An One-Pot Synthesis of Semibullvalenes and Its Mechanism

1,2,4,5-Tetrazines 7 readily react with 3,3′-bicyclopropenyl 8 in a cycloaddition−cycloelimination sequence to give 3,4-diazanorcaradienes 9 with endo configuration of the methyl group at C-7. On gentle heating in inert solvents, these 3,4-diazanorcaradienes 9 are cleanly transformed into semibullvalenes 11. This reaction sequence can also be performed as a one-pot method. Kinetic investigations and comparisons with two model systems are in agreement with the proposed reaction mechanism.