Phosphonate modification for a highly (Z)-selective synthesis of unsaturated esters by Horner-Wadsworth-Emmons olefination

Article abstract of DOI:10.1002/ejoc.200400769

The Horner-Wadsworth-Emmons (HWE) reaction of various ethyl diarylphosphonoacetates with benzaldehyde, cyclohexane carboxaldehyde and octanal is reported. Selectivities of up to 98% at -78°C are obtained with the three substrates. Among all the phosphonates prepared, the reagent based on 2-tert-butylphenol proved to be especially efficient, with Z/E ratios close to 95:5 at 0°C. It appears thus to be the reagent of choice for the (Z)-selective HWE reaction with both aromatic and aliphatic aldehydes. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005.

Full text of DOI:10.1002/ejoc.200400769

FULL PAPER
Phosphonate Modification for a Highly (Z)-Selective Synthesis of Unsaturated
Esters by Horner–Wadsworth–Emmons Olefination
François P. Touchard*[a]
Keywords: Alkenes / Olefination / Wittig reaction
The Horner–Wadsworth–Emmons (HWE) reaction of various
ethyl diarylphosphonoacetates with benzaldehyde, cyclohex-
ane carboxaldehyde and octanal is reported. Selectivities of
up to 98% at –78 °C are obtained with the three substrates.
Among all the phosphonates prepared, the reagent based on
2-tert-butylphenol proved to be especially efficient, with Z/E
ratios close to 95:5 at 0 °C. It appears thus to be the reagent
of choice for the (Z)-selective HWE reaction with both aro-
matic and aliphatic aldehydes.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2005)
Introduction
The Horner–Wadsworth–Emmons (HWE) reaction is a
variant of the Wittig reaction that possesses a number of
significant advantages: not only is the work-up greatly facil-
itated since the phosphate salt formed is water soluble, but
the reactivity of HWE reagents allows them to effect trans-
Figure 1. Phosphonates developed by Still and Ando.
formations that are either difficult or impossible using the Results and Discussion
analogous Wittig ylides. This reaction, which usually pro-
With the objective of reaching selectivities of over 90%
ceeds smoothly and under mild conditions with phos-
phonates bearing stabilising substituents, typically leads to
the more stable (E)-disubstituted olefins.[1] As it is highly
desirable to be able to prepare the (E)- or (Z)-isomer at will,
Still,[2] in 1983, and Ando,[3,4] in 1995, developed two (Z)-
selective reagents, namely methyl bis(trifluoroethyl)phos-
phonoacetate (1) and ethyl diphenylphosphonoacetate (2),
respectively (Figure 1).[5] However, the conditions required
to obtain high Z/E ratios were fairly stringent and usually
implied working at low temperatures.[6] The aim of this
study was to establish an efficient and scalable protocol for
the (Z)-selective olefination of aldehydes and to reinvestig-
ate and modulate the Still/Ando procedures. By using Still’s
reagent, it has already been shown that it is possible to work
at 0 °C in the presence of K2CO3 and 10 mol-% 18-C-6 with
selectivities of up to 98%.[7] However, these conditions are
effective essentially only with aromatic aldehydes. This arti-
cle reports on how to achieve high product selectivities un-
der mild reaction conditions with phosphonates based upon
phenols and both aromatic and aliphatic aldehydes.
at 0 °C with a broad range of aldehydes, we decided to take
advantage of the large availability of phenols to prepare a
series of phosphonates bearing ortho electron-withdrawing,
electron-donating and sterically bulky groups. They were
synthesized by an Arbusov reaction of ethyl bromoacetate
with mixed phosphites P(OEt)(OAr)2 obtained from ethyl
dichlorophosphite (Figure 2).
The yields and purities of the phosphites and phos-
phonates thus prepared are collected in Table 1.
The crude phosphites were generally of good purity
(close to 90% by 31P NMR spectroscopy) but simple fil-
tration through a pad of basic alumina enabled this to be
increased further to 98% by the removal of acidic impuri-
ties [excess phenol and HP(O)(OR)(ORЈ)].[8] The phos-
phonates obtained after the Arbusov reaction with ethyl
bromoacetate were pure enough to be used without any fur-
ther treatment.
All the structures were then tested in the HWE reaction
with benzaldehyde, cyclohexane carboxaldehyde and n-oc-
tanal as representatives of aromatic and aliphatic aldehydes.
