Nickel-catalyzed cross-coupling of dienyl phosphates with Grignard reagents in the synthesis of 2-substituted 1,3-dienes

Full text of DOI:10.1021/jo982060h

J . Org. Chem. 1999, 64, 1745-1749
1745
further investigation of this reaction with application to
both cyclic and acyclic substrates and various Grignard
reagents.
Nick el-Ca ta lyzed Cr oss-Cou p lin g of Dien yl
P h osp h a tes w ith Gr ign a r d Rea gen ts in th e
Syn th esis of 2-Su bstitu ted 1,3-Dien es
Resu lts a n d Discu ssion
A. Sofia. E. Karlstro¨m, Kenichiro Itami,† and
J an-E. Ba¨ckvall*
Dienyl phosphates were obtained from the correspond-
ing R,â-unsaturated ketones in good yields following a
literature procedure.4b Cross-coupling of the dienyl phos-
phates with Grignard reagents were studied employing
catalytic amounts (1 mol %) of a nickel catalyst (NiCl2-
(dppe) or NiCl2(dppp))7 in ether or THF. The reactions
of cyclic dienyl phosphates with n-alkyl and aryl Grignard
reagents were fast, with complete conversion usually
being observed within 30 min at room temperature, to
give 2-substituted dienes as the sole product (Table 1).
One drawback with our previously described copper-
catalyzed cross-coupling is that cyclic dienyl triflates and
n-alkyl Grignard reagents gave moderate yields of cou-
pling products.2 Coupling of these structural elements
can be performed more successfully with dienyl phos-
phates as substrates employing nickel catalysis. For
example, 2-octyl-1,3-cyclohexadiene (8) was obtained in
86% isolated yield from the cross-coupling of 1,3-cyclo-
hexadienyl phosphate 18 with n-octylMgBr using NiCl2-
(dppe) as catalyst (Table 1, entry 2), whereas the corre-
sponding copper-catalyzed reaction employing the dienyl
triflate gave only 60% yield of 8.2 It is noteworthy that
the homocoupling product 2,2′-bis(1,3-cyclohexadienyl)
that was observed as a side product in the copper-
catalyzed reactions is not observed at all in the nickel-
catalyzed version.
The effect of the substituent in the phosphate leaving
group was examined. It was found that diphenyl phos-
phate 1 and the corresponding diethyl phosphate 29 gave
comparable yields in cross-couplings with n-octylMgBr
using NiCl2(dppe) as catalyst (Table 1, entries 2-3).
Change of catalyst to NiCl2(dppp) gave a similar result
(Table 1, entry 4). An aryl substituent could also be easily
introduced as demonstrated by the couplings of dienyl
phosphates 1, 3, and 4 with aryl Grignard reagents
(Table 1, entries 5-8). Sterically hindered phosphate 5,
however, gave a moderate yield of cross-coupling product
13 in reaction with PhMgBr (Table 1, entry 9).
Department of Organic Chemistry, Arrhenius Laboratory,
Stockholm University, SE-106 91, Stockholm, Sweden
Received October 13, 1998
In tr od u ction
Conjugated dienes are important intermediates in
organic synthesis.1 We recently published a method for
the synthesis of 2-substituted cyclic 1,3-dienes via a
copper-catalyzed cross-coupling between dienyl triflates
and Grignard reagents (eq 1).2
To our disappointment, dienyl phosphates, which are
more stable and more readily obtained on a large scale
than dienyl triflates, were not reactive under these
conditions. We therefore turned our attention to the use
of nickel(0) instead of copper(I) as catalyst for coupling
with dienyl phosphates. Nickel- and palladium-catalyzed
cross-couplings between organic halides and organome-
tallic reagents are well-known in the literature.3 Cou-
plings of organic phosphates have been reported with
Grignard reagents,4 organomanganese reagents,5 and
organoaluminum reagents4c,6 with nickel or palladium
catalysis. However, little attention has been paid to the
synthesis of substituted dienes via these methods. Claes-
son et al.4a showed that nickel-catalyzed reaction of
acyclic diethyl dienyl phosphates with Grignard reagents
give substituted dienes. In this paper we report on a
† Present address: Department of Synthetic Chemistry & Biological
Chemistry, Faculty of Engineering, Kyoto University, Kyoto 606-8501,
J apan.
