Catalytic oxidation of homoallylalcohols to α-alkoxytetrahydrofurans by a Pd-Nitro complex and molecular oxygen

Tetrahedron L.euers, Vol. 35, No. 3. pp. 455458. 1994 Elscvier Science hd F’riitcd in Great Britain 0040~4039/94 $6.00+0.00

Catalytic Oxidation of Homoallylalcohols to a-Alkoxytetrahydrofurans by a Pd-Nitro Complex and Molecular Oxygen

Tom M. Meulemans, Niklaas H. Kiers, Ben L. Feringa’ and Piet W.N.M. van Leeuwen+

+ Koninklijke/Shell

Department of Organic and Molecular Inorganic Chemistry, GroningenCenter of Catalysis and Synthesis, University of Groningen. Nijenborgh4, 9747 AG Groningen, The Netherlands Laboratorimn,Amsterdam(Shell ResearchB.V.), PO Box 3003, 1003 AA Amsterdam,The

Netherlands

Abslrucf: Various homoallylalcoholswere highly regioselectiveoxidized with molecularoxygen at theterminal carbon toafford cyclic acetals (a-alkoxytetrahydrofurans) using PdNO,CI(CH,CN), as a catalyst in the presence of CuCl 1 and t-butanol or isopropanol.

Catalytic

oxidation

of substituted

olefins with molecular

to avoid oxygen atom donors like hypochlorite, alcohols

and phenols’,

ketones (scheme cyclizations formation

the indirect

1, route a) has extensively

of hydroxyalkenes of cyclic acetals,

centers

(>

More recently for lactones”,

complex

90 % selectivity)

catalyzed

to

intramolecular

of a diol as a short way

illustrate

capable of converting

of CuCI,, 0, in t-butanol

oxidation

nicely their potential

by the presence

of homoallylalcohols

u-alkenes

oxygen.4

in

of stereogenic

into aldehydes

(up lo 100 o/O selectivity (t-BuOH) without

or isopropanol the necessity

I

*+-

P

a. Wacker b. oxidative

type oxidation cyclization

,,/A i’ \

I ,

to methylketones to alkoxytetrahydrofurans

455

b

---*

/’ 0

(IPA),

-OR

s

and high yields) by (scheme

of directing

OH

,’

(60-70

Now we wish to report the

is described.”

!

1

using

For instance the oxidative

the cyclization

by using molecular

OH

Scheme

palladium(H)

might be achieved

oxygenases

with PdCl, of olefins

means of olefin Iiinctionalization.9

to u-alkoxytetrahydrofurans

in the presence

the lirst selective

at the allylic position

type oxidations

and the i’ormation of aminoalcohols’*

the USCof a Pd-nitro

of l-alken-4-ols

PdNO,Cl(CH,CN), b). In addition

activity is devoted to mimicking

Control oT the stereoselectivity

or methyl ketones

oxidation

attention’ in order

alkenes.

Earlier4,‘” WC reported % selectivity) effective

Frontalin

considerable

and peroxides and to have direct access to epoxides’, in Wacker

been studied.’

which are good precursors

of natural products.

in the hydroxy

use of oxygen

provide an atractive

to both natural and unnatural the synthesis

iodosylbenzne

and ketones ‘. Considerable

aldehydes4

0, as oxidant.6*7 Furthermore

oxygen has attracted

1, path

substituents

456

It appears that competing The oxidation an O? atmosphere

Wacker type oxidation to methylketones

reactions were performed

1, route b). The results

(Scheme

can be largely avoided.

at 30°C using an in situ prepared Palladium-nitro of the oxidation

reactions

OH 5 % Pd(NO~CI(CH,cN) 1-

_,

’ %

1

_

zRf

20 %cucl~

R 40H

R;”

B

I 4 4

Scheme 2 TABLE:

-R3

,’

0

in table

catalyst under 1.

-OR,

,o

RI

5

1”

Entry

Solvent

Homoallylalcohol4

1

React.

Product 5

time.

