Synthesis of 1‐Trifluoromethylated Propargyl Alcohols by Two Successive Reactions of Cyclopentylmagnesium Bromide in a One‐Pot Manner

We have developed a functional‐group‐tolerant one‐pot route to various 3‐substituted 1‐trifluoromethylpropargyl alcohols utilizing two reactions of cyclopentylmagnesium bromide with trifluoroacetic acid esters and terminal alkynes. This new synthetic method involves three successive reactions in a one‐pot process: 1) deprotonation of terminal alkynes with cyclopentylmagnesium bromide, 2) reduction of 2,2,2‐trifluoroethyl trifluoroacetate with cyclopentylmagnesium bromide, and 3) nucleophilic addition of in‐situ‐generated alkynyl Grignard reagents to in‐situ‐formed trifluoroacetaldehyde, leading to the corresponding 3‐substituted 1‐trifluoromethylated propargyl alcohols. This method can be applied to various fluorine‐containing esters as well as terminal alkynes bearing alkyl and aryl groups to give 1‐polyfluoroalkylated propargyl alcohols. The obtained 1‐trifluoromethylpropargyl alcohols with aromatic groups can be converted in good to excellent yields to 1,5‐diaryl‐3‐trifluoromethyl‐dihydropyrazoles, some of the most important motifs in medicine for the treatment of pain and inflammation associated with osteoarthritis in dogs.