Characterization of ylids formed during the photolysis of α-epoxyketones

TetrahedronLettersMO. 29, pp 2727 - 2725. OPergamon Press Ltd. 1979.Printedin Great Britain.

CHARACTERIZATION OF YLIDS FORMED DURING THE PHOTOLYSIS OF a-EPOXYKETONES Philippe

Hallet,

Jacques

Muzart

Laboratoire U.E.R. Sciences

In the preceeding irradiation

paper,

of a-epoxyketones

work of Griffin intermediates

de Photochlmiet 51062 Reims (France)

and coworkers

of aldehydesin by their

them at 25’C when a-epoxyketones

species

absorption

to their

are photolyzed

which gave structureless The coloured

or when thecolouredglass are the absorbing

of styryl spectra

visible

spectra

According

ylids

to the

should be

We now report

that we

at low temperature and to trap of various glass,

dipolarophiles.

epoxyketones

and were characterized

thus observed were stable

samples were rapidly

was irradiated

(1).

epoxides,

in the presence

intermediates

intermediates

are produced during the

states

these irradiations.

absorption

the dark at 77OK. However, the irradiated

temperature

excited

at 77OK in a 2-methyltetrahydrofuran

maxima (table).

that ylrds

3( rr,+:)

(2) on the photolysis

ylids

When photolyzed

we have shown that aldehydes

excited

for the formation

have been able to detect

increased

Pete::

The .L~~~Lation 06 a-epoxytztonen - 3 at 366 nm phoduced yli.h which wem by .th& abbohption bp&ti and-by -%.apping wLth ma&,~c anhydude .

chataOt&zed

coloured

and Jean Pierre

with visible

in the photolysis

bleached light

led to

by their for hours in

when the temperature

at 77’K.

We believe

of these a-epoxyketones

at low

(2, 3). Table

H ,rk 0

Ar’

ET kJ.mol-’

Emitting excited state

,&i

H

x max

Y Ar ’

1

249

Tl,+

585 nm (navy blue)

2

253

Tl,+

560 IUII

(blue)

3

245

71,i+:

575 nm

(blue)

i Equipe de Recherche Associee

au C.N.R.S.

no 688. 2727

2729

Ko. 29

When solutions

of cl-epoxyketones

anhydride (4) cycloadducts cycloadducts

increased

with increasing

These results come from an ylid starting similar

reaction

furan glass,

(6).

we studied

solvent

of the

if we assume that the aldehyde and the adducts

To verify

that products

came from a 3(~,~::)

state

of the

at 366 nm by benzophenone (PT = 289 kJ):

at room temperature while,

the emission

of maleic

Yields

polarity.

sensitization

mixtures was obtained

we detected

in the presence

andnaphthaldehyde were obtained.

can be rationalized

intermediate

epoxyketone,

1 - 2 were irradiated

(S), a-diketones

of the naphthylgroup

a

in a Z-methyltetrahydro-

and the blue colollr

characteristic

of the ylid. Scheme

*r1 Ph

-1

*r2 cl-naphthyl

Solvent

Conversion

MeCN

94

MeCN

o>

References

8-naphthyl

MeCN

8-naphthyl

MeCN

-6

7

traces

43%

33%

87%

75

‘SH1 2

Ph -2 2 8-naphthyl

-5

%

15%

g4 traces

34% 16%

25%

80

:

1) P. Hallet, references

Pete,

and G.W.

3) Recently

species

(1977).

We

in almost not be

have

and

case,

Ed. Dekker,

under

conditions

and R.G. species

from

oxide

J. Chem.

substituted

a

(1973).

by

when

Perkin II,

arylgroup

in

at 77?,

8 position when ylids

using various

have also

as

maleates

used successfully

been reported

photolysis

chalcone and

of the UK 18

Hallet,

recently of observed followed 1379)

to

that

oxide.

stereochemistry

stereospecific

(Received

detected D.J.

shown that

4) Other dipolarophiles

6) When

preceeding

Organic Photochem.

2-methoxyderivativecf.

5) It

Lett.,

therein.

21 N.R. Bertomere and

J.P.

J. Muzart

Lee, J. adducts was stereochemistry by

and

published). cycloadds Chem., 43,

to

cycloaddition.

derived

(1978).

the reaction in agreement

ylid

seen to a disrotatory

the