Diels-alder reactions of 3, 6-diphenyl-1, 2, 4, 5-tetrazine and 3, 6-di(2-pyridyl)-1, 2, 4, 5-tetrazine with some 1-morpholinocycloalkenes

The reactions of 3, 6-diphenyl-1, 2, 4, 5-tetrazine 1 and 3, 6-di(2-pyridyl)-1, 2, 4, 5-tetrazine 2 with the enamines 3a-d derived from morpholine and the 5-,6-,7- and 8-membered cyclic ketones have been investigated. A number of pyridazine derivatives 4–7 most of which are new have been reported. Moreover, a novel procedure for the aromatization of pyridazines 5a-d to the corresponding pyridazine 7b-d via oxidative elimination using hydrogen peroxide is described. The structures of products 4–7 were confirmed by spectral methods and elemental analysis.