A simple method of dethioacetalization

A simple method of dethioacetalization

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 DETH...

169KB Sizes 10 Downloads 145 Views

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).