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

Abstract

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 1trifluoromethylpropargyl alcohols with aromatic groups can be converted in good to excellent yields to 1,5-diaryl-3trifluoromethyl-dihydropyrazoles, some of the most important motifs in medicine for the treatment of pain and inflammation associated with osteoarthritis in dogs.