Acetolysis of exo-bicyclo[2.1.0]pentane-5-methyl tosylate; cyclopropylcarbinyl intermediates in solvolytic reactions

Tetrahedron Letters N0.47, Pp, 4245-4248,

Printed

ACETVLYSIS

OF EXO-BICYCLO[

CY CLOPROPYLCARBINY

Department

B. Wiberg

of Chemistry,

Among solvolytic

stable

and allylcarbinyl

“bicyclobutonium”

al requirements of isomeric

having

6 and 7 carbons reactivity

The starting

isomer acetolysis

ester,

result

cyclopropyl-

degree

of rate acceler-

from the intervention ’ In order

compounds,

important

alc&oA -a#

cyclobutyl,

of a relatively

to determine

the structur-

and allylcarbinyl

We”4 and others5’

‘have

two compounds,

reported

on the

and we now wish to present

observation

concerning

exo-bicyclo-

(I). prep‘xred

fol.lowed by llthlum

was also formed,

involving

cyclopropanecarbinyl

tosylate

Corm.

of this type of ion, we a-e examining

of some of these

[ 2. 1. O]pentane-5-methyl

diazoacetic

to result

respectively.

what we think is a particularly

III

New Haven,

lead to the largest

ion intermediate.

cyclobutyl,

TOSYLATE;

7 August 1965)

those

derivatives

for the formation

series

J. Ashe,

Yale University,

reactions,

This has been suggested

solvolytic

Ltd.

IN SOLVOLY TIC REACTIONS’

and Arthur

(Received

ation.

Pergamon Press

2.l.O]PENTANE-5-METHYL

L INTERMEDIATES

Kenneth

carbinyl

1965.

in Great Britain,

by the reaction

aluminum

but could be separated

is :

4245

hydride

of cyclobutene

reduction.

by gas chromatography.

with

The endo The

HOAc CH,OTs

CHrOAc

H k170

I

= 1.35

X lo-‘. sex-1

Unlike

the homologous

fragmentation

to an allylcarbinyl

about one-fiftieth propylcarbinyl

This

butonium

derivative

was noted. times

tosylate

(II)’ little

The rate of reaction

ir

as fast as that of cyclo-

tosylate.

tosylate

is clearly

3. 1. 0] hexane-6-methyl

as fast as that of II, and 1:3

McDonald hexyl-2

-exe-bicydlo[

and Reineke’

have recently

(III) on acetolysis

a norbornyl

type ion.

to be essentially

mation

of the bicyclobutonium

tween the groups

must

planar.when

unlike Ithat of bicyclobutane,

ion. leading

fused at adjacent

our data on compounds

largely

type rearrangement,

The reason

forced

gives

reported bicyclo[

that -exe-bicyclo[ 2. 1. l] -hexyl

and cannot

involve

be that the two four membered fused

to each other,

We believe

a 60° dihedral

and this appears

in which the cyclobutane

derivati-

a bicyclorings

ring is fused

are

the for-

this ion to have a geometry

to approximately carbons,

preventing

2. 2,

angle

not be-

to be supported 1.3

to another

b ri]

No.47 The reaction

of I cannot proceed

does

not find it possible

less

accelerated,

thus leading

propylcarbinyl

cation

action

of the empty

There

is evidence

action.”

s

p orbital

angle

stable

species

groups

in some

cations from

derivatives

reactive

provides

derivatives

are primary. little,

if any,

the cyclopropyl

The present

have at least

the several

geometry

despite

driving

cation

carbons,

leading

a limited

than are the correspond-

the fact that the latter

force

from

are

secondary

cyclopropyl

for the reaction,

some

also

provide

an explanation

3. 2. Olheptyl-6

tosylates,

9 and for the observation

the above

and from

Several the fusion

feature

of

of the importance

of the bicyclo[

of epimers.’

whereas

to cyclobutyl

special

cyclopropylcarbinyl

mixture

should

that cyclopropylcarbinyl

processes

ring expansion

cations

This

stability.

of the possible

obtained

to a much

ion.

the structures

acetate

requires

be involved.

conclusions

caranyl

for inter-

data show that the unsubsti-

observations

in solvolytic

Since

ring must

These

at adjacent

than the bicyclobutonium

so1vents.s

have been anticipated

the former

by the inter-

been shown that the dialkylcyclopropylcarbinyl

tuted cyclopropylcarbinyl

ing cyclobutyl

fused

cyclo-

with the bent ring orbitals.

the view that this is the best

requirement

are more

stable

to note that the cyclopropylcarbinyl

between

structural

that a relatively

carbon

III

of I is neverthe-

Such an ion may be stabilized

at the carbinyl

supporting

It has recently are

to the conclusion

ion since

The reaction

via such an ion.

is involved.

It is important

a O” dihedral different

to react

via a bicyclobutonium

from

predictions

of a six membered

may be made ring

from

products4

in the acetolysis

cycloheptenyl

the above

1, 2- to a cyclobutane

of

that the nortosylate

conclusions.

ring should

favor

is a

First, the

4248

No.47

bicyclobutonium Second,

structure

the tram-

should

favor

These

and related

fusion

over

the cyclopropylcarbinyl

of a five

the bicyclobutonium predictions

membered structure

are

being

ring more

srructure

for

the ion.

1, Z- to a cyclobutane than in the case

of -cis-

ring fusion.

tested.

REFERENCES 1.

This work was supported by the Army Research wish to -thank the Badische Anilin-& Soda-Fabrik cyclooctatetraene which was used in preparing

2.

R. H. Mazur, J. D. Roberts,

3.

K. B. Wiberg and B. R. Wiberg and R. Fenoglio,

4.

K. B.

5.

R.

6.

M. Hz.nack and H. J. Schneider, Angew. Chem. Int. Ed., Ann. 686, 8 (1965); W.D. Cl osson and G. T. Kwiatkowski, :Letter3831 (1964).

7.

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N.

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Olah,

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McDonald

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M. S. Silver

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Reineke,

Office, Durham, We for a generous gift of cyclobutene.

J.Am.

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and

K. B.

1553 (1965).

g,

Chem.Soc.,

Guillory, Tetrahedron J.Am. Chem.Soc.,

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results

(Ph. D.

Thesis,

F. F.