A facile synthesis and theoretical study of novel stable heterocyclic phosphorus ylides containing a 2,4-dimethyl-3-acetyl moiety

Article abstract of DOI:10.1080/10426500902845753

A general and practical route has been considered for the synthesis of stable heterocyclic phosphorus ylides 3a-c by a one-pot condensation reaction between dialkyl acetylenedicarboxylate and triphenylphosphine in the presence of -NH heterocyclic compounds such as 2,4-dimethyl-3-acetyl pyrrole. The stable ylides 3a-b exist in solution as a mixture of the two isomers, while 3c indicates only one isomer. For this reason, the assignments of more stable Z- or E-isomers as the major or minor forms were investigated using the theoretical calculations. 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.

Full text of DOI:10.1080/10426500902845753

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A Facile Synthesis and Theoretical Study
of Novel Stable Heterocyclic Phosphorus
Ylides Containing a 2,4-Dimethyl-3-
acetyl Moiety
Sayyed Mostafa Habibi-Khorassani a , Ali Ebrahimi a , Malek Taher
Maghsoodlou a , Faramarz Rostami Charati b , Mohammad Amin
Kazemian a & Pouya Karimi a
a Department of Chemistry , The University of Sistan and
Baluchestan , Zahedan, Iran
b High Education Center , Gorgan University of Agricultural Sciences
and Natural Resources , Gonbad, Iran
Published online: 24 Feb 2010.
To cite this article: Sayyed Mostafa Habibi-Khorassani , Ali Ebrahimi , Malek Taher Maghsoodlou ,
Faramarz Rostami Charati , Mohammad Amin Kazemian & Pouya Karimi (2010) A Facile Synthesis
and Theoretical Study of Novel Stable Heterocyclic Phosphorus Ylides Containing a 2,4-Dimethyl-3-
acetyl Moiety, Phosphorus, Sulfur, and Silicon and the Related Elements, 185:3, 559-566, DOI:
10.1080/10426500902845753
To link to this article: http://dx.doi.org/10.1080/10426500902845753
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Phosphorus, Sulfur, and Silicon, 185:559–566, 2010
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500902845753
A FACILE SYNTHESIS AND THEORETICAL STUDY OF
NOVEL STABLE HETEROCYCLIC PHOSPHORUS YLIDES
CONTAINING A 2,4-DIMETHYL-3-ACETYL MOIETY
Sayyed Mostafa Habibi-Khorassani,1 Ali Ebrahimi,1
Malek Taher Maghsoodlou,1 Faramarz Rostami Charati,2
Mohammad Amin Kazemian,1 and Pouya Karimi1
1Department of Chemistry, The University of Sistan and Baluchestan,
Zahedan, Iran
2High Education Center, Gorgan University of Agricultural Sciences and Natural
Resources, Gonbad, Iran
A general and practical route has been considered for the synthesis of stable heterocyclic
phosphorus ylides 3a–c by a one-pot condensation reaction between dialkyl acetylenedicar-
boxylate and triphenylphosphine in the presence of -NH heterocyclic compounds such as
2,4-dimethyl-3-acetyl pyrrole. The stable ylides 3a–b exist in solution as a mixture of the
two isomers, while 3c indicates only one isomer. For this reason, the assignments of more
stable Z- or E-isomers as the major or minor forms were investigated using the theoretical
calculations.
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.
Keywords 2,4-Dimethyl-3-acetyl pyrrole; intramolecular hydrogen bond; stable phosphorus
ylides; theoretical calculations; triphenylphosphine; Z- or E-isomers
INTRODUCTION
Pyrrole derivatives as heterocyclic organophosphorus compounds are important inter-
mediates, not only for the synthesis of drugs, pigments, and pharmaceuticals, but also for the
development of organic functional groups.1 Pyrroles occur in numerous pharmacologically
active natural and unnatural products. Functionalized pyrroles represent building blocks of
natural tetrapyrrole pigments, such as porphobilinogen or bilirubin, and of various other
natural products and their analogues.2,3 Morever, the pyrrole zomepirac possesses analgesic
and antiphlogistic activity and has found clinical applications.2 Substituted oligopyrroles
Received 27 January 2009; accepted 10 February 2009.
We gratefully acknowledge the financial support from the Research Council of Sistan & Baluchestan
University and Gorgan University of Agricultural Sciences and Natural Resources.
