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Short communication
Synthesis of Functionalized Stable Phosphorus Ylides.
New Synthesis of Dimethyl (Z)-2-[2-(ethoxycarbonyl)-1-cyclopentenyl]-2-butenedioates
Sakineh Asghari,* Zahra Sobhaninia and Zahra Naderi
Department of Chemistry, University of Mazandaran, P. O. BOX 453, Babolsar, Iran
* Corresponding author: E-mail: s.asghari@umz.ac.ir, Fax: 00981125233702
Received: 12-11-2007
Abstract
Ethyl 2-oxo-1-cyclopentanecarboxylate undergoes a reaction with dialkyl acetylenedicarboxylate in the presence of triphenyphosphine to produce stable phosphorus ylides in good yields. These ylides undergo intramolecular Wittig reaction in boiling toluene to produce cyclobutene derivatives, which undergo ring-opening reactions to produce dialkyl (Z)-2-[2-(ethoxycarbonyl)-1-cyclopentenyl]-2-butenedioates.
Keywords: Ethyl 2-oxo-1-cyclopentanecarboxylate, dialkyl acetylenedicarboxylate, triphenylphosphine, intramolecular Wittig reaction.
1. Introduction
Organophosphorus compounds, those bearing a carbon atom directly bonded to a phosphorus atom are synthetic targets of interest, at least because of their value for a variety of industrial, biological, and chemical synthetic uses.1–3 Phosphorus ylides are reactive systems, which take part in many valuable reactions in the synthesis of organic products.4–6 We previously reported the synthesis of cyclobutene derivatives by intramolecular Wittig reaction, which were converted to electron-deficient 1,3-dienes.7–9 In continuation of studies in introducing the new methods on synthesis of phosphorus yli-de and electron-deficient compounds, we wish to report the reaction between ethyl 2-oxo-1-cyclopentanecar-boxylate 2 and dialkyl acetylenedicarboxylates in the presence of triphenylphosphine. Thus, reaction of trip-henylphosphine with electron-deficient acetylenic ester 1 in the presene of a CH-acid such as 2 leads to ylide 3 in good yields.
These compounds then undergo intramolecular Wittig reaction in boiling toluene to produce cyclobutene derivatives 4, which undergoes electrocyclic ring-opening reaction to generate highly functionalized 1,3-dienes 5 (Scheme 1).
2. Results and Discussion
On the basis of the chemistry of trivalent phosphorus nucleophiles,10,11 it is reasonable to assume that ylide 3 results from initial addition of triphenylphosphine to the acetylenic ester and subsequent protonation of the 1:1 ad-duct by 2, followed by attack of the carbon atom of the anion of 2 to vinyltriphenylphosphonium cation 6 to generate the stable ylide 3. This compound undergoes intramolecular Wittig reaction in boiling toluene to produce strained cyclobutene derivative 4, which is finally converted to electron-deficient 1,3 – dienes 5 via a ring-opening reaction (Scheme 2).
The structures of compounds 3a–c were deduced from IR, 1H and 13C NMR spectra. The mass spectra of these ylides are fairly similar and display the molecular ion peaks. Other fragmentations involved the loss of the ester moieties or PPh3 from the ion molecule. Although compounds 3 possesses two stereogenic centers, and two diastereomers are expected, the 1H NMR spectrum of the reaction mixture shows only one diastereoisomer.
The 1H and 13C NMR spectra of 3a–c are also consistent with the presence of two isomers (see experimental section). The ylide moiety of these compounds is strongly conjugated to the adjacent carbonyl group and its rotation
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ço2r
PPh,
III C I C02R
+
Q      0
OEt
CH2CI2	<W	OEt -^PPh
r.t.	M	
	H-7 R2OC	C02R
C02R
C02R
ring-opening
OEt
Scheme 1
about the partial double bound in (E)-3 and (Z)-3 geometrical isomers is slow on the NMR timescale at ambient temperature.
The assignment of the configuration (Z) to the major geometrical isomer of 3 is based on the 1H NMR chemical shift of the OR moiety, which is expected to be shielded as a result of the anisotropic effect of the phenyl groups (Scheme 3).