The corresponding reaction with MeMgBr was slow at
room temperature, but reaction between 6 and MeMgBr
in refluxing ether with NiCl2(dppp) as the catalyst
resulted in complete conversion within 5 h, and 5,5-
diphenyl-2-methyl-1,3-cyclohexadiene (14)2 was isolated
in 63% yield (Table 1, entry 10). Cross-coupling of dienyl
phosphates with secondary alkyl Grignard reagents such
as 2-butylMgBr or 2-octylMgBr was slower than the
corresponding coupling with n-alkyl Grignard reagents.
NiCl2(dppe) and NiCl2(dppp) should be suitable catalysts
for coupling with secondary alkyl Grignard reagents since
they do not promote isomerization of the alkyl group.10
(1) Pattenden, G. In Comprehensive Organic Chemistry; Barton, D.,
Ollis, W. D., Eds.; Pergamon: Elmsford, NY,, 1979; Vol. 1, Chapter 2,
pp 171-213.
(2) Karlstro¨m, A. S. E.; Ro¨nn, M.; Thorarensen, A.; Ba¨ckvall, J .-E.
J . Org. Chem. 1998, 63, 2517.
(3) (a) Tamao, K.; Kumada, M. In The Chemistry of the Metal-
Carbon Bond; Hartley, F. R., Ed.; Wiley: NY, 1987; Vol. 4, Chapter 9,
pp 820-887. (b) Kumada, M. Pure Appl. Chem. 1980, 52, 669. (c)
Negishi, E.; Liu, F. In Metal-Catalyzed Cross-Coupling Reactions;
Diederich, F., Stang, P. J ., Eds.; Wiley: Weinheim, 1998; Chapter 1,
pp 1-47. (d) Hosomi, A.; Saito, M.; Sakurai, H. Tetrahedron Lett. 1979,
429. (e) Hayashi, T.; Konishi, M.; Kobori, Y.; Kumada, M.; Higuchi,
T.; Hirotsu, K. J . Am. Chem. Soc. 1984, 106, 158. (f) Organ, M. G.;
Murray, A. P. J . Org. Chem. 1997, 62, 1523.
(4) (a) Sahlberg, C.; Quader, A.; Claesson, A. Tetrahedron Lett. 1983,
24, 5137. (b) Hayashi, T.; Fujiwa, T.; Okamoto, Y.; Katsuro, Y.;
Kumada, M. Synthesis 1981, 1001. (c) Hayashi, T.; Katsuro, Y.;
Okamoto, Y.; Kumada, M. Tetrahedron Lett. 1981, 22, 4449. (d)
Armstrong, R. J .; Harris, F. L.; Weiler, L. Can. J . Chem. 1982, 60,
673.
(7) dppe ) diphenylphosphinoethane, dppp ) diphenylphosphino-
propane.
(8) Blotny, G.; Pollack, R. M. Synthesis 1988, 109.
(9) Gloer, K. B.; Calogeropoulou, T.; J ackson, J . A.; Wiemer, D. F.
J . Org. Chem. 1990, 55, 2842.
(10) Tamao, K.; Kiso, Y.; Sumitani, K.; Kumada, M. J . Am. Chem.
Soc. 1972, 94, 9268.
(5) Fugami, K.; Oshima, K.; Utimoto, K. Chem. Lett. 1987, 2203.
(6) (a) Takai, K.; Sato, M.; Oshima, K.; Nozaki, H. Bull. Chem. Soc.
J pn. 1984, 57, 108. (b) Asao, K.; Iio, H.; Tokoroyama, T. Synthesis 1990,
382.
