F. Castañeda et al. / Journal of Molecular Structure 1004 (2011) 284–291
285
phosphonium phenyl in an anti ester ylide. [7a,7b,9b] Acyl stretch-
2.6. Diethyl 2-triphenylphosphoranylidene-3-oxoglutarate, 2
ing frequencies can be compared with predicted values [11], and
are higher for ester than keto groups in aliphatic keto esters.
Scott and Radom estimated Scale Factors, SF, for various compu-
tational methods by examination of many organic and inorganic
compounds, often with simple structures, and critically discussed
uses of the methods [12]. The DFT functional BLYP/6-31G(d) gave
satisfactory agreement between observed and predicted acyl
stretching frequencies for a range of ylidic diesters, keto esters
and diketones [11].
Atomic charges were estimated with the Natural Population
Analysis (NPA) method because although the significance of
numerical charge values is uncertain, depending on the method
of calculation [12b,14] the charge sequence is structurally useful.
For 1 and 2, the nonylidic ester groups may affect generalizations
regarding expected conformations, as for some mono ylides [6]
and also affect thermolyses.
Yield 68%, mp. 106 °C, 1H NMR (CDCl3) dppm: 0.66 (t, 3H, CH3,
J = 7.1 Hz); 1.28 (t, 3H, CH3, J = 7.1 Hz); 3.72 (q, 2H, OACH2,
J = 7.1 Hz); 3.85 (s, 2H, COACH2); 4.19 (q, 2H, OACH2, J = 7.1 Hz);
7.42–7.74 (m, 15H). 31P NMR (CD Cl3) dppm: 15.4; 13C NMR (CDCl3)
dppm: 13.8 (CH3); 14.4 (CH3); 48.1 (d, COACH2ACO2); 58.6
1
(OACH2); 60.5 (OACH2); 71.5 (d, P@C, JP–C = 111.2 Hz); 126.4
2
(d); 128.7 (d); 131.8 (d); 133.4 (d); 167.9 (d, CO2, JP–C = 15.5 Hz);
4
2
170.4 (d, CO2, JP–C = 1.2 Hz); 189.6 (d, C@O keto, JP–C = 5.2 Hz).
31(KBr): 1538, 1666, 1726 cmÀ1
HR-MS: m/z. for C27H27O5P
[M+H]+: 462.1596, found 462.1591.
.
2.7. Characterization of ylide 2 acid solvate is as Supplementary data
See Supplementary data.
2. Experimental
2.8. Thermolysis – general procedure for keto diester ylides, 1 and 2
2.1. IR spectroscopy
The keto diester ylides (20 mmol) were heated in a round bot-
tom flask fitted with a condenser and external and internal tem-
perature controls. The vertical condenser was modified to allow
collection of condensates. The solid was heated to 150–200 °C,
external temperature, giving a viscous melt and thermolysis pro-
duced a liquid which was distilled under vacuum giving the acety-
lenic ester. The nonvolatile residue is triphenylphosphine oxide,
mp. 150–154 °C. Thermolysis was also made in solid state diluted
conditions using pure sand (Riedel) in 97% excess, showing almost
the same results.
Spectra were examined on a Bruker IFS 56 FT spectrometer with
a KBr disk or in CHCl3 with allowance for solvent signals, in the
range of 400–4000 cmÀ1 although only acyl stretching frequencies
are considered.
2.2. NMR spectroscopy
NMR spectra were monitored on Bruker DRX 300 or Varian Ino-
va 500 spectrometers in acid free CDCl3 and are referred to TMS or
85% H3PO4. 13C NMR spectra were obtained with and without 1H
decoupling.
2.9. Thermolysis of 1
Thermolysis of 1, gave EtO2CAC„CACO2Et, (82%), bp 82–84 °C/
4.5 mm Hg [15]. 1H NMR (CDCl3) dppm: 1.3 (t, 6H, J = 7.1 Hz); 4.3 (q,
4H, J = 7.1 Hz).
2.3. Elemental analysis and mass spectra
Elemental analysis as on a Fison EA 1108 analyzer and mass
spectra were obtained on a MAT 95 XP Thermo Finnigan Spectrom-
eter at 70 eV.
2.10. Thermolysis of 2
2.4. Synthesis – general procedure for preparation of keto diester
triphenylphosphonium ylides 1 and 2
Thermolysis of 2 gave EtO2CAC„CACH2ACO2Et, (74%), bp 60–
64 °C/2.6 mm Hg. 1H NMR (CDCl3) dppm: 1.2 (t, 6H, J = 7 Hz); 3.2
(s, 4H); 4.2 (q, 4H, J = 7 HZ); Anal. Calcd. For C9 H12 O4 (%): C,
58.69; H, 6.57. Found (%): C, 59.03; H, 6.88.
Examples of thermolysis of other ylidic keto esters are as Sup-
porting data.
A solution of monoethyl oxalyl chloride or ethyl malonyl chlo-
ride (40 mmol) in dry benzene (16 ml) was added slowly to (car-
bethoxymethylene)
triphenylphosphorane,
Ph3@CHACO2Et
(80 mmol), in dry benzene (200 ml) under a dry atmosphere. After
stirring at room temperature, reaction was complete in 8hr. and a
white solid, (carbethoxymethyl) triphenylphosphonium chloride,
Ph3P+ACH2ACO2EtClÀ, separated. After filtration the solvent was
removed by rotary evaporation giving a solid. Recrystallization
from ethyl acetate–hexane (1:1) gave the keto diester ylides 1 or 2.
2.11. Computation
Structures were optimized by HF/6-31G(d) and DFT methods,
and acyl stretching frequencies were estimated with uncon-
strained structures. Calculations were made with Spartan ’06 or
’08 for Windows and convergence conditions as described [9]. Fre-
quencies are rounded off to the nearest whole number. The litera-
ture SF = 0.9945 [12a] was used with BLYP/6-31G(d) but with HF/
6-31G(d) we used SF = 0.866 for ester acyl groups and SF = 0.834
for keto acyl groups [11]. The B3LYP/6-31G(d) method with
SF = 0.9614 [12a] was also used. Comparison of geometries of 2
(Tables 5 and 6) involves X-ray crystallography [16]. Structures
for 1 and 2 from the BLYP/6-31G(d) method are in Chart 1. Com-
puted and observed acyl stretching frequencies for keto diester
ylides are in Table 2. Fractional charges (NPA) from B3LYP/6-
31G(d) are in Table 3.
2.5. Diethyl 2-triphenylphosphoranylidene-3-oxosuccinate, 1
Yield 97%, mp. 124–126 °C, 1H NMR (CDCl3) dppm: 0.71 (t, 3H,
CH3, J = 7.1 Hz); 1.29 (t, 3H, CH3, J = 7.1 Hz); 3.77 (q, 2H, OACH2,
J = 7.1 Hz); 4.25 (q, 2H, OACH2, J = 7.1 Hz); 7.7–7.4 (m, 15H). 13C
NMR (CDCl3) dppm: 13.6 (CH3); 14.04 (CH3); 59.0 (OACH2); 60.8
1
(OACH2); 67.6 (d, P@C, JP–C = 110.6 Hz); 124.2 (d); 128.7 (d);
3
132.4 (d); 133.6 (d); 167.1 (d, CO2, JP–C = 13.1 Hz); 167.4 (d, CO2,
2
31
2JP–C = 14.8 Hz); 184.6 (d, C@O keto, JP–C = 6.1 Hz).
P NMR
(CDCl3) dppm: 16.4. IR (KBr): 1539, 1673,1739 cm–1. HR-MS: m/z
for C26 H25O5P [M+H]+: 448.1439, found 448.1430.