The photolysis and pyrolysis of bis-2,3-diphenylcyclopropene anhydrides: benzvalene

'Ibtrrhedron LettersRo. 16, pp 1579 - 15S0, 1972.

Pergmon Pmar.

Printed in Great BAtein.

TRR PROTOLYSISAND PYROLYSIS OF BIS-2,sDIPRRRYLCYCLGPROPRNR ANRYDRIDES: BRNZVALENE Rarle B. Royt, Jr., Edward J. Reiueberg*,Patrick Goodman**,Pam Vaughan*** Northern Arizona University,Flagstaff,Arizona and Ylasios Georgian Tufts University,Medford, Massachusetts (Reoeivedin USA 3 H8roh 1972; moeived in UR for publioetion10 l&oh 1972) When the anhydrideof triphenyl-A2'3 -cyclopropenecarboxylicacid, is irradiated,or pyrolysed,hexaphenylbenseneis formed'. Although a prismaneintermsdiateLcould be postulated, the results of the irradiationor pyrolysisof the anhydrideof 2,3-diphenyl-A 2'3-cyclopropene carboxylicacid (I) indicate a bensvaleneintermediate. When the anhydride (I) is subjectedto photolysis (Hanovia450 light; ether solution,45 minutes,with or without a Pyrex filter)thereis a 72% yield of tetraphenylbenzenes, which consistsof a 50-50 mixture of 1,2,3,5_tetraphenylbenzene and 1,2,4,5_tetraphenylbenzene. These were identifiedby comparisonof the Rf's on T.L.C. (SillcAR7GF, Ccl4 eluent), melting points, the ultraviolet,infrared,and msss spectra with authentictetraphenylbenzenes. No 1,2,3,4-tetraphenylbenseneis observed in the reaction product. Similar results are obtainedwhen the anhydride is subjectedto pyrolysis (sealed tube in vacua, 175", 24 hrs.).

*

N.S.P. UndergraduateResearchParticipant. The support of N.S.F. Grant #GY-3455 is

gratefullyacknowledged.

** N.S.F. UndergraduateResearchParticipant. The support of N.S.F. Grant #GY-7382is gratefullyacknowledged. HI*

N.S.F. UndergraduateResearchParticipant. The support of N.S.F. Grant #GY-8764is gratefully acknowledged.

1579

No. 16

1580

The photochemical

rearrangement wp

monitored by quantitative

ultraviolet determinations.

There is no evidence for the build up of any intermediates.

Ihe anhydride may form (IL) which, models suggest, is a highly stratied species. rearranges to (III), a considerably

less strained species than (VII).

Anhydride

It then

(III) may then

rearrange to a bensvalene3 which on rearrangement yields 1,2,3,5_tetraphenylbenzene

and 1,2,4,5-

tetraphenylbenzenes. An asymmetric tetrasubstituted

prismane (VIII), which on rearrangement would yield the

observed products, could be formed from (II) or from diphenylcyclopropene two diphenylcyclopropene

moieties.

dimers obtainable from

However it would be reasonable to expect some of the symmetrical

prismane (IX) to be formed which on rearrangement would afford some 1,2,3,4_tetraphenyl none of which is observed.

In any event the product distribution'

benzene,

does not support the intermediacy

of such a prismane.

Acknowledgement.

Ihe support of the Institutional

Studies and Research Committee at

Northern Arizona University is gratefully acknowledged. REFERENCES 1.

The reaction was first reported in the Ph.D. thesis of Earle B. Hoyt, Jr., Tufts University,(l966)

2. R. Breslow, P. Gal, H.W. Chang, and L.J. Altman. J.Am.Chem.Soc. S7, 5139 (1965) 3. R.N. Warrener and J-B. Bremner.

Tetrahedron Letters 5691 (1966)