Syntheses of Tetrahydropyridazine and Tetrahydro-1,2-diazepine Scaffolds through Cycloaddition Reactions of Azoalkenes with Enol Diazoacetates

Catalyst-dependent
[4 + 2]-cycloaddition reactions of azoalkenes
from α-halohydrazones with enol diazoacetates have been developed.
A [4 + 2]-cycloaddition of enol diazoacetates with in situ formed
azoalkenes produces tetrahydropyridazinyl-substituted diazoacetates
promoted by only Cs2CO3. In contrast, donor–acceptor
cyclopropenes, which are formed in situ from enol diazoacetates by
Rh2(OAc)4-catalyzed dinitrogen extrusion, undergo
[4 + 2]-cycloaddition with azoalkenes to yield bicyclo[4.1.0]­tetrahydropyridazines.
These stable cycloaddition products undergo subsequent one-step transformations
to form 6-alkylidenetetrahydropyridazines and 4,5,6,7-tetrahydro-1,2-diazepine
derivatives in good yields.