10.1021/jo982060h CCC: $18.00 © 1999 American Chemical Society
Published on Web 02/06/1999

1746 J . Org. Chem., Vol. 64, No. 5, 1999
Ta ble 1. Nick el-Ca ta lyzed Cr oss-Cou p lin g of Cyclic Dien yl P h osp h a tes w ith Gr ign a r d Rea gen tsa
Notes
a
b
Unless otherwise stated the reactions were carried out in ether according to the procedure in the Experimental Section. Isolated
yield of 2-substituted diene after flash chromatography (or distillation for aryl-substituted cyclohexadienes). c GLC yield, n-decane as
internal standard. Reaction was run on a 120 mmol scale. e TBS ) tert-butyldimethylsilyl. f Reaction was run in refluxing ether.
d
g
h
Incomplete conversion after 20 h. Reaction was carried out in THF at 40 °C.

Notes
J . Org. Chem., Vol. 64, No. 5, 1999 1747
Ta ble 2. Cr oss-Cou p lin g of Acyclic Dien yl P h osp h a te 17
w ith Gr ign a r d Rea gen tsa
tion) in 62% isolated yield after a 2 h reaction time (Table
3, entry 4). NiCl2(dppp) gave a similar result but with a
slight decrease in yield and stereoselectivity (Table 3,
entry 5). On the other hand, reaction between (Z)-19 and
BuMgBr was very slow at room temperature with NiCl2-
(dppe) as catalyst (Table 3, entry 6), showing how
sensitive this reaction is to steric effects. A catalyst
change to NiCl2(dppp) increased the reaction rate and
afforded a 78% isolated yield of 20b after 5 h at room
temperature (Table 3, entry 7). However, conservation
of double-bond configuration was not observed and the
product with Z-configuration dominated (E:Z ratio 30:
70). By performing the reaction in refluxing THF, the
trend previously observed (faster conversion, slightly
lower yield, and improved conservation of stereochemis-
try) was followed, and 20b with an E:Z ratio of 55:45 was
obtained (Table 3, entry 8).
solvent /
temp
reactn
time (h)
yield of
entry
RMgBr
L2
18b (%)
1
2
3
4
BuMgBr
MeMgBr
MeMgBr
dppe Et2O/rt
dppe Et2O/rt
dppp Et2O/rt
0.5
20
7
77
<50 convn
76
2-BuMgBr dppp THF/reflux
2
c
a
Experimental procedure as stated in Experimental Section.
Isolated yield after column chromatography. c No cross-coupling
b
product could be isolated.
Reaction between 1 and 2-octylMgBr with NiCl2(dppp)
(1 mol %) as catalyst in ether at room temperature
resulted in low conversion even at prolonged reaction
times (Table 1, entry 11). On the other hand, the reaction
between 6 and 2-butylMgBr with NiCl2(dppe) as catalyst
in THF at 40 °C was complete within 2 h and 5,5-
diphenyl-2-(2-butyl)-1,3-cyclohexadiene (16)2 was isolated
in 45% yield (Table 1, entry 12).
The nickel-catalyzed cross-coupling was also studied
for acyclic dienyl phosphates. Dienyl phosphate 17 (Table
2) was obtained from (E)-6-phenyl-3-hexen-2-one11,12 in
75% yield after chromatography. Reaction of 17 with
n-BuMgBr using NiCl2(dppe) as catalyst yielded the
desired cross-coupling product 18b in 77% yield within
30 min (Table 2, entry 1). On the other hand, reaction
between 17 and MeMgBr was very slow with NiCl2(dppe)
as catalyst (50% conversion after 20 h at room temper-
ature) (Table 2, entry 2). Change of catalyst to NiCl2-
(dppp) gave a significant increase in reaction rate. The
reaction was complete within 7 h, and (3E)-2-methyl-6-
phenyl-1,3-hexadiene (18a )13 was isolated in 76% yield
(Table 2, entry 3). Attempted cross-coupling with 2-BuMg-
Br failed (Table 2, entry 4).