The 1H NMR spectrum of 3a in CDCl3 at 25°C exhibits two sharp singlets at about 2.8 and 3.64 ppm for the methoxy groups of the Z– isomer, and two sharp singlets at about 3.46 and 3.60 ppm for the methoxy groups of the E-isomers. The diastereotopic protons of the CH2 groups appear as multiplet signals in 1H NMR spectrum as a result of the presence of chiral centers in compound 3.
Toluene reflux
OEt
The presence of the 31P nucleus in compound 3 helps to assign the signals by long-range couplings with 1H and 13C nuclei (see experimental section). The 13C NMR spectrum of 3a displays two signals at about 48.4 and 51.7 ppm for two methoxy groups and a doublet at about 39.0 ppm (1JPC = 125.8 Hz) for P=C group of Z-isomer and two signals at about 49.5 and 51.6 ppm for two methoxy groups and also a doublet at about 39.6 ppm (1JPC = 125.5 Hz) for P=C group of E-isomer. Other signals exhibited characteristic resonance with appropriate chemical shifts for two geometrical isomers. The 1H and 13C NMR spectra of 3b and 3c are similar to those of 3a, except that for the ester groups, which exhibited characteristic resonances.
The structures of 5a–c were deduced from their 1H,
Scheme 3
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Ph3P       +      CCX,R—C=C—C02R

ph3p
Ph3P          H
0     o
R20C       C02R
Intramolecular Wittig reaction
C02R
N
C02R
O
^
ring opening
OEt
C02R
Scheme 2
13C NMR and IR spectral data. The strong carbonyl absorption bands at 1722–1735 cm–1 for all the compounds were observed. The 1H NMR spectrum of 5a displays characteristic signals at about 6.75 ppm for the CH group and appropriate chemical shifts in the olefinic region. Because of loss of the chiral center during the conversion of compound 3 to 5, the proton signals of CH2 groups were simplified in 5. The 13C NMR spectrum of 5a exhibits four signals at about 126.1, 132.0, 144.1 and 149.7 ppm for olefinic carbons. The partial assignment of these signals is given in experimental section. The mass spectra of the compound 5a displayed molecular ion peak at m/z = 282. Initial fragmentations involve loss of the alkoxy and esteric groups.
3. Experimental
Ethyl 2-oxo-1-cyclopentanecarboxylate, dialkyl acetylenedicarboxylate and triphenyl phosphine were obtained from Fluka (Buchs, Switzerland) and used without further purifications. Melting points were measured with an Electrothermal 9100 apparatus. 1H, 13C and 31P NMR
spectra were measured at 500.1, 125.8, and 202.5 MHz, respectively, with a Bruker DRX-500 Avance instrument. CDCl3 was used as solvent. IR spectra were recorded on a Shimadzu FT-IR Bruker Vector 22 spectrometer. Mass spectra were recorded on a Finnigan-Matt 8430 mass spectrometer operating at an ionization potential of 70 eV.
General procedure for preparation of dialkyl 2-[l-(et-hoxycarbonyl)-2-oxocyclopentyl]-3-(l,l?l-triphenyl-A,5-phosphanylidene)succinate compounds (exampli-fied by 3a).
To a magnetically stirred solusion of ethyl 2-oxo-1-cyclopentane carboxylate (0.31 g, 2 mmol) and trip-henylphosphine (0.52 g, 2 mmol) in CH2Cl2 (10 ml) was added, dropwise, a mixture of dimethyl acetylenedicar-boxylate (0.28 g, 2 mmol) in CH2Cl2 (3 ml) at -10 °C over 10 min. The mixture was allowed to stand at room temperature for 24 hours. 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 (1:5) as eluent. The solvent was removed under reduced pressure and ylide 3a was obtained.
