Palladium-catalyzed synthesis of 1,3-dienes from allenes and organic halides

Article abstract of DOI:10.1021/jo991651k

A wide range of aryl and vinylic halides react with 1,1-dimethylallene (2a) and potassium carbonate in the presence of Pd(dba)₂ (dba = dibenzylideneacetone) in N,N-dimethylacetamide (DMA) at temperature 100-120 °C to give the corresponding dienes CH₂C(CH₃)CRCH₂ (3a-o), where R is aryl or vinylic, in good to excellent yields. Higher yields of diene products were obtained for aryl bromides than for the corresponding aryl iodides and chlorides. Under similar reaction conditions, tetramethylallene (2b), 1- methyl-1-phenylallene (2c), 1-methyl-3-phenylallene (2d), and 1- cyclohexylallene (2e) also react with aryl and vinylic halides to give diene products (3p-w). For 2d, both E and Z isomers 3t and 3u of the diene product were observed. For 2e, two regioisomers 3v and 3w were isolated with 3w likely from alkene isomerization of 3v. Various palladium systems were tested for the catalytic activity of diene formation. In addition to Pd(dba)₂/PPh₃, Pd(OAc)₂/PPh₃, PdCl₂(PPh₃)₂, and PdCl₂(dppe) are also very effective as catalysts for the reaction of 2a with p-bromoacetophenone (1a) to give 3a. Studies on the effect of solvents and bases show that DMA and K₂CO₃ are the solvent and base that give the highest yield of diene 3a. Possible mechanisms for this catalytic diene formation are proposed.

Full text of DOI:10.1021/jo991651k

J . Org. Chem. 2000, 65, 1767-1773
1767
P a lla d iu m -Ca ta lyzed Syn th esis of 1,3-Dien es fr om Allen es a n d
Or ga n ic Ha lid es
Hao-Ming Chang and Chien-Hong Cheng*
Department of Chemistry, National Tsing Hua University, Hsinchu 30043, Taiwan
Received October 21, 1999
A wide range of aryl and vinylic halides react with 1,1-dimethylallene (2a ) and potassium carbonate
in the presence of Pd(dba)2 (dba ) dibenzylideneacetone) in N,N-dimethylacetamide (DMA) at
temperature 100-120 °C to give the corresponding dienes CH2C(CH3)CRCH2 (3a -o), where R is
aryl or vinylic, in good to excellent yields. Higher yields of diene products were obtained for aryl
bromides than for the corresponding aryl iodides and chlorides. Under similar reaction conditions,
tetramethylallene (2b), 1-methyl-1-phenylallene (2c), 1-methyl-3-phenylallene (2d ), and 1-cyclo-
hexylallene (2e) also react with aryl and vinylic halides to give diene products (3p -w ). For 2d ,
both E and Z isomers 3t and 3u of the diene product were observed. For 2e, two regioisomers 3v
and 3w were isolated with 3w likely from alkene isomerization of 3v. Various palladium systems
were tested for the catalytic activity of diene formation. In addition to Pd(dba)2/PPh3, Pd(OAc)2/
PPh3, PdCl2(PPh3)2, and PdCl2(dppe) are also very effective as catalysts for the reaction of 2a with
p-bromoacetophenone (1a ) to give 3a . Studies on the effect of solvents and bases show that DMA
and K2CO3 are the solvent and base that give the highest yield of diene 3a . Possible mechanisms
for this catalytic diene formation are proposed.
In tr od u ction
π-allylpalladium intermediates to give the final organic
products.5 While numerous catalytic reactions involving
the addition of palladium-carbon bonds to allenes (car-
bopalladation) as key steps are known,2 there is still no
method that leads to the isolation of substituted 1,3-
dienes via intermolecular reaction of allenes and aryl
halides. Very recently, a report by Grigg and co-workers
showed that substituted 1,3-dienes were generated in situ
from allenes and aryl halides in the presence of Ag2CO3
using palladium complexes as the catalysts.6 The dienes
formed were trapped by dienophiles such as N-methyl-
maleimide, but no dienes were isolated by this method
(vide infra). In the cyclic carbopalladation of allenes,
Negishi and co-workers have observed the formation of
cyclic dienes.7 Yamamoto et al. showed that during the
hydropalladation of allenes certain aliphatic allenes were
rearranged to 1,3-dienes.8
Palladium-catalyzed transformation of allenes into
various organic substrates has continued to attract great
attention due to the potential application of these meth-
odologies in organic synthesis.1 The pathways of these
catalytic processes generally involve the addition of a
palladium-carbon,2 a palladium-hydride,3 or a pal-
ladium-heteroatom4 bond to allenes to give π-allylpal-
ladium complexes, followed by nucleophilic attack of the
(1) (a) Trost, B. M.; Gerusz, V. J . J . Am. Chem. Soc. 1995, 117,
5156-5157. (b) Grigg, R.; Gardiner, M.; Sridharan, V.; Vicker, N.
Tetrahedron Lett. 1998, 39, 435-438. (c) Grigg, R.; Brown, S.; Sridha-
ran, V.; Uttley, M. D. Tetrahedron Lett. 1997, 38, 5031-5034. (d) Tsuji,
J .; Shimizu, I.; Sugiura, T. J . Org. Chem. 1985, 50, 537-539. (e) Ma,
S.; Zhao, S. J . Am. Chem. Soc. 1999, 121, 7943-7944. (f) Ma, S.; Shi,
Z. J . Org. Chem. 1998, 63, 6387-6389. (g) Hegedus, L. S.; Kambe, N.;
Ishii, Y.; Mori, A. J . Org. Chem. 1985, 50, 2240-2243. (h) Tanimoto,
S.; Ali, S. M.; Okamoto, T. J . Org. Chem. 1988, 53, 3639-3640. (i) Ito,
Y.; Murakami, M.; Itami, K. Synlett 1999, S1, 951-953. (j) Ito, Y.;
Murakami, M.; Itami, K. Angew. Chem., Int. Ed. Engl. 1998, 37, 3418-
3420. (k) Yamaguchi, M.; Arisawa, M.; Sugihara, T. Chem. Commun.
