Synthesis of sterically congested stabilized phosphorus ylides from acetylenic esters, 4,4,4-trifluoro-1-(2naphthyl)-1,3-butanedione, and triphenylphosphine

Article abstract of DOI:10.1080/10426500701693420

Protonation of the highly reactive 1:1 intermediates, produced in the reaction between triphenylphosphine and dialkyl acetylenedicarboxylates, by 4,4,4-trifluoro-1-(2-naphthyl)-1,3-butanedione leads to vinyltriphenylphosphonium salts, which undergo Michae

Full text of DOI:10.1080/10426500701693420

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Synthesis of Sterically
Congested Stabilized
Phosphorus Ylides from
Acetylenic Esters, 4,4,4-
Trifluoro-1-(2naphthyl)-1,3-
butanedione, and
Triphenylphosphine
Ali Ramazani a , Ali Jafari a , Ebrahim Ahmadi a ,
Farzin Marandi b & Esmail Vessally b
a Department of Chemistry , University of Zanjan ,
Zanjan, Iran
b Department of Science , Payame Noor University of
Zanjan , Zanjan, Iran
Published online: 24 Jun 2008.
To cite this article: Ali Ramazani , Ali Jafari , Ebrahim Ahmadi , Farzin Marandi
& Esmail Vessally (2008) Synthesis of Sterically Congested Stabilized Phosphorus
Ylides from Acetylenic Esters, 4,4,4-Trifluoro-1-(2naphthyl)-1,3-butanedione, and
Triphenylphosphine, Phosphorus, Sulfur, and Silicon and the Related Elements, 183:7,
1564-1570, DOI: 10.1080/10426500701693420
To link to this article: http://dx.doi.org/10.1080/10426500701693420
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Phosphorus, Sulfur, and Silicon, 183:1564–1570, 2008
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500701693420
Synthesis of Sterically Congested Stabilized Phosphorus
Ylides from Acetylenic Esters, 4,4,4-Trifluoro-1-(2-
naphthyl)-1,3-butanedione, and Triphenylphosphine
Ali Ramazani,1 Ali Jafari ,1 Ebrahim Ahmadi,1
Farzin Marandi,2 and Esmail Vessally2
1Department of Chemistry, University of Zanjan, Zanjan, Iran
2Department of Science, Payame Noor University of Zanjan,
Zanjan, Iran
Protonation of the highly reactive 1:1 intermediates, produced in the reaction be-
tween triphenylphosphine and dialkyl acetylenedicarboxylates, by 4,4,4-trifluoro-
1-(2-naphthyl)-1,3-butanedione leads to vinyltriphenylphosphonium salts, which
undergo Michael addition reaction with conjugate base to produce corresponding
sterically congested fluorine-containing phosphorus ylides. Basic alumina powder
was found to catalyze conversion of the sterically congested fluorine-containing
5
phosphorus ylides to dialkyl 2-[2-(2-naphthyl)-2-oxoethyl]-3-(1,1,1-triphenyl-λ -
phosphanylidene)succinates in solvent-free conditions under microwave (0.9 KW,
3 min) and thermal (25◦C, 120 min.) conditions.
Keywords 4,4,4-trifluoro-1-(2-naphthyl)-1,3-butanedione; acetylenic esters; basic alu-
mina; Michael addition; microwave irradiation; solvent-free conditions; vinyltriph-
enylphosphonium salt
INTRODUCTION
Phosphorus ylides are important reagents in synthetic organic
chemistry,1−16 especially in the synthesis of naturally occurring prod-
ucts, compounds with biological and pharmacological activity.6 β-
Additions of nucleophiles to the vinyl group of vinylic phosphonium
salts leading to the formation of new alkylidenephosphoranes has at-
tracted much attention as a very convenient and synthetically use-
ful method in organic synthesis.18−30 Phosphorus ylides are a class
of special type of zwitterions, which bear strongly nucleophilic elec-
tron rich carbanions. The electron distribution around the P+–C−
bond and its consequent chemical implications had been probed
Received 20 August 2007; accepted 21 August 2007.
Address correspondence to Ali Ramazani, Department of Chemistry, University of
Zanjan, P.O. Box 45195-313, Zanjan, Iran. E-mail: aliramazani@gmail.com
1564

