Stereoselective conversion of stabilized phosphorus ylides to dialkyl 2-(2-nitro-phenoxy)-2-butenedioates in the presense of silica gel in solvent-free conditions

Article abstract of DOI:10.1080/10426500600864346

Protonation of the highly reactive 1:1 intermediates, produced in the reaction between triphenylphosphine and dialkyl acetylenedicarboxylates, by 2-nitrophenol leads to vinyltriphenylphosphonium salts, which undergo a Michael addition reaction with a conjugate base to produce dialkyl 2-(2-nitro-phenoxy)- 3-(triphenylphosphoranylidene)butanedioates. Silica-gel powder was found to catalyze the stereoselective conversion of dialkyl 2-(2-nitro-phenoxy)-3- (triphenylphosphoranylidene)butanedioates to dialkyl 2-(2-nitro-phenoxy)-2- butenedioates in solvent-free conditions under microwave (0.5 KW, 3 min) and thermal (90°C, 60 min) conditions. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/10426500600864346

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Stereoselective Conversion of
Stabilized Phosphorus Ylides to
Dialkyl 2-(2-Nitro-phenoxy)-2-
butenedioates in the Presense
of Silica Gel in Solvent-Free
Conditions
Ali Ramazani a & Mahshid Rahimifard a
a Chemistry Department , Zanjan University ,
Zanjan, Iran
Published online: 01 Feb 2007.
To cite this article: Ali Ramazani & Mahshid Rahimifard (2006) Stereoselective
Conversion of Stabilized Phosphorus Ylides to Dialkyl 2-(2-Nitro-phenoxy)-2-
butenedioates in the Presense of Silica Gel in Solvent-Free Conditions,
Phosphorus, Sulfur, and Silicon and the Related Elements, 181:11, 2675-2678, DOI:
10.1080/10426500600864346
To link to this article: http://dx.doi.org/10.1080/10426500600864346
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Phosphorus, Sulfur, and Silicon, 181:2675–2678, 2006
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500600864346
Stereoselective Conversion of Stabilized Phosphorus
Ylides to Dialkyl 2-(2-Nitro-phenoxy)-2-butenedioates
in the Presense of Silica Gel in Solvent-Free Conditions
Ali Ramazani
Mahshid Rahimifard
Chemistry Department, Zanjan University, Zanjan, Iran
Protonation of the highly reactive 1:1 intermediates, produced in the re-
action between triphenylphosphine and dialkyl acetylenedicarboxylates, by
2-nitrophenol leads to vinyltriphenylphosphonium salts, which undergo
a
Michael addition reaction with a conjugate base to produce dialkyl 2-(2-nitro-
phenoxy)-3-(triphenylphosphoranylidene)butanedioates. Silica-gel powder was
found to catalyze the stereoselective conversion of dialkyl 2-(2-nitro-phenoxy)-
3-(triphenylphosphoranylidene)butanedioates to dialkyl 2-(2-nitro-phenoxy)-2-
butenedioates in solvent-free conditions under microwave (0.5 KW, 3 min) and ther-
mal (90◦C, 60 min) conditions.
Keywords 2-nitrophenol; acetylenic esters; Michael addition; microwave irradiation;
silica gel; vinyltriphenylphosphonium salt
INTRODUCTION
Organophosphorus compounds have been extensively used in organic
synthesis.1,2 β-additions of nucleophiles to the vinyl group of vinylic
phosphonium salts leading to the formation of new alkylidenephos-
phoranes has attracted much attention as a very convenient and
synthetically useful method in organic synthesis.1−3 Silica gel as an
additive promotes the Wittig reactions of phosphorus ylides with
aldehydes, including sterically hindered aldehydes to increase the rate
and yields of alkenes.4,5 In the past we have established a convenient,
one-pot method for preparing stabilized phosphorus ylides utilizing in
situ generation of the phosphonium salts.1,3 In this article, we report
Received April 6, 2006; accepted June 6, 2006.
This work was supported by the Sandoogh Hemayate as Pajuoheshgharane Keshvare
Iran via research project number N 84114.
Address correspondence to Ali Ramazani, Zanjan University, Chemistry Department,
PO Box 45195-313, Zanjan, Iran. E-mail: aliramazani@gmail.com
2675

2676
A. Ramazani and M. Rahimifard
on the catalytic role of silica-gel powder in the stereoselective conver-
sion of dialkyl 2-(2-nitro-phenoxy)-3-(triphenylphosphoranylidene)-
butanedioates to dialkyl 2-(2-nitro-phenoxy)-2-butenedioates in
solvent-free conditions under microwave (0.5 KW, 3 min) and thermal
(90◦C, 60 min) conditions Scheme 1.
SCHEME 1
RESULTS AND DISCUSSION
The ylide (5) may result from an initial addition of triphenylphos-
phine 1 to the acetylenic ester 2 and concomitant protonation of
the 1:1 adduct by 2-nitrophenol, which leads to vinyltriphenylphos-
phonium salts 4, which undergo a Michael addition reaction with a
conjugate base to produce dialkyl 2-(2-nitro-phenoxy)-3-(triphenylpho-
sphoranylidene)butanedioates (5). TLC indicated the formation of
ylides 5 in CH2Cl2. Silica-gel powder was found to catalyze the stere-
oselective conversion of dialkyl 2-(2-nitro-phenoxy)-3-(triphenylphos-
phoranylidene)butanedioates (5) to dialkyl 2-(2-nitro-phenoxy)-2-
butenedioates (6) in solvent-free conditions under microwave (0.5 KW,
3 min) and thermal (90◦C, 60 min) conditions. We have also used MgO,
NaH2PO4, Na2HPO4, Na3PO4, KH2PO4, K2HPO4, K3PO4, and K2CO3

