PHOTOLYTIC DECOMPOSITION OF SOME POLYCYCLIC ALPHA-DIAZOKETONES - GENERATION AND REACTIVITY OF 1,2-OXOCARBENES IN BENZENE WITH AND WITHOUT TERT-BUTYLAMINE

Irradiation in benzene of the two isomeric 2,3-diazofluoranethenones 1 1 and 14 results in the formation of only products due to the formal i nsertion of the intermediate oxocarbenes into the C-H bonds of the sol vent, unless the reactions are carried out in the presence of tert-but ylamine, whereupon products of an apparent [3 + 2]-cycloaddition of th e oxocarbene to the solvent are also obtained, viz; dihydrofurans 13 a nd 16, respectively. Wolff rearrangement of the generated oxocarbenes to give products derived from direct trapping of the ketene intermedia tes with tert-butylamine are not observed. The formal insertion produc t, 2-phenylfluoroanthen-3-ol 12 (from 11) undergoes partial oxidation during chromatographic purification on silica to generate a persistent free radical species 17 which has been detected and characterised by EPR spectroscopy. A reinvestigation of the photolytic decomposition of the related polycyclic alpha-diazoketone 5 under the same conditions has established that a more Likely structure for the isolated dihydrof uran is 8, and not the reported isomeric dihydrofuran 20, which is for med from 8 by hydrogen migration during isolation by repeated thick-la yer chromatography.