[4+2] Cycloadditions

Tetrazine 1 is known as a useful diene in [4+2] cycloadditions. For example, 5H-pyridazino[4,5-b]indole was obtained in reaction of 1 with indole as a dienophile.^1a) With a cyclopropene, a tetracyclic aliphatic azo compound which is a versatile starting compound for a thermolysis and photolysis reactions can be obtained.^1b)