Isomerization of alkynes to 1,3-dienes under rhodium or palladium catalysis

Article abstract of DOI:10.1055/s-2006-947325

Treatment of 1-aryl-1-octyne with allyltributylstannane under rhodium catalysis provided 1-aryl-1,3-octadiene in good yield. A combination of ally1 acetate and a palladium catalyst also effected the isomerization of alkynes to 1,3-dienes. Georg Thieme Ver

Full text of DOI:10.1055/s-2006-947325

LETTER
1783
Isomerization of Alkynes to 1,3-Dienes under Rhodium or Palladium Catalysis
I
H
somerization of
A
i
lkynes
r
to 1, 3-D
o
iene
s
to Yasui, Hideki Yorimitsu,* Koichiro Oshima*
Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Kyoto-daigaku Katsura, Nishikyo-ku,
Kyoto 615-8510, Japan
Fax +81(75)3832438; E-mail: yori@orgrxn.mbox.media.kyoto-u.ac.jp; E-mail: oshima@orgrxn.mbox.media.kyoto-u.ac.jp
Received 19 April 2006
After further optimization of reaction conditions, we
Abstract: Treatment of 1-aryl-1-octyne with allyltributylstannane
could reduce the amounts of the rhodium catalyst and
under rhodium catalysis provided 1-aryl-1,3-octadiene in good
allyltributylstannane by using N,N,N¢,N¢-tetramethyl-
ethylenediamine (TMEDA) as an additive (Table 1).
Specifically, treatment of 1a with 1.2 equiv of allyltri-
yield. A combination of allyl acetate and a palladium catalyst also
effected the isomerization of alkynes to 1,3-dienes.
Key words: rhodium, palladium, isomerization, alkynes, 1,3-dienes
butylstannane, 2 mol% of [RhCl(cod)] , and 4 mol% of
2
TMEDA in refluxing xylene for 12 hours furnished 2a in
6
6% yield (entry 1). Other 1-aryl-1-octynes were convert-
Transition-metal-catalyzed isomerization of alkenes to
other alkenes is a well-known process. In contrast, effi-
cient isomerization of alkynes to 1,3-dienes is rare under
ed into the corresponding 1-aryl-1,3-octadienes in reason-
able yields. It is worth noting that the keto groups in 1e
and 1f survived under the reaction conditions (entries 5
and 6). The ratios of (1E,3E)-2 and (1E,3Z)-2 were always
transition-metal catalysis. Although the isomerization of
1
2
-alkyn-1-one and 2-alkynoate proceeds smoothly, there
8
:2 to 7:3.4
are a limited number of reports on the isomerization of
2
simple alkynes. Here we report a couple of new catalytic
Table 1 Rhodium-Catalyzed Isomerization of Alkynes to 1,3-
Dienes in the Presence of Allyltributylstannane
systems that realize the isomerization of simple alkynes to
1
,3-dienes.
Treatment of 1-[3,5-bis(trifluoromethyl)phenyl]-1-octyne
1a) with allyltributylstannane (2.0 equiv) in the presence
2
mol% [RhCl(cod)]2
4 mol% TMEDA
.2 equiv
n
1
Sn Bu3
(
nBu
nHex
C C Ar
Ar
of 7 mol% of [RhCl(cod)] in refluxing toluene for 12
xylene, reflux, 12 h
2
1
2
hours provided 1-[3,5-bis(trifluoromethyl)phenyl]-1,3-
octadiene (2a) in 74% yield (Scheme 1). The diene 2a
consisted of (1E,3E)-2a and (1E,3Z)-2a in a ratio of 7:3.
Interestingly, the addition of allyltributylstannane is es-
sential for the rhodium-catalyzed isomerization. Without
the allylstannane, no reaction took place. Instead of allyl-
tributylstannane, tributylmethallylstannane similarly pro-
moted the reaction to yield 2a in 58% yield. The use of
other allylmetal reagents such as allylmagnesium chlo-
ride, allylzinc bromide, and allyltrimethylsilane resulted
in the recovery of 1a. Organostannanes including tributyl-
stannane, tributylvinylstannane, 3-butenyltributylstan-
Entry
1
Ar
3,5-(CF ) C H
3
1
2
Yield (%)a
66
1a
1b
1c
1d
1e
1f
2a
3
2
6
(
79:21)
2
3
4
5
Ph
2b
2c
2d
2e
2f
84
(
69:31)
4-MeOC H
72
(76:24)
6
4
2-MeC H
48
6
4
(
71:29)
3
nane failed to promote the isomerization.
3-AcC H
68
6
4
(
73:27)
7
2
mol% [RhCl(cod)]2
6
4-AcC H
49
(77:23)
6
4
n
Sn Bu3
.0 equiv
nBu
nHex
C
C
Ar
(1)
a
Ar
1
E,3E/1E,3Z ratios in parentheses.
toluene, reflux, 12 h
Ar = 3,5-(CF3)2C6H3
1
a
2a
74%
1
E,3E/1E,3Z = 7:3
Cyclododecyne (1g) underwent the rhodium-catalyzed
isomerization to yield 1,3-dodecadiene (2g) with the aid
of tributylmethallylstannane (Scheme 2). Similar treat-
ment of cyclic allene 1h provided 1,3-tridecadiene (2h,
Scheme 2). Both of the products mainly comprised of the
E,Z isomers, and no E,E isomers were detected. Unfortu-
nately, the isomerization of an internal linear alkyne, 6-
dodecyne, led to the formation of a mixture of conjugated
dodecadienes. The reaction of 1-dodecyne provided a
Scheme 1
SYNLETT 2006, No. 11, pp 1783–1785
1
2
.0
7
.2
0
0
6
Advanced online publication: 04.07.2006
DOI: 10.1055/s-2006-947325; Art ID: U04406ST
Georg Thieme Verlag Stuttgart · New York
1
complex mixture containing no vinylic H NMR signals.
©

