Synthesis of Tetrazines from N-Allenylpyrrole-2-carbaldehydes and pH-Controlled Reversible Fragmentation.

A one-pot highly selective approach to the synthesis of hitherto unknown tetrahydropyrrolo[2',1':3,4]pyrazino[1,2-b]pyrrolo[2',1':3,4]pyrazino[1,2-e][1,2,4,5]tetrazine ensembles from simple and available N-allenylpyrrole-2-carbaldehydes and hydrazines has been developed. The reaction proceeds in a very facile manner and tolerates different substituents in both pyrroles and hydrazines. The novel class of organic compounds, tetrahydrodipyrrolodipyrazinotetrazines, proves to be promising pH-sensitive switchers to deliver N-aminopyrrolopyrazinium salts in acidic media and then again tetrahydrodipyrrolodipyrazinotetrazines in basic media. Both transformations give the products in quantitative yields.