Tetrazo[1,2‐b]indazoles: Straightforward Access to Nitrogen‐Rich Polyaromatics froms‐Tetrazines

Abstract

The straightforward access to a new class of aza‐polyaromatics is reported. Starting from readily available fluorinated s‐tetrazine, a cyclization process with azide leads to the formation of an unprecedented tetrazo[1,2‐b]indazole or a bis‐tetrazo[1,2‐b]indazole (cis and trans conformers). Based on the new nitrogen core, further N‐directed palladium‐catalyzed ortho‐C−H bond functionalization allows the introduction of halides or acetates. The physicochemical properties of these compounds were studied by a joint experimental/theoretical approach. The tetrazo[1,2‐b]indazoles display solid‐state π‐stacking, low reduction potential, absorption in the visible range up to the near‐infrared, and intense fluorescence, depending on the molecular structure.

Novel helix-shape bis[1,2,4]triazolo[4,3-b:3′,4′-f][1,2,4,5]tetrazines: synthesis, optical and charge-transfer properties

“…However, unexpectedly in our studies we did not observe another type of isomerism. It was reported 25 that upon annulation of two indazole fragments to a tetrazine ring, the formation of cis - and trans -isomers was observed with a predominance of the [ b , e ]-annelated ( trans -) form, which is a zwitterionic structure. During the oxidative cyclization of hydrazones 2 , under all studied conditions, the formation of only [ b , f ]-annelated derivatives 3- cis was observed, [ b , e ]-annelated 3- trans structures were not detected at all in the reaction mixtures (Scheme 2).…”