Advantages: ambient condition and simple procedure. Additive and metal free method. Up to 25 examples and 79% yield. Wide functional groups tolerance.

In the present work, an efficient regioselective synthesis of 1,3,4-tri- and 1,3,4,5-tetrasubstituted pyrazoles via a methanesulfonic acid (MSA)-catalyzed reaction of hydrazones with enaminones or enamines is reported.

A catalyst-free [4+2] cycloaddition-elimination of α-halogeno hydrazones with enaminones has been achieved under mild conditions. This protocol provided a novel and efficient method for the synthesis of pyridazine and tetrahydrocinnoline...