The initial experiments were carried out in THF as the sol-
vent and NaI/TMG (tetramethyl guanidine) as the basic
system (Figure 3).[9]
[a] Rhodia Recherches, Centre de Recherches de Lyon,
85, rue des frères Perret, BP 62, 69192 Saint-Fons Cedex,
France
The selectivities [S = Z/(Z + E)×100] and 5 h aldehyde
conversions [Conv. (%)] both at –78 °C and 0 °C are given
Fax: +33-4-7289-6894
E-mail: francois.touchard@eu.rhodia.com
1790
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/ejoc.200400769
Eur. J. Org. Chem. 2005, 1790–1794

A Highly (Z)-Selective Synthesis of Unsaturated Esters
FULL PAPER
Figure 2. Synthesis of phosphonates 2–10.
Table 1. Phosphite and phosphonate yields and purities.[a]
Entry
Phenol
Phosphite
Purity [mol-%]
Phosphonate
Yield [%] (time)
Yield [%]
Purity [mol-%]
1
2
3
4
5
6
7
8
9
Y = H
85
79
87
86
92
89
92
94
80
98
98
90
98
98
98
98
98
98
2
3
75 (24 h)
91 (24 h)
84 (6 h)
98
98
90
98
98
98
98
98
98
Y = CO2Me
Y = CH(OCH2)2
Y = OMe
Y = Ph
Binol
Y = Me
4
5
92 (1 h)
6
92 (24 h)
82 (24 h)
93 (24 h)
91 (30 h)
88 (30 h)
7
8
Y = tBu
2,4-di-tBu-phenol
9
10
[a] See the Experimental Section for further details.
structures led to selectivities close to 90% at –78 °C, except
Y = Me, which was less selective. Concerning the reaction
kinetics, conversions of over 85% were always obtained at
0 °C after 5 h. At this temperature, only the phosphonates
with OMe and ketal substituents gave close to 90% (Z)-
selectivity.
Table 2. Reaction of phosphonates with benzaldehyde under NaI/
TMG conditions.[a]
Entry
Phenol
T = –78 °C
T = 0 °C
S
Conv.
S
Conv.
Figure 3. Initial HWE experiments.
1
2
3
4
5
6
7
8
9
Y = OMe
Y = CO2Me
Y = Ph
Y = tBu
Y = ketal
Y = H
Binol
Y = Me
2,4-di-tBu-phenol
98
98
95
95
92
89
89
82
–
75
50
98
75
70
98
90
100
–
89
–
97
–
83
82
89
78
77
69
81
98
100
85
92
85
100
95
below. The phosphonates have been ranked by selectivities
observed first at –78 °C and then at 0 °C.
Reaction with Benzaldehyde
We were pleased to obtain selectivities of over 95% with
Y = OMe, CO2Me, Ph and tBu at –78 °C (Table 2). This
indicates that the reaction is not very sensitive to electronic
effects. We were even quite surprised to obtain close to 98%
(Z)-selectivity with guaiacol, as Ando has reported only
moderate Z/E ratios with the same phosphonate using Tri-
ton B as the base.[4a] We will see hereafter that there is a
[a] See the Experimental Section for further details; S: selecticity.
Reaction with Cyclohexane Carboxaldehyde
Selectivities close to 90% and even higher were obtained
noticeable salt effect with this structure. With Y = CO2Me, with all the phosphonates at –78 °C (Table 3). 2-tert-Bu-
low conversions were always obtained. In fact, we observed tylphenol led to the best result with a 98:2 Z/E ratio. The
the release of large amounts of methyl salicylate in the reac- phosphonates based upon 2-Ph, 2-Me, 2-CO2Me phenols
tion mixture, which indicates the instability of the phos- and binol were less selective, with ratios close to 95:5. As
phonate or its anion in the reaction conditions. The other already mentioned, Y = CO2Me gave low conversion. With
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F. P. Touchard
FULL PAPER
both tBu and ketal substituents, the reaction was slow at Table 5. NaI effect with the phosphonate based on guaiacol 5 and
TMG as the base.[a]
–78 °C, and increasing the temperature to 0 °C caused a
marked enhancement of the conversions. The most remark-
able results were obtained with 2-tBu and 2,4-di-tBu-phe-
nols with 95% Z-selectivity at 0 °C. The corresponding
phosphonates are thus as selective at 0 °C as the others at
–78 °C (!).
Entry
Aldehyde
NaI [equiv.]