Address correspondence to Sayyed Mostafa Habibi-Khorassani, Department of Chemistry, The University
of Sistan and Baluchestan, P.O. Box 98135-674, Zahedan, Iran. E-mail: smhabibius@yahoo.com
559

560
S. M. HABIBI-KHORASSANI ET AL.
are of interest in the field of material sciences.2,3 With respect to the importance of het-
erocyclic organophosphorus compounds, the development of simple synthetic routes for
widely used organic materials, and especially for organophosphorus compounds, from read-
ily available reagents is one of the major tasks in organic synthesis.4 Organophosphorous
compounds are of particular interest as synthetic targets due to their importance in in-
dustrial, biological, and chemical syntheses.4–10 Many strategies have appeared describing
novel syntheses of organophosphorus compounds, including previous reports.11–27 In this
article, we report an efficient synthetic route to sterically congested nitrogen-containing
phosphorus ylides 3a–c using triphenylphosphine, dialkyl acetylenedicarboxylates 1, and
2,4-dimethyl-3-acetyl pyrrole 2. In addition, an atoms–in-molecules (AIM) analysis at
the HF/6-31G level of theory has been performed in order to gain a better understand-
ing of the most geometrical parameters of both the Z-3(a,c) and the E-3(a,c) phosphorus
ylides.
RESULTS AND DISCUSSION
The reaction between triphenylphosphine and dialkyl acetylenedicarboxylates 1(a,
b, or c) led to zwiterion 2, which was followed by an attack by the nitrogen amine of
the 2,4-dimethyl-3-acetyl pyrrole, to generate the phosphorus ylides E-3 and Z-3. These
reactions were carried out in diethyl ether at ambient temperature and were completed
1
after approximately 6 h. The H, 13C, and 31P NMR spectra of the crude product clearly
indicated the formation of stable phosphorus ylides 3 (Figure 1). No product other than 3
could be detected by NMR spectroscopy. The structures of compounds 3a–c were deduced
from the elemental analyses, IR, 1H, 13C, and 31P NMR spectra. The mass spectra of these
compounds displayed molecular ion peaks at appropriate m/z value. The 1H NMR spectrum
(500 MHz) of 3a displayed six singlets at δ = 1.42, 1.36, 2.04, 2.05, 2.13, 2.14 ppm arising
from methyl protons on pyrrole ring along with two methyl protons from two ester groups
and two significant signals at δ = 6.7 and 6.6 ppm from the hydrogen on C-5 of pyrrole ring
for the major Z-3a and minor E-3a isomers, respectively. The aromatic protons (30 protons
of six phenyl groups) appeared as a multiplet at δ = 7.20–7.38. Although the presence of the
31P nucleus has complicated both the 1H and 13C NMR spectra of 3a, it helps in assignment
of signals by long-range, spin–spin couplings with 1H and 13C nuclei. The 1H and 13C NMR
Figure 1 The reaction between triphenylphosphine, dialkyl acetylendicarboxylate 1 (1a, 1b, or 1c), and 2,4-
dimethyl-3-acetyl pyrrole 2 for generating stable phosphorus ylide 3 (3a, 3b, or 3c).

NOVEL STABLE HETEROCYCLIC PHOSPHORUS YLIDES
561
Figure 2 Two isomers (major and minor) of stable phosphorus ylides 3a–b.
spectra of 3b are similar to those of 3a, except for the signals from ester groups, which
1
appear as characteristic resonance lines with the corresponding chemical shifts. The H,
13C, and 31P NMR spectra of compounds 3a and 3b showed the mixture of the two isomers
(see Figure 2). The assignments of E-3(a,b) and Z-3(a,b) isomers as the major or minor
forms in phosphorus ylides have been reported previously.28–32 The 1H NMR spectrum of 3a
exhibited two signals at 2.98 and 3.52 ppm arising from methoxy group in the Z-isomer, and
two signals at 3.38 and 3.50 ppm for that in the E-isomer. The methyl group at 2.98 in the
Z-isomer is shielded due to the anisotropic effect of a phenyl group of triphenylphosphine.
