<scp>Et₃N‐Catalyzed</scp> Cycloaddition Reactions of α‐(Trifluoromethyl)styrenes with 2,2,<scp>2‐Trifluorodiazoethane</scp> to Access Bis(trifluoromethyl)‐Substituted Pyrazolines

Abstract

Main observation and conclusion A novel and practical method for the synthesis of 3,5‐bis(trifluoromethyl)‐4,5‐dihydro‐1 H ‐pyrazoles by [3+2] cycloaddition reactions of α‐(trifluoromethyl)styrenes with 2,2,2‐trifluorodiazoethane (CF 3 CHN 2 ) has been developed. The cyclization reaction proceeds smoothly in the presence of a catalytic amount of Et 3 N, affording a variety of bis(trifluoromethyl)‐substituted 2‐pyrazolines in good to excellent yields. This method also exhibits a broad substrate scope and tolerates various functional groups.