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1         Dimethyl 2-[l-(ethoxycarbonyl)-2-oxocyclopentyl]-3-
2        (l,l?l-triphenyl-A.5-phosphanylidene) succinate (3a):
3        White powder; m.p. 170 -172 °C, yield 0.9 g (80%); IR
4        (KBr) (v      cm4): 3050 (CH), 2985 (CH), 1735, 1725
 max,
5        (C=0), 1640 (C=C); MS, m/z (%): 279 (OPPh 3+ +l, 3),
6        262 (+PPh3,  5),   180  [M+-(PPh3+2C02Me),   19],  83
7        [M+-(C02Et+PPh3+Me2OCC=CC02Me)+l,    45],    57
8        (CH3CH20+, 100); Anal. Calcd for C32H3307P (560.59):
9        C, 68.56; H, 5.93; Found: C, 68.49; H, 5.89.
10                Major isomer, 3a-(Z) (68%), :H NMR (500.1 MHz,
11        CDC13): SH 1.03 (3H, t, 3JHH 7.1 Hz, CH3), 1.99-2.05 (2H,
12       m,  CH2),  2.14-2.20  (2H,  m,  CH2),  2.64-2.68  and
13       2.90-2.95 (2H, 2m, CH2), 2.8 (3H, s, OCH3), 3.58 (IH, d,
14       3JPH 18.8 Hz, CH), 3.64 (3H, s, OCH3), 3.76-3.83 (2H, m,
15       OCH 2 ), 7.43-7.53 (15H, m, arom); 13 C NMR (125.8
16       MHz, CDC13): 8C 13.9 (CH3), 20.3, 30.6 and 36.8 (3CH2),
17       39.0 (d, Jpc 125.8 Hz, P=C), 48.4 and 51.7 (20CH3), 49.1
18       (d, 2Jpc 13.7 Hz, CH), 60.9 (OCH2), 67.5 (quaternary car-
19       bon of cyclopentanone), 127.0 (d,  Jpc 92.7 Hz, C;   ),
20        128.3 (d, 3Jpc 11.9 Hz, Cmeta), 131.7 (C ara), 133.9 (d, Jpc
21        9.6 Hz, Cortho), 169.2 (C=0, ester), 170.0 (d, 2Jpc 13.8 Hz,
22       C=0 ester), 174.6 (d, 3 Jpc 6.5 Hz, C=0 ester), 213.5
23       (C=0, ketone); 31P NMR (202.5 MHz, CDC13): ôp 26.23.
24                Minor isomer, 3a-(E) (32%), :H NMR (500.1 MHz,
25       CDC13): ôH 1.17 (3H, t, 3JHH 7 Hz, CH3), 1.74-1.84 (4H,
26       m, 2CH2), 2.32-2.4 and 2.55-2.62 (2H, 2m, CH2), 3.46
27       (3H, s, OCH3), 3.56 (IH, d, 3JPH 17.9 Hz, CH), 3.54-3.57
28       (2H, m, OCH 2 ), 3.60 (3H, s, OCH 3 ), 7.66-7.72 (15H, m,
29       arom); 13C NMR (125.8 MHz, CDC13): 8C 13.9 (CH3),
30       20.3, 30.6 and 36.7 (3CH2), 39.6 (d, 1JPC 125.5 Hz, P=C),
31        48.2 (d, 2Jpc 14.1 Hz, CH), 49.5 and 51.6 (20CH3), 61.1
32       (OCH2), 67.1 (quaternary carbon of cyclopentanone),
33        127.1 (d, 1JPC 93.4 Hz, C; so), 128.4 (d, 3Jpc 11 Hz, C), 34
132.0 (C    ), 134.0 (d, 2J   9.6 Hz, C     ), 169.1
para
(C=O, ester), 171.1 (d, J    14.8 Hz, C=O ester),
35                                                        2 PC
174.6 (d, J    6.5 Hz, C=O ester), 212.8 (C=O, ketone).
36                       3 PC 37
31P NMR (202.5 MHz, CDCl3): ?P 25.94.