This effect confirms why the Z-3a and E-3a isomers could appear as the major and minor
forms, respectively, with the percentage of both isomers, as reported in the Experimental
section. The signals for methine protons appeared as two doublets at δ = 4.24 Hz (3JPH
=
4.43) and δ = 4.29 Hz (3JPH = 5.50), respectively, for the Z- and E- isomers. The 13C NMR
spectrum of 3a exhibited 36 distinct resonances in a good agreement with the mixture of the
two isomers. For the 13C NMR spectroscopy, the anisotropic effect could not be reported for
the methoxy group in the Z-isomer because of the small difference of their chemical shifts.
The structural assignments made on the basis of the 1H and 13C NMR spectra of compounds
3a and 3b were supported by the IR spectra. The carbonyl region of these compounds 3a–b
exhibited absorption bands for each compound. The ester absorption is at 1600–1735 cm−1
,
the conjugation of negative charge of the ylide moiety with the adjacent carbonyl group
accounting for the reduction in frequency of the carbonyl bands, and allows determination
of the ratio between the E- and Z-isomers. The ylide moiety of these compounds is strongly
conjugated with the adjacent carbonyl group, and rotation around the partial double bond in
the E-3(a,b) and the (Z)-3(a,b) isomers (Figure 2) is slow on the NMR time scale at ambient
temperature.
As can be seen in the Experimental section, the 13C NMR spectrum of 3c displays 11
distinct resonances, which is accord with only one isomer. This observation, presumably, is
attributed to the steric factor of the bulky tert-butyl groups and more plausible intramolec-
ular hydrogen bond in stable phosphorus ylides 3c (see Figure S2 available online in the
Supplemental Materials). On the basis of the well established chemistry of trivalent phos-
phorus nucleophiles,3–5 it is reasonable to assume that phosphorus ylide 3 results from the
initial addition of triphenylphosphine to the acetylenic ester and subsequent protonation of
the 1:1 adduct by the 2,4- dimethyl-3-acetyl 2 (see Figure 1).

562
S. M. HABIBI-KHORASSANI ET AL.
THEORETICAL STUDY
Recently, different reports have been published on the synthesis of stable phosphorus
ylides from the reaction between triphenylphosphine and reactive acetylenic esters in the
presence of N H, C H, or S H heterocyclic compounds. These ylides usually exist as
a mixture of two isomers. The determination of a more stable isomer is impossible by the
31P, 13C, and 1H NMR techniques. For this reason, theoretical study has been employed in
order to gain a better understanding of the most important geometrical parameters and also
relative energies of both isomers.
CALCULATIONS: STRUCTURE AND STABILITIES
In order to determine which is the more stable form of both Z-3(a,c) and E-3(a,c)
isomer of the ylides (3a and 3c), their structures were first optimized at the HF/6–31G level
of theory33 by Gaussian 98 program package.34 Also the relative energies of the two isomers
have been calculated at the HF/6–31G and B3LYP/6–311++G (d,p) levels (see Figures S1
and S2, Supplementary Materials). The relative stabilization energies for both Z-3(a,c) and
E-3(a,c) isomers are reported in Table I. As can be seen, Z-3a and Z-3c isomers are more
stable than E-3a and E-3c forms at the HF/6–31G and B3LYP/6–311++G(d,p) levels.
Further investigations were undertaken in order to determine more effective factors
on the stability of both isomers, on the basis of AIM calculations35 at the HF/6–31G level
of theory by the AIM2000 program package.36 As noted in the literature,37 the ranges of
2
5
ρ(r) and ∇ ρ(r) are 0.002–0.035 e/a03 and 0.024–0.139 e/a0 , respectively, if H-bonds exist.
The number of hydrogen bonds in both categories (E-3a and Z-3a) and (E-3c and Z-3c)
are 10 and 7 and also 14 and 12, respectively. In addition, the ranges of their electron
densities are in 0.003–0.018 and 0.007–0.018 au and also 0.005–0.018 and 0.001–0.018
au), respectively. With respect to the large number of hydrogen bonds in both the Z- and
the E-isomers, it is difficult to make a precise decision for determination of the more stable
isomer. (See Figures S1 and S2, Supplemental Materials.)
