Synthesis of cyclopentadiene derivatives starting from norbornadiene was investigated using dimethyl 1,2,4,5-tetrazine-3,6-dicarboxylate. The products obtained were either cyclopentadienes or diazines depending on the substituents. The driving force for the formation of these products was discussed in terms of electronic effects. (C) 2015 Elsevier Ltd. All rights reserved.