Modification of the Swern Oxidation
J . Org. Chem., Vol. 61, No. 22, 1996 7859
tion. Any excess sulfoxide reagent 1 is not recovered by this
procedure since it is water soluble.
P u m m er er P r od u cts 4 a n d 5. The general procedure for
the modified Swern oxidation was followed except no alcohol
(20 mL). The solution was concentrated and dried under
vacuum for 2 days. The resulting potassium salt was mixed
with DMF (50 mL) and p-chloromethylated polystyrene resin
(2.00 g, 8.30 mmol, Bio-Beads S-X-1, Bio-Rad, 4.15 mequiv/g).
The mixture was heated at 100 °C for 20 h with a gentle
stirring. After cooling, the resin was filtered, washed (MeOH,
was added. Dimer 4 and trimer 5 were isolated by SiO
chromatography. For 4 (13%): IR (CHCl ) 1739 (s), 1157 (m)
) δ 5.16 (s, 4H), 2.68 (t, 4H,
2
flash
3
-
1 1
cm ; H NMR (360 MHz, CD
2
Cl
2
THF, CH
2
Cl
2
(3 × each)), and dried at 60 °C in vacuo for 40 h.
J ) 7.4 Hz), 2.33 (t, 4H, J ) 7.3 Hz), 1.67 (m, 8H), 1.45 (m,
A total of 2.96 g (93%) of white resin was obtained: IR
(microscope) 3025 (m), 2929 (s), 1736 (s), 1173 (m), 1029 (m)
1
3
4
2
H); C NMR (100 MHz, CD
2
Cl
2
) δ 173.06, 67.30, 34.75, 32.76,
320.1116,
-
1
13
9.98, 27.98, 25.02; MS (EI) calcd for C14
H
24
+
O
4
S
2
cm
;
2 2
C NMR (75 MHz, CD Cl ) δ 173.33, 128.51, 66.34,
+
+
found 320.1128 (M ); (CI, NH
For trimer 5 (7%): IR (CHCl
NMR (360 MHz, CD Cl ) δ 5.15 (s, 6H), 2.67 (t, 6H, J ) 7.4
Hz), 2.33 (t, 6H, J ) 7.3 Hz), 1.66 (m, 12H), 1.45 (m, 6H);
NMR (100 MHz, CD Cl ) δ 173.24, 67.17, 34.55, 32.79, 30.14,
8.33, 24.75; MS (EI) calcd for C21 480.1674, found
3
) 338 (MNH
4
) 321 (MH ).
54.83, 40.87, 39.12, 34.23, 28.67, 24.91, 22.70. Anal. Calcd
based on 100% conversion: C, 71.12; H, 8.07; S, 8.33. Found:
C, 70.33; H, 7.64; S, 8.33.
P olym er -Su p p or ted Sw er n Oxid a tion . Polymer-sup-
ported sulfoxide 12 (1.00 g, 2.60 mmol, based on elemental
) 1737 (s), 1127 (m) cm 1; 1H
-
3
2
2
1
3
C
2
2
2
4
36 6 3
H O S
analysis) was swollen in CH
for 15 min and then cooled to ca -50 °C. Oxalyl chloride (1
equiv) in CH Cl (5 mL) was added dropwise. After 1 h at
that temperature, endo-borneol (201 mg, 1.30 mmol, 0.5 equiv)
in CH Cl (10 mL) was added, and the mixture was stirred
2 2
Cl (20 mL) at room temperature
+
+
+
80.1668 (M ); (CI, NH
Meth yl 6-(Meth ylsu lfin yl)h exa n oa te (9). To a solution
) 498 (MNH ), 481 (MH ).
