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D. E. MINTER ET AL.
Carbonation of sodium cyclopentadienide.1,15 Sodium
sand was prepared by refluxing a suspension of Na
(28.0 g, 1.2 mol) in toluene under argon for 1.5 h. The
reaction vessel was cooled rapidly to 0 ꢂC via immersion
in an ice–water bath. Toluene was decanted under argon
and was replaced with dry THF (250 ml). To the reaction
vessel maintained at 0 ꢂC was added dropwise with
stirring under argon freshly cracked cyclopentadiene16
(80.0 g, 1.3 mol) over 1 h. After addition of cyclopenta-
diene had been completed, the external ice–water bath
was removed and the reaction mixture was allowed to
warm gradually to ambient temperature while stirring
overnight. The reaction mixture then was poured rapidly
over crushed dry-ice (500 g, 11.3 mol), and the resulting
mixture was allowed to stand at ambient temperature for
3 h. The reaction mixture was diluted with water (150 ml)
and the resulting mixture was acidified by addition of 6 N
H2SO4 (180 ml). The precipitated reaction product (crude
Thiele’s acid)1,15 was collected by suction filtration and
then air-dried. The crude product, a tan solid (65.0 g,
58%), was used as obtained, without additional purifica-
tion or characterization.
2 (i.e. either 2b or 2c, 200 mg, 1%) as a colorless
microcrystalline solid: m.p. 120–121 ꢂC; IR (KBr) 2980
(m), 2953 (m), 2872 (sh, m), 1714 (vs), 1699 (vs), 1437
(s), 1277 (vs), 1082 (s), 733 cmꢀ1 (s); 1H NMR (CDCl3),
ꢀ 1.40 (AB, JAB ¼ 11.2 Hz, 1 H), 1.65 (AB, JAB ¼ 11.2 Hz,
1 H), 1.90–2.10 (m, 1 H), 2.40–2.60 (m, 1 H), 2.90–3.10
(m, 1 H), 3.10–3.20 (m, 1 H), 3.30–3.40 (br s, 1 H), 3.40–
3.60 (m, 1 H), 3.70 (s, 3 H), 6.45–6.55 (m, 1 H), 6.80–
6.90 (m, 1 H); 13C NMR (CDCl3), ꢀ 33.1 (t), 41.5 (d),
47.1 (d), 47.8 (d), 51.3 (t), 52.0 (q), 54.9 (d), 138.1 (s),
139.3 (s), 145.8 (d), 147.7 (d), 165.9 (s), 170.3 (s). Exact
mass (CI HRMS): calcd for C13H14O4, [MrþH]þ m/z
235.0970; found, [MrþH]þ m/z 235.0968.
NMR spectra. NMR spectra were acquired by using a 5%
solution in CDCl3 at 25 ꢂC with a Varian INOVA 400
spectrometer operating at 399.968 MHz for 1H and
100.581 MHz for 13C. Chemical shifts were referenced
1
to 0.1% internal TMS. In the H NMR experiments, the
spectral width was 3200 Hz, number of data points 38 400
with zero-filling to 64 K, acquisition time 6.0 s, relaxation
delay 5.0 s and number of transients ¼ 8. In the 13C NMR
experiments, the spectral width was 25 000 Hz, number of
data points 60 000 with zero-filling to 64 K, acquisition
time 1.2 s, relaxation delay 2.0 s and number of transients
10 000. In the COSY experiment, the spectral range was
3200 Hz in both directions, acquisition time 0.32 s, re-
laxation delay 3.0 s. A total of 533 increments were
collected with 32 transients per increment and processed
as a 2 K ꢃ 2 K matrix. In the HMQC18 experiment, the
spectral ranges were 3200 Hz (1H axis) and 15 000 Hz
(13C axis), acquisition time 0.32 s, relaxation delay 0.9 s.
A total of 2 ꢃ 373 increments were collected with 16
transients per increment and processed as a 2 K ꢃ 2 K
matrix. In the gradient HMBC19 experiment, the spectral
ranges were 3200 Hz (1H axis) and 15 000 (13C axis),
acquisition time 0.32 s, relaxation delay 1.4 s. A total of
373 increments were collected with 16 transients per
increment and processed as a 2 K ꢃ 2 K matrix.
Esterification of the crude reaction product obtained via
carbonation of sodium cyclopentadienide. A solution of
crude Thiele’s acid (20.0 g, 102 mmol), prepared as
described above, in MeOH (100 ml) was placed in a
250 ml round-bottomed flask. This solution was heated
to 50 ꢂC, then concentrated H2SO4 (8 ml) was added
dropwise. After the addition of H2SO4 had been com-
pleted, the resulting mixture was refluxed overnight. The
reaction mixture was concentrated in vacuo, and the
residue was neutralized via careful addition of saturated
aqueous NaHCO3 (50 ml). The resulting aqueous suspen-
sion was extracted with EtOAc (2 ꢃ 100 ml). The com-
bined organic extracts were dried (Na2SO4) and filtered,
and the filtrate was concentrated in vacuo. The residue
was purified via column chromatography on silica gel by
eluting with 25% EtOAc–hexane. Workup of the first
chromatographic fraction thereby obtained afforded pure
Thiele’s ester (2a, 8.0 g, 46%) as a colorless microcrystal-
line solid: m.p. 85 ꢂC (lit.1b,17 m.p. 85 ꢂC); IR (KBr) 2980
(s), 2953 (s), 2872 (m), 2672 (w), 2573 (w), 1714 (s),
1437 (s), 1277 (s), 1250 (m), 1082 (s), 733 cmꢀ1 (s). The
1H and 13C NMR spectra of the material thereby obtained
were essentially identical with the corresponding spectra
reported previously for Thiele’s ester.3
Acknowledgement
A.P.M. (Grant B-0963) and D.E.M. (Grant P-1519) thank
the Robert A. Welch Foundation for financial support of
this study. In addition, we thank Professor Jennifer
S. Brodbelt, Department of Chemistry and Biochemistry,
University of Texas at Austin, for having kindly obtained
the high-resolution chemical ionization mass spectral
data reported here.
Continued elution of the chromatographic column
afforded a second fraction. Workup of this fraction
afforded 3a (1.0 g, 4%) as a colorless microcrystalline
solid: m.p. 106–107 ꢂC; IR (KBr) 2953 (m), 2361 (w),
1720 (s), 1629 (w), 1437 (m), 1273 (s), 1094 cmꢀ1 (s).
Proton and 13C NMR data for 3a are given in Tables 1 and
2. Exact mass (CI HRMS): calcd for C15H20O5, [MrþH]þ
m/z 281.1389; found, [MrþH]þ m/z 281.1391.
REFERENCES
1. (a) Thiele J. Chem. Ber. 1900; 33: 666; (b) Thiele J. Chem. Ber.
1901; 34: 68.
2. Dunn GL, Donohue JK. Tetrahedron Lett. 1968; 3485–3487.
3. Minter DE, Marchand AP, Lu S-P. Magn. Reson. Chem. 1990; 28:
623–627, and references cited therein.
Continued elution of the chromatographic column
afforded a third fraction. Workup of this fraction afforded
Copyright # 2004 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2004; 17: 174–179