On the basis of theoretical calculations (Table I), the difference between the relative
stability of the E-3a and Z-3a isomers in gas phase is small (0.91 kcal/mol), while it is
considerably greater in the E-3c and Z-3c (3.22 kcal/mol). Perhaps this noticeable difference
is taken more in solution media for 3c and, for this reason, it is possible to observe only
one isomer of 3c (E or Z). In the Experimental section, both the 1H NMR and 13C NMR
spectroscopies indicated only one isomer for the 3c ylide. Nevertheless, the result of our
calculations is different for 3a (observed as the two isomers), which may be attributed to
the negligible difference in relative stability of the E-3a and the Z-3a isomers. Perhaps
this negligible difference (0.67 or 0.91 kcal/mol) is not taken more considerably for 3a in
solution media, and for this reason it is possible to see the two isomers of 3a (both Z and E
Table I The relative energy (kcal/mol) for Z- and E-isomers of ylides 3a
and 3c calculated at HF/6–31G and B3LYP/6–311++G(d,p) levels
Conformer
HF
B3LYP
Z-3a
E-3a
Z-3c
E-3c
0.00
0.67
0.00
3.08
0.00
0.91
0.00
3.22

NOVEL STABLE HETEROCYCLIC PHOSPHORUS YLIDES
563
isomers). In recent case, the 1H, 13C, and 31P NMR data exhibited the two isomers of ylide
3a, which were consistent with the obtained result from the theoretical investigations.
CONCLUSION
In conclusion, we have prepared the novel stable phosphorus ylides using a one-
pot reaction between triphenylphosphine and acetylenic compounds in the presence of a
NH heterocyclic compound such as 2,4-dimethyl-3-acetyl pyrrole. The present method
carries the advantage that not only is the reaction performed under neutral conditions, but
also the substances can be mixed without any activation or modification. In addition, the
assignments of the Z and E isomers as the major or minor forms in both of 3a and 3c ylides
were undertaken by the theoretical study.
EXPERIMENTAL
Dialkyl acetylenedicarboxylates, triphenylphosphine, and 2,4-dimethyl-3-acetyl pyr-
role were obtained from Fluka (Buchs, Switzerland) and used without further purification.
Melting points and IR spectra of all compounds were measured on an Electrothermal 9100
1
apparatus and a Shimadzu IR-460 spectrometer, respectively. The H, 13C, and 31P NMR
spectra were obtained from a Bruker DRX-500 Avance instrument with CDCl3 as solvent at
500.1, 125.8, and 202.4 MHz, respectively. The mass spectra were recorded on a Shimadzu
QP 1100 EX mass spectrometer operating at an ionization potential of 70 eV. Elemental
analysis for C, H, and N were performed using a Heraeus CHN-O-Rapid analyzer.
General Procedure for Preparation of the Ylides 3
To a magnetically stirred solution of triphenylphosphine (0.262 g, 1 mmol) and
2,4-dimethyl-3-acetyl pyrrole (0.137 g, 1 mmol) in 5 mL of ethyl acetate, a solution of
dialkyl acetylendicarboxylate(1 mmol) in 1 mL of ethyl acetate was added dropwise at
−5◦C over 10 min. The reaction mixture was allowed to warm up to room temperature
and stirred for 1 h. The products 3a–c were filtered and washed with (3 × 10 mL) cold
diethyl ether. The characterization data of dialkyl 2-(2,4-dimethyl-3-acetyl pyrrole-1-yl)-
3-(triphenylphosphoranilidene)butandioate (3a–c) are given below.
Dimethyl 2-(2,4-Dimethyl-3-acetyl pyrrole-1-yl)-3-(triphenylphosphoran-
ylidene)butanedioate (3a). The product of 3a (Z) was obtained as pale orange powder,
mp 146–148◦C, and yield 95%. IR (νmax, cm−1): 1735 (C O of acetyl), 1730 (C O of
ester), 1600 (C C). MS (m/z,%): 510 (M OCH3, 5), 405 (M-(C8H10ON-), 60), 279
(M PPh3, 20), 262 (PPh3, 75), 77 (Ph, 25). Anal. Calcd for C32H32NO5P (Mw = 541), C,
70.97; H, 5.91; N, 2.58, Found: C, 71.3; H, 5.84; N, 2.63.
