Building Diversity in ortho-Substituted s-Aryltetrazines By Tuning N-Directed Palladium C–H Halogenation: Unsymmetrical Polyhalogenated and Biphenyl s-Aryltetrazines

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We report a general route for synthesizing ortho-substituted unsymmetrical biphenyl and polyaromatic s-aryltetrazines. These compounds are inaccessible by classical Pinner hydrazine condensation or by the current s-aryltetrazine aromatic core functionalization methods described up to now. We exploited multiple versatile N-directed palladium C–H activation/halogenation of s-aryltetrazine to form C–X bonds (X = I, Br, Cl, F), which collectively produced polyhalogenated unsymmetrical building blocks. We achieved a sequence of selective C–H halogenation reactions in a specific order to produce reactive aryl halides. Polyhalogenated s-aryltetrazines can then be used for controlled cross-coupling reactions toward ortho-substituted polyaromatic s-aryltetrazines. In general, this C–H functionalization route gives access to a large number of variously halogenated building blocks practical for further synthetic implementation of tetrazines (arylation, cycloaddition, etc.). Herein, we exemplified their potential by ...