Collaborative Activation of Trifluoroacetyl Diazoester by a Lewis Acid and Base for the Synthesis of Polysubstituted 4-Trifluoromethylpyrazoles.

A Lewis acid- and base--mediated cyclization of trifluoroacetyl diazoester and ketones is developed. Cooperative functioning of the Lewis acid and Lewis base with trifluoroacetyl diazoester results in increased electrophilicity of terminal nitrogen atoms. The reaction affords polysubstituted 4-trifluoromethyl pyrazoles in moderate to excellent yields.