The reaction of ethyl chloroformate with 3,6-diphenyl-1,2-dihydro-1,2,4,5-tetrazine gave the title compound, diethyl 3,6-diphenyl-1,2-dihydro-1,2,4,5-tetrazine-1,2-dicarboxylate, rather than the expected diethyl 3,6-diphenyl-1,4-dihydro-1,2,4,5-tetrazine-1,4-dicarboxylate. The structure of the title compound was determined by X-ray diffraction analysis. Thetitle compound crystallized in triclinic system with space group P-1, a=0.8915(2) nm, b=1.0444(2) nm, c=1.1509(3) nm, α=103.268(3)°, β=102.844(3)°, γ=100.765 (3)°, Z=2, R₁=0.0593, and wR₂=0.1691. The 2,3-diazabutadiene group in the central six-membered ringisnot coplanar, indicating a lack of conjugation. The ring has a twisted conformation, in which adjacent atoms N(1) and N(2) deviate from the plane of the ring by -0.03611(41) and 0.02944(40) nm, respectively.

Key words: 1,2,4,5-tetrazine, crystal structure, conjugation, twisted conformation