8406
J . Org. Chem. 1999, 64, 8406-8408
Sch em e 1
Con ven ien t P r ep a r a tion s of
(Dip h en ylp h osp h on o)a cetic Acid Ester s
a n d th e Com p a r ison of th e Z-Selectivities
of Th eir Hor n er -Wa d sw or th -Em m on s
Rea ction w ith Ald eh yd es Dep en d in g on th e
Ester Moiety
Kaori Ando*
Sch em e 2
College of Education, University of the Ryukyus,
Nishihara-cho, Okinawa, 903-0213
Received April 28, 1999
The Horner-Wadsworth-Emmons (HWE) reaction is
a widely used method for the preparation of R,â-unsatur-
ated esters.1 Since this reaction preferentially gives more
stable E-olefins in general,2 extensive effort has been
devoted to the stereoselective construction of Z-R,â-
unsaturated esters.3 Recently we have reported the
preparation of ethyl (diarylphosphono)acetates (1) and
the HWE reaction of 1 with several kinds of aldehydes
to give Z-unsaturated esters with high selectivity (Scheme
1).4 Our method provides a simple, economical, and
highly selective route to a wide range of Z-unsaturated
esters in almost quantitative yields. Since our reagents
1 are useful in synthesis,5,6 we saw the need to improve
the preparation procedure. Originally we prepared 1 from
triethyl phosphonoacetate, PCl5, and the corresponding
phenol via ethyl (dichlorophosphono)acetate. Since we
could not isolate those reagents by distillation and there
were some byproducts with Rf values similar to the
reagents, this method required a tedious and careful
column chromatography purification. Now we report two
new and convenient preparations of ethyl (diphenylphos-
phono)acetate. These procedures also gave us an op-
portunity to make other (diphenylphosphono)acetic acid
esters. Two decades ago Kishi showed that the ratio of
E- and Z-esters in the HWE reaction is in proportion to
the bulkiness of phosphonate reagents.7 A phosphonate
reagent with a larger phosphonate or a larger ester group
gave higher E-selectivity. To our surprise, the comparison
of the HWE reaction of (diphenylphosphono)acetic acid
Ta ble 1. Acyla tion of Dip h en yl Meth ylp h osp h on a te 2
entry
ClCO2R
ClCO2Me
ClCO2Me
ClCO2Et
ClCO2iPr
ClCO2CH2CHdCH2
base
LDA
LiHMDS
LiHMDS
LiHMDS
LiHMDS
product, % yield
1
2
3
4
5
3b, 76
3b, 87
3a , 89
3c, 71
3d , 87
Ta ble 2. Rea ction of Dip h en yl P h osp h ite w ith Alk yl
Br om oa ceta te
entry
BrCH2CO2R
conditions
% yield
1
2
3
4
5
6
7
BrCH2CO2Et
BrCH2CO2Et
BrCH2CO2Et
BrCH2CO2Et
BrCH2CO2Et
BrCH2CO2Et
benzene, Et3N, 2 h
benzene, pyridine, 2 d
DMSO, NaH, 2 h
CH3CN, Et3N, 2 h
CH2Cl2, i-Pr2EtN, 40 °C, 4 h 47
19
trace
trace
29
CH2Cl2, Et3N, 1 h
53
77
BrCH2CO2t-Bu CH2Cl2, Et3N, 1 h
esters showed that a phosphonate reagent with a bulkier
ester moiety gave higher Z-selectivity.
Resu lts
Im p r oved P r ep a r a tion s of (Dip h en ylp h osp h on o)-
a cetic Acid Ester s. In the first preparation procedure,
(diphenylphosphono)acetic acid esters (3) were prepared
by acylation of diphenyl methylphosphonate (2), which
was prepared from triphenyl phosphite and methyl iodide
in a quantitative yield (Scheme 2).8 Unlike the anions
derived from dialkyl methylphosphonate,9,10 the anion
from 2 is unstable even at -78 °C. When 2 was treated
with lithium diisopropylamide (LDA) at -78 °C, followed
by methyl chloroformate, only a trace of product was
obtained, and decomposition of 2 was the main reaction.
Treatment of 2 with base in the presence of acylating
reagent circumvented this difficulty. Also, it is essential
* E-mail: ando@edu.u-ryukyu.ac.jp
(1) Reviews of Horner-Wadsworth-Emmons reaction: Maryanoff,
B. E.; Reitz, A. B.; Chem. Rev. 1989, 89, 863-927; Boutagy, J .; Thomas,
R. Chem. Rev. 1974, 74, 87-99. For asymmetric versions of the HWE
reaction, see: Rein, T.; Reiser, O. Acta Chem. Scand. 1996, 50, 369-
379.
(2) For mechanistic studies of HWE reaction: Ando, K. J . Org.
Chem. 1999, 64, 6815-6821 and references therein.
(3) Breuer, E.; Bannet, D. M. Tetrahedron Lett. 1977, 1141-1144;
Still, W. C.; Gennari, C. Tetrahedron Lett. 1983, 24, 4405-4408; Patois,
C.; Savignac, P. Tetrahedron Lett. 1991, 32, 1317-1320; Kokin, K.;
Motoyoshiya, J .; Hayashi, S.; Aoyama, H. Synth. Commun. 1997, 27,
2387-2392.
(4) (a) Ando, K. Tetrahedron Lett. 1995, 36, 4105-4108. (b) Ando,
K. J . Org. Chem. 1997, 62, 1934-1939. (c) Ando, K. J . Org. Chem.
1998, 63, 8411-8416.
(5) Ishii, K.; Ohno, H.; Takemoto, Y.; Ibuka, T. Synlett 1999, 228-
230.
(8) Landauer, S. R.; Rydon, H. N. J . Chem. Soc. 1953, 2224-2234.
(9) Mikolajczyk, M.; Mikina, M. J . Org. Chem. 1994, 59, 6760-6765.
Geirsson, J . K. F.; Njardarson, J . T. Tetrahedron Lett. 1994, 35, 9071-
9072. Gil, J . M.; Hah, J . H.; Park, K. Y.; Oh, D. Y. Tetrahedron Lett.
1998, 39, 3205-3208.
(10) The anion derived from bis(trifluoroethyl) alkylphosphonate is
also not stable even at low temperature: Patois, C.; Savignac, P. Synth.
Commun. 1991, 21, 2391-2396.
(6) Abiko, A.; Masamune, S. Tetrahedron Lett. 1996, 37, 1077-1080.
Kreuder, R.; Rein, T.; Reiser, O. Tetrahedron Lett. 1997, 38, 9035-
9038. Zhang, T. Y.; O’Toole J . C.; Dunigan, J . M. Tetrahedron Lett.
1998, 39, 1461-1464.
(7) Nagaoka, H.; Kishi, Y. Tetrahedron 1981, 37, 3873-3888.
Schmid, G.; Fukuyama, T.; Akasaka, K.; Kishi, Y. J . Am. Chem. Soc.
1979, 101, 259-260.
10.1021/jo9907181 CCC: $18.00 © 1999 American Chemical Society
Published on Web 10/07/1999