cl (Z)-4qa
[b]
[c]
[d]
[a]
Reaction conditions: 1 (0.5 mmol), 3d (0.75 mmol), LiBr
Determined by GC.
(1.0 mmol) and Pd
CH3CN at 608C.
Isolated yield.
ACHTUNGRTEN(NUNG OAc)2 (0.025 mmol) in 2 mL of
[b]
[c]
of Z:E isomers (entry 1, Table 1). This demonstrated
that the vinylpalladium intermediate, generated by
halopalladation of the C C triple bond, could be suc-
cessfully trapped by 2,3-butadienol under mild condi- moalkynes and chloroalkynes, although the reaction
tions. Encouraged by this result, we further examined of bromoalkynes was relatively sluggish. Both elec-
the reaction conditions and the results are listed in tron-rich and electron-deficient aromatic haloalkynes
Determined by GC.
ꢀ
Table 1.
were smoothly converted into the dienylation prod-
Firstly, we studied the effect of leaving groups on ucts in good yields with excellent stereoselectivities
the coupling reaction. Of the groups (X=OH, OBz, (Table 2). For instance, the reaction of phenylethynyl
Br, OAc) we tested, 2,3-butadienyl acetate (3d) led to chloride (1c) gave the dienylation product (Z)-4ca in
the best yield, albeit with moderate selectivity (en- 87% yield with excellent stereoselectivity (Z/E> 98/
tries 1–4, Table 1). Accordingly, 2,3-butadienyl acetate 2) (entry 3, Table 2). As for the sterically hindered
(3d) was chosen for screening of the solvent for this chloroalkyne 1k, the reaction furnished the corre-
reaction (entries 5–9, Table 1). A promising result was sponding dienylation product (Z)-4ka in a yield simi-
obtained by the use of CH3CN as the solvent, giving lar to that of (Z)-4ia or (Z)-4ja (entries 9–11,
(Z)-4aa in 85% yield with an excellent Z-stereoselec- Table 2). Heteroaromatic chloroalkynes, such as 1l
tivity (Z/E> 95/5 by GC). A brief survey of palladi- and 1m, provided the desired products (Z)-4la and
um sources proved Pd
use of other palladium sources, such as PdCl2, PdBr2, and 13, Table 2). Moreover, aliphatic haloalkynes par-
Pd(MeCN)2Cl2 and Pd(PhCN)2Cl2, led to no improve- ticipated well in this reaction (entries 15–17, Table 2).
ment of the stereoselectivities (entries 10–13, For example, 1-chloroheptyne (1o) reacted smoothly
Table 1). Thus, we chose 5 mol% of Pd(OAc)2 as the with 3d to afford the dienylation product (Z)-4oa in
ACHTUNGERTN(NUNG OAc)2 to be the best, while the (Z)-4ma in 58 and 67% yields, respectively (entries 12
A
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
catalyst, 2 equivalents of LiBr as halide sources, 72% yield. In sharp contrast, terminal alkynes, such
CH3CN as the solvent, and 608C as the optimized re- as phenylacetylene, for instance, failed to react with
action conditions for the dienylation reaction of hal- 3d to afford the desired product under the standard
oalkynes.
reaction conditions.
With the optimal conditions in hand, we further in-
The regio- and stereochemistry of the dienylation
vestigated the scope and limits of this reaction. The products were established by NOE measurements and
reaction was found to be applicable to various bro- further confirmed by X-ray analysis. For instance, X-
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Dongxu Chen et al.
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as 3e and 3f, afforded the desired dienylation prod-
ucts (1Z,3E)-4ce and (1Z,3E)-4cf in 69 and 65%
yields, respectively (entries 1 and 2, Table 3). Remark-
ably, the (1Z,3E)-1,2-dihalo-3-vinyl-1,3-diene was de-
tected as the single stereoisomer in both cases. It is
believed that both the thermodynamic effect and the
steric interaction between allene and vinlypalladium
intermediate may account for the excellent stereose-
lectivity.[9] However, further attempts to extend the
reaction to 1-substituted or 2-subtituted 2,3-butadien-
yl acetates, such 3g and 3h, resulted in failure, majorly
due to the unfavorable steric repulsion in the carbo-
palladation step (see proposed mechanism) (entries 3
and 4, Table 3).