For simple alkenyl halides, reaction with Grignard
reagents under nickel catalysis generally results in a
stereospecific reaction with retention of configuration of
the double bond in the cross-coupling product.14 1,2-
Dihaloethylenes on the other hand react nonstereospe-
cifically with Grignard reagents to yield disubstituted
olefins.14,15 However, by using 1 equiv of Grignard
reagent, 1-chloroalkenes can be stereospecifically syn-
thesized from dichloroethylene.16 The cross-coupling be-
tween dienyl halides and Grignard reagents under nickel
catalysis has, to our knowledge, not been studied. (E)-
and (Z)-dienyl sulfides, however, were found to react
stereospecifically with retention of configuration with
MeMgI under nickel catalysis to yield 1,3-dienes.17
Regardless of the double-bond configuration in dienyl
phosphate 19, a mixture of E and Z cross-coupling
products was obtained in reaction with MeMgBr or
BuMgBr under nickel catalysis. An explanation of the
low stereoselectivity observed is that the dienyl-nickel
complex obtained from oxidative addition is in equilib-
rium with an allenyl-nickel intermediate (Scheme 1).
Con clu sion
To study the stereoselectivity of the nickel-catalyzed
cross-coupling, dienyl phosphate 19 (Table 3) was em-
ployed as substrate. Phosphate 19 was obtained in 60%
yield from (E)-8-phenyl-5-octen-4-one11 as a 55:45 mixture
of (Z)- and (E)-isomers, which was separated by column
chromatography. Cross-coupling of purified (Z)-19 with
MeMgBr using NiCl2(dppp) as catalyst in ether at room
temperature produced a 50:50 mixture of stereoisomeric
cross-coupling products 20a (Table 3, entry 1). The E:Z
ratio could be slightly improved to 57:43 in refluxing
THF, with the major isomer being that with retained
stereochemistry (Table 3, entry 2). Reaction of (E)-19 with
MeMgBr also showed poor stereoselectivity (Table 3,
entry 3). However, reaction of (E)-19 with BuMgBr with
NiCl2(dppe) as catalyst at room temperature resulted in
stereoselective formation of the cross-coupling product
20b with retention of double-bond geometry (95% reten-
For the synthesis of 2-substituted dienes, nickel-
catalyzed cross-coupling of dienyl phosphates with Grig-
nard reagents is a good complement to our previously
reported copper-catalyzed cross-coupling of dienyl tri-
flates with Grignard reagents. The nickel-catalyzed
coupling has the advantage that it works with dienyl
phosphates and gives good results for aryl and n-alkyl
Grignard reagents. The copper-catalyzed reaction, which
requires dienyl triflates, is advantageous for methyl and
s-alkyl Grignard reagents, but the low stability of acyclic
dienyl triflates makes this reaction unsuitable for the
synthesis of acyclic dienes. The nickel-catalyzed reaction
works for acyclic dienyl phosphates, but the reaction
shows low stereoselectivity. The nickel-catalyzed reaction
is sensitive to changes in substrate and Grignard reagent
(11) Acyclic R,â-unsaturated ketones were prepared from 3-phenyl-
propionaldehyde and dimethyl 2-oxoalkanephosphonates according to
the method of Villieras, J .; Rambaud, M. Synthesis 1983, 300.
(12) (a) New, D. G.; Tesfai, Z.; Moeller, K. D. J . Org. Chem. 1996,
61, 1578. (b) Hon Y.-S.; Lu, L. Tetrahedron 1995, 51, 7937. (c)
Masuyama, Y.; Sakai, T.; Kato, T.; Kurusu, Y. Bull. Chem. Soc. J pn.
1994, 67, 2265.
(13) (a) Vedejs, E.; Fang, H. W. J . Org. Chem. 1984, 49, 210. (b)
Tamura, R.; Saegusa, K.; Kakihana, M.; Oda, D. J . Org. Chem. 1988,
53, 2723. (c) Narasaka, K.; Kusama, H.; Hayashi, Y. Tetrahedron 1992,
48, 2059.