38
39       Diethyl   2-[l-(ethoxycarbonyl)-2-oxocyclopentyl]-3-
40       (l,l?l-triphenyl-X5-phospha nylidene)succinate (3b):
41        White powder, m.p. 160-162 °C, yield 1.1 g (90%); IR
42       (KBr) (vmax, cm-1): 3040 (CH), 2982 (CH), 1745, 1726
43       (C=0), 1645 (C=C); MS, m/z (%): 279 (OPPh 3+ +l, 10),
44       262 (+PPh3,  2),   180  [M+-(PPh3+2C02Et),   100],  86
45       (CHC02Et+, 100), 57 (CH3CH2CO+, 36); Anal. Calcd. for
46       C34H3707P (588.64): C, 69.38; H, 6.34; Found: C, 69.32;
47        H, 6.30.
48                Major isomer, 3b-(Z) (69%), :H NMR (500.1 MHz,
49       CDC13): 8H 0.32 (3H, t, 3JHH 7.1 Hz, CH3), 0.97 (3H, t,
50       3JHH 7.1 Hz, CH3), 1.26 (3H, t, 3JHH 7.1 Hz, CH3),
51        1.96-2.01  (2H, m,  CH 2 ),  2.11-2.21   (2H m,  CH 2 ),
52       2.85-2.89 and 3.12-3.16 (2H, 2m, CH2), 3.49 (IH, d, 3JHP
53        18.6 Hz, CH), 3.69-3.7 (2H, m, OCH2), 3.85-3.88 (2H,
54       m, OCH2), 3.95^.18 (2H, m, OCH2), 7.44-7.54 (15H, m,
55       arom); 13C NMR (125.8 MHz, CDC13): 8C 13.6, 13.8 and
56        13.9 (3CH3), 20.4, 30.7 and 36.8 (3CH2), 38.5 (d,  Jpc
125.8 Hz, P=C), 48.1 (d, 2JPC 14 Hz, CH), 60.4, 60.8 and       1
60.8 (3OCH2), 67.6 (d, 3JPC 4 Hz, quaternary carbon of       2
cyclopentanone), 127.2 (d, 1JPC 92.1 Hz, Cipso), 128.2 (d,       3
3JPC 12 Hz, Cmeta), 131.6 (d, 4JPC 2.4 Hz, Cpara), 134.0 (d,
4
2JPC 9.6 Hz, Cortho), 170.0 (d, 2JPC 13.1 Hz, C=O ester),       5
170.2 (C=O ester), 174.1 (d, 3JPC 7 Hz, C=O ester), 214.9       6
(C=O, ketone); 31P NMR (202.5 MHz, CDCl3): ?P 26.14.        7
Minor isomer, 3b–(E) (31%), 1H NMR (500.1 MHz,       8
CDCl3): ?H 1.03 (3H, t, 3JHH 7.1 Hz, CH3), 1.14 (3H, t,       9
3JHH 7 Hz, CH3), 1.32 (3H, t, 3JHH 7.1 Hz, CH3), 1.74–1.81      10
(2H, m, CH2), 2.38–2.5 and 2.26–2.68 (2H, 2m, CH2),      11
2.92–3.03 and 3.18–3.25 (2H, 2m, CH2), 3.52 (1H, d, 3JPH      12
18.8 Hz, CH), 3.52–3.70 (2H, m, OCH2), 3.76–3.83 (2H,      13
m, OCH2), 3.95–4.18 (2H, m, OCH2), 7.70–7.80 (15H, m,      14
arom); 13C NMR (125.8 MHz, CDCl3): ?C 14.3, 14.9 and      15
15.1 (3CH3), 20.3, 29,9 and 36.6 (3CH2), 38.9 (d, 1JPC      16 121.5 Hz, P=C), 49.1 (d, J   14.0 Hz, CH), 60.6, 60.7 and
2 PC                                                  17
61.0 (3OCH2), 66.0 (d, 3JPC 4 Hz, quaternary carbon of      18
cyclopentanone), 127.2 (d, 1JPC 92.1 Hz, Cipso), 128.3 (d,      19 3J   11.5 Hz, C    ), 131.6 (d, 4J   2.4 Hz, C    ), 134.0 (d,
2JPC 9.6 Hz, Cortho), 169.6 (d, 2JPC 14.2 Hz, C=O ester), 169.3 (C=O, ester), 174.5 (d, 3JPC 6.9 Hz, C=O ester), 213.5 (C=O, ketone; 31P NMR (202.5 MHz, CDCl3): ?P 25.82.