Temp. [°C]
S
1
2
3
4
5
6
7
8
PhCHO
PhCHO
PhCHO
CyCHO
CyCHO
CyCHO
CyCHO
n-octanal
n-octanal
n-octanal
n-octanal
1.3
2.2
5
1.3
2.2
5
0
0
0
89
93
93
93
97
98
92
92
96
96
90
–78
–78
–78
0
–78
–78
–78
0
Table 3. Reaction of phosphonates with cyclohexane carboxal-
dehyde under NaI/TMG conditions.[a]
5
1.3
2.2
5
9
10
11
Entry
Phenol
T = –78 °C
T = 0 °C
S
Conv.
S
Conv.
5
1
2
3
4
5
6
7
8
9
Y = tBu
Y = Ph
Y = Me
Binol
Y = CO2Me
Y = OMe
Y = ketal
Y = H
98
95
95
95
95
93
91
90
–
70
94
98
75
40
90
50
95
–
95
91
89
86
–
100
97
100
86
–
[a] See the Experimental Section for further details.
As the reaction with benzaldehyde was highly selective
at –78 °C, the additive effect was studied at 0 °C. We ob-
served an increase from 89% to 93% (Z)-selectivity on go-
ing from 1.3 to 2.2 equivalents of NaI. Adding more NaI
had no noticeable effect. With cyclohexane carboxaldehyde,
the selectivity increased from 93 to 97–98% on going from
1.3 to 2–5 equivalents at –78 °C, and working with five
equivalents at 0 °C led to a 92:8 Z/E ratio. Finally, the same
increase was also observed with octanal: from 92 to 96%
at –78 °C and 90% (Z)-selectivity at 0 °C with five equiva-
lents of NaI.
–
–
85
87
94
81
95
93
2,4-di-tBu-phenol
[a] See the Experimental Section for further details.
Reaction with n-Octanal
As this effect was much less pronounced and even not
observed with most of the other structures, we think it is
directly due to the methoxy group in the ortho position.
However, these observations, although interesting from the
selectivity point of view, do not really lead to any simplifi-
cation of the protocol.
As Ando has already shown that the phosphonate based
upon o-cresol is the reagent of choice both with aliphatic
aldehydes using NaH and aromatic aldehydes using Triton
B as bases, we then tested 9 with other basic systems to
evaluate the cation influence. The first experiments were
carried out with sodium hexamethyldisilazide (NaHMDS)
and KHMDS in THF (Table 6). These results show that the
selectivity is not sensitive to the strength of the base, as
NaHMDS and NaI/TMG led to the same Z/E ratios (en-
tries 2 and 3, 6 and 7, and 10 and 11). The selectivity is
We observed similar tendencies here to the reaction with
cyclohexane carboxaldehyde. Z/E ratios of over 90:10 were
obtained at –78 °C (Table 4). 2-tBu-phenol led again to the
best result, with a selectivity of 98%. The phosphonates
based on 2-Ph and 2-CO2Me phenols were then close to
95% (Z)-selective, with low conversion for the latter. Here
again, 2-tBu and 2,4-di-tBu substituents proved to be also
efficient at 0 °C, with a 92:8 Z/E ratio.
Table 4. Reaction of phosphonates with n-octanal under NaI/TMG
conditions.[a]
Entry
Phenol
T = –78 °C
T = 0 °C
S
Conv.
S
Conv.
1
2
3
4
5
6
7
8
9
Y = tBu
Y = Ph
Y = CO2Me
Y = Me
Y = ketal
Y = OMe
Y = H
98
96
95
93
92
92
91
90
–
94
89
65
100
80
95
98
88
–
92
89
–
85
85
–
83
79
91
100
98
–
100
88
–
100
90
95
Table 6. Cation effect with the phosphonate based on 2-tert-bu-
tylphenol (9).[a]
Entry
Aldehyde
Conditions
S
Conv.
Binol
2,4-di-tBu-phenol
1
2
3
4
5
6
7
8
PhCHO
PhCHO
PhCHO
PhCHO
CyCHO
CyCHO
CyCHO
CyCHO
octanal
octanal
octanal
octanal
NaI-TMG/–78 °C/17 h
NaI-TMG/0 °C/1 h
NaHMDS/0 °C/1 h
KHMDS/0 °C/1 h
NaI-TMG/–78 °C/17 h
NaI-TMG/0 °C/1 h
NaHMDS/0 °C/1 h
KHMDS/0 °C/1 h
NaI-TMG/–78 °C/17 h
NaI-TMG/0 °C/1 h
NaHMDS/0 °C/1 h
KHMDS/0 °C/1 h
95
81
81
93
98
95
95
94
98
92
93
93
100
100
100
100
100
100
97
[a] See the Experimental Section for further details.