1998, 2615-2616. (l) Tamaru, Y.; Kimura, M.; Fugami, K.; Tanaka,
S. J . Org. Chem. 1992, 57, 6377-6379. (m) Gallagher, T.; Fox, D. N.
A.; Lathbury, D.; Mahon, M. F.; Molloy, K. C. J . Am. Chem. Soc. 1991,
113, 2652-2656.
(2) (a) Grigg, R.; Xu, L.-H. Tetrahedron Lett. 1996, 37, 4251-4254.
(b) Cazes, B.; Gore, J .; Chaptal, N.; Colvray-Gottelaned, V.; Grandjean,
C. Tetrahedron Lett. 1991, 32, 1795. (c) Kang, S.-K.; Baik, T.-G.; Kulak,
A. N. Synlett. 1999, 324-326. (d) Larock, R. C.; Tu, C.; Pace, P. J .
Org. Chem. 1998, 63, 6859-6866. (e) Grigg, R.; Savic, V. Tetrahedron
Lett. 1996, 37, 6565-6568. (f) Larock, R. C.; Berrios-Pena, N. G.; Fried,
C. A. J . Org. Chem. 1991, 56, 2615-2617. (g) Larock, R. C.; He, Y.;
Leong, W. W.; Han, X.; Refvik, M. D.; Zenner, J . M. J . Org. Chem.
1998, 63, 2154-2160.
Our continuing interest in the palladium-mediated
allene chemistry9 prompted us to investigate the trans-
formation of allenes into 1,3-dienes via eq 1 and to search
for suitable conditions that can lead to the isolation of
the 1,3-diene products. In this paper, we wish to report
that aryl and vinylic halides, particularly the bromides,
react smoothly with substituted allenes and potassium
carbonate in the presence of a palladium complex to give
(5) (a) Tsuji, J .; Shimizu, I. Chem. Lett. 1984, 233-236. (b) Larock,
R. C.; Zenner, J . M. J . Org. Chem. 1995, 60, 482-483. (c) Yamamoto,
Y.; Al-Masum, M.; Asao, N. J . Am. Chem. Soc. 1994, 116, 6019-6020.
(d) Yamamoto, Y.; Meguro, M. J . Org. Chem. 1999, 64, 694-695.
(6) Grigg, R.; Brown, S.; Sridharan, V.; Uttley, M. D. Tetrahedron
Lett. 1998, 39, 3247-3250.
(7) (a) Negishi, E.; Ma, S. J . Am. Chem. Soc. 1995, 117, 6345-6357.
(b) Negishi, E.; Ma, S. J . Org. Chem. 1994, 59, 4730-4732.
(8) (a) Yamamoto, Y. Meguro, M.; Kamijo, S. Tetrahedron Lett. 1996,
37, 7453-7456. (b) Yamamoto, Y., Meguro, M. Tetrahedron Lett. 1998,
39, 5421-5424. (c) Yamamoto, Y.; Al-Masum, M. J . Am. Chem. Soc.
1998, 120, 3809-3810.
(9) (a) Cheng, C. H.; Wu, M. Y.; Yang, F. Y. J . Org. Chem. 1999, 64,
2471-2474. (b) Cheng, C. H.; Yang, F. Y.; Wu, M. Y. Tetrahedron Lett.
1999, 40, 6055-6058
(3) (a) Yamamoto, Y.; Kamijo, S. Tetrahedron Lett. 1999, 40, 1747-
1750. (b) Yamamoto, Y.; Al-Masum, M.; Fujiwara, N.; Asao, N.
Tetrahedron Lett. 1995, 36, 2811-2814. (c) Cazes, B.; Besson, L.; Gore,
J . Tetrahedron Lett. 1995, 36, 3857-3860. (d) Yamamoto, Y.; Al-
Masum, M. Synlett 1995, 969-970. (e) Yamamoto, Y.; Kamijo, S.; Al-
Masum, M. Tetrahedron Lett. 1998, 39, 691-694. (f) Yamamoto, Y.;
Al-Masum, M.; Meguro, M. Tetrahedron Lett. 1997, 38, 6071-6074.
(g) Grigg, R.; Monteith, M.; Sridharan, V.; Terrier, C. Tetrahedron
1998, 54, 3885-3894.
(4) Ogawa, A.; Kawakami, J .; Sonoda, N.; Hirao, T. J . Org. Chem.
1996, 61, 4161-4163.
10.1021/jo991651k CCC: $19.00 © 2000 American Chemical Society
Published on Web 02/24/2000

1768 J . Org. Chem., Vol. 65, No. 6, 2000
Chang and Cheng
substituted 1,3-dienes (eq 1) and for the first time that
1,3-dienes are isolated from carbopalladation of allenes.
