CYCLIZATIONS .2. ELECTROCHEMICAL, PHOTOCHEMICAL AND CHEMICAL CYCLIZATION OF 4'-FLUORO-2-HALOGENO-N-METHYLBENZANILIDES

Radicals generated by cleavage of the carbon-chlorine, bromine or iodi ne bond of 4'-fluoro-2-halogeno-N-methylbenzanilides (1) cyclise on an adjacent benzene ring. Yields of products are easily determined by F- 19-nmr spectrometry since a fluorine substituent in the N-methylbenzan ilide substrates is not cleaved during these reactions. Chemical react ion with tributyltin hydride gives the least satisfactory results. The cyclised product, 3-fluoro-5-methylphenanthridin-6-one (2), is the pr incipal product from photochemical reaction after long reaction times. Electro-chemical reaction yields three products which are identified and the highest yield of (2) is generated using the chloro-substrate.