The conversion of furans to 2(3H)-butenolides

Tetrahedron Letters,Vol.28,No.ll,pp Printed in Great Britain

THE CONVERSION

Andrew Department

of Chemistry,

Z-Aryl- and 2-alkylfurans butenolides

Due to our interest fadyenolides2 synthesis4

elaboration.

procedures

and Martin

Rowlands.

University College of Swansea, Swansea SA2 8PP, U.K.

into the corresponding

in butenolides,I

those related

based on 2-organylfurans,

prior to a mild controlled

We first accomplished shown in equation

oxidation

the synthesis

of a wide variety

to the

for further ,J,seemed desirable,

through

to the required

acid.

for lignan

of 5-organylbutenolides

,$,should be stable enough to be safely carried

Park,

5-organyl-2(3H)-

of our need for synthons

preparation

a synthesis

Singleton

with m-chloroperbenzoic

particularly

and because

a general

In particular

as compounds

Pelter*

of boron derivatives

and piperolides3

we required

OF FURANS TO 2(3H)-BUTENOLIDES

are converted

by the oxidation

0040-4039/87 $3.00 + .( Pergamon Journals Ltd.

1203-1206,1987

a variety

of

butenolides.

of furans J, by the process

(1).

PdW,), MetX

-

(11

THF, SO’C, 20h

R

( Met X = ZnBr, Li)

We could find no example This paper describes substituted

of the direct conversion

of & to 5-organylbutenolides.

such a process which can give rise to a large number of + Of relevance to our work is the conversion by oxygen of

buteno1ides.o

Z-trimethylsilylfurans

to the corresponding

oxidation

and 2-ethyl-5-(dimethoxyboryl)thiophenes

peroxide

of Z-methyl-

5-hydroxy-2(5H)-butenolides7

and the

by alkaline

hydrogen

to the 5-alkyl-1-thio-2(3H)-butenolides.8

We felt that the sequence route, though we were unable J or 2(5H)-butenolides,

shown in equation

to predict

,j or mixtures,

(2) held promise

in any specific would

result.

1203

of being a general

case whether

2(3H)-butenolides,

1205

Oxidation

with oxygen

Oxidation

lack of reaction. unsuccessful

in a Brown hydrogenatorl' with alkaline

due to preferential

reagents

(exp.2,3)lZ

furan.

Lithiation

(MCPBA) was also ineffective, Sodium

carbonate

(exp.7).

Finally,

lowering

necessary Again,

advantageous,

with @-chloroperbenzoic

lowering

&

butenolide

(exp.5,6).

the temperature yield

the yield

hydrolysis

added

of the oxidation

and ring

furan ,&, and this

used 100% MCPBA14

was previously

acid

at 0°C. in order to

based on starting

we generally

Although

sodium carbonate

an excellent

in ether

to -78°C inhibited

the temperature

procedure.

when anhydrous

although

by oxidation

of recovered

acid as it formed and this increased

to give 94% of isolated

became our favoured

with chromium

and gave low yields

was added to the ether prior to oxidation

the meta-chlorobenzoic

(exp.4) due to

(exp.1) was also

oxidation

but some product was obtained

neutralise

opening13

to control

in THF followed

peroxide

Anhydrous

hydrolysis.

proved difficult of &

hydrogen

was ineffective

this was not

(exp.8,10,13,14).

to -78°C was generally

of 5-octyl-2(3H)-butenolide

was obtained

at 0°C

(exp.15). Of particular product was always distinguishable mixture

the 2(3H)-butenolide,

2(5H)-butenolide,

in the presence

any equilibration, The sequence complex

note is that in every case, even when R = alkyl

of sodium carbonate,

in the conditions high yield,

into 5-organyl-2(3H)-butenolides

n-Butyl to a stirred under argon.

lithium solution

and &, tried.

one-pot

Boron trichloride

were allowed

chlorodimethoxyborane

at C-3 only

in each case because With these exceptions

sequence

for the conversion

&

from 2-phenylfuran

(6.4 ml of 1.57M, 10 mm01

of Z-phenylfuran

mixtures

occurs

without

lithiation

the process of 2-organylfurans

(1.449,

in hexane

10 mmol)

(3.33 ml,

(25 ml) in dry ether

1 was

&. slowly added by syringe

n dry ether

(50 ml) at 0°C

lM, 3.33 mmol) was added with

(50 ml

at 0°C under argon.

to stir for 3h at room temperature

and then the

solution

needle to the stirred

of 2-phenyl-5-lithiofuran

was added by double-ended

at 0°C.

to stir for a further

was

, and as such should find wide application.

in hexane

to trimethoxyborane

protonation

is added to the reaction

products.

of 5-phenyl-2(3H)-butenolide,

stirring

allowed

Thus, when water

failed with furans &

is a mild,

Preparation

2, and no trace was found of the readily

even for the 5-alkyl

or difficult

described

$,.

(exp.14 and 15) the

Lithium

chloride

precipitated

hour at room temperature.

Both

solution

and the mixture

was

1206

MCPBA containing

(3.45 g of 1001, 20 mmol) was added to a 250 ml round bottomed anhydrous

sodium carbonate

(75 ml) was added and the mixture whilst

the solution

solution

of &

was allowed

The organic The combined

100 mnol) under argon.

cooled to -78°C and maintained

was rapidly

added by double-ended

to warm to 0°C and then water

layer was removed

organic

sodium bicarbonate

and the aqueous

and dried

(MgS04).

(50 ml)

Filtration

1M sodium

support

After

layer washed with ether sodium sulphite

5 min.,

the

m.p. 91-92"C,

(2 x 25 ml).

(50 ml),

(50 ml), water

of solvent was followed

mn Hg to give 5-phenyl-2(3H)-butenolide

We thank the SERC for financial

at this temperature

needle.

bicarbonate

and evaporation

Dry ether

(50 ml) added.

phases were washed with saturated

saturated

at 75"C/O.O05

(10.59,

flask

(3 x 50 ml)

by sublimation

(1.45 g, 90.6%).

of this work.

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