expected, the reaction of p-bromochlorobenzene (1e) with
1,1-dimethylallene (2a ) gave only 1-chloro-4-(2-methyl-
1-methyleneallyl)benzene (3e) (Table 1, entry 5). There
is no corresponding 1-bromo-4-(2-methyl-1-methyleneal-
lyl)benzene product observed, indicating that only the
C-Br bond in p-bromochlorobenzene (1e) undergoes
oxidative addition to the palladium center. The yields of
diene products increase for aryl chlorides possessing an
electron-withdrawing substituent. For example, 4-chlo-
roacetophenone (1p ) and 1-chloro-4-nitrobenzene (1q)
react with 1,1-dimethylallene (2a ) to give the correspond-
ing 1,3-dienes in 21 and 29% yields, respectively (Table
1, entries 16 and 17). These results may be understood
on the basis of the fact that an electron-withdrawing
group on an aryl halide generally enhances the rate of
oxidative addition of this substrate to the palladium
center.10
Under similar reaction conditions, vinylic bromides
including R-bromostyrene (1s) and 3-bromo-5,5-dimethyl-
2-cyclohexen-1-one (1t) react with 1,1-dimethylallene (2a )
and potassium carbonate to give cross trienes 3n and 3o
in 82 and 67% yields, respectively (Table 1, entries 19
and 20). To the best of our knowledge, few of these
unusual cross trienes are known in the literature.11 The
Diels-Alder cycloaddition of these trienes with dieno-
philes should be interesting. Investigation in this direc-
tion is in progress.
Resu lts a n d Discu ssion
Dien es fr om Rea ction of 1,1-Dim eth yla llen e w ith
Or ga n ic Ha lid es a n d P ota ssiu m Ca r bon a te. Treat-
ment of 1,1-dimethylallene (2a ) with p-bromoacetophe-
none (1a ) and potassium carbonate in N,N-dimethyl-
acetamide (DMA) in the presence of 5 mol % of Pd(dba)2
and 5 mol % of PPh3 at 120 °C for 12 h gives diene 3a in
94% isolated yield (Table 1, entry 1). Control experiments
indicate that in the absence of either Pd(dba)2 or potas-
sium carbonate no diene product was observed. The yield
of diene 3a was reduced to 74%, if PPh3 was omitted.
Under similar conditions, a vast number of aryl
bromides including o-bromoacetophenone, p- and m-
bromotoluene, p-bromochlorobenzene, p- and o-bromoni-
trobenzene, p- and o-bromobenzonitrile, p-bromoanisole,
ethyl o-bromobenzoate, 9-bromoanthracene, and 1,4-
dibromobenzene (1b-m ) react with 1,1-dimethylallene
(2a ) and potassium carbonate to afford the corresponding
dienes (3b-m ) in good to excellent yields. Table 1 shows
the reaction conditions and the product yields of these
reactions (Table 1, entries 2-13). Aryl bromides with
either an electron-withdrawing substituent or an electron-
donating group react smoothly with 1,1-dimethylallene
(2a ) to yield 1,3-diene derivatives. However, fine-tuning
of the reaction conditions is required for each aryl halide
employed in order to achieve high yield. For example,
the reaction of p-bromoanisole (1j) with 1,1-dimethylal-
lene (2a ) using 5 mol % Pd(dba)2/PPh3 as the catalyst
requires 120 °C and 24 h in DMA to afford the best yield
(90%) (Table 1, entry 10), but for p-bromonitrobenzene
(1f) and p-bromobenzonitrile (1h ) the yields of the
corresponding dienes are higher at 100 °C than at 120
°C (Table 1, entries 6 and 8). All these diene products
Rea ction of Oth er Allen es w ith Or ga n ic Ha lid es
a n d P ota ssiu m Ca r bon a te. Several substituted allenes
including tetramethylallene (2b), 1-methyl-1-phenylal-
lene (2c), 1-methyl-3-phenylallene (2d ), and 1-cyclohexy-
lallene (2e) were also investigated for the reactions with
aryl and vinylic halides and potassium carbonate. Thus,
in the presence of 5 mol % Pd(dba)2, 2b reacts with
p-bromoacetophenone (1a ), R-bromostyrene (1s), or 3-bro-
mo-5,5-dimethyl-2-cyclohexen-1-one (1t) and potassium
carbonate to give the corresponding dienes 3p -r in 38-
77% yields (Table 1, entries 21-23); the reaction of 2c
with 1a and 1u affords 2,3-disubstituted dienes 3s and
3n in 42 and 45% yields, respectively. Two isomers 3t
and 3u were isolated in 53% combined yield from the
reaction of 2d with 1t (Table 1, entry 26). The stereo-
chemistry of these isomers was established on the basis
of the NOE experimental results of these products.
1
show four characteristic H NMR singlets in the region
1
δ 4.8-5.6 ppm for the terminal olefinic protons. The mass
and 13C NMR spectra of these compounds are also in
agreement with the proposed diene structures.
Isomer 3t exhibits H NMR signals at 6.61 and 2.45 ppm
for olefin proton Ha and methylene protons Hb, respec-
tively. Irradiation at Hb led to increase of the intensity
of Ha by 2.8%. In contrast, irradiation at methylene
protons Hd of 3u showed essentially no change of the
intensity of Hc (Scheme 1). These NOE results indicate
that 3t has the E structure, while 3u is a Z isomer.
The reaction of allene 2e with 1a affords two isomers
3v and 3w in 28 and 31% yields, respectively (Table 1,
entry 27). Product 3w is likely from alkene isomerization
of 3v. The stereochemistry of 3w is also based on the
NOE technique. In the 1H NMR spectrum, compound 3w
exhibits signals at 2.16 and 2.19 ppm for methylene (Hd)
and methyl protons and at 5.74, 6.23, and 7.47 ppm for
olefin and aromatic protons Ha, Hb, and Hc, respectively.