From these preliminary results, the phosphonates based
on guaiacol (5) and 2-tert-butylphenol (9) seem to be candi-
dates of choice for benzaldehyde and cyclohexane carboxal-
dehyde/octanal, respectively. However, intrigued by the
good results obtained with 5, we decided to look at the
effect of NaI. As described by Pihko et al.,[10] we also ob-
served that adding an excess of sodium ions caused an in-
crease in the selectivities (Table 5).
97
9
100
100
99
10
11
12
98
[a] See the Experimental Section for further details.
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© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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A Highly (Z)-Selective Synthesis of Unsaturated Esters
FULL PAPER
excess ethyl bromoacetate under reduced pressure and the phos-
phonate thus obtained was used without further purification.
Phosphonate 3: Pale-yellow oil. Yield: 73% (from PCl2OEt). 1H
rather influenced by the cation: with benzaldehyde, it in-
creased from 81 to 93% on going from Na+ to K+ at 0 °C.
With the other aldehydes Na+ and K+ gave similar selectivi-
ties. This difference can be explained by the fact that the NMR (CDCl3): δ = 1.06 (t, J = 7.4 Hz, 3 H), 3.47 (d, J = 22.2 Hz,
2 H), 3.79 (s, 6 H), 4.04 (q, J = 7.4 Hz, 2 H), 7.17 (tt, J = 7.7, J =
1.3 Hz, 2 H), 7.26 (dt, J = 8.5, J = 1.3 Hz, 2 H), 7.36 (td, J = 8.5,
J = 1.6 Hz, 2 H), 7.81 (broad d, J = 7.7 Hz, 2 H) ppm. 31P NMR
(CDCl3): δ = 14.1 ppm. C20H21O9P (436.4): calcd. C 55.05, H 4.85,
P 7.10; found C 55.37, H 4.92, P 6.83.
reaction is more prone to reversibility with benzaldehyde
due to the phenyl group being electron withdrawing. The
potassium cation causes an increase in the rate of the elimi-
nation step and thus helps to maintain a high level of (Z)-
stereoselection.
Phosphonate 4: Pale-yellow oil. 2-(1,3-Dioxolan-2-yl)phenol was
prepared according to an already described procedure.[11] Yield:
1
73% (from PCl2OEt). H NMR (CDCl3): δ = 1.15 (t, J = 7.15 Hz,
Conclusions
3 H), 3.33 (d, J = 21.7 Hz, 2 H), 3.93–4.02 (m, 8 H), 4.10 (q, J =
This study clearly indicates that the phosphonate based 7.15 Hz, 2 H), 6.05 (s, 2 H), 7.13 (broad t, J = 7.7 Hz, 2 H), 7.24
(td, J = 7.4, J = 1.6 Hz, 2 H), 7.34 (dt, J = 8.2, J = 1.3 Hz, 2 H),
7.51 (dt, J = 7.7, J = 1.3 Hz, 2 H). 31P NMR (CDCl3): δ =
13.7 ppm. C22H25O9P (464.4): calcd. C 56.90, H 5.43, P 6.67; found
C 56.50, H 5.50, P 6.50.
upon 2-tert-butylphenol is a reagent of choice for the (Z)-
selective HWE reaction both with aromatic and aliphatic
aldehydes. Z/E ratios close to 95:5 have indeed been ob-
tained with the two kinds of substrate at 0 °C. Further de-
velopment in order to design a scalable process will be re-
ported in due course.
