Synthesis of alkyl 2-(2-oxo-1,2-dihydronaphtho [2,1-b]thiophen-1-yl)-2-(1, 1,1-triphenyl-λ5-phosphanylidene)acetates from triphenylphosphine, acetylenic esters, and 2-naphthalenethiol

Article abstract of DOI:10.1080/10426500701839825

A one-pot synthesis of alkyl 2-(2-oxo-1,2-dihydronaphtho[2,1-b]thiophen-1- yl)-2-(1,1,1-triphenyl-λ5 -phosphanylidene)acetates in fairly high yields by the reaction of 2-naphthalenethiol, dialkyl acetylenedicarboxylates and triphenylphosphine is reported. The formulas of these compounds were confirmed by IR, 1 H,31P, and 13C NMR spectroscopy. The NMR spectra indicated that solutions of the phosphorus ylides (CDCl3 as solvent) contain two rotamers (E and Z). The relative percentages of rotamers in CDCl3 for each phosphorus ylide were determined from the 31P NMR spectra. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/10426500701839825

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Synthesis of Alkyl 2-(2-
Oxo-1,2-dihydronaphtho
[2,1-b]thiophen-1-yl)-2-
5
(1,1,1-triphenyl-λ -
phosphanylidene)acetates from
Triphenylphosphine, Acetylenic
Esters, and 2-Naphthalenethiol
Issa Amini a , Ali Ramazani b & Hamideh Ahankar c
a Chemistry Department , Payam Noor University of
Abhar , Abhar, Iran
b Chemistry Department , Zanjan University ,
Zanjan, Iran
c Chemistry Department , Islamic Azad University-
Abhar Branch , Abhar, Iran
Published online: 28 Jul 2008.
To cite this article: Issa Amini , Ali Ramazani & Hamideh Ahankar (2008) Synthesis
of Alkyl 2-(2-Oxo-1,2-dihydronaphtho [2,1-b]thiophen-1-yl)-2-(1,1,1-triphenyl-λ
5-phosphanylidene)acetates from Triphenylphosphine, Acetylenic Esters, and 2-
Naphthalenethiol, Phosphorus, Sulfur, and Silicon and the Related Elements, 183:8,
1994-1999, DOI: 10.1080/10426500701839825
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Phosphorus, Sulfur, and Silicon, 183:1994–1999, 2008
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500701839825
Synthesis of Alkyl 2-(2-Oxo-1,2-dihydronaphtho
[2,1-b]thiophen-1-yl)-2-(1,1,1-triphenyl-λ5-
phosphanylidene)acetates from Triphenylphosphine,
Acetylenic Esters, and 2-Naphthalenethiol
Issa Amini,1 Ali Ramazani,2 and Hamideh Ahankar3
1Chemistry Department, Payam Noor University of Abhar, Abhar, Iran
2Chemistry Department, Zanjan University, Zanjan, Iran
3Chemistry Department, Islamic Azad University-Abhar Branch,
Abhar, Iran
A one-pot synthesis of alkyl 2-(2-oxo-1,2-dihydronaphtho[2,1-b]thiophen-1-yl)-2-
(1,1,1-triphenyl-λ5 -phosphanylidene)acetates in fairly high yields by the reaction
of 2-naphthalenethiol, dialkyl acetylenedicarboxylates and triphenylphosphine is
reported. The formulas of these compounds were confirmed by IR, 1 H,31P, and 13C
NMR spectroscopy. The NMR spectra indicated that solutions of the phosphorus
ylides (CDCl3 as solvent) contain two rotamers (E and Z). The relative percentages
of rotamers in CDCl3 for each phosphorus ylide were determined from the 31P NMR
spectra.
Keywords 2-Naphthalenethiol; acetylenic esters; Michael addition; phosphorus ylide;
vinyltriphenylphosphonium 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 6 September 2007; accepted 13 September 2007.
This work was supported by the Islamic Azad University-Abhar Branch.
Address correspondence to Ali Ramazani, Chemistry Department, Zanjan University,
P O Box 45195-313, Zanjan, Iran. E-mail: aliramazani@gmail.com
1994

Phosphanylidene Acetates
1995
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. In the past
we have established a convenient, one-pot method for preparing stabi-
lized phosphorus ylides utilizing in situ generation of the phosphonium
salts.18−28 In this paper, we wish to describe a simple method for the
preparation of alkyl 2-(2-oxo-1,2-dihydronaphtho[2,1-b]thiophen-1-yl)-
2-(1,1,1-triphenyl-λ5-phosphanylidene)acetates from three-component
reaction of 2-naphthalenethiol, dialkyl acetylenedicarboxylates and
triphenylphosphine in fairly high yields (Scheme 1).
RESULTS AND DISCUSSION
The phosphorus ylide (7) may result from initial addition of triph-
enylphosphine 1 to the acetylenic ester 2 and concomitant protonation
of the 1:1 adduct by 2-naphthalenethiol 3 leads to vinyltriphenylphos-
phonium salts 4, which undergo the Michael addition reaction with
conjugate base to produce sterically congested phosphorus ylide (5).
The phosphorus ylide 5 convert to the stable phosphorus ylide 7 via
organophosphorus intermediate 6 in the reaction conditions. TLC indi-
cated formation of ylides 7 in acetone at room temperature. The reac-
tion was completed at room temperature in 2 h. The reaction proceeds
smoothly and cleanly under mild conditions and no side reactions were
observed. The mechanism of the reaction has not been established ex-
perimentally. However, a possible explanation is proposed in Scheme 1.
The formulas of the products 7 were deduced from their IR, 1H NMR, 13
C
NMR, and 13P NMR spectra (See Experimental section). The 31P NMR
spectra indicated that solutions of compound 7 (CDCl3 as solvent) con-
tain two rotamers (7E and 7Z). The relative percentages of rotamers in
CDCl3 for each ylide 7 were determined from the 31P NMR spectra. The
IR spectrum of 7a showed strong adsorptions at 3054 (CH, aromatic),
1739 (C O, ester), 1592 (C O, ester), 1439 (C C), 1262 (CH, aliphatic),
1192 (C-O, ester), and 1123 (C-O, ester) cm−1 indicating the presence of
the mentioned groups in its formula. The 1H NMR spectrum of 7a com-
pound exhibited four signals readily recognized as arising from methoxy
3
group (δ = 3.81 ppm, s), two aliphatic CH groups (δ = 4.28 (d, JHP
=
3
19.3 Hz) and 4.41 (d, JHP = 18.5 Hz) ppm, for two rotamers of the
phosphorus ylide) and aromatic moieties (δ = 7.2–7.7 ppm, m). The
1H decoupled 13C NMR spectrum of 7a showed 16 distinct resonances
(52.59 (OCH3); 125.56, 126.00, 127.24, 127.50, 127.66, 128.59, 131.93,