Congested Stabilized Phosphorus Ylides
1565
and assessed through theoretical, spectroscopic and crystallographic
investigations.30 Proton affinity of these ylides can be used as a molec-
ular guide to assess their utility as synthetic reagents and their func-
tion as ligands in coordination and organometallic chemistry.17,30 The
nucleophilicity at the ylidic carbon is a factor of essential mechanistic
importance in the use of these ylides as Wittig reagents.
Waste prevention and environmental protection are major require-
ments in an overcrowded world of increasing demands. Synthetic
chemistry continues to develop various techniques for obtaining bet-
ter products with less environmental impact. One of the more promis-
ing approaches is solvent-free organic synthesis.31 In this regard sol-
vent free catalytic organic reaction has received tremendous attention
in recent times.32 In the past we have established a convenient,
one-pot method for preparing stabilized phosphorus ylides utiliz-
ing in situ generation of the phosphonium salts.18−28 In this arti-
cle, we report on the catalytic role of Basic alumina powder in the
conversion of the sterically congested fluorine-containing phosphorus
ylides (5) to dialkyl 2-[2-(2-naphthyl)-2-oxoethyl]-3-(1,1,1-triphenyl-λ5-
phosphanylidene)succinates (9) in solvent-free conditions33 under mi-
crowave (0.9 KW, 3 min) and thermal (25◦C, 120 min) conditions
(Scheme 1).
RESULTS AND DISCUSSION
The phosphorus ylide (5) may result from initial addition of triph-
enylphosphine 1 to the acetylenic ester 2 and concomitant protona-
tion of the 1:1 adduct by 4,4,4-trifluoro-1-(2-naphthyl)-1,3-butanedione
3 leads to vinyltriphenylphosphonium salts 4 which undergo Michael
addition reaction with conjugate base to produce sterically congested
fluorine-containing phosphorus ylide (5). TLC indicated formation of
ylides 5 in CH2Cl2. Basic alumina powder was found to catalyze conver-
sion of the phosphorus ylide (5) to dialkyl 2-[2-(2-naphthyl)-2-oxoethyl]-
3-(1,1,1-triphenyl-λ5-phosphanylidene)succinates (9) in solvent-free
conditions33 under microwave (0.9 KW, 3 m) and thermal (25◦C, 120
m) conditions (Scheme 1). We have also used silica gel powder in this
reaction instead of basic alumina powder, but the yield of product was
very low and several products were observed. The reaction also was
not occurred in dichloromethane solutions after two days and several
others products were observed. The mechanism of the reaction has not
been established experimentally. However, a possible explanation is
proposed in Scheme 1. The formulas of the products 9 were deduced
1
from their IR, H NMR, 13C NMR, and 13P NMR spectra (See Experi-
mental section). The NMR spectra indicated that solutions of compound

1566
A. Ramazani et al.
SCHEME 1 M = major rotamer and m = minor rotamer.
9 (CDCl3 as solvent) contain two rotamers (9E and 9Z). The relative
percentages of rotamers in CDCl3 for each ylide 9 were determined
1
from the H NMR spectra. The IR spectrum of 9a showed strong ad-
sorptions at 1734 (C=O, ester), 1695 (C O, ester), 1634 (C O, ketone),

Congested Stabilized Phosphorus Ylides
1567
and 1109 (C-O, ester) cm−1 indicating the presence of two the ester
carbonyls and the ketone carbonyl functionalities, respectively. The 1H
NMR spectrum of 9a [major rotamer (M)] compound exhibited four sig-
nals readily recognized as arising from two OMe groups (δ = 3.05 and
3.70 ppm), CH2 and CH (δ = 3.00–4.00 ppm,m) and aromatic moieties
1
(δ = 7.26–8.59 ppm, m). The H decoupled 13C NMR spectrum of 9a
[major rotamer (M)] showed 22 distinct resonances in agreement with
the 9a [major rotamer (M)] formula. Partial assignment of these res-
onances is given in the spectral analysis section (See Experimental
section). The 31P NMR spectrum of 9a [major rotamer (M] exhibited
one signal readily recognized as arising from phosphorus atom of P=C
group (δ = 23.32 ppm). The 1H, 31P, and 13C NMR signals of minor ro-
tamer (m) of 9a are similar to those of major rotamer (M) of 9a, except
for the signal intensities, which related to the relative populations of
two rotamers of 9a in CDCl3 solution (see Spectral Analysis section).
The 1H, 31P, and 13C NMR spectra of compound 9b are similar to those of
9a, except for the ester groups (1H and 13C NMR), which exhibit charac-
teristic signals with appropriate chemical shifts (see spectral analysis
section).28,34
CONCLUSION
In summary, we have found a new and efficient method for the prepa-
ration of dialkyl 2-[2-(2-naphthyl)-2-oxoethyl]-3-(1,1,1-triphenyl-λ5-
phosphanylidene)succinates (9) from triphenylphosphine (1), acetylenic
ester (2), and 4,4,4-trifluoro-1-(2-naphthyl)-1,3-butanedione (3) in the
presence of basic alumina powder ( Scheme 1). We believe the reported
method offers a simple and efficient route for the preparation of the ster-
ically congested stabilized phosphorus ylides 9 (Scheme 1) . Its ease of
work up and fairly good yields make it a useful addition to modern
synthetic methodologies.28,34 Other aspects of this process are under
investigation.
EXPERIMENTAL
Melting points were measured on an Electrothermal 9100 apparatus
and are uncorrected. Commercial oven Butane M245 was used for mi-
crowave irradiation. IR spectra were recorded on a FT-IR Mattson 1000
spectrometer. 1H, 31P, and 13C NMR spectra were measured with a
BRUKER DRX-250 AVANCE spectrometer at 250.00, 101.25, and 62.50
MHz respectively.

