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 alpha-halohydrazones with enol diazoacetates have been developed. A [4 + 2]-cydoaddition 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 Rh-2(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.