Major isomer (Z)-3a: (60%) 1H NMR (500.1 MHz, CDCl3): δH 1.41 (3H, s, CH3),
3
2.04 (3H, s, CH3), 2.13 (3H, s, CH3), 2.98, 3.52 (6H, s, 2 OCH3), 4.24 (1H, d, JPH
=
4.43 Hz, P C CH), 6.7 (1H, s, C5 of pyrrole), 7.20–7.27 (15H, m, 3C6H5), 13C NMR
1
(125.8 MHz, CDCl3): δ 11.03, 14.4 and 22.9 (s, 3CH3 on pyrrole ring), 42.8 (d, JPC
=
135 Hz, P C), 49.4, 52.9 (s, 2 OCH3), 58.6 (d, 2JPC = 16.1 Hz, P C CH), 118.2, 118.9
1
3
and 120.8 (3C, of pyrrole ring), 126.4 (d, JPC = 92.1 Hz, Cipso), 129.1 (d, JPC = 4 Hz,
Cmeta), 132.4 (s, Cpara), 133.6 (d, 2JPC = 5.9 Hz, Cortho), 135.5 (s, C2 of pyrrole ring), 169.8
2
3
(d, JPC = 12.9 Hz, C O), 172.3 (d, JPC = 6.5 Hz, C O), 196.0 (s, C O of acetyl).
31P NMR (202.4 MHz, CDCl3): δP 24.2 (s, Ph3P+ C).

564
S. M. HABIBI-KHORASSANI ET AL.
Minor isomer (E)-3: (40%),1H NMR (500.1 MHz, CDCl3): δH 1.36 (3H, s, CH3),
3
2.05 (3H, s, CH3), 2.14 (3H, s, CH3), 3.38, 3.50 (s, 6H, 2OCH3), 4.29 (1H, d, JPH
=
5.5 Hz, P C CH), 6.6 (1H, s, C5 of pyrrole), 7.31–7.38 (15H, m, 3C6H5), 13C NMR
(125.8 MHz, CDCl3): δC 11.13, 14.6 and 23.1 (s, 3CH3 on pyrrole ring), 42.2 (d, 1JPC
=
127.3 Hz, P C), 50.47, 52.72 (s, 2 OCH3), 58.2 (d, 2JPC = 16.3 Hz, P C CH), 118.04,
118.4 and 121.1 (3C, of pyrrole ring), 125.7 (d, JPC = 92.2 Hz, Cipso), 128.9 (d, 3JPC
=
1
2
3.9 Hz, Cmeta), 132.3 (s, Cpara), 133.5 (d, JPC = 5.8 Hz, Cortho), 135.8 (s, C2 of pyrrole
ring), 170.5 (d, 2JPC = 17.7 Hz, C O), 172.1 (d, 3JPC = 7.1 Hz, C O), 195.9 (s, C O of
acetyl). 31P NMR (202.4 MHz, CDCl3): δP 24.9 (s, Ph3P+- C).
Diethyl 2-(2,4-Dimethyl-3-acetyl pyrrole-1-yl)-3-(triphenylphosphoran-
ylidene)butanedioate (3b). The product of 3b (Z) was obtained as pale orange
powder, mp 134–136◦C, and yield 80%. IR (νmax, cm−1): 1735 (C O of acetyl), 1730
(C O of ester), 1600 (C C), 1100 (C-O ether). MS (m/z,%): 443 (M-(C8H10ON-), 50),
262 (PPh3, 90), 77 (Ph, 25).Anal. Calcd for C34H36NO5P (Mw = 569), C, 71.73; H, 6.33;
N, 2.46, Found: C, 71.85; H, 6.19; N, 2.66.
Major isomer (Z)-3b: (55%) 1H NMR (500.1 MHz, CDCl3): δH 1.03, 1.38 (6H, t,
3JHH = 7.1 Hz, 2CH3), 2.04, 2.13 and 2.98, (9H, s, 3CH3 on pyrrole ring), 3.53 (2H, m,
CH2), 3.86 (2H, m, CH2), 6.72 (1H, s, C5 of pyrrole), 7.33–7.41 (15H, m, 3C6H5), 13C
NMR (125.8 MHz, CDCl3): δC 11.08, 14.9 and 23.2 (s, 3CH3 on pyrrole ring), 14.02, 14.26
(s, CH3 of 2OEt), 41.91 (d, 1JPC = 127.6 Hz, P C), 58.6 (d, 2JPC = 16.2 Hz, P C CH),
58.6, 61.52 (s, 2CH2 of OEt), 118.9, 119.0 and 120.74 (3C, of pyrrole ring), 126.6 (d,
1JPC = 91.9 Hz, Cipso), 128.9 (d, 3JPC = 4.2 Hz, Cmeta), 132.3 (s, Cpara), 133.7 (d, 2JPC
=
2
5.6 Hz, Cortho), 135.6 (s, C2 of pyrrole ring), 169.4 (d, JPC = 12.9 Hz, C O), 171.6 (d,
3JPC = 13.13 Hz, C O), 195.9 (s, C O of acetyl). 31P NMR (202.4 MHz, CDCl3): δP
25.17 (s, Ph3P+- C).