Phosphonate 6: Colourless oil. Yield: 85% (from PCl2OEt). 1H
NMR (CDCl3): δ = 1.00 (t, J = 7.15 Hz, 3 H), 2.41 (d, J = 21.7 Hz,
2 H), 3.89 (q, J = 7.15 Hz, 2 H), 7.18–7.27 (m, 18 H). 13C NMR
(CDCl3): δ = 13.8 (s, CH3), 34.1 (d, J = 138.6 Hz, PCH2), 61.6 (s,
CH2), 121.3 (d, J = 2.7 Hz, 2 CHarom), 125.5 (d, J = 1.0 Hz, 2
CHarom), 127.3 (s, 2 CHarom), 128.1 (s, 4 CHarom), 128.6 (d, J =
1.3 Hz, 2 CHarom), 129.3 (s, 4 CHarom), 131.1 (s, 2 CHarom), 133.6
(d, J = 5.9 Hz, 2 Carom), 137.1 (s, 2 Carom), 147.1 (d, J = 8.9 Hz, 2
Carom), 164.2 (d, J = 6.2 Hz, C=O) ppm. 31P NMR (CDCl3): δ =
12.7 ppm. C28H25O5P (472.5): calcd. C 71.18, H 5.33, P 6.56; found
C 71.23, H 5.59, P 6.58.
Experimental Section
General Remarks: NMR spectra were recorded from CDCl3 solu-
tions at 300 K with a Bruker AMX 300 (300 MHz) spectrometer.
The GC analyses were performed with a Varian 3400Cx apparatus
equipped with a SGE BPX5 (764) 25 m×0.53 mm×1 μm column
and FID detector. He was used as the vector gas (5 mLmin–1) and
N2 as make-up (25 mLmin–1). Program: 80 °C (4 min) Ǟ 170 °C
(rate: 7 °Cmin–1) Ǟ 300 °C (4 min; rate: 30 °Cmin–1). The reten-
tion times of the analyzed compounds under these conditions are
given in Table 7.
Phosphonate 9: White solid. Yield: 85% (from PCl2OEt). M.p.:
1
90 °C. H NMR (CDCl3): δ = 1.08 (t, J = 7.15 Hz, 3 H), 1.30 (s,
18 H), 3.29 (d, J = 21.7 Hz, 2 H), 4.05 (q, J = 7.15 Hz, 2 H), 7.02–
7.07 (m, 4 H), 7.29 (dt, J = 7.7, J = 1.6 Hz, 2 H), 7.61 (dt, J = 7.9,
J = 1.1 Hz, 2 H). 31P NMR (CDCl3): δ = 10.4 ppm. C24H33O5P
(432.5): calcd. C 66.65, H 7.69, P 7.16; found C 66.40, H 7.80, P
7.10
Table 7. Retention times of the analyzed compounds.
Compound
tR [min]
PhCHO
CyCHO
Octanal
5.1
4.4
5.7
14.1
15.6
12.6
14.4
13.9
15.0
Phosphonate 10: Colourless oil. Yield: 70% (from PCl2OEt). 1H
NMR (CDCl3): δ = 1.07 (t, J = 7.15 Hz, 3 H), 1.22 (s, 18 H), 1.32
(s, 18 H), 3.26 (d, J = 21.4 Hz, 2 H), 4.04 (q, J = 7.15 Hz, 2 H),
7.07 (dd, J = 8.8, J = 2.4 Hz, 2 H), 7.30 (t, J = 2.2 Hz, 2 H), 7.49
(dd, J = 8.5, J = 1.1 Hz, 2 H). 31P NMR (CDCl3): δ = 10.3 ppm.
C32H49O5P (544.7): calcd. C 70.56, H 9.07, P 5.69; found C 70.20,
H 9.10, P 5.80.
Ph-CH=CH-CO2Et [(Z)-isomer]
Ph-CH=CH-CO2Et [(E)-isomer]
Cy-CH=CH-CO2Et [(Z)-isomer]
Cy-CH=CH-CO2Et [(E)-isomer]
n-C7H15-CH=CH-CO2Et [(Z)-isomer]
n-C7H15-CH=CH-CO2Et [(E)-isomer]
HWE Reaction With NaI/TMG. General Procedure: The appropri-
ate phosphonoacetate (0.50 mmol, 1.1 equiv.) and NaI (89 mg,
0.59 mmol, 1.3 equiv.) were dissolved in anhydrous THF (10 mL).
The mixture was then cooled to 0 °C and TMG (70 μL, 0.55 mmol,
1.2 equiv.) was added. The mixture was further stirred for 30 min
before the aldehyde addition (0.45 mmol, 1 equiv.). For reaction
at –78 °C, the mixture was first cooled to –78 °C and stirred for
30 min before the aldehyde addition (0.45 mmol, 1 equiv.). The re-
action was then monitored by gas chromatography for the selectiv-
ity and conversion determination after quenching aliquots with sat-
urated ammonium chloride and extracting the mixture with tolu-
ene.
