Highly Efficient Catalytic Asymmetric Sulfa-Michael Addition of Thiols to trans-4,4,4-Trifluorocrotonoylpyrazole

A new protocol for the efficient construction of chiral trifluoromethylated building blocks was developed via organocatalyzed sulfa-Michael addition of thiols to the cost-efficient trans-trifluorocrotonamide. Introducing the pyrazole moiety is crucial to providing H-bond acceptor sites for better activation and hence affording comparable asymmetric induction with that obtained when employing the expensive cis-4,4,4-trifluorocrotonate as the Michael acceptor.