The chemistry of s-tetrazines (1,2,4,5-tetrazines) has attracted increasing interest over the years owing to multiple biochemical, energy applications and materials resulting from their unique physicochmecal properties. Accordingly, many improvements in tetrazine synthesis have been reported. The tetrazine frameworks with aromatic heterocycles are classically derived from the Pinner-like synthesis using hydrazine derivatives with either cyanoaryl or chlorobenzoyle coreagents. Because of sterics and other factors these syntheses failed to give efficient access to 3-position-functionalized thiophene tetrazines.
Electron-rich heterocycle like thiophene show the superior inherent reactivity of the 5-poisition of thiophene thus synthesis of selective 3-position-halogenated thiophene tetrazines is very difficult. And the tetrazine ring is well-known to act as a ligand for metals, and thus poisons the catalytic activity. moreover, tetrazines can be reduced by metals, and subsequent ring opening may occur. thus the tetrazine compounds are limited catalytic recations.
Now we report a general and direct catalyzed C-H functionalization of tetrazines for the introduction of various useful functional groups, such as halides. Introducing halogen atoms(Br, I) on the thiophene ring is a first step towards extending the conjugation of the ring system and the construction of more sophisticated structures through the use of metal-catalyzed coupling reactions. Hence, we report the first efficient C-H functionalization of thiophene tetrazines using Rh catalyst. This presentation will provide the catalytic reaction conditions and charecterlization of 3-poition-halogenated thiophene tetrazine compounds.