(14) Tamao, K.; Zembayashi, M.; Kiso, Y.; Kumada, M. J . Orga-
nomet. Chem. 1973, 55, C91.
(15) (a) Tamao, K.; Sumitani, K.; Kiso, Y.; Zembayashi, M.; Fujioka,
A.; Kodama, S.; Nakajima, I.; Minato, A.; Kumada, M. Bull. Chem.
Soc. J pn. 1976, 49, 1958. (b) Tamao, K.; Sumitani, K.; Kumada, M. J .
Am. Chem. Soc. 1972, 94, 4374.
(16) Ratovelomanana V.; Linstrumelle, G. Tetrahedron Lett. 1981,
22, 315.
(17) Furuta, K.; Ikeda, Y.; Meguriya, N.; Ikeda, N.; Yamamoto, H.
Bull. Chem. Soc. J pn. 1984, 57, 2781. Ukai, J .; Ikeda, Y.; Ikeda, N.;
Yamamoto, H. Tetrahedron Lett. 1984, 25, 5173.

1748 J . Org. Chem., Vol. 64, No. 5, 1999
Ta ble 3. Cr oss-Cou p lin g of Acyclic Dien yl P h osp h a te 19 w ith Gr ign a r d Rea gen tsa
Notes
entry
substrate
R
L2
solvent/temp
reactn time (h)
yieldb (%)
E:Z ratio of 20
1
2
3
4
5
6
7
8
(Z)-19
(Z)-19
(E)-19
(E)-19
(E)-19
(Z)-19
(Z)-19
(Z)-19
Me
Me
Me
Bu
Bu
Bu
Bu
Bu
dppp
dppp
dppp
dppe
dppp
dppe
dppp
dppp
Et2O/rt
48
2
2
2
3
20
5
1
68
53
55
62
56
43c
78
54
50:50
57:43
40:60
5:95
10:90
35:65
30:70
55:45
THF/reflux
THF/reflux
Et2O/rt
Et2O/rt
Et2O/rt
Et2O/rt
THF/reflux
a
b
Procedure as stated in the Experimental Section. Isolated yield after column chromatography. c 60% conversion after 20 h, unreacted
(Z)-19 recovered.
10), (Z)-19, Rf 0.26, (E)-19 Rf 0.21 (TLC, pentane:Et2O 80:20).
Stereochemistry was determined by NOE experiments. (Z)-19:
1H NMR δ 7.37-7.30 (m, 4H), 7.28-7.11 (m, 11H), 5.92 (m, 2H),
5.10 (dt, J ) 2.1, 7.5 Hz, 1H), 2.61 (m, 2H), 2.34 (m, 2H), 2.20
(dqvintet, J ) 2.5, 7.5 Hz, 2H), 0.95 (t, J ) 7.5 Hz); 13C NMR δ
150.6 (d, J (13C,31P) ) 7.6 Hz), 144.6, 141.6, 130.5, 129.7, 128.3
(d, J (13C,31P) ) 5.3 Hz), 125.8, 125.3, 124.9, 121.2 (d, J (13C,31P)
) 6.1 Hz), 120.2 (d, J (13C,31P) ) 5.3 Hz), 35.4, 34.3, 19.3, 13.6;
31P NMR δ 55.3. (E)-19: 1H NMR δ 7.38-7.30 (m, 4H), 7.28-
7.12 (m, 11H), 6.12 (dq, J ) 15.3, 1.7 Hz, 1H), 5.89 (dt, J ) 15.3,
7.1 Hz), 5.46 (dt, J ) 2.6, 7.9 Hz, 1H), 2.63 (m, 2H), 2.37 (q, J )
7.6 Hz, 2H), 2.12 (dqvintet, J ) 2.1, 7.6 Hz, 2H), 0.98 (t, J ) 7.6
Hz); 13C NMR δ 150.6 (d, J (13C,31P) ) 7.6 Hz), 144.2 (d, J (13C,31P)
) 8.6 Hz), 141.5, 132.3, 129.7, 128.3 (d, J (13C,31P) ) 4.7 Hz),
125.9, 125.4, 120.2 (d, J (13C,31P) ) 4.6 Hz), 119.9 (d, J (13C,31P)
) 6.0 Hz), 118.5 (d, J (13C,31P) ) 4.0 Hz), 35.4, 34.5, 19.6, 14.2;
31P NMR δ 55.5.
