The photosensitized singlet oxygen addition to a silyl enol ether

Tetrahedron Lettere Boo. 24,pp 2423-

Printed in Great Britain.

2425,1972. Pergamon Prers.

THE PHOTOSENSITIZED SINGLET OXYGENADDITION TO A SILYL ENOL ETHER George Department

of

M. Rubottom

Chemistry,

and Mayda I.

University

of

Puerto

(Reoeived in USA11 April 19721 received The photosensitized to

afford

systems

products containing

oxygenation of

allylic

hydrogens

enol

the well

Rico,

Nieves

Rio

Piedras,

in BK for publication

of

typical

Lopez

esters

has

documented’ (Scheme

recently

“ene”

I).

P.R.

been

reaction

We have

00931

8 Bhy 1972)

of

prepared

shown’ olefinic

the

*

Scheme I Further Reaction

w Products (Ref.

trimethylsilyl dures3*4,

enol

ether

and subsequently

The irradiation 5 ml of

toring

for

which

gave

1685

disappearance

(carbonyl);

88-94

of

in

less

reaction

of

of

ca 2 mg of than

0.5

iodide

test

characteristics

ir

:

88 (s,6,-CO-

l_ by standard

tetraphenyl

reaction

cm -‘)

94 (m,3,vinyl

(TTP)

by nmr monimixture

(nmr),

linkage,

had

3420

(O-H),

3540,

TMS) 6 (s,9,Si-CH3),

$H3)2),

ofl_in

porphyrin

the peroxide

(CC14,

oxygen.

g (2mmol)

0.44@

hr as evidenced

for

proce-

singlet

of J_with

oxygen

nmr (60 MHz) Hz (CC14,

(broad,l,O-H),

ketone

The two component

1. w

potassium

spectral

the

containing

was complete

following

phenyl

the presence

in

a positive

isopropyl

studied

carbontetrachloride

as sensitizer’

the

of

9 (s,9,Si-CH3), CH3),

296

(m,l,

ii vinyl

H),

analysis

6

the major

320 of

(m,l,vinyl the mixture

peak

Catalytic

H),

showed

it

426-492

gave

irreproducible

to be

hydrogenation

(m,lO,aromatic

the J,L)

(Pd/C)

peaks,

- unsaturated

in methanol

2423

of

H).

Gas chromatographic

however, ketone the

collection 2.’

oxidation

1)

mixture

of

No. 24

2424

obtained of 2,

from

0.220

g (lmmol)

A and an unidentified

firmed

by comparison

oxidation

mixture

afforded

2’.

a derivative tion

triphenyl

while

treatment

of 2.

Control

conditions We feel

authentic

and that

our

results

are

8

materials.

phosphine

with

silica

not

g of

a 62

react

compatible

with

con-

of

the

at room temperature

afforded

in the

were

treatment

Further,

show that

: 35 : 3 mixture

of 3_ andL

in hexane gel

experiments

1 does Y

0.291

The structures

compound.

with

with

of l_ afforded

a mixture

3_ is

inert

absence

Scheme II

of

to

of2

andL4,

the

oxygena-

sensitizer.

outlined

below.

Scheme II

Normal

Silicagel

5

1 “ene”

0

H2 (Pd/C)

Reaction \

&JL (Pd/C)

Competition Invol.ving Oxygenation 2 which silica

is gel

affords normal

successful

of _l_ in the normal

subsequently or hydrogen.

6_ via “ene”

Reaction Silicon

a novel reaction.

competition,

converted

“ene”

* l1 in direct this

and in contrast

to be to

the

the

the

hydroperoxide

triphenyl

of l_ involving

reaction”

We believe

132 affords

to 2 by thermolysis,

The reaction “ene”

sense

silicon

migration

competition first

reaction

phosphine,

example

with of

the

such

shown by en01

a