Synthesis of Pyridazines via Two Bond Formation

Combining 3+3 atoms to constitute a pyridazine ring is a rather new approach. Two methodologies have been reported. In the first, cyclopropenes and diazoalkenes are used as the 3 atom component, while the other utilizes a reaction between aldehyde hydrazones and a,)S-unsaturated nitrile as the 3+3 atom components. 

A thesis of l,4-dihydrop3nidazines has been reported by reacting pyruvaldehyde-l-arylhydrazones 17 with a,jS-unsaturated nitriles 18. Thus, 17a reacts readily with a-substituted cinnamonitriles 18 through Michael addition at the CH site to yield dihydroamino pyridazines 20. NMR cannot however exclude a possible initial addition of the hydra-zone NH site to the activated double bond in 18 yielding 21 that then would cyclize to isomeric 6H-pyridazine derivatives 22. The structure of the products was shown to be 4H-pyridazines 20 by an X-ray crystal structure of compound 20c (2007JHC105, 2007JHC877  

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