Mechanisms of transoxymercuration reactions

Tetmhedron

Letters

No.

MECHANISMS Robert

D.

Department

reversible

Bach,

with

was

l-methylcyclohexene

mercurinium

above

sequence

tion

state

the

involving

elimination

including

reactions 1.

significance

of these

own work,

oxymercurials Our strained alcohol examine

pathways

(eq.

olefin

1).

olefin

at 25 o was se=-‘).

found

This

evidence

pertinent

behavior,

upon

reported

process

a variety

“OR +

CH30H

order

kinetics dependent

by analogy

acetate

attempt

to “trap”

against

a

a rate-deterIn the 5

cations

exchange

by

reactions

that

Transoxymercura-

as well

as alkoxy

and olefin

pathways

as outlined

to evaluating

the

conditions. study

relative

Since

inception

of the exchange

of

solution. was

the isomerization

(2) by the action

provided

HgX

with

mercuric

general

reaction

us with

of oxymercurials.

determination

reaction

1, 4, 7,

ion intermediate.

a kinetic

to -cis-cyclooctene

irreversible

to be concentration

kinetic

by three

reaction

chromatographic psuedo-first

exchange

olefin

isomerization,

in aqueous

with

in quantitative

mercurinium

for

proceed

alcohols

(1)

to the

hindered

on the oxymercurial.

a transoxymercuration

1

exhibited

relatively

observation60f

dependence

‘.I

reaction

of norbornene

deoxymercuration-oxymercuration

pathway

of olefin

experimental and their

This

1

Richter

cyclohexene

the

an olefin

reversible

might

u c? by gas

liberates

a mercurinium

recent

by attack

\

followed

a

The

unsaturated

interactions

F.

amount

from

to undergo

a reaction

trans-cis --

trans-cyclooctene

solvent

system

and co-workers7have

observationof

olefin

of an equimolar

involving

of HgX2.

to report

Halpern

and Robert

of trans-2-hydroxycyclohexyl

as

oxymercurials,

with various

initial

shown

reaction

us to propose

a novel

with

We wish

been

induced

Britain.

REACTIONS

derived

wereinterpreted

prompts

reactions,

in Scheme

Brummell,

oxymercuration

deoxymercuration

exchange

of our

for

results

spectroscopy

involves

N.

in Great

also recently carried out in an unsuccessful 4 These data were interpreted as evidence

ion intermediate.

transition cases,

nmr

also

exchange

Printed

Wayne State University, Detroit, Michigan 48202 received in UK for publicttion 28 June 1971)

trifluoroacetate

has

mining

Roger

the exe-ck-acetoxymercurial

7-tetramethylnorbornene 3 The olefin norbornene.

Press.

TRANSOXYMERCURATION

of Chemistry,

cyclohexene-mercuric

Similarily,

yield.

OF

(Ret ived in USA 18 Mayt971: recently been reported that addition

It has

Per/anon

30, pp. 2879-2882,1971.

The

of the

of oxymercurials

a unique

opportunity

isomerization

ofJ

0I

in to

was

(1)

2 of the mixture in methanol

of&and

solvent.

trans The

rate

in both l_ and oxymercurial2

to the oxymercuration

2879

mechanism,

olefins.

The

of isomerization (k2-7.

8 x 10-2Mvi-’

is consistent

2880

no.30

U

W t

CH, OH

mHgX t

A

C6H,3CH=CH2

“‘..0CH3

a, b, a transoxymercuration

mercury

atom

(Scheme

1) may

of ,@

distinguish

J, in aprotic alcohol

this

solvents

electrophilic

attack

olefinl.

The

-bis-olefin-mercury

the more

reactive

THF

acetate

I& (isolated

resulting

of solvent

and the formation

and liberation

of 2.

and CH2C12

accompanied

X=C1

involving

a cis-addition

mechanism

such as

is also

cyclooctylmercuric compound

X ‘NO3

, while

JJ -via

of methanol

solvent

c, X =OAc d,

mechanism

eliminates

between loss

x =c104

on the nucleophilic

then

the trans-oxymercurial

preceeds

OCH 4 3

2

2

with

C6H$HCH2HgX

by

of2

with1.