Irradiation at Hb led to an increase of the intensity of Hc
by 10.3% and of Ha by 2.3%. Irradiation at Ha also led to
an increase of the intensities of the methyl protons and
Aryl iodides also react with 1,1-dimethylallene (2a ) and
potassium carbonate to give the corresponding diene
derivatives. The yields of these reactions are also listed
in Table 1 (Table 1, entries 14 and 15). The results show
that aryl iodides give lower yields of the diene derivatives
than the corresponding aryl bromides at 120 °C. This is
surprising in view of the fact that, for most palladium-
catalyzed reactions, aryl iodides are generally more
reactive and give higher product yields than the corre-
sponding aryl bromides. Attempts to optimize the reac-
tion conditions for aryl iodides by varying the reaction
temperature, base, and solvent did not significantly
improve the yields of dienes. The reason for the observed
higher yields of diene products for aryl bromides than
for aryl iodides is not clear.
Unlike aryl bromides and aryl iodides, most aryl
chlorides react very slowly with 1,1-dimethylallene (2a )
and potassium carbonate in the presence of Pd(dba)2/
PPh3 to give trace amounts of the diene products. As
(10) Suzuki, A.; Miyaura N. Chem. Rev. 1995, 95, 2457-2483.
(11) Tanna, C. H.; Kiefer, E. F. J . Am. Chem. Soc. 1969, 91, 4478-
4480.

Synthesis of 1,3-Dienes from Allenes and Organic Halides
J . Org. Chem., Vol. 65, No. 6, 2000 1769
Ta ble 1. Resu lts of P a lla d iu m -Ca ta lyzed Dien e F or m a tion s fr om Allen es a n d Or ga n ic Ha lid esa

1770 J . Org. Chem., Vol. 65, No. 6, 2000
Chang and Cheng
Ta ble 1. (Con tin u ed )
a
All reactions were carried out using allene (2.00 mmol), aryl or vinylic bromide (1.00 mmol), Pd(dba)2 (0.0500 mmol), PPh3 (0.0500
b
mmol), K2CO3 (2.00 mmol), and DMA (1.0 mL). Isolated yields.

Synthesis of 1,3-Dienes from Allenes and Organic Halides
J . Org. Chem., Vol. 65, No. 6, 2000 1771
Ta ble 3. Effect of Solven t, Tem p er a tu r e, a n d Ba se on
th e Yield of Dien e 3a a
Sch em e 1
entry
X
solvent
T (°C)
base (equiv)
yieldb (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19d
20
21
22
23d
24d
25
26
Br
DMA
DMA
DMA
DMA
DMF
120
100
120
120
120
120
120
120
120
120
120
120
120
120
70
rt
120
70
80
rt
rt
rt
rt
80
K2CO3 (2)
K2CO3 (2)
K2CO3 (3)
K2CO3 (4)
K2CO3 (2)
K2CO3 (2)
K2CO3 (2)
Na2CO3 (2)
NaHCO3 (2)
NaOAc (2)
LiOAc (2)
Li2CO3 (2)
Cs2CO3 (2)
Ag2CO3 (2)
K2CO3 (2)
K2CO3 (2)
K2CO3 (2)
K2CO3 (2)
NEt3 (2)
94 (98)c
90
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
I
85
65
68
DMSO
Toluene
DMA
DMA
DMA
DMA
DMA
DMA
DMA
DMA
DMA
DMA
DMA
CH3CN
DMF
60
55c
47
16c
79c
48
Sch em e 2
23c
47c
23
60
I
I
I
I
30c
KOH (2)
KOH (2)
KOH (2)
K2CO3 (2)
DMAP (2)
K2CO3 (2)
K2CO3 (2)
52
28
41
DMA
DMA
DMA
Toluene
DMA
DMA
Br
I
I
Cl
OTf
Ta ble 2. Effect of Ca ta lysts a n d Liga n d on th e Yield of
3a a
21c
52
entry
Pd catalyst
PPh3 (equiv)b
yieldb (%)
120
120
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Pd(PPh3)4
Pd(dba)2
Pd(dba)2
Pd(dba)2
Pd(dba)2
44
74
98
82
50
33
79
89
55
94
91
33
74
67
41
52
a
All reactions were carried out using 1,1-dimethylallene (2a )
(2.00 mmol), p-CH3COC6H4X (1.00 mmol, X ) Br, I, Cl or OTf),
Pd(dba)2 (0.0500 mmol), PPh3 (0.0500 mmol), base (2.00 mmol),
1
2
4
6
and solvent (1.0 mL) at 120 °C, 12 h. Isolated yield. c Yields
b
determined by 1H NMR. 24 h.
d
Pd(dba)2
PdCl2(PPh3)2
PdCl2(dppe)
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
PdCl2
PdCl2
PdCl2
PdCl2(CH3CN)2
PdCl2(CH3CN)2
In addition to the Pd(dba)2/PPh3 system, PdCl2(dppe) and
Pd(OAc)2/PPh3 are also effective for the diene formation
(Table 2, entries 8 and 9-11). Several bases including
Na2CO3, NaHCO3, NaOAc, LiOAc, Li2CO3, Cs2CO3, Ag2-
CO3, NEt3 (triethylamine), and DMAP (4-(dimethylami-
no)pyridine) were tested (Table 3, entries 8-14, 19, and
24). All but Ag2CO3, NEt3, and DMAP show certain
activities. Among the bases used, K2CO3 gives the highest
yield of diene 3a . It is interesting to note that Ag2CO3,
which did not give the expected diene under the present
reaction conditions, was used by Grigg and co-workers
in the in situ generation of diene from allenes and aryl
iodides for Diels-Alder reaction.7 It is not clear why we
were unable to isolate the diene product under the
reaction conditions. A possible reason is that the diene
produced is further transformed into unknown products
under the reaction conditions. The activity of strong base,
KOH, was also tested. Although this base gives a poor
yield of diene 3a at temperatures above 100 °C, it shows
substantial activity for the reaction of p-iodoacetophenone
(1n ) and p-bromoacetophenone (1a ) with 2a at room
temperature (Table 3, entries 20-22). At this tempera-
ture, K2CO3 exhibits no activity toward the diene forma-
tion reaction.