20 21 22 23 24 25 Di-tert-butyl 2-[l-(ethoxycarbonyl)-2-oxocyclopentyl]- 26 3-(l,l?l-triphenyl-A,5-phosphanyllidene) succinate 27 (3c): White powder, m.p. 150-152 °C, yield 0.9 g (75%); 28 IR (KBr) (vmax, cm-1): 3030 (CH), 2978 (CH), 1750, 1725, 29 1714 (C=0), 1638 (C=C); MS m/z (%): 279 (OPPh3++l,
30 31 32 33
57), 180 [M+-(PPh3+2C02 Bu), 30], 83 (M+-(C02Et+PP-h3 +'Bu02CC^CC02'Bu), 24], 57 (C4H9+, 63), 43 (CH3CO+, 55); Anal. Calcd. for C38H4507P (644.75): C,
70.79; H, 7.04; Found: C, 70.73; H, 7.00.                             34
Major isomer, 3c-(Z) (81%), :H NMR (500.1 MHz,     35
CDC13): 8H 0.87 (9H, s, CMe3), 0.92 (3H, t, 3JHH 7.1 Hz,     36
CH3), 1.50 (9H, s, CMe3), 1.98-2.04 (2H, m, CH2),     37
2.06-2.33 (2H, m, CH2), 2.87-2.92 and 3.33-3.35 (2H,     38
2m, CH2), 3.4 (d, 3JPH 18.2 Hz, CH), 3.80-3.85 (2H, m,     39
OCH 2 ), 7.42-7.52 (15H, m, arom); 13 C NMR (125.8     40
MHz, CDC13): 8C 13.7 (CH3), 20.35 (CH2), 28.3 (CMe3),     41
28.4 (CMe3), 31.1 (CH2), 38.2 (d, Jpc 122 Hz, P=C), 40.2     42
(CH2), 48.9 (d, 2Jpc 14.2 Hz, CH), 60.7 (OCH2), 66.1 (d,     43 3Jpc 4.1 Hz, quaternary carbon of cyclopentanone), 76.8
44 45 46 47 48 49
and 80.0 (2OCMe3), 127.2 (d, 1JPC 93.1 Hz, Cipso), 127.9 (d, 3JPC 12.1 Hz, Cmeta), 131.5 (Cpara), 134.5 (d, 2JPC 9.5 Hz, Cortho), 169.1 (d, 2JPC 12.8 Hz, C=O ester), 170.6 (C=O, ester), 173.7 (d, 3JPC 7.2 Hz, C=O ester), 215.5 (C=O, ketone); 31P NMR (202.5 MHz, CDCl3): ?P 26.05.
Minor isomer, 3c–(E) (19%), 1H NMR (500.1 MHz, 50 CDCl3): ?H 1.18 (3H, t, 3JHH 7.1 Hz, CH3), 1.38 (9H, s, 51 CMe3), 1.49 (9H, s, CMe3), 1.98–2.04 (2H, m, CH2), 52 2.06–2.3 (2H, m, CH2), 2.87–2.9 and 3.11–3.17 (2H, 2m, 53 CH2), 3.46 (d, 3JPH 16.9 Hz, CH), 3.42–3.46 (2H, m, 54 OCH ), 7.6–7.99 (15H, m, arom);   C NMR (125.8 MHz,
2                                                   13                                             55
CDCl ): ?  15.2 (CH ), 20.5 (CH ), 28.5 and 28.8 (2CM-    56
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e3), 30.2 (CH2), 39.7 (CH2), 40.4 (d, 1 J PC 122 Hz, P=C),
48.3  (d, 2J PC 14 Hz, CH), 60.8 (OCH2), 65.7 (d, 3J PC 4 Hz, quaternary carbon of cyclopentanone), 77.6 and 79.9 (2OCMe3), 127.2 (d, 1JPC 93.1 Hz, Cipso), 128.1 (d, 3J PC
12.4 Hz, Cmeta), 131.7 (C ), 134.7 (d, 2 J PC 9.6 Hz, Cortho), 170.9 (d, JPC 13.5 Hz, C=O 170.2 (C=O ester), 172.9 (d, 3J PC 7.2 Hz, C=O ester), 214.9 (C=O, ketone); 31P NMR (202.5 MHz, CDCl3): ? P 25.75.
