Formation of an Unsual Fused-Ring Cyclic Carbonate and Its Photolytic Rearrangement into the Novel Heterocycle 2,5-Diphenylphenanthrooxepin

Article abstract of DOI:10.1021/jo01294a005

Vinylene carbonate (1) and phencyclone (2) react in refluxing bromobenzene to yield the cyclic carbonate ester of 1,4-diphenyl-1,2-dihydrotriphenylene-1,2-diol (90percent,3), presumably by decarbonylation of the intermediate Diels-Alder adduct 6 followed by a <1,5> shift of the carbonate moiety.On photolysis (254 nm) 3 undergoes conversion to 1,4-diphenyltriphenylen-2-ol (15percent,9) and 2,5-diphenylphenanthro<9,10-b>oxepin (43percent,8), the first example of the hitherto unknown phenanthro<9,10-b>oxepin ring system.The structural assignments for 3 and 9 are based on spectroscopic andchemical evidence, while that of 8 follows unequivocally from single-crystal X-ray analysis.A possible rationalization for the formation of 8 and 9 from 3 is discussed, and evidence is presented which indicates that oxepin 8, rather than arene oxide 14, is the major component of any equilibrium which may exist between these two valence tautomers.