P r op osed Mech a n ism . Based on the known pal-
ladium chemistry and our observations during these
present studies, we propose a catalytic cycle shown in
Scheme 3 to account for the present catalytic diene
formation reaction (eq 1). The initial step likely involves
oxidative addition of aryl halide to palladium(0) to give
an arylpalladium(II) species. Coordination of allene fol-
lowed by insertion of the coordinated allene into the Pd-
aryl bond affords a π-allylpalladium species. Deprotona-
tion at the R-carbon of the π-allylpalladium intermediate
by a base produces the final diene product and regener-
ates the palladium(0) species. Oxidative addition of
1
2
1
2
1
a
All reactions were carried out using 1,1-dimethylallene (2.00
mmol), 4-bromoacetophenone (1.00 mmol), 5 mol % of Pd catalyst
(0.0500 mmol), K2CO3 (2.00 mmol), and DMA (1.0 mL) at 120 °C;
reaction time: 12 h. Yields were determined by 1H NMR.
b
Hb by 9.8% and 3.6%, respectively (Scheme 2). These
NOE results clearly show that isomer 3w is an E product.
The corresponding Z isomer was not observed in the
reaction.
Effect of Rea ction Con d ition s on th e Yield of
Dien e P r od u ct. The present palladium-catalyzed 1,3-
diene formations from allenes and aryl halides are greatly
sensitive to the reaction temperature, solvent, base, and
amount of phosphine used. The results for the reaction
of p-CH3COC6H4X (X ) Br, I, Cl, OTf) with 1,1-dimethy-
lallene (2a ) using various palladium systems under
different conditions are shown in Tables 2 and 3. When
potassium carbonate was used as the base, a suitable
temperature range for the catalytic reaction was 100-
120 °C. At reaction temperatures below 70 °C, the rate
of 1,3-diene formation was slow and a low yield of the
diene product was obtained (Table 3, entries 15 and 16).
Several solvents, DMF, DMA, DMSO, and toluene, were
employed in the catalytic reactions at 120 °C with DMA
giving the highest yield of product (Table 3, entries 1 and
5-7). Addition of 1 or 2 equiv of PPh3 to the reaction
solution using Pd(dba)2 as the catalyst greatly increases
the product yield. However, a further increase of the
amount of PPh3 reduces the yield (Table 2, entries 1-6).

1772 J . Org. Chem., Vol. 65, No. 6, 2000
Chang and Cheng
distilled prior to use. Pd(PPh3)4,16 PdCl2(PPh3)2,17 PdCl2-
(dppe),16 PdCl2(CH3CN)2,16 Pd(dba)2,18 1,1-dimethylallene,19
1-methyl-1-phenylallene,20 1-methyl-3-phenylallene,21 cyclo-
hexylallene,21 and 3-bromo-5,5-dimethyl-2-cyclohexen-1-one22
were prepared by procedures previously reported. Other
reagents were commercially available and used as purchased.
Gen er a l P r oced u r e for th e Syn th esis of 1,3-Dien e
Der iva tives fr om Or ga n ic Ha lid es (1) a n d Allen e (2). A
25-mL round-bottom flask containing Pd(dba)2 (0.0287 g,
0.0500 mmol), PPh3 (0.0131 g, 0.0500 mmol), organic halide
(1.00 mmol), and potassium carbonate (0.282 g, 2.00 mmol)
was purged with nitrogen gas several times. To the flask were
then added DMA (1 mL) and allene (2.00 mmol). The reaction
mixture was heated with stirring at 100 or 120 °C for 12-24
h. The solution changed color from purple red to black in 2 h
and maintained at the same color during the reaction. As the
reaction approached completion, the black precipitate of pal-
ladium metal surrounding the wall of the flask appeared
gradually. At the end of the reaction, the solution was filtered
through Celite and silica gel using CH2Cl2 as eluent. The
filtrate was concentrated, and the residue was separated on a
silica gel column using hexane and ethyl acetate as eluent to
give the desired product 3.
Sch em e 3
organic halide to palladium(0) species12 and insertion of
allene to palladium(II)-aryl bond to give a π-allylpalla-
dium species5a,13 were demonstrated in many palladium-
mediated reactions. Deprotonation of a substituted π-al-
lylmetal complex to yield the corresponding 1,3-diene
species was also reported previously.14
Alternatively, the π-allylpalladium species is converted
to a Pd-σ-allyl via coordination of an extra ligand.15 This
Pd-allyl species then undergoes â-hydrogen elimination
to give the diene product and a palladium-hydride
species. Deprotonation of the palladium-hydride with a
base regenerates the palladium(0) species. In view of the
fact that diene formation depends greatly on the base and
the use of a strong base decreases drastically the tem-
perature required for the reaction to proceed (Table 3,
entries 20-22), the mechanism via deprotonation path-
way appears more favorable than that via â-hydrogen
elimination. The former is expected to depend greatly on
the base used, and the latter is likely independent of the
base.
Compounds 3a -w were prepared according to this method.
Product yields of these reactions are listed in Table 1, while
important spectral data of these diene compounds are shown
below or listed in the Supporting Information.