General procedure for preparetion of Dialkyl (Z)-2[2-(ethoxycarbonyl)-l-cyclopentenyl]-2-butenedioate compounds (examplified by 5a)
Compound 3a (0.56 g, 1mmol) was refluxed in toluene for 24 hours. The solvent was removed under educed pressure and the residue was purified by silica gel (Merck gel, 230–400 mesh) column chromatography using hexane:ethyl acetate as eluent. The solvent was removed under reduced pressure and 5a was obtained.
Dimethyl (Z)-2-[2-(ethoxycarbonyl)-l-cyclopentenyl]-2-butene dioate(5a): Yellow oil, yield 0.14 g (50%); IR (KBr) (v      cm–1): 1735, 1725 (C=O), 1648(C=C); 1H
 max
NMR (500.1 MHz, CDCl3): ?H 1.18 (3H, t, 3JHH 7.1 Hz, CH3), 2.02 (2H, quintet, 3JHH 7.4 Hz, CH2), 2.70 (2H, t, 3JHH 7.4 Hz, CH2), 2.74 (2H, t, 3JHH 7.4 Hz, CH2), 3.71 (3H, s, OCH3), 3.77 (3H, s, OCH3), 4.07 (2H, q, 3JHH 7.1 Hz, OCH2), 6.75 (1H, s, CH); 13C NMR (125.8 MHz, CDCl3): ? C 14.1 (CH3), 29.7, 33.2 and 38.9 (3CH2), 51.8 and 52.7 (2OCH3), 60.2 (OCH2), 126.1, 132.6, 144.1 and 149.7 (olefinic carbons), 164.7, 165.1 and 165.3 (3C=O, ester); MS m/z (%): 282 (M+, 2), 232 (M+-OEt, 7), 223 (M+-CO2Me, 54), 209 (M+-CO2Et, 100), 195 [M+-(CO2Me+C2H4), 63], 176 [M+-(CO2Et+MeOH)+1, 22], 149 [M+-(2OMe+CO2+C2H4)+1, 27]; Anal. Calcd. for C14H18O6 (282.29): C, 59.57; H, 6.43; Found: C, 59.53; H, 6.39.
Diethyl (Z)-2[2-(ethoxycarbonyl)-1-cyclopentenyl]-2-
butenedioate (5b): Yellow oil, yield 0.19 (60%); IR (KB-r) (v    , cm–1): 1732, 1725(C=O), 1665 (C=C); 1H NMR
 max
(500.1 MHz, CDCl3): ?H 1.18 (3H, t, 3JHH 7.1 Hz, CH3), 1.25 (3H, t, 3JHH 7.2 Hz, CH3), 1.26 (3H, t, 3JHH 7.1 Hz, CH3), 2.01 (2H, quintet, 3JHH 7.5 Hz, CH2), 2.68-2.73 (4H, m, 2 CH2), 4.07 (2H, q, 3JHH 7.1 Hz, OCH2), 4.15 (2H, q, 3JHH 7.2 Hz, OCH2), 4.22 (2H, q, 3JHH 7.1 Hz, OCH2), 6.74 (1H, s, CH); 13C NMR (125.8 MHz, CDCl3): ?C 14.1 (2CH3), 14.1 (CH3), 29.7, 33.2 and 39.0 (3CH2), 60.2, 60.8 and 61.7 (3OCH2), 126.4, 132.3, 144.0 and 149.9 (olefinic carbons), 164.7, 164.8 and 164.8 (3C=O, ester); MS m/z (%): 310 (M+, 100), 237 (M+-CO2Et, 5), 209 [M+-(CO2Et+C2H4), 7], 149 [M+-(2OEt+CO2+C2H4) +1, 6]; Anal. Calcd. for C16H22O6 (310.35): C, 61.92; H, 7.14; Found: C, 61.88; H, 7.09.