Gen er a l P r oced u r e for Nick el-Ca ta lyzed Cr oss-Cou -
p lin g Rea ction s. NiCl2(L2) (0.01 mmol) and the dienyl phos-
phate (1 mmol) were mixed in Et2O (10 mL) at 0 °C under a dry
nitrogen atmosphere. The Grignard reagent (1.5 mmol of a 0.5
M solution in ether) was then added via syringe. The reaction
mixture was stirred at room temperature until judged complete
according to TLC. The initially yellow solution gradually became
cloudy as the reaction proceeded. The reaction was quenched
by addition of a 0.1 M aqueous HCl solution. The organic phase
was collected, and the water phase was extracted with ether (2
× 10 mL). The combined organic layers were washed with brine,
dried (MgSO4), and evaporated in vacuo. The resulting crude
products were purified by column chromatography except for
aryl-substituted cyclohexadienes that were purified by distilla-
tion.
Sch em e 1
structure. The catalyst and other reaction conditions have
to be varied accordingly.
Exp er im en ta l Section
NMR spectra were recorded for CDCl3 solutions (1H at 400
MHz, 13C at 100.5 MHz, and 31P at 161.8 MHz) using tetra-
methylsilane (0.0 ppm) or residual CHCl3 (7.26 ppm) as internal
standards in 1H NMR, and CDCl3 (77.0 ppm) in 13C NMR.
Phosphoric acid was used as external standard (0.0 ppm) in 31P
NMR. Ether and THF were dried over Na-benzophenone prior
to use. Diisopropylamine was dried over CaH2 and distilled
immediately before use. Grignard reagents were made according
to standard procedures and titrated before use.18 All reactions
were run under a dry nitrogen atmosphere.
P r ep a r a tion of 1,3-Cycloh exa d ien -2-yl Dip h en yl P h os-
p h a te (1). Gen er a l P r oced u r e for P r ep a r a tion of Dien yl
P h osp h a tes.4b A solution of LDA (5.7 mmol) in THF (10 mL),
prepared from diisopropylamine (0.75 mL, 5.7 mmol) and
n-butyllithium (1.6M in hexane, 3.6 mL, 5.7 mmol) at 0 °C under
N2, was cooled to -78 °C by means of a dry ice/acetone bath.
2-Cyclohexenone (500 mg, 5.2 mmol) in THF (10 mL) was added
dropwise, and the reaction mixture was stirred for 30 min at
-78 °C. Diphenyl chlorophosphate (1.19 mL, 5.7 mmol) was
added in one portion, and the reaction mixture was allowed to
warm to 0 °C and stirred at this temperature until the reaction
was judged complete according to TLC. The solvent was evapo-
rated, the crude material was dissolved in ether, and the organic
phase was washed twice with water. The organic layer was dried
(MgSO4) and concentrated in vacuo. The crude product was
purified by column chromatography (pentane:Et2O 75:25) to
yield 1.61 g (94%) of 1 as a white solid. Spectral data were in
agreement with those previously reported.8
Spectral data for 2-butyl-1,3-cyclohexadiene (7),2 2-octyl-1,3-
cyclohexadiene (8),2 2-phenyl-1,3-cyclohexadiene (9),19 2-phenyl-
1,3-cycloheptadiene (11),2 5,5-diphenyl-2-methyl-1,3-cyclohexa-
diene (14),2 5,5-diphenyl-2-but-2-yl-1,3-cyclohexa-diene (16),2 and
(E)-2-methyl-6-phenyl-1,3-hexadiene (18a )13 were consistent
with data reported in the literature.
