An efficient one-pot synthesis of 2,3-dialkyl-1,1-diethyl-1-(acetylamino)- 3-(1,1,1-triphenylphosphanilidene)-1,1,2,3-propanetetracarboxylates and their temperature-dependent NMR spectra

Article abstract of DOI:10.1080/10426507.2011.590951

Stable crystalline phosphorus ylides of 1,1-diethyl 2,3-dimethyl 1-(acetylamino)-3-(1,1,1-triphenylphosphanilidine)-1,1,2,3- propanetetracarboxylates were obtained in excellent yields from the 1:1:1 addition reaction between triphenylphosphine and dialkyl

Full text of DOI:10.1080/10426507.2011.590951

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Phosphorus, Sulfur, and Silicon and the
Related Elements
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An Efficient One-Pot Synthesis
of 2,3-Dialkyl-1,1-Diethyl-1-
(Acetylamino)-3-(1,1,1-
Triphenylphosphanilidene)-1,1,2,3-
Propanetetracarboxylates and Their
Temperature-Dependent NMR Spectra
Sakineh Asghari a , Azin Salimi a & Vali Taghipour a
a Department of Organic Chemistry, Faculty of Chemistry, University
of Mazandaran, Babolsar, Iran
Published online: 05 Apr 2012.
To cite this article: Sakineh Asghari , Azin Salimi & Vali Taghipour (2012): An Efficient One-Pot
Synthesis of 2,3-Dialkyl-1,1-Diethyl-1-(Acetylamino)-3-(1,1,1-Triphenylphosphanilidene)-1,1,2,3-
Propanetetracarboxylates and Their Temperature-Dependent NMR Spectra, Phosphorus, Sulfur, and
Silicon and the Related Elements, 187:6, 669-676
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Phosphorus, Sulfur, and Silicon, 187:669–676, 2012
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2011.590951
AN EFFICIENT ONE-POT SYNTHESIS OF
2,3-DIALKYL-1,1-DIETHYL-1-(ACETYLAMINO)-3-(1,1,1-
TRIPHENYLPHOSPHANILIDENE)-1,1,2,3-
PROPANETETRACARBOXYLATES AND THEIR
TEMPERATURE-DEPENDENT NMR SPECTRA
Sakineh Asghari, Azin Salimi, and Vali Taghipour
Department of Organic Chemistry, Faculty of Chemistry,
University of Mazandaran, Babolsar, Iran
GRAPHICAL ABSTRACT
Abstract Stable crystalline phosphorus ylides of 1,1-diethyl 2,3-dimethyl 1-(acetylamino)-3-
(1,1,1-triphenylphosphanilidine)-1,1,2,3-propanetetracarboxylates were obtained in excellent
yields from the 1:1:1 addition reaction between triphenylphosphine and dialkyl acetylenedi-
carboxylates in the presence of diethyl acetamidomalonate as a CH-acid. These stable ylides
exist in solution as a mixture of two geometrical isomers (E and Z) as a result of restricted
rotation around the carbon–carbon partial double bond resulting from conjugation of the ylide
moiety with the adjacent carbonyl group on the nuclear magnetic resonance (NMR) time scale
at ambient temperature. The dynamic effects in the ylide moieties were investigated by 1H NMR
spectra.
Supplemental materials are available for this article. Go to the publisher’s online edition of
Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.
1
Keywords Diethyl acetamidomalonate; stable phosphorous ylides; dynamic H NMR; geo-
metrical isomers
INTRODUCTION
Synthesis of phosphorus ylides is important in organic chemistry because of their
applications in the synthesis of organic products,1–9 especially the synthesis of naturally
Received 8 March 2011; accepted 21 March 2011.
Address correspondence to Sakineh Asghar, Department of Organic Chemistry, Faculty of Chemistry,
University of Mazandaran, Babolsar 47416-95447, Iran. E-mail: s.asghari@umz.ac.ir
669

