Regioselective construction of pyridazine and tetrahydrocinnoline derivativesvia[4+2] cycloaddition-elimination with α-halogeno hydrazones and enaminones

A catalyst-free [4 + 2] cycloaddition-elimination of alpha-halogeno hydrazones with enaminones has been achieved under mild conditions. This protocol provides a novel and efficient method for the synthesis of pyridazine and tetrahydrocinnoline derivatives in good yields, with high functional group tolerance and remarkable regioselectivity. The process involves mechanistically distinct, cycloaddition and elimination reactions.