1568
A. Ramazani et al.
General Procedure for the Preparation of Ylides 5
and Compounds 9a–b
To a magnetically stirred solution of triphenylphosphine 1 (0.262 g,
1.00 mmol) and 4,4,4-trifluoro-1-(2-naphthyl)-1,3-butanedione 3 (0.268
g, 1.00 mmol) in CH2Cl2 (5 ml) was added dropwise a mixture of 2
(0.13 ml, 1.0 mmol) in CH2Cl2 (2 ml) at −10◦C over 15 min. Then 1
g of basic alumina powder (Merck) was added to the reaction mixture
quickly, and the mixture was allowed to warm up to room temperature.
The solvent was removed under reduced pressure and the residue was
kept for 2 h at room temperature (or under microwave; 0.9 KW, 3 min)
in the solvent-free conditions. The reaction mixture was placed in a
short glassy column. The column was washed using MeOH as eluent.
The solvent was removed under reduced pressure and products were
obtained as white crystals (9a–b) (Scheme 1). The products were re-
crystallized from ethanol. The characterization data of the compounds
(9a–b) are given below.
Methyl 2-[2-(2-Naphthyl)-2-oxoethyl]-3-(1,1,1-triphenyl-λ5-
phosphanylidene)succinate (9a)
White crystal; mp: 209–211◦C; Yield: 72.4% IR (KBr) (νmax, cm−1):
1734 and 1695 (2 C O, Ester); 1634 (C O); 1109 (C-O); 3061 (C-H, Aro-
1
matic). H NMR (CDCl3) [major rotamer (M) 71% and minor rotamer
(m) 29%].
1H NMR (CDCl3) [major rotamer (M)] δ: 3.05 and 3.70 (6 H, 2 s, 2
OMe); 3.00–4.00 (3 H, m, CH2 and CH); 7.26–8.59 (22 H, Aromatic).
13C NMR (CDCl3) [major rotamer (M)] δ: 41.44 (d, 1 J = 122.5 Hz);
PC
40.12 (d, 2 J = 13.3 Hz); 40.25 (s); 48.72 and 51.89 (2 OMe); 127.39
PC
1
2
(d, J = 91.3 Hz, Cipso); 128.40 (d, J = 12.2 Hz, Cortho); 131.73 (d,
PC
PC
4 J = 0.4 Hz, Cpara); 133.83 (d, 3 J = 9.63 Hz Cmeta); 130.41 (s, C1,
PC
PC
Naphthyl); 135.46 (s, C2, Naphthyl); 129.73 (s, C3, Naphthyl); 128.21
(s, C4, Naphthyl); 126.54 (s, C5, Naphthyl); 128.03 (s, C6, Naphthyl);
127.63 (s, C7, Naphthyl); 124.20 (s, C8, Naphthyl); 135.00 (s, C9, Naph-
thyl); 132.65 (s, C10, Naphthyl); 169.62 (d, 2 JPC = 13.4 Hz, CO of ester);
176.36 (d, 3 J = 5.7 Hz, CO of ester); 200.35 (s, CO of ketone).
PC
31P NMR (CDCl3) [major rotamer (M)] δ: 23.32.
1H NMR (CDCl3) [minor rotamer (m)] δ: 3.61 and 3.68 (6 H, 2 s, 2
OMe); 3.00-4.00 (3 H, m, CH2 and CH); 7.26–8.6 (22 H, Aromatic).
13C NMR (CDCl3) [minor rotamer (m)] δ: 42.00 (d, 1 J = 134.38
PC
Hz); 39.61 (d, 2 J = 13.3 Hz); 41.55 (d, 3 J = 5 Hz); 50.11 and 51.79
PC
PC
(2 OMe); 126.71 (d, 1 J = 91.6 Hz, Cipso); 128.51 (d, 2 J = 12.1 Hz,
PC
PC
C
ortho); 130.08 (s, C1, Naphthyl); 129.66 (s, C3, Naphthyl); 134.91 (s, C9,

