Regioselectivity of metalation of alkylmercaptoolefins

0040-4039/79/1029-4277$02/00/O

Tetrahedron Letters No. 44, pp 4277 - 4280. @Pergamon Press Ltd. 1979. Printed in Great Britain.

REGIOSELECTIVITY

Richard

OF METALATION

Chemie,

Postfach

Abstract:

')

+, Heike Speer, and Bruno Schmid

R. Schmidt

Fachbereich

OF ALKYLMERCAPTOOLEFINS

UniversitBt

5560, D-7750

Konstanz

Konstanz

The monosulfoxide of cis-dialkylmercaptoethylene 5 and the B-aZkyZmercapto acrylnitri-

le =15 deZiver on deprotonation with tert.-butyllithiwnalmost exclusively a-deprotonuted species. According to reactions with electrophiles these functionally substituted vinyllithiwn derivatives are configurationakly labile.

Cis-1.2-dialkylmercaptoethylenes philes delivering

(L) are easily deprotonated

2 2). Hydrolysis

compounds

thon for 4 or 2 3). Alkylmercapto

ductive

effect of the alkoxy

is also effective Monooxidation 7 = according quenching

group

with methanol-O-d

steric,

labile,

leading

intramolecular supported

complexation

results

via 2. In addition, experiments

effects,

which

12 does not isomerize

positions

(table of

small amounts

of A&J __- via ip are that 2 is configura-

demonstrate lability

clearly

in THF and

group a-deprotonation

is supported

by electronic,

give B a lower energy.

under these reaction

conditions,

may favour

the formation

of LA. The deuteration

of lithiated

6 with methyl

iodide and dimethyl

As expect-

even though

experiments

are

disulfide

as electro-

A@ ___ and 136, _-_ iis, respectively. All experiments demonstrate g-i9 react with electrophiles with retention of configuration.

that vinyl-

to Qb, _--

lithium derivatives Similar

complexation

at the vinylic

effect of the sulfoxide

dependent

to the cyclic compound

of 8 with tert.-butyllithium

to &?a ___ via 8. This configurational

derivative

by the reaction

leading

to &

effect

to the alkoxy group

7) .

mono-deprotonation

inductive

leading

complexation

2, which does not rearrange

deprotonation

Temperature

and intramolecular

ed, vinyllithium

philes

of deprotonation

shows complete

with the stronger

formed by B-deprotonation.

for by the anion stabilizing

6) . Possibly, intramolecular

investigations;

$ takes place preferentially

tionally

of 2 are aimed to show if 4 is a syn-

group is at least compensated

in ag

of 2 leads to cis-monosulfoxide

1). In accordance

electro-

enolethers

in the regioselectivity

to 1H-NMR

positions;

and dienolethers react with strong bases to the 435) 22, zh, respectively . Acidification by the strong negative in-

vinyllithium-derivatives

of the alkylmercapto

experiments

at the vinylic

are obtained

Only little !3-deprotonation

with R-ethylmercapto is observed

acrylonitrile

with tert.-butyllithium

4277

ii (cis:trans

= 1:3); table 2.

in THF; quenching

with methanol-

4278

No. 44

CN

I

RS

%

I

R=

g

Et

/a 1. Base 2. Ee

7

4

H \/CN

HO..

SR

=a:

E =

D

$:

E =

CH3

=c:

E =

C2H5S

i: E =

eN

II

NC

Lie i RSii,

C2H5-;IH

==

’

,,I:’

g

22

OH Table 2:

Deprotonation

Compound

E-X

of 12 and Reaction Temperature COCI

with Electrophiles Yield [%I

a) Reaction $j

product

[partsIb)

42

g

P

D-OCH3

-113

95

60

32

8

b =

CH3-J

-113

80

80

15

5

- 80

60

75

20

5

- 20

30

75

20

5

C =

C2H5S-SC2H5

-113

51

16 c,

82 c) <

1

C2H5-CH=O

-113

52

82

16

a) Solvent:

THF; base 1.2 equivalents

b) lH-NMR-determination. Table

3:

'H-NMR-Data

b =

HB: 6.98

assignments

of the electrophile

after 60 min.

a)

a =

a) 80 MHz, CDC13,

addition

c) see table 3.

