Regio- and Stereoselective Switchable Synthesis of ()- and ()--Carbonylvinylated Pyrazoles.

Regio- and stereoselective switchable synthesis of ()- and ()--carbonylvinylated pyrazoles is first developed by using the Michael addition reaction of pyrazoles and conjugated carbonyl alkynes. AgCO plays a key role in the switchable synthesis of ()- and ()--carbonylvinylated pyrazoles. AgCO-free reactions lead to thermodynamically stable ()--carbonylvinylated pyrazoles in excellent yields whereas reactions with AgCO give ()--carbonylvinylated pyrazoles in good yields. It is noteworthy that ()- or ()--carbonylvinylated pyrazoles are obtained with high regioselectivity when asymmetrically substituted pyrazoles react with conjugated carbonyl alkynes. The method can also extend to the gram scale. A plausible mechanism is proposed on the basis of the detailed studies, wherein Ag acts as coordination guidance.