Tetrahedron Letters, Vo1.30, Printed in Great Britain
No.3,
1989
pp 287-290,
0040-4039/89 $3.00 Pergamon Press plc
+ -00
A SIMPLE METHOD OF DETHIOACETALIZATION Gilbert Stork* and Kang Zhao Department
of Chemistry,
Columbia
University
New York, New York 10027 Summary: yields
Thioacetals
by treatment
and thioketals with
The potential carbonyl
compounds
the carbonyl selective
iodine water
1.
with
and ketals
of either
a variety
An example
is initiated
center,
a method
thioketals
of other
or an alcohol)
in high
is shown
in Scheme
at some
groups.
for
of regenerating
can be used
for the
and which
The new method
at room temperature
1.
attack
later
groups
difficulty
which
or thioacetals
functional
by nucleophilic
followed
compounds
as protecting
by the not infrequent
We now report
with bis(trifluoroacetoxy)iodobenzene
short time. cleavage
is limited
function
to carbonyl
(trifluoroacetoxy)iodobenzene
of thioacetals
deprotection
compatible treatment
bis
be cleaved
can
It is quite of sulfur
evidence
involves for a
reasonable
that
on the hypervalent
stage by addition
, but we have no concrete
is
of a hydroxyl to support
(from
this
possibility.
SchemeI Aldehydes
are obtained
by treating
bis(trifluoroacetoxy)-iodobenzene2 mixture
of methanol
and water
can also be used
(table 2). In contrast
to earlier
oxidative
these
hydrolysis3,
thioacetals
in aqueous
methods
conditions
(table I). A
in the case
involving
of thioketals
metal-ion,
are sufficiently
287
with
acetonitrile
mild
alkylative, that
various
or
288
functional
groups
such as esters,
halides,
alkenes
survive;
the latter,
trifluoroacetic
and alkynes
acid
presumably, formed
nitriles,
secondary
are unaffected. because
they
amides4,
Even thioesters are protected
alcohols, and amines
by the
in the reaction.
Table
1: Dethioacetalization5
OW%W’h MeOH, H&I (91)
RCHO
*
RCHO
Time (min.) CHO
YiM@
10
99%
Meo2c(CH2)4
MeO$!( CHi)4CH0
5
91%
HWW,
HO(CH&CHO
2
97%
AcO(CH&
AcO(CH&CHO
2
TsO(CH&
TsO(CH&C!HO
1
85%
92%
1
91%
1
91%
CH$HCH$HOC(CH2),
1
91%
CH=CCH,O$JCHd,
2
84%
1
85%
WCHW$(CHd&HO
PhSOC(CHd4
C
0 )_CHi), 0
C
0 ot-(CW4~0
289
2: Dithioketalization
Table
solvents
Product
Thi&.gtal 3ime
>
MeOHH20
0
(9:l)
5 min.
85%
Ph
MeOEH20
CN
(9:l)
86%
CN MeCNN20
a) Isolated
5 min.
(9:l)
5 min.
90%
yields.
Table
3: Dithioacetalization
phSLSR (cFEzph,
in alcohols
phs&OR’
XR
OR’ Time
(minutes)
Yielda
X
R'
Solvent
Et
S
Me
MeOH
5
97%
Ph
S
CH2CH2
HOCH2CH2OH
5
91%
S
Me
MeOH
5
86%
Me
MeOH
5
MeOH
360
90%
R
(CH2) 3
(CH2)2 LU2L2 a) Isolated
S 0 yields.
Me
93%
290
The cleavages can also be run in alcohol or ethylene glycol to form the corresponding acetals directly from the thioacetals
(Table 3).
-al
(15mmol) was added at room
wrocedu:
Bis(trifluoroacetoxy)iodobenzene
temperature to a stirred solution of thioacetal or thioketal
(1Ommol) in the
solvents indicated in the tables (10ml). After the reaction was completed, as judged by TLC (usually
We thank the National Science Foundation and the National
Institutes of Health for the support of this work. References and notes. 1.
2. 3.
E. Vedejs and P. L. Fuchs, J. Org. m., 36, 366 (1971). R. H. Boutin and G. M. Loudon, J. Ora. Chem 49, 4277 (1984). M. Balogh, A. Cornelis and P. Laszlo, Tetrahedron 7~tt,, 31, 3313 1984); I.Degani, R. Fochi and V. Regondi, .5yDthesis. 51 (1981), and references therein.
4.
Primary amides are rearranged to amines under these conditions:
see
reference 2. 5.
The starting thioacetals were prepared and purified by known procedures6. The was made from the ester7, the thioester from the acid8.
6. 7.
R. K. Olsen and J. 0. Currie, in "The Chemistry of the Thiol Group", S. Patai, ed., John Wiley and Sons, New York, 1974, part 2, p. 5197. S. M. Weinreb, -tic Commun. , 989 (1982).
8.
B. Neises and W. Steglich,
Bnaew Chem..
(Received in USA 20 October 1988)
Ed. EngL,
522 (1978).