670
SAKINEH ASGHARI ET AL.
occurring products with potentially useful biological and pharmacological activities.10–13
Several methods have been developed for the preparation of phosphorus ylides, which take
part in many valuable reactions as reactive intermediates in organic synthesis.14–18 Some
of these compounds exhibited the dynamic 1H nuclear magnetic resonance (NMR) effect
that afforded important kinetic data regarding the interchange process of the rotational
isomers.19–21
Recently, we have reported the reactions of ethyl acetamidocyanoacetate 1 with
dialkyl acetylenedicarboxylates and triphenylphosphine that lead to the corresponding
phosphorus ylides 2. These ylides converted to α,β-unsaturated γ -lactam derivatives in
refluxing toluene.22
During our continuous efforts for the synthesis of other α,β-unsaturated γ -lactam
derivatives, we performed the reaction of diethyl acetamidomalonate 3 (similar to compound
1) and dialkyl acetylenedicarboxylate 4 in the presence of triphenylphosphine to produce
the stable phosphorus ylide 5. When the compounds 5a–c were refluxed in boiling toluene,
only the compound 5a underwent a cyclization reaction by loss of ROH to produce the
corresponding cyclic phosphorus ylide 6a in low yield (<30%) (Scheme 1).
O
CO2Et
CO2Et
CH2Cl2
r.t. 24 h
PPh3
+
+
RO2C
CO2R
N
H
4
3
R= Me, Et, t-Bu
O
CO2Et
CO2Et
CO2R
O
Toluene
reflux
N
H
CO2Et
O
CO2Et
CO2R
N
H
-ROH
Ph3P
CO2R
Ph3P
R=Me
5
6
Yield of 5 (%)
Yield of 6 (%)
R
28
-
88
90
91
a = Me
b = Et
c = tBu
-
Scheme 1
RESULTS AND DISCUSSION
On the basis of the chemistry of trivalent phosphorus nucleophiles,23–28 it is reasonable
to assume that zwitterionic intermediate 7, formed from triphenylphosphine and acetylenic
ester 4, is protonated by diethyl acetamidomalonate 3. Thus, the positively charged ion 8
is attacked by the enolate of compound 3 to from the stable ylides 5a–c. Compound 5a
undergoes a cyclization reaction to afford 6 in boiling toluene (Scheme 2).

SYNTHESIS OF PHOSPHORUS YLIDES
671
O
EtO2C
H
EtO2C
+
Ph3P
N
..
H
_
PPh3
+
RO2C
CO2R
RO2C
CO2R
7
+
Ph3P
CO2Et
CO2Et
O
R
O
EtO2C
-
H
CO2R
..
N
CO2R
N
EtO2C
H
RO2C
H
O
PPh3
8
O
5
Cyclization
-ROH
O
CO2Et
N
O
CO2Et
CO2R
Ph3P
6
Scheme 2
The structures of 5a–c were deduced from 1H, 13C, and 31P NMR, infrared (IR), and
1
mass spectra. The H NMR spectrum of 5a exhibited a singlet at 2.04 ppm for methyl
group of CH3CO, two singlets at 3.02 and 3.70 ppm for two methoxy groups, a doublet at
3.50 ppm (3JPH = 15.6 Hz) for methine proton of CHCO2Me group, and a singlet at
9.21 for NH group, respectively. The 13C NMR spectrum of 5a displayed 19 characteristic
signals with appropriate chemical shifts. The 31P NMR spectrum of 5a showed a signal at
25.2 ppm. The mass spectrum of 5a displayed a molecular ion peak at m/z 623. The
1
structural assignment made on the basis of H, 13C, and 31P NMR for compound 5a was
supported by a measurement of its IR spectrum.
1
The H, 13C, and 31P NMR spectra of ylides 5b and 5c show the presence of two
isomers. The ylide moiety is strongly conjugated with the adjacent carbonyl group, and the
rotation about the partial double bond in 5b(c)-Z and 5b(c)-E isomers is slow on the NMR
time scale at ambient temperature. Assignment of the (Z)-configuration to major geometric
isomer is based on the 1H chemical shift of OR moiety, which is expected to be shielded as
a result of the anisotropic effect of phenyl groups (Scheme 3).
For example, the 1H NMR spectrum of 5c exhibited two sharp singlets at 2.04 and
2.18 ppm with an intensity of 89:11 for the acetyl groups of the Z- and E-isomer at room
temperature, respectively. Increasing the temperature resulted in coalescence of their acetyl