(3E)-5-Meth yl-1-p h en yl-3,5-octa d ien e (20a ) was isolated
as an inseparable mixture of Z- and E-isomers after column
chromatography (pentane). Stereochemistry was determined via
NOE experiments. 20a : 1H NMR δ 7.32-7.16 (m, 10H), 6.46
(dm, J ) 15.6 Hz, 1H, (Z)), 6.10 (d, J ) 15.6 Hz, 1H, (E)), 5.70
(dt, J ) 15.6, 6.7 Hz, 1H, (Z)), 5.60 (dt, J ) 15.6, 6.7 Hz, 1H,
(E)), 5.38 (t, J ) 7.5 Hz, 1H, (E)), 5.26 (t, J ) 7.5 Hz, 1H, (Z)),
2.71 (q, J ) 7.5 Hz, 4H), 2.43 (m, 4H), 2.13 (m, 4H), 1.78 (q, J )
1.2 Hz, 3H, (Z)), 1.71 (q, J ) 0.6 Hz, 3H, (E)), 0.98 (t, J ) 7.5
Hz, 3H), 0.97 (t, J ) 7.5 Hz, 3H).
1,3-Cycloh exa d ien -2-yl Dieth yl P h osp h a te (2). Yield: 56%
as a pale oil. Spectral data are consistent with those previously
reported.9
(3E)-1-P h en yl-3,5-octadien -5-yl Diph en yl P h osph ate (19).
Yield: 60% as a 55:45 mixture of Z- and E-isomers that were
separated by column chromatography (eluent pentane:Et2O 90:
(3E)-5-Bu tyl-1-p h en yl-3,5-octa d ien e (20b) was isolated as
an inseparable mixture of Z- and E-isomers after column
(18) (a) Watson, S. C.; Eastman, J . F. J . Organomet. Chem. 1967,
9, 165. (b) Bergbreiter, D. E.; Pendergrass, E. J . Org. Chem. 1981, 46,
219.
(19) Reich, H. J .; Wollowitz, S. J . Am. Chem. Soc. 1982, 104, 7051.
Becker, K. B. Synthesis 1980, 238.

Notes
J . Org. Chem., Vol. 64, No. 5, 1999 1749
chromatography (pentane). Stereochemistry was determined via
NOE experiments. (Z)-20b: 1H NMR δ 7.32-7.27 (m, 2H), 7.23-
7.17 (m, 3H). 6.34 (dq, J ) 15.8, 1.3 Hz, 1H) 5.72 (dt, J ) 15.8,
7.0 Hz, 1H), 5.25 (t, J ) 7.4 Hz, 1H), 2.74 (m, 2H), 2.45 (q, J )
7.6 Hz, 2H), 2.14 (quintet, J ) 7.2 Hz 4H), 1.45-1.25 (m, 4H),
0.97 (t, J ) 7.5 Hz, 3H), 0.91 (t, J ) 7.3 Hz, 3H); 13C NMR δ
142.0, 135.5, 130.2, 128.8, 128.5, 128.2, 126.6, 125.7, 36.2, 35.3,
33.8, 31.2, 22.7, 20.6, 14.5, 14.1. (E)-20b: 1H NMR δ 5.99 (m,
1H), 5.63 (m, 1H), 5.34 (t, J ) 7.4, 1H).
Research Council for Engineering Sciences is gratefully
acknowledged.
Su p p or tin g In for m a tion Ava ila ble: Characterization
data (1H, 13C NMR) for compounds 3-6, 10, 12, 13, 17, and
18b and copies of 1H and 13C NMR spectra of compounds 3-6,
10, 12, 13, 17, 18b, (E)-19, (Z)-19, 20a , 20b, and (Z)-20b. This
material is available free of charge via the Internet at
http://pubs.acs.org.
Ackn owledgm en t. Financial support from the Swed-
ish Natural Science Research Council and the Swedish
J O982060H