1
784
H. Yasui et al.
LETTER
2
4
mol% [RhCl(cod)]2
mol% TMEDA
5 mol% Pd(OAc)2
20 mol% PPh3
1.2 equiv
OAc
n
Ph
C
C
Ph
Sn Bu
3
(4)
1.2 equiv
OMe
OMe
(
2)
xylene, reflux, 5 h
1j
xylene, reflux, 15 h
2j 57%
E,3E/1E,3Z = 56:44
1
1g
2
g 63%
Scheme 3
E,Z/Z,Z = 94:6
2
4
mol% [RhCl(cod)]2
(entry 7). The palladium-catalyzed isomerization of
homopropargyl methyl ether 1j afforded dienyl ether 2j
•
mol% TMEDA
n
Sn Bu
3
1.2 equiv
(
Scheme 3), whereas the rhodium-catalyzed system did
(3)
toluene, reflux, 12 h
not promote the isomerization.
In summary, we have devised rhodium- and palladium-
catalyzed isomerization reactions of alkynes to 1,3-
dienes. The rhodium and palladium catalysts require allyl-
tributylstannane and allyl acetate, respectively, to attain
satisfactory results.
1
h
2h 57%
E,Z/Z,Z = 88:12
Scheme 2
An alternative system for the isomerization utilizes a com-
bination of palladium catalyst and allyl acetate. Heating a Acknowledgment
mixture of 1b, 1.2 equiv of allyl acetate, 5 mol% of
This work was supported by Grants-in-Aid for Scientific Research
from the Ministry of Education, Culture, Sports, Science and
Pd(OAc) and 20 mol% of PPh in xylene for five hours
2
3
afforded 2b in 87% yield (Table 2, entry 1). Allyl acetate Technology, Government of Japan.
proved to enhance the efficiency of the reaction (entry 2).
The exact role of allyl acetate is not clear at this stage. We
are tempted to assume that an allylpalladium complex can
be the actual catalyst. The palladium-catalyzed conditions
usually provided the better yields of 2 than the rhodium-
catalyzed reactions. Functional group compatibility was
so satisfactory that the aldehyde moiety left untouched
References and Notes
(
1) (a) Trost, B. M.; Schmidt, T. J. Am. Chem. Soc. 1988, 110,
2301. (b) Ma, D.; Lin, Y.; Lu, X.; Yu, Y. Tetrahedron Lett.
1988, 29, 1045. (c) Ma, D.; Yu, Y.; Lu, X. J. Org. Chem.
1989, 54, 1105. (d) Ma, D.; Lu, X. Tetrahedron Lett. 1989,
30, 843.
(
2) Isomerization of propargyl ethers: (a) Hirai, K.; Suzuki, H.;
Morooka, Y.; Ikawa, T. Tetrahedron Lett. 1980, 21, 3413.
(b) Isomerization of perfluoroalkylalkynes: Wang, Z.; Lu,
X. Tetrahedron 1995, 51, 11765. (c) Isomerization as a side
reaction: Kadota, I.; Shibuya, A.; Lutete, L. M.; Yamamoto,
Y. J. Org. Chem. 1999, 64, 4570. (d) Ruthenium-catalyzed
isomerization: Shiotsuki, M.; Ura, Y.; Ito, T.; Wada, K.;
Kondo, T.; Mitsudo, T. J. Organomet. Chem. 2005, 689,
3168.
Table 2 Palladium-Catalyzed Isomerization of Alkynes to 1,3-
Dienes in the Presence of Allylacetate
5
2
mol% Pd(OAc)2
0 mol% PPh3
OAc
1.2 equiv
nBu
nHex
C C Ar
Ar
xylene, reflux, 5 h
1
2
(
3) The role of allyltributylstannane is not clear at this stage. The
formation of chlorotributylstannane was confirmed upon
Entry
1
Ar
1
2
Yield (%)a
87
mixing equimolar amounts of [RhCl(cod)] and allyltributyl-
2
Ph
1b
2b
2b
2a
2c
2d
2f
stannane in refluxing xylene.
(
83:17)
(4) (a) General Procedure for Rhodium-Catalyzed
Isomerization of Alkynes.
2b
Ph
1b
1a
1c
1d
1f
60
[
RhCl(cod)] (4.9 mg, 0.01 mmol) was placed in a 20 mL
(
83:17)
2
reaction flask under argon. TMEDA (2.3 mg, 0.02 mmol,
dissolved in 2 mL of xylene), alkyne 1b (93 mg, 0.50 mmol,
dissolved in 2 mL of xylene), and allyltributylstannane (199
mg, 0.6 mmol, dissolved in 2 mL of xylene) were sequen-
tially added at ambient temperature. After being stirred for
3
4
5
6
3,5-(CF ) C H
3
97
3
2
6
(
85:15)
4-MeOC H
53
6
4
(
80:20)
12 h at 140 °C, the reaction mixture was cooled to ambient
temperature, and HCl (6 M, 5 mL) was added. After being
stirred for additional 1 h, the product was extracted with
hexane (2 ×10 mL). The combined organic phase was dried
2-MeC H4
68
6
(
84:16)
over Na SO . Evaporation followed by silica gel column
4-AcC H4
90
2
4
6
purification afforded 1,3-diene 2b (78.2 mg, 0.42 mmol,
4%). The obtained 2b showed the identical spectra in the
(
83:17)
8
7c
4-HC(=O)C H
1i
2i
73
literature, see: Miyaura, N.; Yamada, K.; Suginome, H.;
Suzuki, A. J. Am. Chem. Soc. 1985, 107, 972. (b) General
Procedure for Palladium-Catalyzed Isomerization of
Alkynes.
6
4
(
78:22)
a
1
E,3E/1E,3Z ratios in parentheses.
b
c
Performed in the absence of allyl acetate.
-(1-Hexynyl)benzaldehyde was used.
Pd(OAc) (5.6 mg, 0.025 mmol) and PPh (26 mg, 0.10
4
2
3
mmol) were placed in a 20 mL reaction flask under argon.
Synlett 2006, No. 11, 1783–1785 © Thieme Stuttgart · New York