672
SAKINEH ASGHARI ET AL.
O
H3C
H3C
O
H3C
H3C
O
O
NH
EtO2C
EtO2C
NH
EtO2C
EtO2C
EtO2C
RO2C
NH
EtO2C
EtO2C
NH
-
O
EtO2C
RO2C
OR
RO2C
O
OR
H
RO2C
H
+
+
H
H
Ph3P
O
Ph3P
OR
-
Ph3P
OR
Ph3P
O
E-isomer
Z-isomer
Scheme 3
resonances. This resonance coalescence occurred at approximately 36 ◦C (309 ◦K), which
is relevant to the restricted rotational process around the carbon–carbon double bond.
Investigation of 1H NMR spectrum of 5b and 5c at variable temperatures allowed us
to calculate the rotational energy barrier (ꢀG#) for the restricted rotational process around
√
the carbon–carbon bond. Using the expression kc = πꢀν/ 2, the first-order rate constant
at the temperature of coalescence (Tc) was calculated for the bond rotational process. Then
the free Gibbs rotational energy (ꢀG#) for this process was calculated by the absolute rate
theory29,30 with a transmission coefficient (K) of near unity. The Gutowsky equation
ꢀG#= 4.57TC(10.32 + logTC − logkC)
is used for the measurement of exchange kinetics by the coalescence method. However,
if we substitute the values of kc and Tc in the above equation, the free Gibbs activation
energy for this process can be evaluated. The calculated energy for 5c is 15.1 kcal/mol. The
calculated free Gibbs rotational energies for 5a, 5b, and 2 (its synthesis has been reported
previously) are shown in the Table 1.
The calculated data of the free Gibbs rotational energies for rotation around the
carbon–carbon double bond of compounds 2 and 5 show that barrier energies for compound
2 derivatives are 2–3 kcal/mol higher than those for compound 5. Also, it seems that in
each group of these compounds, barrier energy increases by increasing the size of the alkyl
groups. This might be because of the steric hindrance of the bulkier alkyl groups.
Table 1 The calculated free Gibbs rotational energies (ꢀG#) for rotation around the carbon–carbon double bond
of compounds 2a–c and 5a–c
EtO2C
O
X
CO2R
N
H
Ph3P
CO2R
Entry
X
R
ꢀG# (kcal/mol)
2a
2b
2c
5a
5b
5c
CN
CN
CN
CO2Et
CO2Et
CO2Et
Me
Et
17.19
17.26
17.48
14.36
14.65
15.10
tBu
Me
Et
tBu

SYNTHESIS OF PHOSPHORUS YLIDES
673
The structure of 6 was deduced from 1H, 13C, and 31P NMR, IR, and mass spectra.
1
The H NMR spectrum of 6 exhibited a singlet at 3.32 ppm for one methoxy group, a
doublet at 3.72 ppm (3JPH = 16.6 Hz) for the methine hydrogen of the CHCO2Me group,
and a multiplet at 7.45–7.65 for aromatic protons of triphenylphosphine moieties. It is
obvious that the characteristic signals for NH and one of alkoxy groups disappeared in the
1H NMR spectrum of 6. The 13C NMR spectrum of 6 displayed 18 characteristic signals
with appropriate chemical shifts.
EXPERIMENTAL
Diethyl acetamidomalonate, triphenylphosphine, and dialkyl acetylenedicarboxylates
were obtained from Fluka (Buche, Switzerland) and used without further purification. IR
spectra were recorded on a FT-IR Bruker Vector 22 spectrometer. Mass spectra were
recorded on Finnigan-Matt 8430 mass spectrometer operating at an ionization potential of
70 eV. 1H, 13C, and 31P NMR spectra were measured with Bruker DRX-500 and 400 Avance
spectrometers. Melting points were measured on an Electrothermal 9100 apparatus.
Preparation of Dialkyl 2-(2-Oxo-1,2-diphenyl
ethyl)-3-(triphenylphosphoran yliden) succinate (5): General Procedure
A solution of dialkyl acetylenedicarboxylate (2 mmol) in CH2Cl2 (3 mL) was added
dropwise to a magnetically stirred solution of diethyl acetamidomalonate (0.39 g, 2 mmol)
◦
and triphenylphosphine (0.52 g, 2 mmol) in CH2Cl2 (10 mL) at −10 C in 10 min. The
mixture was allowed to stand at room temperature for 24 h. The solvent was removed under
reduced pressure and the residue was purified by silica gel (Merck silica gel, 230–400
mesh) column chromatography using hexane:ethyl acetate (60:40) as eluent. The solvent
was removed under reduced pressure and the product 5a–c was obtained as colorless
crystals.
1,1-Diethyl 2,3-dimethyl 1-(acetylamino)-3-(1,1,1-
triphenylphosphanilidene)-1,1,2,3-propanetetracarboxylate (5a)
Colorless crystal (yield 88%); mp 173 ◦C–174 ◦C, IR (KBr) (νmax/cm−1): 3244 (NH),
1741, 1720, and 1685 (C O); 1H NMR (500.1 MHz, CDCl3): δH 1.04–1.10 (m, 6H, 2CH3),
2.04 (s, 3H, CH3CO), 3.02 and 3.70 (2s, 6H, 2OCH3), 3.50 (d, 3JHH = 15.6 Hz, 1H, CH),
3.85–3.88 and 4.0–4.04 (2m, 4H, 2OCH2), 7.74–7.82 (m, 15H, aromatic protons), 9.21
(s, 1H, NH); 13C NMR (125.8 MHz, CDCl3): δC 13.7 and 13.8 (2CH3), 23.3 (CH3CO),
40.4 (d, 1JPC = 125.2 Hz, P C), 49.1 (d, 2JPC = 13.5 Hz, CH), 49.2 and 51.8 (2OCH3),
3
1
61.2 and 61.3 (2OCH2), 69.8 [d, JPC = 4.4 Hz, C(CO2Et)2], 126.5 (d, JPC = 93.5 Hz,
Ci), 128.4 (d, 3JPC = 12.3 Hz, Cm), 131.9 (Cp), 134.2 (d, 2JPC = 9.6 Hz, Co), 166.1 (C O,
2
amide), 167.8 and 170.1 (2C O, 2CO2Et), 171.7 (d, JPC = 12.7 Hz, C O, CO2Me),
3
173.2 (d, JPC = 6.2 Hz, C O, CO2Me); Ms, m/z (%): 623 (M+, 6), 406 (98), 287 (7),
262 (7), 183 (43), 174 (22), 77 (25), 44 (100); Anal. Calcd. for C33H35NO9P: C, 63.87; H,
5.68; N, 2.25. Found: C, 63.79; H, 5.62; N, 2.21.