Di-tert-butyl(Z)-2[2-(ethoxycarbonyl)-l-cyclopen-tenyl]-2-butenedioate (5c): Yellow oil, yield 0.14 g
(40%); IR (KBr) (v    , cm–1): 1733, 1722 (C=O), 1635
 max
(C=C); 1H NMR (500 MHz, CDCl3): ?H 1.18 (3H, t, 3J HH 7.1 Hz, CH3), 1.41 (9H, s, CMe3), 1.44 (9H, s, CMe3), 1.97 (2H, quintet, 3JHH 7.6 Hz, CH2), 2.64-2.71 (4H, m, 2 CH2), 4.07 (2H, q, 3JHH 7.1 Hz, OCH2), 6.6 (1H, s, CH); 13C NMR (125.8 MHz, CDCl3): ?C 14.1 (CH3), 29.7, 33.2 and 39.2 (3 CH2), 27.9 and 28.0 (2 CMe3), 60.1 (OCH2), 81.3 and 81.9 (2OCMe3), 127.9, 131.6, 143.4 and 150.4 (olefinic carbons), 164.0, 164.4 and 164.9 (3 C=O, ester); MS m/z (%): 366 (M+, 2), 310 (M+-C4H8, 11), 265 (M+-CO2tBu, 2), 209 [M+-(CO2tBu+C4H8), 39], 181 [M+-(CO2tBu+C2H4+C4H8), 39], 57 (C4H9+, 45); Anal. Calcd. for C20H30O6 (366.46): C, 65.55; H, 8.25;. Found: C, 65.49; H, 8.21.
4. Conclusion
The present method may be used as a practical route for the synthesis of stable phosphorous ylides, and as convenient preparation of functionalized 1,3-dienes using intramolecular Wittig reaction under neutral conditions. This procedure has advantages of high yields, mild reaction conditions, and simple experimental and work-up conditions.
5. References
1. H. R. Hudson, The Chemistry of Organophosphorus Compounds, Volume 1. Primary, Secondary and Tertiary Posphi-nes, Poly Phosphines and Heterocyclic Organophosphorus (in) Compounds; Wiley: New York, 1990, pp 386–472.
2. R. Engel, Synthesis of Carbon-Phosphorus Bonds; CRC Press: Boca Raton, FL, 1988.
3. J. I. G. Cadogan, Organophosphorus Reagents in Organic Synthesis; Academic Press: New York, 1979.
4. I. Yavari, M. H. Mosslemin, Tetrahedron 1998, 54, 9169-9174.
5. I. Yavari, M. Adib, M. H. Sayahi, Tetrahedron Letters 2002, 43, 2927-2929.
6. S. Asghari, A. Khabbazi-Habibi, Phosphorus, Sulfur, and Silicon, 2005, 180, 2451-2456.
7. I. Yavari, S. Asghari, Tetrahedron 1999, 55, 11853-11858.
8. S. Asghari, M. Zaty, S. Safiri, Russ. Chem. Bull., Int. Ed. 2004, 54, 1763-1764.
9. S. Asghari, R. Baharfar, S. Safiri, Phosphour, Sulfur and Silicon, 2005, 180, 2805-2812.
10. K. B. Becker, Tetrahedron 1987, 36, 1717-1745.
11. E. Zebiral, Synthesis 1974, 775-777.
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Povzetek
1		1
2	Prispevek obravnava reakcijo etil 2-okso-1-cklopentan karboksilatov z acetilendikarboksilati v prisotnosti trifenilfosfi-	2
3	na. Pri tem nastanejo stabilni fosforjevi ilidi z dobrimi izkoristki. Tako pripravljeni ilidi pri refluksu toluena v intramo-	3
4	lekularni Wittigovi reakciji dajejo derivate ciklobutena, ki pri nadalnjih reakcijah odpiranja obro~a tvorijo dialkil (Z)-2-	4
5	[2-(etoksikarbonil)-1-ciklopentenil]-2-butendioate.	5
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Asghari et al: Synthesis of functionalized stable phosphorus ylides. New synthesis …