PHOTOLYSIS OF NAPHTH[2,3-D]-1,2,3-OXADIAZ OLE - A CONTRIBUTION TO THEOXIRENE PROBLEM

The photolysis of [9a-C-13]naphth[2,3-d]-1,2,3-oxadiazole ([9a-C-13]14 ) in methanol, water, and cyclohexane is studied. In the protic solven ts, the Wolff rearrangement products 2-(methoxycarbonyl)indene ([C-13= O]16) and 2-indenecarboxylic acid ([C-13=O]23) exclusively labelled at the carbonyl carbon are obtained. Furthermore, the photolysis of [9a- C-13]14 in methanol yields [2-C-13]-2-naphthol (19) as hydrogen abstra ction product. The photolytic decomposition of 14 in cyclohexane affor ds 2-(2-naphthoxycarbonyl)indene (25) and 1-cyclohexyl-2-(2-naphthoxyc arbonyl)indene (26). The formation of 25 is explained by nucleophilic addition of 2-naphthol (19) to the intermediate ketene 21. 2-Naphthol (19) is generated in situ by hydrogen abstraction from cyclohexane. Th e cyclohexyl radicals, thereby obtained, convert 25 to 26. Similar pho tolysis of [9a-C-13]14 affords [C-13-O-C-13=O]25 and [C-13-O-C-13=O]26 labelled at the carbonyl carbon and C-2 of the naphthalene ring. Thus , independent of the nature of the solvent (methanol, water, cyclohexa ne), no labelling distribution is found in the photolysis products of [9a-C-13]14. This excludes the participation of naphth[2,3-b]oxirene ( 17) as reactive intermediate.