Comparative study of the ring opening of 1-CF3-epoxy ethers mediated by Brönsted acids and hexafluoro-2-propanol

In order to evaluate more deeply the nature of the activation of oxirane ring opening reactions by HFIP, ring opening of both CF₃-epoxy ethers 1a (R = Ph) and 1b (R = CH₂CH₂Ph) with HFIP alone, and with hard (MeOH) or soft (PhSH) nucleophiles in HFIP, were investigated and compared to reactions performed with Brönsted acids. Nucleophilic ring opening reactions in HFIP were facilitated with PhSH and only α-substituted trifluoromethyl ketone 5 was isolated (nucleophilic ring opening), while with MeOH, both processes, nucleophile and electrophile-assisted ring opening were in competition. In the Brönsted acid-catalysed ring opening of 1-CF₃-epoxy ethers 1 in HFIP, only the acid-catalysed ring opening process occurred with an inversed regioselectivity.