Takashi Furuta

Photochemical reactions. Part 20. Photolysis of o-nitrobenzaldehyde N-acylhydrazones leading to benzyne and 5-nitrophthalazines

Irradiation of o-nitrobenzaldehyde N-acetyl-N-alkylhydrazones resulted in the generation of benzyne via decomposition of o-(N-acetyl-N-alkyltriazeno)benzoic acids derived from o-nitrosobenzoyl-N-acetyl-N-alkylhydrazides which are initially formed in an analogous fashion to the o-nitrobenzylideneaniline rearrangement. Photolysis of o-nitrobenzaldehyde N-acylhydrazones, however, resulted in photocyclisation leading to 1-substituted 5-nitrophthalazines, with benzyne generation only as a minor process.

Photochemistry of N-acyl-2-nitrodiphenylamines. A novel photochemical synthesis of phenazine N-oxides

In contrast with 2-nitrodiphenylamines and their N-alkyl derivatives, N-acetyl- and N-benzoyl-2-nitrodiphenylamines are converted into phenazine N-oxides by u.v. irradiation. The requirement of N-acyl groupings is best explained in terms of oxygen transfer from the nitro-group to the amide carbonyl group. The reaction has been applied to the synthesis of some condensed pyrazine N-oxides (imidazo- and thieno-quinoxaline N-oxides).

Photochemical reactions. Part 21. Photochemical isomerization of pyridazinium and triazinium betaines

Irradiation of 5-oxidopyridazinium betaines (1) results in the smooth isomerization leading to pyrimidin-4(3H)-ones (2). When 1 -oxidophthalazinium betaine (6) and 3-oxidopyridazinium betaine (11) are photolysed in water, the corresponding phthalazin-1 (2H)-one (8) and pyridazin-3(2H)-one (13) are isolated in high and low yields, respectively. Upon employment of acetonitrile instead of water as solvent, irradiation of the betaines (6) and (11) gives the stable fused diaziridines (7) and (12) which are converted easily into the phthalazin-1 (2H)-one (8) and pyridazin-3(2H)-one (13) by the action of water. Photolysis of 4-oxido-1,2,3-benzotriazinium betaines (15) causes photoisomerization to give benzotriazin-4(3H)-ones (16) in high yields.