9%

regenerates

these

data

cannot

bis-oxymercurial’ extensive

ors.

of the alkoxy

charged cation

ion ofJ,

However,

to observe

in presence

as 39).

r

alcohol.

of a transient

upon transoxymercuration

and characterized

mercurinium

We failed

exchange

of the positively

group. in CH30H

Exchange Thus

which

isomerization

of

of olefin

in

trans-Z-acetoxy-

afforded

the Z-methoxy

I+

OMe

(Scheme The alkene results

transoxymercuration as evidenced

reaction

by the data presented

in the liberation

olefin.

CC analysis

of the

The hydroxy in the absence

perchlorate

under

The position

identical

resulting

and alkoxy

was

mixture group

olefin.

@)

reaction

of equilibrium

of added

in Table

of 91% -cis-cyclooctene

of 2-methoxy-l-octylmercuric with -cis-cyclooctene

1)

is a general

1.

that may

Treatment

of $

be catalyzed

of a corresponding

in 15 min

Conversely,

(eq.

conditions

2).

liberated

by reduction

less

by H’- or

with I-octene

and the formation

established

of ethers

reaction

in methanol quantity

treatment

of 2

than 1% of the acyclic

with NaBH4

and subsequent

and olefins.

of oxymercurials

may

also

trans-2-Hydroxycyclooctylmercuric

be exchanged

in protic

perchlorate

solvents

readily

affords

No.30

2881

3a in methanol mercuric ration

perchlorate reactions

min.).

much

A parallel

electrophilic

exchanging

olefin.

catalyst

is more

We have

established

exchange

reactions

octene.

A similar that

This

is best

exemplified

HgC12]

provides

exchange

reactive

reaction

towards

relative

exhibit

was

enhanced

made

by norbornene

only

salts for

goes

as the ionic

has

an olefin

exchange double

to completion

mercury

when

than the olefin

rapidly

.under.go

displaces

half-life

alkoxy

of the

being

displaced.

and olefin

aikoxy

olefms,

for

mechanism bond

>a-cyclo-

oxymercurials

However,

HgX.2,

(X=C104>

the attacking

>cyclohexene

7

toward

an estimated

is ionic

in the oxymercuration

in the oxymercuration

by Halpern.

which

Transoxymercu-

to the carbon-carbon

of olefins

reactivity

3a.

of the oxymercurial

support

electrophilic

reactivity

its -cis-exo-mercurial even

bond

of trans-2-ethoxycyclooct,vl-

affording

of mercuric

of the oxymercurial

observation

olefins

although

the Hg-X

when

of reactivity

group

to be trans-cyclooctenenorbornene>l-octene

from

months

in CH30H

order

olefin

the

the ethoxy

in 1 hour

faster

addition The

Similarily,

94$ exchanged

LHg(C104)2>Hg(OAc)2>>

involving

olefin

was

occur

N03>OAc>>C1). reaction

=35

at 25 o (tl,2

derived

exchange

from

slowly,

oxymercurials,

exchange

of

$everal

perchlorate. TABLE Transoxymercuration

1 reactions

in Ethanol=

HgX

HgX EtOH

“* OCH,

Y “*IOEt

4)

II Parent

XCIO,

Olefin

Cyclohexene

Catalyst HOAc -_

4 x 10

NO3

HOAc

3.5 4.3

NO3

HN03

1.7

NO3

-1 b )

kobs(sec

-5 x 10 -5 x 10 x 1o-3

Cl cis-Cyclooctene Norbornened

--

2.6

x

7.4

HOAc

4.4

x 10 10::

4.4

ClO,

HOAc HNO, HOAc __

2.0

ve y slow x 10 -’ e 960 .

