PHOTO-INDUCED REACTIONS .17. A BICYCLO[3.1.0]HEX-3-EN-2-ONE INTERMEDIATE IN PHOTOAROMATIZATION OF 2,4,6-TRIALKYL-6-ACETOXY-2,4-CYCLOHEXANDIENONE

Photolysis of 2,4,6-tri-t-butyl-6-acetoxy-2,4-cyclohexadienone (VIa) in benzene yielded a bicyclo[3.1.0]hexen-2-one VIII, a dienone IX, and a phenol X together with 2,4,6-tri-t-butylphenol. The bicyclohexenone VIII was shown to be an intermediate in the formation of the dienone IX. On the other hand, irradiation of 2,6-di-t-butyl-4-methyl-6-acetoxy-2,4-cyclohexadienone (VIb) afforded a dienone XI, two phenols XII and XIII, and a ketone XIV. The phenol XII and the dienone XI were not obtained by the photolysis of the ketone XIV which may be formed by a skeletal rearrangement of VIb. The results suggest that the photoaromatization of 2,4,6-trialkyl-6-acetoxy-2,4-cyclohexadienones of type VI may proceed via an intermediate of type VIII which may be formed from the dienone VI by acetoxyl migration concomitant with bond alternation. The dienones IX and XI provide the first example of the ortho-ketone tautomer of monohydric phenols. © 1968.