674
SAKINEH ASGHARI ET AL.
Tetra-Ethyl-1-(acetylamino)-3-(1,1,1-triphenylphosphanilidene)-
1,1,2,3-propanetetra Carboxylate (5b)
◦
◦
Colorless crystals (yield 90%); mp 112 C–113 C; IR (KBr) (νmax/cm−1): 3435
(NH), 1744, 1727, and 1692 (C O); 1H NMR (500.1 MHz, CDCl3): δH 0.38 (t, 3H, 3JHH
=
3
7.1 Hz, CH3), 1.0–1.05 (m, 6H, 2CH3), 1.22 (t, JHH = 7.1 Hz, 3H, CH3), 2.03 (s, 3H,
3
CH3CO, E-isomer), 2.07 (s, 3H, CH3CO, Z-isomer), 3.50 (d, JHH = 19.2 Hz, 1H, CH,
Z-isomer), 3.52 (d, 3JHH = 21.6 Hz, 1H, CH, E-isomer), 3.35–3.41 and 3.63–3.72 (2m, 4H,
2OCH2), 3.90–4.0 and 4.08–4.40 (2m, 4H, 2OCH2), 7.43–7.69 (m, 15H, aromatic protons),
9.31 (s, 1H, NH); 13C NMR (125.8 MHz, CDCl3): δC 13.6, 13.7, 13.8, and 14.2 (4CH3),
23.3 (CH3CO), 40.1 (d, 1JPC = 125.2 Hz, P C), 49.1 (d, 2JPC = 13.9 Hz, CH), 58.1, 60.8,
3
1
61.0, and 61.2 (4OCH2), 69.9 [d, JPC = 4.3 Hz, C(CO2Et)2], 126.4 (d, JPC = 93.5 Hz,
Ci), 128.3 (d, 3JPC = 12.2 Hz, Cm), 131.9 (Cp), 134.2 (d, 2JPC = 8.1 Hz, Co), 166.1 (C O,
2
amide), 168.8 and 170.0 (2C O, 2CO2Et), 171.4 (d, JPC = 12.8 Hz, C O, CO2Me),
172.7 (d, 3JPC = 6.3 Hz, C O, CO2Me); Ms, m/z(): 651 (M+, 5), 434 (20), 287 (7), 262
(5), 182 (20), 174 (19), 44 (100); Anal. Calcd. for C35H39NO9P: C, 64.81; H, 6.05; N, 2.15.
Found: C, 64.72; H, 5.97; N, 2.10.
2,3-Di-tert-butyl-1,1-diethyl-1-(acetylamino)-3-
(1,1,1-triphenylphosphanilidene)-1,1,2,3-propane Tetra Carboxylate (5c)
◦
◦
Colorless crystals (yield 91%); mp 109 C–111 C; IR (KBr) (νmax/cm−1): 3450
(NH), 1752, 1748, and 1698 (C O); 1H NMR (500.1 MHz, CDCl3): δH 0.90 and 1.45 (2s,
18H, 2CMe3, Z-isomer), 1.47 and 1.48 (2s, 18H, 2CMe3, E-isomer), 0.96 (t, 3JHH = 7.2, 3H,
CH3), 1.02 (t, 3JHH = 7.2, 3H, CH3), 1.41 (s, 9H, CMe3), 2.04 (s, 3H, CH3CO, Z-isomer),
3
2.18 (s, 3H, CH3CO, E-isomer), 3.27 (d, JHH = 22.0 Hz, 1H, CH, E-isomer), 3.30 (d,
3JHH = 20.0 Hz, 1H, CH, Z-isomer), 3.55–3.79, 3.84–4.05 (2m, 4H, 2OCH2), 7.28–7.82
(m, 15H, aromatic protons), 9.90 (s, 1H, NH); 13C NMR (125.8 MHz, CDCl3): δC 13.6
and 13.8 (2CH3), 23.1 (CH3CO), 28.1 (2CMe3), 39.7 (d, 1JPC = 125.0 Hz, P C), 49.1 (d,
2JPC = 13.8 Hz, CH), 60.8 and 60.9 (2OCH2), 70.02 [d, 3JPC = 4.4 Hz, C(CO2Et)2], 76.0
and 80.7 (2OCMe3), 126.5 (d, 1JPC = 93.5 Hz, Ci), 128.5 (d, 3JPC = 12.1 Hz, Cm), 131.9
(Cp), 132.1 (d, 2JPC = 9.8 Hz, Co), 166.0 (C O, amide), 169.1 and 170.0 (2C O, 2CO2Et),
171.3 (d, 2JPC = 12.1 Hz, C O, CO2Me), 171.6 (d, 3JPC = 6.8 Hz, C O, CO2Me); Ms,
m/z (%): 707 (M+, 4), 544 (5), 440 (15), 377 (61), 288 (25), 262 (10), 183 (16), 174 (22),
77 (7), 58 (100), 44 (29); Anal. Calcd. for C39H47NO9P: C, 66.47; H, 6.71; N, 1.99. Found:
C, 66.38; H, 6.65; N, 1.93.
Preparation of 2,2-Di-diethyl–3-methyl-1-acetyl-5-oxo-4-
(1,1,1-triphenylphosphanil-idene)-2,2,3-pyrolidine Tricarboxylate (6)
Compound 5a was refluxed in toluene and after 24 h it was converted to compound
6 by loss of ROH. The solvent was removed under reduced pressure and viscous residue
was purified by silica gel (Merck silica gel, 230–400 mesh) column chromatography using
hexane:ethyl acetate (30:70). The solvent was removed under reduced pressure and the
product 6a was obtained as white powder.