Minor isomer (E)-3b: (45%), δH 1H NMR (500.1 MHz, CDCl3): δH 0.9, 1.09 (6H,
t, 3JHH = 7.1 Hz, 2CH3), 2.05, 2.15 and 3.4, (9H, s, 3CH3 on pyrrole ring), 3.55 (2H, m,
CH2), 3.89 (2H, m, CH2), 6.68 (1H, s, C5 of pyrrole), 7.21–7.27 (15H, m, 3C6H5), 13C
NMR (125.8 MHz, CDCl3): δC 11.17, 14.6 and 23.6 (s, 3CH3 on pyrrole ring), 14.23, 14.47
(s, CH3 of 2OEt), 42.69 (d, 1JPC = 136 Hz, P C), 58.1 (d, 2JPC = 15.8 Hz, P C CH),
58.5, 61.46 (s, 2CH2 of OEt), 117.88, 118.64 and 120.94 (3C, of pyrrole ring), 125.93 (d,
1JPC = 92.3 Hz, Cipso), 128.4 (d, 3JPC = 4.1 Hz, Cmeta), 132.2 (s, Cpara), 133.5 (d, 2JPC
=
5.4 Hz, Cortho), 135.5 (s, C2 of pyrrole ring), 170.3 (d, 2JPC = 18.03 Hz, C O), 171.4 (d,
3JPC = 12.23 Hz, C O), 195.7 (s, C O of acetyl). 31P NMR (202.4 MHz, CDCl3): δP 25.0
(s, Ph3P+ C).
Di-tert-butyl 2-(2,4-Dimethyl-3-acetyl pyrrole-1-yl)-3-(triphenylphospho-
ranylidene)butanedioate (3c). The product (Z)-3c was obtained as pale white powder,
mp 160–162◦C, and yield 90%. IR (νmax, cm−1): 1735 (C = O of acetyl), 1730 (C = O
t
of esteres), 1600 (C = C). MS (m/z,%): 489 (M (C8H10ON , 5), 423 (M 2CO2 Bu, 5),
t
t
332 (M CO2 Bu (C8H10ON ), 25), 287 (M 2CO2 Bu (C8H10ON , 30), 77 (Ph, 8),
57 (tBu, 75). Anal. Calcd for C38H44NO5P C, 72.96; H, 7.04; N, 2.24, Found: C, 73.18; H,
7.21; N, 2.33. 1H NMR (500.1 MHz, CDCl3): δH 0.9 (9H, s, tBu), 1.54 (9H, s, tBu), 1.57,
2.30 and 2.36 (9H, s, CH3 on pyrrole ring), 4.33 (1H, d, 3JPH = 17.54 Hz, P C CH), 7.01
(1H, s, C5 of pyrrole), 7.45–7.6 (15H, m, 3C6H5), 13C NMR (125.8 MHz, CDCl3): δC 10,9,
1
2
14.6 and 22.8 (s, 3CH3 on pyrrole ring), 41.5 (d, JPC = 128 Hz, P C), 58.9 (d, JPC
=
16.7 Hz, P C CH), 77.6, 81.02 (s, 2 O C), 117.9, 119.1 and 120.6 (3C, of pyrrole ring),
127.2 (d, 1JPC = 91.8 Hz, Cipso), 128.7 (d, 3JPC = 12.23 Hz, Cmeta), 132.1 (d, 4JPC = 2.8
Hz, Cpara), 133.6 (d, 2JPC = 9.7 Hz, Cortho), 135.4 (s, C2 of pyrrole ring), 168.78 (d, 2JPC
=

NOVEL STABLE HETEROCYCLIC PHOSPHORUS YLIDES
565
12.4 Hz, C = O), 170.2 (d, 3JPC = 13.1 Hz, C = O), 195.8 (s, C = O of acetyl). 31P NMR
(202.4 MHz, CDCl3): δP 23.7 (s, Ph3P+ C).
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