HOAc

1.9 2.6

x 10 -5 -6 x 10 -5 x 10 x 1O-4

4.2

very slowe x lo-3M-rsec-’

ClO,

after three Calculated Our

OAc NO3

l- octene

(Scheme

1).

derived.

at 25 “C with

of at least

acid

and mercurial

two experiments

that

weeks; d) Adduct stereochemistry tl,2 at O.lM 1-octene.

results

is kinetically was

were

suggest

that alkoxy

exchange

The methoxymercurial indistinguishable Ethanolysis

6.5 2.2

HNO, HOAc

NO3

an average

0.1

NO3

NO3

are

5.5 4.8

NO3

NO3

a) Reactions

0.5

no reaction

NO3

l-Octene

tl/2(hr)

-4

from

of 5 effects

may

concentration agree

is -cis

within and -exo;

and olefin

the alkoxy

e) l-2$

8.4f b) Rate

detectable after

proceed

f)

by different

pathways

and the olefin

(Path

A).

constants exchange

two weeks;

with the mercurinium

between2

exchange

10. 0.7

= O.lM;

10%; c)No

exchange

be in equilibrium

the equilibrium

3.0 88.

from

Alternatively,

ion 2 which which

it

m.30

transoxymercuration equilibrium

with_5

exhibited

(Path

pseudo-first

essentially reaction even

may

for

with ionic

more

facile

only

observed

consistent

kinetic

each

mercuric

with’ionic

ligands

Path

side

0.1,

,

This

H

t

for

were

(K = IO4 - 107)7 eq reactions are much

tend to exclude y&

reaction

concentrations

deoxymercuration

largely

from

the oxymercuration

of the oxymercurial

while

arising

overall

and ROH

constant

[ Ht]

reactions Path

are

B and are

a mercurinium

t k2[ RCHCH,HgX]

ion

[ olefin]

I

OMe

[k,(H’)

+ k2(olefin)]

(Path

k 2 is

by olefin

transoxymercuration

kl[RCHCH,HgX] AMe

HCH,HgX]

C).

the olefin,

that proceeds

1 of olefEcatalysis

exceeds

(Path

data would

reaction

= [R

in the absence

to oxymercurial

in the

These

halides.8

=

catalyst

far

induced

equilibrium

importantly,

-d(RlzHzHgx$

intermediate

since

on the oxymercurial

exchange

k ohs

catalyst

The

lies

More

mercuri

an alkoxy

behavior

salts

solution.

with

olefin

experiment.

acid

with

by deoxymercuration

B) or by added

order

constant

in strongly

be achieved

several

However,

A). orders

when

the ratio

of magnitude

greater

of olefin than kl and

C is dominate. These

“trap”

data provide

a mercurinium

reaction

scheme

exchange

is

k2,

We propose mercury

reversible

kinetic

the major

several

orders for

a mechanism

for

exchange the

of

than the

reversible

rate

Path

the observed

since rate

is -not a reversible

and co-workers4

to include

explains

authors

greater

Whitham

the failure

by these

of magnitude

involving

,

reactions

reported

olefin

the failure

Moreover

oxymercuration

preference

pathway

cation

explanation

ion 6 intermediate.

for

thermodynamic”

Thus

a rational

the

rate

C in the “contra-

constant

of alkoxy

for

exchange,

deoxymercuration

determining

formation

to

olefin

kl.

sequence. of the -bis-olefin

_$. ACKNOWLEDGEMENT

We Fund

gratefully

(Grant

acknowledge

No.

partial

support

for

this

research

by the Petroleum

Research

1829(Gl). REFERENCES

1. NDEA 2.

3.

a)H. b)H.

Predoctoral C. C.

T. T.

Brown Brown

and M. H. and M. H.

Tidwell

and T. G.

4.

S.

5.

W.Kitching,

6.

G.A.

Olah

and P.R.

7.

J.E.

Byrd

and J.

For

a recent

8.

Bentham,

Fellow.

J.Amer.

P.

Rei, Rei, Traylor,

Chamberlain

Organometal.

and G.H.

Clifford,

Sot.,

Rev.,

J.Amer.

4018

reaction (1970).

1296 (1969). J.Amer. Chem.

Chem.,

3,

Whitham,

2,

2614

Chem.

Sot.,

53

1760

(1970).

(1968).

Commun.,

1528

(1970).

61 (1968).

Chem.

J.Amer.Chem.

of this

92,

J.Org.

Chem.

Halpern,

discussion

Chem.

Chem.Commun., and K. T. Liu,

Sot.,

tic., see:

W. S.

3, 92,

1261 (1971); 6967

Linn,

2,

2320

(1971).

(1970). W. L.

Waters

and M. C.

Caserio,