CC Yield/%

R,

R*

R,

(&OH)

(h)

(isolatedYield/%)

H

H

H

IPA

3

26b (2

70%)

2

H

H

H

t-BuOH

16

94b (30)

3

H

CH,

CH,

IPA

2

1tW (50)

4

H

CH,

CH,

t-BuOH

2

ItNIb (80)

5

H

CH,

CH,CH,

IPA

1OLl

9s (55)

6

H

CH,

CH,CH,

t-BuOH

40

loo (70)

7

H

Phenyl

Phenyl

IPA

16

80 (70)

8

H

Phenyl

Phenyl

t-BuOH

4

75 (32)

9

CH,

CH,

CH,

IPA

1

99 W)

10

CH,

CH,

CH,

t-BuOH

2

96 (70)

IPA

1

t-BuOH

2.5

11

OH

//‘\h

‘\

7 12

a: In a typicat procedure

the calalyst was made in situ by dissolving 5 mol% PdNOJZl(CH$ZN), , 20 mol% CuCl, in IPA or 1 g. of substrate together with

and stirred under oxygen at 55°C for 2 hours. Afler cooling the reaction mixture to WC,

t-BuOH

an internal standard reactions

(isooctane)

were completed

catalyst followed pressure.All

was added.The

products showed IR, ‘H, ‘W-NMR,

dime&es

reaction

was monitored

within 4 hours. Work up was done by

by extraction with pentane/water

2-t-butoxytctrahydrofuran partly

are given

was prepared

to bisdihydrohran

6.

with CC.

and molecular distillation MS data in accordance

independently”.

Most

filtration (Al *O,) of the

b: during

under reduced

R

o

.‘Gy”e:

with the structures; isolation

the product

6

W&C&I

457

Most oxidations

are highly selective at the terminal carbon. Thus the oxidation of 3-buten-l-01

yields a-t-butoxytetrahydrofuran It should

and all tertiary homoallylalcohols

be noted that, except

ref. 13 for the t-butanol

for t-homoallylalcohols,

effect)

When the carbon

is no selective

oxidation

the formation

of a five membered

at the terminal

carbon.

but only partly converted

to u-alkoxypyrans The catalyst

(3 mol % of catalyst)

once more. The observed

showing

that the catalyst

conversions

more than three runs. For comparison using molecular

oxygen

was observed

is necessary

p-benwquinone (scheme

small amounts

a number

of oxidation

A selective

than

(table

but the oxidation

11, 12).

in several

was added

gram of substrate

of unidentified

are not oxidized

I, entries

was investigated

1 g. of substrate

reactions

oxidation

subsequent

to the catalytic

was added and this was and third run respectively

side products

were formed

with PdCl,(CH,CN),,

of 4-methyl-1-penten-4-01

of 3,4-dimethyl-1-penten-4-01

found that a substituent

to achieve

selective

on the allylic position

oxidation

(scheme

in wet DMF). The absence of a substituent

1, path a). lnomata

oxidation,

ring is less favourable

after

CuCl, in t-BuOH to 5,5-dimethyl-2-t-

was very slow and did not

conversion.

Nokami and co-workers” sulfonyl)

furans

another

(c.f. there

were 100% and 95% alter the second

However,

were performed.

butoxytetrahydrofuran

Typically

as solvent.

by one carbon

and 2-allylphenol

of the catalyst

conversion

in t-butanol

is lengthened

of a six membered

Z-methyl-5hexen-2-01

as the substrate.

is still active.

are higher

into the corresponding

and after complete

repeated

give complete

The formation

is still active after one run. The activity

runs using 3,Cdimethyl-1-penten-Co1 system

selectivities

chain of the hydroxyalkene

ring. Therefore,

in t-BuOH

are oxidized to wdkoxytetrahydrofurans.

and co-workers

i.e. a tosyl group

tetramethylurea,

ethyl acetate

(R,=

on the allylic position (4, R=H)

t5 found that a coordinating

was used on the allylic based system

alkyl, alkoxy,

1, path b) using a Wacker

position

in methanol

under nitrogen

with a PdCl,,

to oxidize

(PdCl,,

afforded a methylketone

group is necessary

(4, R,=Ts)

alkoxycarbonyl,

type system to afford CuCI,,

homoallylalcohols

selective

N,N,N’,N’to cyclic

acetals. Our results clearly show that a substituent the highly selective a Palladium-nitro In a further

oxidation

of homoallylic

extension

the oxidative

The results of this investigation

by allylation

of a-hydroxyesters.‘”

Entry

alcohok

or a “directing group” is not required for

to a-afkoxytetrahydrofurans

with 0, as the oxidant using

catalyst.

investigated.