LETTER
Allyl acetate (60 mg, 0.60 mmol, dissolved in 2 mL of
Isomerization of Alkynes to 1,3-Dienes
1785
1 × 0.85 H), 6.56 (d, J = 16.0 Hz, 1 × 0.15 H), 6.89 (dd,
J = 16.0, 10.5 Hz, 1 × 0.85 H), 7.19 (ddd, J = 16.0, 11.0, 1.0
Hz, 1 × 0.15 H), 7.68 (s, 1 × 0.85H), 7.70 (s, 1 × 0.15H), 7.77
xylene) and alkyne 1a (161 mg, 0.50 mmol) were
sequentially added at ambient temperature. After being
stirred for 5 h at 140 °C, the reaction mixture was filtered.
Evaporation followed by silica gel column purification
afforded 1,3-diene 2a (156 mg, 0.49 mmol, 97%).
1
3
(s, 2 × 0.85 H), 7.80 (s, 2 × 0.15H). C NMR (125.7 MHz,
CDCl ): d (1E,3E isomer) = 14.11, 22.45, 31.41, 32.81,
3
120.34–120.37 (m), 123.56 (q, J = 273 Hz), 125.86 (m),
126.76, 129.80, 132.06 (q, J = 33.2 Hz), 132.45, 139.65,
140.02; d (1E,3Z isomer) = 14.17, 22.53, 28.11, 31.91,
120.58–120.64 (m), 126.08 (m), 127.97, 128.12, 128.91,
132.12 (q, J = 32.7 Hz), 136.76, 139.97; the signals for the
carbons of CF were not observed. Anal. Calcd for C H F
1
,3-Diene 2a: IR (neat): 2962, 2932, 1645, 1468, 1381,
–
1 1
1279, 1134, 986, 939, 893, 846, 684 cm . H NMR (500
MHz, CDCl ): d = 0.92 (t, J = 7.5 Hz, 3 × 0.85 H), 0.96 (t,
3
J = 7.5 Hz, 3 × 0.15H), 1.33–1.49 (m, 4 H), 2.20 (dt, J = 7.5,
6
5
.5 Hz, 2 × 0.85 H), 2.35 (dt, J = 7.5, 6.0 Hz, 2 × 0.15 Hz),
.70 (dt, J = 10.5, 7.5 Hz, 1 × 0.15 H), 5.99 (dt, J = 15.0, 7.5
3
16 16
6
(%): C, 59.63; H, 5.00; Found: C, 59.70; H, 4.94.
Hz, 1 × 0.85 H), 6.16–6.26 (m, 1 H), 6.47 (d, J = 16.0 Hz,
Synlett 2006, No. 11, 1783–1785 © Thieme Stuttgart · New York