Novel synthesis of 3,6-disubstituted-1,2,4,5-tetrazine derivatives from hydrazones by using [hydroxyl(tosyloxy)iodo]benzene

A mild and efficient protocol for the construction of 1,4-dihydro-3,6-disubstituted-1,4-bis(p-toluenesulfonyl)-1,2,4,5-tetrazines from p-toluenesulfonyl hydrazones mediated by [hydroxyl(tosyloxy)iodo]benzene in the presence of pyridine has been developed. This protocol affords the products in good to excellent yields. The corresponding 3,6-disubstituted-1,2,4,5-tetrazines can be easily obtained through one-step N-deprotection of p-toluensulfonyl groups and aromatization by tetrabutyl ammonium fluoride in THF. A mechanism has been proposed.