Thus far, we have developed a highly efficient and
stereoselective method for the synthesis of (1Z)-1,2-
dihalo-3-vinyl-1,3-dienes. As we know, 1,3-dienes are
valuable building blocks in organic synthesis, especial-
ly for the Diels–Alder reaction.[10] Therefore, we ex-
Figure 1. X-ray structure of (Z)-4ca.
ray analysis[8] of (Z)-4ca clearly indicated the struc- amined the utility of (Z)-4ca in the cycloaddition re-
ture (Figure 1).
action. To our delight, (Z)-4ca reacted smoothly with
The versatility of this protocol was further exam- diethyl acetylenedicarboxylate (5) in toluene at reflux
ined by the reaction of 1c with a variety of functional- to generate the 1,4-cyclohexadiene derivative 6 in
ized 2,3-butadienyl acetates, and the results were sum- 76% yield. The subsequent dehydrogenation employ-
marized in Table 3.
ing 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ)[11]
As shown in Table 3, under the optimized reaction led to the cis-1,2-dihalostyrene derivative 7 in 69%
conditions, 4-substituted 2,3-butadienyl acetates, such yield (Scheme 2).
Pioneered by Ma and others,[12] it is widely docu-
mented that 1,3-dienes could be accessed by the car-
bopalladation of 2,3-allenyl alcohols or acetates. As
Table 3. Pd-catalyzed coupling of 1c with 3.[a]
such, a working mechanism as demonstrated in
Scheme 3 was proposed for this Pd-catalyzed coupling
Entry
1
3
4
Yield [%][b]
69
2
3
65
Scheme 2. Transformations of (Z)-4ca.
0
0
4
[a]
Reaction conditions: 1c (0.5 mmol), 3 (0.75 mmol), LiBr
(1.0 mmol) and Pd
CH3CN at 608C.
Isolated yield.
ACHTUNGRTEN(NUNG OAc)2 (0.025 mmol) in 2 mL of
Scheme 3. Proposed mechanism for dienylation of alkynyl
halides.
[b]
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Adv. Synth. Catal. 2011, 353, 1474 – 1478

Palladium-Catalyzed Dienylation of Haloalkynes using 2,3-Butadienyl Acetates
of haloalkynes with 2,3-butadienyl acetates. The hal- Acknowledgements
oalkyne 1 underwent the trans-addition[13] pathway in
We thank the National Natural Science Foundation of China
the presence of excess halide to form the alkenyl-pal-
ladium intermediate I, followed by the carbopallada-
tion reaction with 2,3-butadienyl acetate 3 to give an
allyl-palladium intermediate II. Finally, a b-hetero-
(No. 20902084), The Project–sponsored by SRF for ROCS of
SEM, Qianjiang Talents Project of the Science and Technolo-
gy Office in Zhejiang Province (2010R10016) and Zhejiang
Normal University for their financial support.
ACHTUNGTRENNUNGatom elimination furnished the dienylation product
(Z)-4 and regenerated the palladium catalyst
(Scheme 3).
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col, in our opinion, mainly originated from the obser-
vation that haloalkynes exhibit much more reactivity
than terminal alkynes and allenes under the halopal-
ladation reaction conditions (Scheme 1).
In summary, we have developed an efficient and
practical procedure for the synthesis of (1Z)-1,2-
dihalo-3-vinyl-1,3-dienes with perfect control of ste-
reochemistry through Pd-catalyzed dienylation of al-
kynyl halides using 2,3-butadienyl acetates. It em-
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Experimental Section
General Procedure for Pd-Catalyzed Coupling of
Alkynyl Halides with 2,3-Butadienyl Acetates
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To a mixture of 3d (84 mg, 0.75 mmol) and PdACTHUNRGTNEUNG(OAc)2
(5.6 mg, 0.025 mmol) in 2 mL of acetonitrile was added 1a
(73 mg, 0.5 mmol). After stirring for 5 h at 608C, the reac-
tion mixture was concentrated and purified by column chro-
matography on silica (petroleum ether) to give (Z)-4aa as a
yellow solid; yield: 115 mg (85%); mp 59–618C (petroleum
ether); Z/E:> 95/5. The stereochemistry was assigned by
NOE measurements. 1H NMR (CDCl3, 400 MHz): d=5.11
(s, 2H), 5.32 (d, J=10.8 Hz, 1H), 5.47 (d, J=17.6 Hz, 1H),
6.21 (dd, J=17.6, 10.8 Hz, 1H), 7.26–7.28 (m, 3H), 7.33–7.35
(m, 2H); 13C NMR (CDCl3, 100 MHz): d=118.1, 121.4,
122.7, 126.7, 128.0 (2C), 128.3 (2C), 128.7, 135.3, 139.3,
145.9; MS (70 eV, EI): m/z (%)=316 (2.5), 314 (4.6), 312
(M+, 2.5), 235 (22), 233 (M+-Br, 21); HR-MS: m/z=
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Dongxu Chen et al.
COMMUNICATIONS
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