Authentic samples were either commercially available (ethyl trans-
cinnamate and ethyl trans-2-decenoate) or were prepared according
to well known procedures.[4a]
Synthesis of Phosphonates 2–10. General Procedure: The appropri-
ate substituted phenol (0.130 mol, 1.95 equiv.) and triethylamine
(14 g, 0.137 mol, 2.05 equiv.) were mixed in toluene (100 mL) and
cooled to 0 °C. Ethyldichlorophosphite (10 g, 0.067 mol, 1 equiv.)
in diethyl ether (40 mL) was then added slowly in order to maintain
the temperature below 5 °C. After 30 min at 0 °C, the mixture was
left to warm to room temperature. Three hours later the salts were
filtered and washed twice with toluene (2×50 mL). The organic
phase was then passed through a pad of basic alumina and the
solvent was removed under reduced pressure. This phosphite
(48.0 mmol, 1 equiv.) was added over 1 h to ethyl bromoacetate
(12.3 g, 72.4 mmol, 1.51 equiv.) at 120 °C. After reaction comple-
tion (31P NMR monitoring), the mixture was heated to remove
HWE Reaction With Na/KHMDS. General Procedure: Phos-
phonate 9 (216 mg, 0.5 mmol, 1.1 equiv.) was first dissolved in an-
hydrous THF (10 mL). The mixture was then cooled to 0 °C and
a
solution of NaHMDS (1 m solution in THF, 0.47 mmol,
1.05 equiv.) or KHMDS (0.5 m solution in toluene, 0.47 mmol,
1.05 equiv.) was added. The mixture was stirred for a further
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F. P. Touchard
FULL PAPER
[5] For recent reviews, see: a) K. Ando, Yuki Gosei Kagaku Kyokai-
shi 2000, 58, 869–876; b) J. Motoyoshiya, Trends Org. Chem.
1998, 7, 63–73.
[6] The phosphonate based on 2,4-difluorophenol described by
Motoyoshiya et al. (ref. 4e–4f) was the only one reported to
date leading to selectivities over 92% at 0 °C with various alde-
hydes.
10 min before the aldehyde addition (0.45 mmol, 1 equiv.). The re-
action was then monitored by gas chromatography for the selectiv-
ity and conversion determination after quenching aliquots with sat-
urated ammonium chloride and extracting the mixture with tolu-
ene.
[7] F. P. Touchard, Tetrahedron Lett. 2004, 45, 5519–5523.
[8] This purification could not be performed with the ketal as the
phosphite remained adsorbed on alumina.
[9] Ando has shown that NaI/DBU is an effective combination,
especially with aliphatic aldehydes. In a preliminary screening,
we have seen that TMG and DBU lead to the same results and
that NaI/TMG also gives promising selectivities with benzalde-
hyde.
[1]
[2]
For a general review concerning the Wittig olefination reaction
and modifications see: B. E. Maryanoff, A. B. Reitz, Chem.
Rev. 1989, 89, 863–927.
W. C. Still, C. Gennari, Tetrahedron Lett. 1983, 24, 4405–4408.
[3] K. Ando, Tetrahedron Lett. 1995, 36, 4105–4108.
[4] Since the first publication of Ando (ref. 3) many phosphonate
modifications have been reported a) K. Ando, J. Org. Chem.
1997, 62, 1934–1939; b) K. Ando, J. Org. Chem. 1998, 63, [10] During this work, an article entitled “Excess sodium ions im-
8411–8416; c) K. Ando, J. Org. Chem. 1999, 64, 8406–8408; d)
K. Ando, T. Oishi, M. Hirama, H. Ohno, T. Ibuka, J. Org.
Chem. 2000, 65, 4745–4749; e) K. Kokin, J. Motoyoshiya, S.
Hayashi, H. Aoyama, Synth. Commun. 1997, 27, 2387–2392; f)
K. Kokin, K. Iitake, Y. Takaguchi, H. Aoyama, S. Hayashi, J.
Motoyoshiya, Phosphorus, Sulfur Silicon 1998, 133, 21–40.
prove (Z)-selectivity in Horner–Wadsworth–Emmons ole-
finations with the Ando phosphonate” was published: P. M.
Pihko, T. M. Salo, Tetrahedron Lett. 2003, 44, 4361–4364.
[11] B. E. Pape, M. F. Para, M. J. Zabik, J. Agric. Food Chem. 1970,
18, 490–493.
Received: October 27, 2004
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