Conversion of Stabilized Phosphorus Ylides
2677
in this reaction, but no product was observed, and in all cases, decom-
position was observed. In the absence of silica-gel powder, the pow-
dered ylide 5 was not reacted under microwave irradiation at microwave
power 0.5 KW after 3 min. or under thermal (90◦C, 60 min) conditions,
and decomposition of the starting materials were observed.
CONCLUSION
In conclusion, we have found that silica gel powder is able to catalyze
the stereoselective conversion of ylides 5 to compounds 67 in solvent-
free conditions6 (Scheme 1). Other aspects of this process are under
investigation.
EXPERIMENTAL
Commerical-oven Butane M245 was used for microwave irradiation.
1
IR spectra were recorded on a Shimadzu IR-460 spectrometer. H and
13C NMR spectra were measured with a BRUKER DRX-500 AVANCE
spectrometer at 500 and 125 MHz, respectively.
The General Procedure for the Preparation of Ylides 5
and Compounds 6a–b
To a magnetically stirred solution of triphenylphosphine 1 (0.262 g,
1 mmol) and 2-nitrophenol 3 (0.139 g, 1 mmol) in CH2Cl2 (4 mL) was
added dropwise a mixture of 2 (1 mmol) in CH2Cl2 (3 mL) at −10◦C
over 15 min. The mixture was allowed to warm up to r.t. Silica-gel
powder (1.5 g) was added, and the solvent was evaporated. Dry silica
gel and the residue were heated (yield for 6a, 37.3%; yield for 6b, 31.5%)
for 90 min at 60◦C (or irradiated in a microwave oven for 3 min at
a microwave power of 0.5 KW; yield for 6a, 36%; yield for 6b, 33%)
and then placed over a column of silica gel powder (12 g). The column
chromatography was washed using ethyl acetate-light petroleum ether
(1:10) as aneluent. The solvent was removed under reduced pressure,
and products were obtained as colorless viscous oils (6a–b). The relative
population of E and Z isomers were determined via their 1H NMR
spectra (Scheme 1). The characterization data of the compounds (6a–b)
are given below.
Dimethyl 2-(2-nitro-phenoxy)-2-butenedioate (6a)
Viscous yellow oil. IR(neat) (νmax, cm−1): 3092, 2961, 2860, 1742, 1665
1
and 1611. H NMR (CDCl3) for Z isomer, δH: 3.72, and 3.78 (6H, 2s,

2678
A. Ramazani and M. Rahimifard
3
2OCH3), 6.74 (1H, s, vinylic), 6.98 (1H, d, J = 8.2 Hz, arom.), 7.21
HH
3
3
(1H, t, J = 7.8 Hz, arom.), 7.51 (1H, t, J = 7.9 Hz, arom.), 7.99
HH
HH
(1H, d, 3 J = 8.1 Hz, arom.). 13C NMR (CDCl3) for Z isomer, δC: 52.26
HH
and 53.39 (2OCH3), 116.65 (=CH, vinylic), 117.62, 123.50, 126.07 and
134.18 (4CH, arom.), 139.96 and 148.49 (2C, arom.), 149.90 (OC =,
vinylic), 161.67 and 163.26 (2C = O, ester).
1H NMR (CDCl3) for E isomer, δH: 3.71, and 3.92 (6H, 2s, 2OCH3),
5.26 (1H, s, vinylic), 7.32 (1H, d, 3 J = 8.2 Hz, arom.), 7.44 (1H, t,
HH
3 J = 7.8 Hz, arom.), 7.69 (1H, t, 3 J = 7.5 Hz, arom.), 8.07 (1H,
HH
HH
d, 3 J = 8.1 Hz, arom.). 13C NMR (CDCl3) for E isomer, δC:52.05
HH
and 53.30 (2OCH3), 102.10 (=CH, vinylic), 126.99, 123.76, 126.29 and
134.99 (4CH, arom.), 141.76 and 146.05 (2C, arom.), 158.21 (OC =,
vinylic), 162.19 and 165.03 (2C = O, ester).
Diethyl (Z)-2-(2-nitro-phenoxy)-2-butenedioate (6b)
Viscous yellow oil; IR(neat) (νmax, cm−1): 3085, 2923, 2854, 1727, 1658
1
and 1596. H NMR (CDCl3) δH: 1.14–1.24 (6H, m, 2CH3 of 2Et), 4.15–
4.24 (4H, m, 2OCH2 of 2Et), 6.74 (1H, s, vinylic), 6.98 (1H, d, 3 J = 8.3
Hz, arom.), 7.19 (1H, t, J = 7.8 Hz, arom.), 7.50 (1H, t, JHH = 7.9
3
3
HH
HH
3
Hz, arom.), 7.98 (1H, d, J = 8.2 Hz, arom.). 13C NMR (CDCl3) δC:
HH
13.88 and 13.99 (2CH3 of 2Et), 61.37 and 62.74 (2OCH2), 117.14 (=CH,
vinylic), 117.62, 123.35, 126.03 and 134.12 (4CH, arom.), 139.98 and
148.46 (2C, arom.), 150.07 (OC =, vinylic), 161.20 and 162.97 (2C = O,
ester).
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179, 1459 (2004), and references cited therein.
[2] J. I. G. Cadogan, Organophosphorus Reagents in Organic Synthesis, Ed. J. I. G.
Cadogon, (Academic Press, New York, 1979).
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[4] V. J. Patil and U. Mavers, Tetrahedron Lett., 37, 1281 (1996).
[5] C. Xu, G. Chen, C. Fu, and X. Huang, Synth. Commun., 25, 2229 (1995).
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