1,2,4,5-Tetrazines 1 readily react with cyclopropenes 2 to form 3,4-diazanorcaradienes 3, 4, 7 and 8 in a cycloaddition − cycloelimination sequence. Compounds 3 and 4 still act as 1,3-dienes with cyclopropenes 2, producing aliphatic azocompounds 5 and 6, versatile starting compounds in thermolysis and photolysis reactions.
The synthesis of a new class of stable coloured azomethineylides 3 derived from 3,4-diazanorcaradienes is reported, which under acid catalysis are transformed to again coloured stable azomethineylides 4 containing a five-membered 1-aza-1,3-cyclopentadiene skeleton. Azomethineylides 3 in boiling methanol rearrange to 3,5-diazahomotropilidenes 8 in good yields.