Nucleophile-induced intramolecular dipole 1,5-transfer and 1,6- cyclization: Experimental and ab initio studies of formation, thermolysis, and molecular and electronic structures of 3,6-diphenyl-1-propanesulfenimido- 1,2,4,5-tetrazine

Reaction of dichlorobenzaldazine (2) with sodium azide followed by 1- propanethiol/Et₃N furnished tetrazine ylide 1 as the main product. The structure of this unprecedented ylide was confirmed with single-crystal X-ray analysis [C¹⁷H¹⁷N₅S, monoclinic P2₁/n a = 6.8294(4) Å, b = 13.6781 (9) Å, c = 17.5898(12) Å, β = 90.666(1)°, Z = 4] and favorably compared with the results of ab initio calculations. The mechanisms of formation of the ylide and its thermal decomposition to 2,5-diphenyltetrazine (5) were investigated using ab initio methods and correlated with the experimental observations. The results suggest that formation of 1 involves intramolecular cyclization of a nitrile imine and thermolysis of 1 might generate a sulfenylnitrene. The formation of 1 is considered to be the first example of a potentially more general reaction.