Chemistry Reference
In-Depth Information
A general method for the preparation of a-alkoxyacroleins, which includes a Swern
oxidation step, has been reported [1348]. Swern oxidation of 1806 with oxalyl
chloride/Me
2
SO at
78
C, followed by treatment with triethylamine, gave the
corresponding aldehydes 1807. As the crude reaction mixtures were allowed to
warm to ambient temperature (0.5-3 h), b-elimination gave alkoxy aldehydes 1808
in 70-93% yield.
room
(COCl)
2
-DMSO
OR
H
2
COR
OR
S
S
temp
- 78 °C
CHO
CHO
CH
2
OH
1806
1808
1807
R = OCH
2
CH
2
OMe, CH=CH
2
, oxiranyl, (CH
2
)
3
Br, (CH
2
)
3
N
3
Swern oxidation of various indolic substrates has been described, and a range of
products resulting from overall oxidation at the 2-position have been observed. For
example, indolylpropanol 1809 [R
(CH
2
)
3
OH] is oxidized with DMSO and either
trifluoroacetic anhydride or oxalyl chloride to give the unsaturated aldehyde 1810
[R
¼
¼
(CH
2
)
2
CHO] [1333].
NHCOPh
NHCOPh
TFAA-DMSO
or
(COCl)
2
-DMSO
N
N
OH
O
Ph
Ph
1809
1810
Depending on the substrate and the reaction conditions, indolealkyl alcohols may
be oxidized to a,b-unsaturated systems, and indoles can either be oxidized to in-
troduce a nucleophile regioselectively at the 2-position or to introduce both a nu-
cleophile at the indole 2-position and a MeSCH
2
group at the indole 4-position
through an unprecedented rearrangement of a Swern intermediate [1333].
For example, after oxidation of N-acetyltryptophan methyl ester 1811 with
DMSO and trifluoroacetic anhydride at
78
C, subsequent addition of triethyl-
amine at this temperature gives the dihydropyrroloindole 1812 (R
1
H) in 35%
yield, while warming to room temperature and then adding triethylamine gives
1812 (R
1
¼
¼
MeSCH
2
) in 35% yield [1333].
NHCOMe
R
1
COOMe
CH
2
CHNHCOPh
N
COOMe
N
H
N
H
1811
1812
