Fourteen compounds of 3, 6-disubstituted-1, 4-dihydro-1, 2, 4, 5-tetrazine derivatives were prepared and their structures were confirmed by single-crystal X-ray diffraction and the semi- empirical calculation of PM3 method. This reaction yields the 1, 4-dihydro derivatives rather than the 1, 2-dihydro derivatives. The central six-membered ring of 1, 4-dihydro-1, 2, 4, 5- tetrazine has a chair conformation and therefore is not homoaromatic. Their antitumor ...