3 4
2
2
of 1 (1.00 g, 5.61 mmol) in CH
2
Cl
2
(40 mL) cooled in an ice
/Et O solution until a pale
bath was added dropwise a CH
2
N
2
2
2
2
yellow color was obtained. The mixture was stirred at room
temperature for 30 min, and a few drops of formic acid were
for 3 h before the addition of triethylamine (3 equiv). The
mixture was allowed to slowly warm to room temperature and
stirred overnight. The resin was removed by filtration and
added to destroy the excess CH
2 2
N . Evaporation of solvent
under reduced pressure gave 1.07 g (99%) of 9 as a pale yellow
washed with CH
and then diluted with Et
with H O. The ethereal phases were dried (Na
2
Cl
2
. The filtrate was condensed to 50 mL
O (50 mL) and washed three times
SO ) and
-
1 1
oil. IR (CHCl
CD Cl ) δ 3.61 (s, 3H), 2.63 (m, 2H), 2.48 (s, 3H), 2.30 (t, 2H,
J ) 7.4 Hz), 1.72 (m, 2H), 1.64 (m, 2H), 1.46 (m, 2H); C NMR
75 MHz, CD Cl ) δ 173.93, 54.78, 51.61, 38.99, 33.91, 28.54,
4.79, 22.58; MS (EI) calcd for C S 192.0820, found
S: C, 49.97; H, 8.39;
3
) 1735 (s), 1033 (m) cm ; H NMR (400 MHz,
2
2
2
2
2
4
1
3
concentrated under reduced pressure. The product was ana-
(
2
2
1
lyzed by H NMR spectrometry, which showed complete
2
1
8
H
16
O
3
oxidation with no trace of borneol. A total of 188 mg (95%) of
camphor was obtained, with the loss being due to its volatility
during evaporation. In a separate experiment, 1 equiv of endo-
borneol was used for the reaction with 1 equiv of polymer-
supported sulfoxide: 92% of the alcohol was oxidized to give
camphor with 8% left unchanged.
+
92.0820 (M ). Anal. Calcd for C
8
H
16
O
3
S, 16.67. Found: C, 50.10; H, 8.55; S, 16.50.
1
3
Low Tem p er a tu r e C NMR An a lysis. Spectra were
acquired on a Bruker AM200 spectrometer with a 20 mm probe
at -60 °C. CD Cl was dried by distillation from CaH before
2 2 2
use. The reaction was done on 1 mmol scale in a 12 mm NMR
tube cooled to -60 °C. After attachment of the apparatus to
a pressure-equalizing argon line, the reagents were added via
a syringe. Chlorosulfonium intermediate 10 was added via a
cannula which was cooled with dry ice. After each addition
the NMR tube was kept at -60 °C for 15 min with occasional
Ackn owledgm en t. These investigations were funded
by the Natural Sciences and Engineering Research
Council of Canada and by the Alberta Heritage Founda-
tion for Medical Research. Y.L. acknowledges support
from an Izaak Walton Killam Scholarship.
1
3
shaking before the spectral analysis. The C NMR chemical
shifts (δ) for the intermediates are as follows: 1, 176.31, 52.32,
3
2
2
1
1
6.92, 33.22, 27.50, 23.84, 22.13; 6, 180.80, 65.76, 47.64, 33.25,
6.84, 24.00, 23,48; 7, 180.77, 43.78, 33.22, 27.19, 25.93, 25.60,
3.35; 9, 173.81, 53.47, 51.54, 38.05, 33.11, 27.66, 24.02, 22.18;
0, 173.95, 65.78, 51.69, 47.63, 32.99, 26.92, 23.99, 23.79; 11,
78.94, 83.64, 49.69, 34.78, 33.10, 26.83, 23.49, 22.33, 21.98.
P olym er -Bou n d Rea gen t 12. Sulfoxide 1 (2.95 g, 16.6
1
Su p p or tin g In for m a tion Ava ila ble: Copies of H NMR
spectra of 4 and 5 (2 pages). This material is contained in
libraries on microfiche, immediately follows this article in the
microfilm version of the journal, and can be ordered from the
ACS; see any current masthead page for ordering information.
mmol) and KOH (0.93 g, 16.6 mmol) were dissolved in H
2
O
J O961438D