1-[4-(2-Met h yl-1-m et h ylen ea llyl)p h en yl]-1-et h a n on e
(3a ). The reaction mixture was chromatographed using a
mixture of ethyl acetate/hexane (1:50) as eluent to yield a light
yellow liquid: 1H NMR (400 MHz, CDCl3) δ 7.89 (d, J ) 8.4
Hz, 2 H), 7.35 (d, J ) 8.4 Hz, 2 H), 5.35 (s, 1 H), 5.15 (s, 1 H),
5.10 (s, 1 H), 4.79 (s, 1 H), 2.58 (s, 3 H), 1.98 (s, 3 H); 13C NMR
(100 MHz, CDCl3) δ 197.72 (s), 150.10 (s), 146.51 (s), 143.02
(s), 135.93 (s), 128.77 (d), 128.01 (d), 117.28 (t), 115.01 (t), 26.56
(q), 21.04 (q); IR (neat) 2955, 1684, 1266, 902 cm-1; HRMS
calcd for C13H14O 186.1045, found 186.1053.
1-[2-(2-Met h yl-1-m et h ylen ea llyl)p h en yl]-1-et h a n on e
(3b). The reaction mixture was chromatographed using a
mixture of ethyl acetate/hexane (1:50) as eluent to yield a pale
yellow liquid: 1H NMR (400 MHz, CDCl3) δ 7.56-7.17 (m, 4
H), 5.41 (s, 1 H), 5.06 (s, 2 H), 4.59 (s, 1 H), 2.38 (s, 3 H), 2.02
(s, 3 H); 13C NMR (100 MHz, CDCl3) δ 202.70 (s), 149.81 (s),
143.50 (s), 140.48 (s), 139.98 (s), 130.17 (d), 130.59 (d), 127.78
(d), 127.31 (d), 117.53 (t), 115.64 (t), 29.42 (q), 20.54 (q); IR
(neat) 2959, 1689, 1244, 900, 764 cm-1; HRMS calcd for
Con clu sion
C
13H14O 186.1045, found 186.1050.
1-Met h yl-3-(2-m et h yl-1-m et h ylen ea llyl)b en zen e (3d ).
We have demonstrated that it is possible to design a
catalytic reaction based on carbopalladation of allenes,
deprotonation of the resulting π-allylpalladium(II) inter-
mediate, and careful selection of suitable reaction condi-
tions to transfer allenes into substituted 1,3-butadienes.
A series of new 1,3-butadiene derivatives can thus be
synthesized.
The reaction mixture was chromatographed using hexane as
eluent to yield a light yellow liquid: 1H NMR (400 MHz,
CDCl3) δ 7.20 (m, 1 H), 7.12-7.06 (m, 3 H), 5.28 (d, J ) 1.6
Hz, 1 H), 5.11 (d, J ) 1.6 Hz, 1 H), 5.09 (d, J ) 1.6 Hz, 1 H),
4.87 (d, J ) 1.6 Hz, 1 H), 2.34 (s, 3 H), 1.99 (s, 3 H); 13C NMR
(100 MHz, CDCl3) δ 151.14 (s), 143.69 (s), 141.49 (s), 137.39
(s), 129.27 (d), 127.85 (d), 127.74 (d), 125.68 (d), 116.86 (t),
113.71 (t), 21.38 (q), 21.17 (q); IR (neat) 2944, 1591, 887 cm-1
HRMS calcd for C12H14 158.1096, found 158.1096.
;
Exp er im en ta l Section
1-Ch lor o-4-(2-m eth yl-1-m eth ylen ea llyl)ben zen e (3e).
The reaction mixture was chromatographed using hexane as
eluent to yield a colorless liquid: 1H NMR (400 MHz, CDCl3)
δ 7.28 (d, J ) 8.6 Hz, 2 H), 7.20 (d, J ) 8.6 Hz, 2 H), 5.30 (s,
Gen er a l Meth od s. All reactions were run under a nitrogen
atmosphere, unless otherwise mentioned, in oven-dried glass-
ware. All solvents were dried according to known methods and
(16) Colquhoum, H. M.; Halton, J .; Thompson, D. J .; Twigg, M. V.
New Pathways for Organic Synthesis; Plenum Press: New York, 1988;
p 383.
(17) Heck, R. F. Palladium Reagents in Organic Syntheses; Academic
Press: New York, 1978.
(12) (a) Tsuji, J . Organic Synthesis with Palladium Compounds;
Springer-Verlag: New York, 1980. (b) Hegedus, L. S. Transition Metals
in the Synthesis of Complex Organic Molecules; University Science
Books: Mill Valley, CA, 1994; Chapter 9.
(13) Stevens, R. R.; Shier, G. D. J . Organomet. Chem. 1970, 21, 495-
(18) Takahashi, Y.; Ito, T.; Sakai, S.; Ishii, Y. J . Chem. Soc., Chem.
Commun. 1970, 1065-1066.
499.
(14) (a) Trost, B. M.; Fortunak, J . M. J . Am. Chem. Soc. 1980, 102,
2841-2843. (b) Hegedus, L. S.; Inoue, Y. J . Am. Chem. Soc. 1982, 104,
4917-4921. (c) Hegedus, L. S.; Perry, R. J . J . Org. Chem. 1984, 49,
2570-2574. (d) Hauser, F. M.; Tommasi, R.; Hewawasam, P.; Rho, Y.
S. J . Org. Chem. 1988, 53, 4886-4887. (e) Trost, B. M.; Schmidt, T. J .
Am. Chem. Soc. 1988, 110, 2301-2303.
(19) Pasto, D. J .; Warren, S. E.; Morrison, M. A. J . Org. Chem. 1981,
46, 2837-2841.
(20) Peters, D. G.; Stemple, J . Z. J . Org. Chem. 1989, 54, 5318-
5323.
(21) Brandsma, L.; Verkruijisse, H. D. Synthesis of Acetylenes,
Allenes and Cumulenes; Elsevier: New York, 1981.
(22) Piers, E.; Grierson, J . E.; Lau, C. K.; Nagakura, I. Can. J . Chem.
1982, 60, 210-233.
