Table 2.

(Scheme 2) Synthesis of the tetrazine dicarbonic acid 5. Reagents and conditions: are described in the methods section The reaction steps were initiated and carried out in i) 1, a) 50% NaOH, b) H₂SO₄; ii) NaNO₂ in glacial acetic acid; iii) SOCl₂, MeOH; NaNO₂ iv) R-NH2; NaNO₂, glacial acetic acid.