Congested Stabilized Phosphorus Ylides
1569
Naphthyl); 132.59 (s, C10, Naphthyl); 170.70 (d, 2 J = 18.8 Hz, CO of
PC
ester); 176.45 (d, 3 J = 6.1 Hz, CO of ester); 199.94 (s, CO of ketone).
PC
31P NMR (CDCl3) [minor rotamer (m)] δ: 23.15.
Ethyl 2-[2-(2-Naphthyl)-2-oxoethyl]-3-(1,1,1-triphenyl-λ5-
phosphanylidene)succinate (9b)
White crystal; mp: 139–141◦C; Yield: 69.0% IR (KBr) (νmax, cm−1):
1730 and 1676 (2 C O, Ester); 1630 (C O); 1446 (C=C, Aromatic); 1107
(C-O); 3061 (C-H, Aromatic); 2938 and 2869 (C-H, Aliphatic). 1H NMR
(CDCl3) (major rotamer (M) 68% and minor rotamer (m) 32%).
1H NMR (CDCl3) [major rotamer (M)] δ: 0.35 (3 H, t, 3 J = 7.1 Hz,
HH
CH3); 1.22 (3 H, t, 3 J = 7.1 Hz, CH3); 3.00–4.00 (3 H, m, CH2 and
HH
CH); 3.9–4.3 (4 H, m, OCH2); 7.30–8.61 (22 H, Aromatic).
13C NMR (CDCl3) [major rotamer (M)] δ: 13.90 and 14.29 (2 Me)
1
2
3
41.03 (d, J = 126.4 Hz); 40.47 (d, J = 13.3 Hz); 40.18 (d, J
=
PC
PC
PC
4.1 Hz); 57.24 and 60.57 (2 OCH2); 127.57 (d, 1 J = 91.3 Hz, Cipso);
128.31 (d, 2 JPC = 12.1 Hz, Cortho); 131.68 (d, 4 J =P3C.9 Hz Cpara); 133.91
PC
(d, 3 JPC = 9.6 Hz, Cmeta); 130.46 (s, C1, Naphthyl); 135.44 (s, C2, Naph-
thyl); 129.75 (s, C3, Naphthyl); 128.21 (s, C4, Naphthyl); 126.48 (s, C5,
Naphthyl); 127.98 (s, C6, Naphthyl); 127.61 (s, C7, Naphthyl); 124.27
(s, C8, Naphthyl); 135.10 (s, C9, Naphthyl); 132.66 (s, C10, Naphthyl);
169.26 (d, 2 J = 13.8 Hz, CO of ester); 175.84 (d, 3 J = 5.6 Hz, CO of
PC
PC
ester); 200.64 (s, CO of ketone).
31P NMR (CDCl3) [major rotamer (M)] δ: 23.17.
1H NMR (CDCl3) [minor rotamer (m)] δ: 1.2–1.4 (6 H, m, 2 CH3);
3.00–4.00 (3 H, m, CH2 and CH); 3.9–4.3 (4 H, m, OCH2); 7.30–8.61
(22 H, Aromatic).
13C NMR (CDCl3) [minor rotamer (m)] δ: 18.43 and 15.29 (2 Me);
1
2
3
42.18 (d, J = 134.3 Hz); 39.89 (d, J = 13.8 Hz); 41.53 (d, J
=
PC
PC
PC
4.6 Hz); 58.01 and 58.33 (2 OCH2); 126.86 (d, 1 J = 93.9 Hz, Cipso);
PC
2
126.91 (d, J = 13.9 Hz, Cortho); 130.05 (s, C1, Naphthyl); 170.34 (d,
PC
2 J = 17.8 Hz, CO of ester); 175.97 (d, 3 J = 6.0 Hz, CO of ester);
PC
PC
200.21 (s, CO of ketone).
31P NMR (CDCl3) [minor rotamer (m)] δ: 23.10.
ACKNOWLEDGMENTS
This work was supported by the Zanjan University.
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