Intramolecular reaction between nitro and carbodi-imide groups; a new synthesis of 2-arylbenzotriazoles

Abstract

1-(2-Nitrophenyl)-5-phenyltetrazole (5b) decomposes when heated to give nitrogen, carbon dioxide, and 2-phenylbenzotriazole (6) in high yield. This new molecular rearrangement proceeds via 2-nitrophenyl(phenyl)carbodi-imide (8). Other precursors of this carbodi-imide, i.e. oxadiazolone (10), oxadiazolethione (11), oxathiadiazole 2-oxide (12), and the aminimide (16), and carbodi-imide itself, all give 2-phenylbenzotriazole (6) on thermolysis, the last three in high yield. This reaction is general for diarylcarbodi-imides with an ortho nitro group, and their precursors, and it provides a useful new route to 2-arylbenzotriazoles. A sequence of electrocyclic ring closing and opening reactions (Scheme 5) is proposed as the mechanism of this process. The key intermediate, 2-phenyl-1,2,4-benzotriazin-3-one 1-oxide (19), has been isolated from a careful thermolysis of (12) in toluene; in solution it is in reversible equilibrium with the ring-opened form (20). This new nitro-carbodi-imide group interaction has been extended to the more stable nitrobiphenyl(phenyl)carbodi-imide (25) and nitronaphthyl(phenyl)-carbodi-imide (24) which, on flash vacuum pyrolysis, give benzimidazo[1,2-f]phenanthridine (29) and benz[cd]indazole 1-oxide (32) respectively, in new rearrangements.