TABLE

at the allylic position

cyclization

of allyl-substituted-a-hydroxyesters

are summarized

in table2. The starting materials

(4, R,=CO,Et)

are readily available

2 Homoallylalcohol&’

Solvent

React. time.

Product2

(‘9

(%I

Yield

R’

R=

R3

1

H

CH,

COOEt

IPA

2

60

T

H

CH,

COOEt

t-BuOH

18

63

35

H

Phenyl

COOEt

IPA

2

70

4

H

Phenyl

COOEt

t-BuOH

20

>Ya

a: Typical procedure, see footnotetable

1. b: racemate.

was

c: 1 mol% of catalyst. d: 4 mol % of catalyst.

458

All

homoallyl

methylketones selective

esters

are

formed.

compared

precursors

are

to

The

oxidative

reaction

because:

selectivity

However,

the

for substituted

cyclisration (1)

less

for

the

preparation

reaction

particularly

the

u-alkoxytetrahydrofurans

reactions IPA.

and carbohydrate

range

of

active

optically

support

based

only

significantly

small

slower,

amounts

but

a-alkoxytetrahydrofurans

catalyst

proved

lo related

of substrates

also

are

Technische

(2)

Mimoun,

H. “Metal Complexes

Wilkinson, 2.

Groves,

3.

Karlin,

G., Pergamon

The availability makes

for Scientific

this

catalytic

Research

We are grateful

to Prof.

Coordination

Chemistry,

T. G., Wiley,

New York,

R.M.

(NWO) Kellogg

esters.

Zubieta, 22, 241.;

Gelling,

ofdioxygen” Y. ; Cruse,

J. C.; Gultneh,

1984, 106, 2121.;

J., J.Am. Chem.Soc.

0. J.; Feringa,

Feringa,

B. L., .I. Chem. Sot. Chem. Commun.

5.

Sheldon,

R. A.; Kochi,

Press,

New York,

6.

Hayaishi,

7.

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R. W.; MC Kown, Tyeklar,

1990,

1980. J. P.;

K. D., Acc.Chem.Res.

1989,

112, 7599.

1986, 909.

“Metal-catalyzed

oxidations

of Organic

Compounds”

Academic

1981. “Oxygenases”,

Academic

Press,

B. L., in “Bioinorganic

Chemistry

of Copper”,

0. ed.,

J. W.; Hutchinson,

Z; Karlin,

B. L., J.Am.Chem.Soc.

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J. K.,

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J. T., in “Metal ion acfivation K. D. ; Hayes,

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K. D. ed., Chapman

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1993, ch. 24. 8.

Henry,

9.

Hosokawa,

P. M.,

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T.; Miyagi, J.; Ogawa,

catalyzed

Oxidation

S.; Murahashi,

S.; Mandai,

H.; Miyamoto,

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N. H.; Feringa,

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K., Chem.Lett.

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Asymm.

1991,2, 705.

12 November

1993; accepted

R. M., Tetrahedron

1993; revised

19 November

19%)

high

of enzymatic

tetrahydrofurans.

Wetenschappen.

in Oxidations”

Press,

more

synthetic

REFERENCES 1.

of

attractive

a very

of substituted

Organization

a-hydroxy

systems,

u-hydroxyesters”

synthesis

by the Dutch

of allyl-substituted

to be an attractive

Wacker

are obtained.

allylsubstitutcd

for the asymmetric

by the Stichting for samples

are

substituted

compared

for a broad attractive

and

derivatives.

is required

This work was supported

and Dr. H. Moorlag

in t-BuOH

Ester

by a palladium-nitro

yields

methods

Acknowledgement:

in

catalyst

oxidation

to the

reactions

lactones

and (3) good

with financial

oxidized

1989,