Carbazole deriv photochemical

Change of solvent to benzene also yields these dimers which are accompanied by the adducts (78) and the furan (79). The adducts (78) are formed via a hydrogen abstraction pathway. The photochemical isomerization of the spirocyclopropane derivatives (80) affords the carbazole derivatives (81). This reaction involves ring-opening of a cyclopropyl bond followed by cyclization of the resultant biradical. An oxidative step must also be operative. 

Dihydrooxepino[3,2-a]carbazole derivatives are formed in moderate to rather high yields on photochemical rearrangement of pyranocarbazole alkaloids, for example mahanimbine <88TL6625>. 

In the second step the reaction is less efficient because of quenching of the excited state of the diphenylamine component by the adjacent carbazole. Other cyclisations such as the conversion of (41) into (42) by irradiation in acetic acid have also been reported. As mentioned earlier cw-azobenzene derivatives cyclise under conditions where the nitrogens are protonated or complexed. A series of heavily substituted azobenzenes has been shown to undergo photochemical cyclodehydrogenation on irradiation in methylene dichloride solution with added SnCU- The reaction has been shown to be an efficient path to the heavily methylated cinnolines in good yield. 

Indoles and Carbazoles. - Formation. 2-Arylindoles (132) are formed by intramolecular Wittig reaction of the phosphonium salts (131). The hydroxamic acids PhN(OH)COCH2COR (R = alkyl or aryl) cyclize in boiling toluene to mixtures of indoles (133) and 3-isoxazolones (134). Irradiation of a solution of o-iodoaniline and the potassium enolate of acetone affords 2-methylindole. The enamino-ketone (135) cyclizes photochemically to 1,2-dimethylindole (136) with elimination of acetaldehyde/ The styrene derivative (137), obtained by the action of Meerwein s acetal, Me2NCH(OMe)2, on o-nitrotoluene, yields 1-hydroxyindole on treatment with zinc/ Azidobenzocyclobutanes (138 R = Me, Ph, or CH2Ph) are converted into indoles (133) by the action of concentrated sulphuric acid/ ... 

One-pot photochemical annulation of 3-acyl-2-haloindoles (209) (211) afforded fused benzo[c]carbazoles (210) (212) in high yields. Substituted dihydrexidine analogues (214) having A -benzoyl enamine units were prepared by intramolecular photocyclization. Visible light-induced intramolecular cyclization of V-3-butenylindole derivatives (215) and diamines (217) was sensitized by Ru(bpy)3 " "... 

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