Compound

b) These

t-BuLi;

2

<2

E

!I

(t)

HB: 6.80 (t)

HB: 6.37

Hc1: 6.02

(s)

HB: 7.28 (s)

(t)

H : 5.99 (s)

Ha: 6.37 (s)

Ha: 7.10 (t)

H;: 6.71 (q)

Ha: 7.10 (s) b)

HB: 7.17 (s)

HB: 7.27 (t)

HB: 7.21 (q)

HB: 7.21 (s) b,

HB: 7.27 (s)

Hc,: 5.07 (t)

Ha: 4.87 (q)

s-values, can

be

Tetramethylsilan interchanged.

internal.

No. 44

4279 RS

x

H

I

RS RS

x

1 =

H

H

I

RS

E

2 =

9’. R--S

Table

1:

RS

H

Deprotonation

Compound

E-X

D-OCH3

x =9

R! RS

H

Temperature

11 =

g

of i and Reaction

PC1 a =

A

I

& =8

‘fLi

with Electrophiles

Yield

r.%I

a)

Reai;ion

pr;;uct

[P$I

=_

-120

100

95

5

-100

100

31

59

10

- 80

100

73

17

10

b =

CH3-J

-120

89

95

5

‘;

CH3S-SCH3

-120

100

85

15

a) Solvent:

THF, base: 1.1 equiv.

b) NMR-determination. c) Compounds

14 were not isolated. _=

t-BuLi;

addition

of the electrophile

after 10 min.

b,

No. 44

O-d leads to little 18s; ___ cis-compound !s was not found at all. Even though the anion stabilizing effect of an a-alkylmercapto group is very important in "Umpolung" reactions 8) , it is outweighed

by the electronic

tion. However,

effect of the cyano group: deprotonation

the intermediate

brium with the cis-compound @.

An influence

trophile; sulfide

Xb, ___

EE or the cumulene

of temperature

and propionaldehyde

calculations

if electronic

effects,

the B hydrogen

&,

'H-NMR-Data

was not observed

17g were received; ___ in table 3.

with trans+aminoacrylonitrile

atom depends

greatly

complexation

18~ and ___ &lg were present only ---

and solvation

are included

7) . Acidity

effect, which

a-deprotonation

with the experimental

the kinetically

of

is lower for the alkylmer-

and thermodynamically

findings,

if compared

preferred

with the !3-

system 7yg).

References

and Footnotes

Part 8. This work was supported

Fonds der Chemischen 2) 8. Schmid,

di-

a-deprotonation,

therefore,

1) Vinyl Anions,

iodide as elec-

with diethyl

preferential

on the inductive

of iz is in agreement

at the a-posi-

support

capto group than for the amino group;

aminoacrylonitrile

with methyl

Accordingly,

17'~ and Ni, ___

intramolecular

occurs

20 -_ is even at -113'C in equilianion Ei, leading not only to &i'n but also to

in the same proportion.

are compiled

mainly

derivative

on this behaviour

lib --- and I& -__ were formed

in trace amounts. Theoretical

trans-vinyllithium

Industrie.

Diplomarbeit

by the Deutsche

Forschungsgemeinschaft

and the

- Part 7: see ref. 7.

Univ. Stuttgart

1976; R.R. Schmidt

and B. Schmid,

Tetrahedron

lett.

1977, 3583 3) B. Schmid,

Thesis,

in preparation.

4) I. Vlattas,

L.D. Vecchia,

5) W. Kreiser,

Second

6) This effect

is shown, for instance,

tion: D.W. Sloccum 7) R.R. Schmidt, 8) D. Seebach, 9) R.R. Schmidt

A.O. Lee, J.Am.Chem.Soc.

IUPAC Symposium

and L. Gieser,

J. Talbiersky

Angew.Chem.

2008 (1976)

Synthesis,

in the convenient

J.Org.Chem.

and P. Russegger,

Israel, September

deprotonation

and J. Talbiersky,

Angew.Chem.

in Germany 6 August

1979)

1978.

of thiophenes

41, 3668 (1976) and references Tetrahedron

Lett. submitted

-91, 259 (1979); Angew.Chem.Int.Ed.Engl.

(1977). (Received

on Organic

98,

at 2 posi-

cited therein.

for publication.

-18, 239 (1979).

-89, 891 (1977); Angew.Chem.Int.Ed.Engl.

-16, 853