1996
I. Amini et al.
SCHEME 1 M = major rotamer and m = minor rotamer.
131.98, 133.54, 133.74, and 133.89 (CH and C groups)) in agreement
with the 7a formula. Partial assignment of these resonances is given
in the spectral analysis section (See Experimental section). The 31P
NMR spectrum of 7a exhibited two signals readily recognized as aris-
ing from phosphorus atom of P C groups (δ = 22.66 and 23.06 ppm, Z
and E rotamers). The 1H, 31P, and 13C NMR spectra of compound 7b are
similar to those of 7a, except for the ester groups (1H and 13C NMR),
which exhibit characteristic signals with appropriate chemical shifts
(see Spectral Analysis section).28,31

Phosphanylidene Acetates
1997
CONCLUSION
In summary, we have found a simple and efficient method for
the preparation of alkyl 2-(2-oxo-1,2-dihydronaphtho[2,1-b]thiophen-1-
yl)-2-(1,1,1-triphenyl-λ5-phosphanylidene)acetates (7) from the three-
component reaction of 2-naphthalenethiol, dialkyl acetylenedicarboxy-
lates and triphenylphosphine in fairly high yields. We believe the
reported method offers a simple and efficient route for the prepa-
ration of the stabilized phosphorus ylides 7 (Scheme 1). Its ease of
work-up and fairly good yields make it a useful addition to modern
synthetic methodologies.28,31 Other aspects of this process are under
investigation.
EXPERIMENTAL
Melting points were measured on an Electrothermal 9100 apparatus
and are uncorrected. 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.
General Procedure for the Preparation of Ylides 7a-b
To a magnetically stirred solution of triphenylphosphine 1 (0.262 g, 1.00
mmol) and 2-naphthalenethiol (0.16 g, 1.0 mmol) in acetone (4 ml) was
added dropwise a mixture of dialkyl acetylenedicarboxylate (0.13 ml,
1.0 mmol) in acetone (3 ml) at −10◦C over 15 min. The mixture was
allowed to warm up to room temperature and stirred for 2 h. The vol-
ume of solvent in the mixture was reduced (ca. up to 3 ml) and white
crystals of the product were separated by simple filtration. The crystals
were washed with cold acetone (2 ml) and then dried at room temper-
ature (7a, white crystals, m.p. 176.8–177.2◦C, yield 74.0%; 7b, white
crystals, m.p. 144.7–145.2◦C, yield 69.0%). The characterization data
of the compounds (7a–b) are given below.
Spectral Data for Methyl 2-(2-Oxo-1,2-dihydronaphtho
[2,1-b]thiophen-1-yl)-2-(1,1,1-triphenyl-λ5-phosphanylidene)
acetate 7a
IR (KBr) (vmax, cm −1): 3054; 2954; 1739; 1592; 1439; 1262; 1192,
3
and 1123. 1H NMR, δH : 3.81 (3 H, s, OCH3); 4.28 (1 H, d, JHP = 19.3
3
Hz, major rotamer) and 4.41 (1 H, d, JHP = 18.5 Hz, minor rotamer);
7.2–7.7 (21 H, m, arom).13C NMR (CDCl3) δC: 52.59 (OCH3); 125.56,
126.00, 127.24, 127.50, 127.66, 128.59, 131.93, 131.98, 133.54, 133.74,

1998
I. Amini et al.
and 133.89. 31P NMR (CDCl3, major rotamer (M) 59% and minor ro-
tamer (m) 41%), (CDCl3) δP: 22.66 and 23.06.
Spectral Data for Ethyl 2-(2-Oxo-1,2-dihydronaphtho
[2,1-b]thiophen-1-yl)-2-(1,1,1-triphenyl-λ5-phosphanylidene)
acetate 7b
IR (KBr) vmax, cm−1): 3054, 2985, 1731, 1592, 1439, 1192, and 1123.
1H NMR, δH: 1.2–1.4 (3 H, m, CH3); 4.0–4.1 (2 H, m, OCH2); 4.25 (1
H, d, 3JHP = 14.3 Hz, major rotamer) and 4.43 (1 H, d, 3JHP = 19.0 Hz,
minor rotamer); 7.2–7.7 (21 H, m, arom). 13C NMR (CDCl3)δC : 14.11
(CH3); 61.34 (OCH2); 125.45, 125.91, 127.22, 127.48, 127.55, 127.72,
128.37, 128.54, 129.94, 130.21, 131.83, 131.88, 131.95, 132.01, 132.16,
133.56, 133.78, and 133.94.31P NMR (CDCl3, major rotamer (M) 51%
and minor rotamer (m) 49%), δP: 22.58 and 22.95.
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