Heteropentalenes. On 5H-pyrazolo[1′,2′:1,2]-1,2,3-triazolo[5,4-a]-phenazinyliumide

Abstract

Some properties of the heteropentalenes 5H-pyrazolo[1′,2′:1,2]-1,2,3-triazolo[5,4-a]phenazinyliumide (1) and 1,3-dimethyl-5H-pyrazolo[1′,2′:1,2]-1,2,3-triazolo [5,4-a]phenazinyliumide (2) are discussed. The u.v. absorption spectra of the free and of the protonated from are reported. Catalytic hydrogenation at room temperature reduces the C-6–C-7 double bond so that the loss of aromaticity is minimized. Compound (2) is oxidized by peracids at room temperature, with attack at the carbon atom in position 12b (negatively charged in the ‘azomethinylide’ structure of this heteropentalene) and formation of a quinone imine.