Photolysis of 4-p-nitrophenylimino-1,2,4-triazolium ylids

TetrahedronLettera lY0.34, pp.3187- 3188,1971. PergamonPress. Printed in Great Britain.

PHOTOLYSISOF 4-p-NITROPWEWYLIMINO-1,2,4-TRIA2OLIDM YLIDS C.W. Bird and D. Y. Woug Departmentof Chemistry,Queen ElizabethCollege,London US 7AW G. V. Boyd and A. J. 8. Sumers Departmentof Chemistry,Chelsea College of Science and Technology,London, S.W. 3. (Deceivedin IH 15 July 1971; acceptedfor publication20 July 1971) The 4-p-nitrophenylimino-ylide (Ia,b) of 3,5-dimethyl-1-phenyl and 1,3,5-triphenyl1,2,4-triaaoles may be preparedby deprotonationof the corresponding4-p-nitrophenylaminotriazoliumperchloratesl. The photolysisof these ylids in benzene,with the exclusion of oxygen, provides quantitativeyields of 4,4'-dinitroazobeneene and the appropriatetriaaoles. n

By analogywith the photolysisof 4-acylimino-1,2,4-triaeolium ylide‘ and ylide of other nitrogen heterocycles3we assume that the present ylide (Ia,b) dissociateyielding P-nitrophenyl nitrene, which either dimerisesor attacks anothermolecule of ylid forming the observed axo compound. However,when our photolyseeare repeated in the presence of oxygen the quantitativelyformed products are 4,4'-dinitroazoxybenzene and the correspondingtriazoles. Appropriatecontrol experimentsexclude the occurrenceof direct photooxidationof 4,4'-dinitroazobenzene and, indeed, no such reactionappears to have been reported.

It is not possible,however, to

exclude photosensitisation of the reactionby the ylid.

I

(a) It= Me (b) ‘1p=‘ph

An alternativeexplanationis suggestedby the recent observation4of the interceptionof a litreneby oxygen, as exemplifiedby the formationof aitroferroceneduring the thermolysisor 3187

3168

no.

photolysis intermediary

of ferrocenyl p-nitrophenyl

p-nitronitrosobenzene aaoxy

aside

compound.

in

nitrene,

then

this

the presence or even

could

An intramolecular

oxygen.

the ylid,

intercept

example

of

of

another

If

undergoes nitrene

in

the present

oxidation with

case

34

the

to

formation

of

the

such a reaction is provided by the thermal

or photolytic conversion of 2-azido-2'-nitrosobiphenyl

to benzocinnoline N-oxide.

References 1.

G. V. Boyd and A. J. H. Summers, J. Chem. Sot. (C), 1971, 409.

2.

H. G. 0. Becker, D. Beyer and H.-J. Timpe, Z.Chem., 1970, lo, 264.

3.

V. Snieckus, Chem.Coma.,

1969, 831;

V. Snieckus and G. Kan, Chem. g,

1970, 172;

T. Shiba, K. Yamane and 8. Kato, Chem. Coma., 1970, 1592. 4.

R. A. Abramovitch,

5.

L. A. Reimau, V. I. Maimind and M. H. Shemyakin, -Izv. Akad. Nauk SSSR, -Ser. Khim., 1964, -1357.

C. I. Azogu and R. G. Sutherland, -Chars. Coma., 1971, 134.