(15) (a) Tibbets, D. L.; Brown, T. L. J . Am. Chem. Soc. 1970, 92, 2,
3031-3034. (b) Powell, J .; Shaw, B. L. J . Chem. Soc. A 1967, 1839.

Synthesis of 1,3-Dienes from Allenes and Organic Halides
J . Org. Chem., Vol. 65, No. 6, 2000 1773
1 H), 5.11 (s, 2 H), 4.82 (s, 1 H), 1.98 (s, 3 H); 13C NMR (100
MHz, CDCl3) δ 149.94 (s), 143.34 (s), 139.97 (s), 133.02 (s),
129.90 (d), 128.06 (d), 117.08 (t), 114.33 (t), 21.07 (q); IR (neat)
2889, 1488, 1093, 831 cm-1; HRMS calcd for C11H11Cl 178.0550,
found 178.0558.
1,4-Di(2-m eth yl-1-m eth ylen ea llyl)ben zen e (3m ). The
reaction mixture was chromatographed using hexane eluent
to yield a colorless liquid: 1H NMR (400 MHz, CDCl3) δ 7.29
(s, 4 H), 5.34 (d, J ) 1.2 Hz, 2 H), 5.20 (d, J ) 1.2 Hz, 2 H),
5.15 (d, J ) 1.2 Hz, 2 H), 4.96 (d, J ) 1.2 Hz, 2 H), 2.04 (s, 6
H); 13C NMR (100 MHz, CDCl3) δ 150.83 (s), 143.65 (s), 140.33
(s), 128.09 (d), 116.86 (t), 113.73 (t), 21.24 (q); IR (neat) 3092,
2951, 1591, 899 cm-1; HRMS calcd for C16H18 210.1409, found
210.1404.
1-(3-Met h yl-1,2-d im et h ylen e-3-b u t en yl)b en zen e (3n ).
The reaction mixture was chromatographed using hexane as
eluent to yield a pale yellow liquid: 1H NMR (400 MHz, CDCl3)
δ 7.43-7.20 (m, 5 H), 5.50 (d, J ) 1.4 Hz, 1 H), 5.37 (d, J )
1.4 Hz, 1 H), 5.25 (d, J ) 1.4 Hz, 1 H), 5.20 (d, J ) 1.4 Hz, 1
H), 4.98 (s, 1 H), 4.93 (s, 1 H), 1.96 (s, 3 H); 13C NMR (100
MHz, CDCl3) δ 150.57 (s), 149.63 (s), 141.91 (s), 140.27 (s),
128.17 (d), 127.46 (d), 126.41 (d), 117.01 (t), 115.21 (t), 114.52
(t), 20.64 (q); IR (neat) 2925, 1662, 1042, 702 cm-1; HRMS calcd
for C13H14 170.1096, found 170.1084.
5,5-Dim et h yl-3-(2-m et h yl-1-m et h ylen ea llyl)-2-cyclo-
h exen -1-on e (3o). The reaction mixture was chromato-
graphed using a mixture of ethyl acetate/hexane (1:50) as
eluent to yield a yellow liquid: 1H NMR (400 MHz, CDCl3) δ
5.98 (s, 1 H), 5.20 (s, 1 H), 5.16 (s, 1H), 5.04 (s, 1 H), 4.88 (s,
1 H), 2.33 (s, 2 H), 2.24 (s, 2 H), 1.86 (s, 3 H), 1.04 (s, 3 H),
1.02 (s, 3 H); 13C NMR (100 MHz, CDCl3) δ 200.34 (s), 158.90
(s), 151.12 (s), 142.14 (s), 126.37 (d), 116.19 (t), 114.72 (t), 51.10
(t), 42.60 (t), 33.75 (s), 28.23 (q), 21.62 (q); IR (neat) 2949, 1686,
1370, 906 cm-1; HRMS calcd for C13H18O 190.1358, found
190.1358.
5,5-Dim et h yl-3-{1-[(E)-1-p h en ylm et h ylid en e]a llyl}-2-
cycloh exen -1-on e (3t). The reaction mixture was chromato-
graphed using a mixture of ethyl acetate/hexane (1:50) as
eluent to yield a yellow liquid: 1H NMR (400 MHz, CDCl3) δ
7.34-7.32 (m, 5 H), 6.69-6.63 (m, 1 H), 6.61, (s,1 H), 6.17 (t,
J ) 1.6 Hz, 1 H), 5.40-5.36 (m, 1 H), 5.29-5.23 (m, 1 H), 2.44
(d, J ) 1.6 Hz, 2 H), 2.29 (s, 2 H), 1.09 (s, 6 H); 13C NMR (100
MHz, CDCl3) δ 200.12 (s), 160.19 (s), 140.48 (s), 136.14 (s),
132.56 (d), 130.39 (d), 129.81 (d), 128.19 (d), 127.80 (d), 127.01
(d), 120.18 (t), 51.24 (t), 42.97 (t), 33.93 (s), 28.22 (q); IR (neat)
2949, 1685, 1278, 700 cm-1; HRMS calcd for C18H20O 252.1515,
found 252.1521.
5,5-Dim et h yl-3-[1-[(Z)-1-p h en ylm et h ylid en e]a llyl]-2-
cycloh exen -1-on e (3u ). The reaction mixture was chromato-
graphed using 1:50 a mixture of ethyl acetate/hexane (1:50)
as eluent to yield a yellow liquid: 1H NMR (400 MHz, CDCl3)
δ 7.35-7.17 (m, 5 H), 6.51-6.42 (m, 2 H), 6.05 (t, J ) 2 Hz, 1
H), 5.20-5.13 (m, 2 H), 2.28 (s, 2 H), 2.19 (d, J ) 2 Hz, 2 H),
1.00 (s, 6 H); 13C NMR (100 MHz, CDCl3) δ 199.27 (s), 158.19
(s), 140.13 (s), 138.51 (d), 135.90 (s), 130.60 (d), 129.72 (d),
128.72 (d), 128.37 (d), 127.74 (d), 115.46 (t), 51.01 (t), 42.98
(t), 33.41 (s), 28.48 (q); IR (neat) 2944, 1667, 756 cm-1; HRMS
calcd for C18H20O 252.1515, found 252.1521.
