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

Abstract

Regio- and stereoselective switchable synthesis of (E)- and (Z)-N-carbonylvinylated pyrazoles is first developed by using the Michael addition reaction of pyrazoles and conjugated carbonyl alkynes. Ag2CO3 plays a key role in the switchable synthesis of (E)- and (Z)-N-carbonylvinylated pyrazoles. Ag2CO3-free reactions lead to thermodynamically stable (E)-N-carbonylvinylated pyrazoles in excellent yields whereas reactions with Ag2CO3 give (Z)-N-carbonylvinylated pyrazoles in good yields. It is noteworthy that (E)- or (Z)-N1-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.