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S. Lai, D. G. Lee / Tetrahedron 58 (2002) 9879–9887
p-Toluenesulfonic acid (0.10 g) was added to a stirred
solution of 3,4,5-trimethoxybenzyl alcohol (1.02 g,
5.15 mmol) and thiophenol (1.07 g, 9.73 mmol) in benzene
(20 mL). The resulting mixture was stirred under reflux for
1 h and concentrated to give a yellow oil. Purification by
column chromatography (SiO2; eluant 4:1 hexane/methyl-
ene chloride) gave a colorless solid (1.24 g, 4.28 mmol,
83%). The spectroscopic properties (1H NMR and 13C
NMR) of this compound are consistent with its assigned
structure and in agreement with those described in the
literature.21
from the cooling bath and allowed to gradually warm up to
room temperature (,2 h) and stirred overnight. The
resulting suspension was diluted with dichloromethane
(20 mL), filtered through filter paper and the residue was
washed with dichloromethane (20 mL£2). The filtrate and
washings were combined, dried (MgSO4), decolorized
(charcoal) and concentrated to give tetradecanoic acid
(205 mg, 90%) as the sole product. The identity of this
product was confirmed spectroscopically (1H NMR, 13C
NMR and MS).
Heptanoic acid was obtained from the oxidation of
7-tetradecene as follows. A solution consisting of 7-tetra-
decene (197 mg, 1.0 mmol) in acetone (10 mL) was placed
in a 50 mL round bottomed flask and cooled to 2788C using
a dry ice/acetone bath and stirred magnetically. KMnO4
(1.6 g, 10 mmol) and FeCl3 (1.0 g, 6.2 mmol) were added
and after stirring for 2 h at 2788C, the flask was removed
from the cooling bath and allowed to gradually warm up to
room temperature (,2 h) and held overnight with con-
tinuous stirring. 2-Propanol (1.5 mL) was added to reduce
excess oxidant and after stirring for an additional 30 min,
the suspension was diluted with dichloromethane (20 mL)
and precipitated manganese dioxide was removed by
filtration. The precipitate was washed in the funnel with
dichloromethane (2£20 mL) and the filtrate and washings
combined, dried over anhydrous magnesium sulfate,
decolorized using charcoal and concentrated to give a
colorless liquid that was identified to be heptanoic acid
(231 mg, 1.78 mmol, 89%). The identity of this product was
confirmed spectroscopically (1H NMR, 13C NMR and MS).
3.2. Calculation of product ratios
Since extensive work-up procedures could alter the
composition of the product mixtures, various methods for
analyzing the crude products were investigated. Of the
1
approaches considered, it was found that use of H NMR
integrals provided the most reliable measurements of the
relative amounts of product present. When artificially
prepared product mixtures were used, the 1H NMR integrals
reproduced the known product ratios within ^3%. For all
products, except aldehydes, the signals from the benzylic
hydrogens were in regions where the integrals could be
accurately measured; for aldehydes, the integral for the
hydrogen attached to the carbonyl was used. The product
ratios were then calculated by taking the integral for a
particular product over the sum of the integrals for all of the
other products, the aldehyde integrals being doubled. The
1H NMR signals used are found at the following chemical
shifts: benzyl phenyl sulfide (d¼4.22), benzyl phenyl
sulfoxide (d¼3.94–4.18), benzyl phenyl sulfone (d¼4.31),
benzaldehyde (d¼10.03), 4-methoxybenzyl phenyl sulfide
(d¼4.10), 4-methoxybenzyl phenyl sulfoxide (d¼3.87–
4.08), 4-methoxybenzyl phenyl sulfone (d¼4.24), 4-meth-
oxybenzyl nitrate (d¼5.35), 4-methoxybenzyl acetate
(d¼5.04), 4-methoxybenzyl alcohol (d¼4.48), 4-methoxy-
benzaldehyde (d¼9.90), 3,4,5-trimethoxybenzyl phenyl
sulfide (d¼4.02), 3,4,5-trimethoxybenzyl phenyl sulfoxide
(d¼3.86–4.08), 3,4,5-trimethoxybenzyl phenyl sulfone
(d¼4.23), 3,4,5-trimethoxybenzyl nitrate (d¼5.29) and
3,4,5-trimethoxybenzaldehyde (d¼9.86). All spectra were
recorded on a Bruker AC-200 spectrometer using CDCl3 as
the solvent.
8,9-Dioxohexadecane was obtained from the oxidation of
8-hexadecyne as follows. A solution consisting of 8-hexa-
decyne (229 mg, 1.03 mmol) in acetone (10 mL) was placed
in a 50 mL round bottomed flask and cooled to 2788C using
a dry ice/acetone bath and stirred magnetically. KMnO4
(0.80 g, 5.0 mmol) and FeCl3 (0.4 g, 2.5 mmol) were added
and after stirring for 80 min at 2788C, the flask was
removed from the cooling bath, allowed to warm gradually
to 08C and stirred for an additional 1 h. The resulting
suspension was diluted with dichloromethane (20 mL) and
filtered to separate precipitated MnO2. The precipitate was
washed with dichloromethane (2£20 mL) and the filtrate
and washings were combined, dried over anhydrous
MgSO4, decolorized with charcoal and concentrated to
give a pale yellow oil that slowly solidified (238 mg,
0.937 mmol, 91%). The spectroscopic properties (1H NMR
and 13C NMR) of this compound are consistent with its
assigned structure and in agreement with those described in
the literature.22
Diphenyl disulfide was also produced as a coproduct in
many of the reactions. Although its presence could easily be
detected using TLC, its 1H NMR signals were not
sufficiently distinct from those of other aromatic compounds
present to be used quantitatively.
3.3. Typical oxidation procedures
2-Nonanone was obtained from the oxidation of 2-nonanol
as follows. A solution consisting of 2-nonanol (144 mg,
1.0 mmol) in acetone (10 mL) was placed in a 50 mL round
bottomed flask and cooled to 2788C using a dry ice/acetone
bath and stirred magnetically. KMnO4 (0.8 g, 5.0 mmol)
and FeCl3 (0.4 g, 2.5 mmol) were added and after stirring
for 2 h at 2788C, the flask was removed from the cooling
bath and allowed to warm gradually to 08C over a period of
2 h. The resulting mixture was filtered through filter paper
and the residue was washed with dichloromethane
(20 mL£2). The filtrate and washings were combined,
No special precautions were taken to avoid the presence of
oxygen or moisture in these reactions.
Tetradecanoic acid was obtained from the oxidation of
1-pentadecene as follows. A solution consisting of 1-penta-
decene (210 mg, 1.0 mmol) in acetone (10 mL) was placed
in a 50 mL round bottomed flask and cooled to 2788C using
a dry ice/acetone bath and stirred magnetically. KMnO4
(1.6 g, 10 mmol) and FeCl3 (1.0 g, 6.2 mmol) were added
and after stirring for 2 h at 2788C, the flask was removed