1-[4-[1-(Cycloh exylid en m et h yl)vin yl]p h en yl]-1-et h a -
n on e (3v). The reaction mixture was chromatographed using
a mixture of ethyl acetate/hexane (1:100) as eluent to yield a
light yellow liquid: 1H NMR (400 MHz, CDCl3) δ 7.89 (d, J )
8.4 Hz, 2 H), 7.49 (d, J ) 8.4 Hz, 2 H), 5.87 (s, 1 H), 5.56 (s, 1
H), 5.15 (s, 1H), 2.58 (s, 3 H), 2.23 (t, J ) 5.6 Hz, 2 H), 2.14 (t,
J ) 5.6 Hz, 2 H), 1.68-1.51 (m, 4 H), 1.50-1.40 (m, 2 H); 13
C
NMR (100 MHz, CDCl3) δ 197.65 (s), 146.07 (s), 145.55 (s),
144.11 (s), 135.93 (s), 128.50 (d), 126.62 (d), 121.01 (d), 116.14
(t), 37.44 (t), 30.03 (t), 28.69 (t), 27.86 (t), 26.58 (q), 26.55 (t);
IR (neat) 2943, 1684 cm-1; HRMS calcd for C17H20O 240.1515,
found 240.1512.
1-[4-(1-Isopr open yl-2-m eth yl-1-pr open yl)ph en yl]-1-eth -
a n on e (3p ). The reaction mixture was chromatographed using
a mixture of ethyl acetate/hexane (1:50) as eluent to yield a
light yellow liquid: 1H NMR (400 MHz, CDCl3) δ 7.88 (d, J )
8.4 Hz, 2 H), 7.25 (d, J ) 8.4 Hz, 2 H), 5.06 (d, J ) 2.6 Hz, 1
H), 4.86 (d, J ) 2.6 Hz, 1 H), 2.57 (s, 3 H), 1.86 (s, 3 H), 1.63
(s, 3 H), 1.61 (s, 3 H); 13C NMR (100 MHz, CDCl3) δ 197.74
(s), 146.64 (s), 145.42 (s), 138.17 (s), 135.09 (s), 130.03 (s),
129.43 (d), 127.97 (d), 115.01 (t), 26.48 (q), 22.59 (q), 22.09 (q),
1-[4-[(E)-2-(1-cycloh exen yl)-1-m eth yl-1-eth en yl]ph en yl]-
1-eth a n on e (3w ). The reaction mixture was chromatographed
using a mixture of ethyl acetate/hexane (1:100) as eluent to
yield a light yellow liquid: 1H NMR (400 MHz, CDCl3) δ 7.88
(d, J ) 8 Hz, 2 H), 7.46 (d, J ) 8 Hz, 2 H), 6.23 (s, 1 H), 5.74
(s, 1 H), 2.56 (s, 3 H), 2.21-2.13 (m, 7 H), 1.71-1.56 (m, 4 H);
13C NMR (100 MHz, CDCl3) δ 197.56 (s), 149.32 (s), 135.42
(s), 135.17 (s), 133.00 (s), 132.73 (d), 128.63 (d), 128.30 (d),
125.79 (d), 29.16 (t), 26.46 (q), 25.68 (t), 22.86 (t), 22.04 (t),
17.34 (q); IR (neat) 2933, 1681, 1268, 738 cm-1; HRMS calcd
for C17H20O 240.1515, found 240.1512.
21.66 (q); IR (neat) 3077, 2919, 1683, 1268, 834, 600 cm-1
HRMS calcd for C15H18O 214.1358, found 214.1365.
;
1-[4-(1-Meth ylen e-2-ph en ylallyl)ph en yl]-1-eth an on e (3s).
The reaction mixture was chromatographed using a mixture
of ethyl acetate/hexane (1:50) as eluent to yield a yellow
liquid: 1H NMR (400 MHz, CDCl3) δ 7.84 (d, J ) 8.4 Hz, 2 H),
7.46 (d, J ) 8.4 Hz, 2 H), 7.39-7.34 (m, 2 H), 7.29-7.21 (m, 3
H), 5.64 (d, J ) 1.2 Hz, 1 H), 5.58 (d, J ) 1.2 Hz, 1 H), 5.44 (d,
J ) 1.2 Hz, 1 H), 5.34 (d, J ) 1.2 Hz, 1 H), 2.54 (s, 3 H); 13C
NMR (100 MHz, CDCl3) δ 197.54 (s), 149.13 (s), 148.88 (s),
144.69 (s), 139.54 (s), 135.97 (s), 128.28 (d), 128.21 (d), 127.65
(d), 127.52 (d), 127.28 (d), 118.01 (t), 116.65 (t), 26.48 (q); IR
Ack n ow led gm en t. We thank the National Science
Council of the Republic of China (NSC 89-2113-M-007-
031) for support of this research.
Su p p or tin g In for m a tion Ava ila ble: 1H NMR spectra of
compounds 3a -w and spectral data for compounds 3c,f-l,q-
r . This material is available free of charge via the Internet at
http://pubs.acs.org.
(neat) 3055, 1682, 1266, 847 cm-1; HRMS calcd for C18H16
248.1202, found 248.1205.
O
J O991651K