SYNTHESIS OF PHOSPHORUS YLIDES
675
2,2-Di-diethyl–3-methyl-1-acetyl-5-oxo-4-
(1,1,1-triphenylphosphanilidene)-2,2,3-pyrolidine Tricarboxylate (6)
◦
◦
White powder (yield 28%); mp 85 C–87 C; IR (KBr) (νmax/cm−1): 1760, 1756,
1
and 1748 (C O); H NMR (500.1 MHz, CDCl3): δH 1.20–1.26 (m, 6H, 2CH3), 2.49(s,
3H, CH3CO), 3.32 (s, 3H, OCH3), 3.72 (d, 3JPH = 16.6 Hz, 1H, CH), 4.10–4.30 (m, 4H,
2OCH2), 7.45–7.65 (m, 15H, aromatic proton); 13C NMR (125.8 MHz, CDCl3): δC 13.9
and 14.0 (2CH3) 23.8 (CH3CO), 49.6 (d, 2JPC = 12.2 Hz, CHCO2Me), 51.8 (OCH3), 42.29
(d, 1JPC = 138.9 Hz, P C), 62.3 and 62.4 (2OCH2), 63.1 [C(CO2Et)2], 124.5 (d, 1JPC
=
=
92.8 Hz, Ci), 129.1 (d, 3JPC = 12.7 Hz, Cm), 132.8 (d, 4JPC = 2.8 Hz, Cp), 133.7(d, 2JPC
2
10.4 Hz, Co), 165.8 (C O, acetyl group), 168.2 (d, JPC = 12.5 Hz, C O imide), 169.2
3
(d, JPC = 17.9 Hz, C O, CO2Me), 171.0 and 173.1 (2C O, 2CO2Et); Anal. Calcd for
C32H34NO8P: C, 64.97; H, 5.78; N, 2.36. Found: C, 64.88; H, 5.72; N, 2.31.
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