Catalytic Synthesis of Trifluoromethylated Allenes, Indenes, Chromenes, and Olefins from Propargylic Alcohols in HFIP

A general method to access CF3-substituted
allenes from
propargylic alcohols under Lewis acid catalysis in 1,1,1,3,3,3-hexafluoro-2-propanol
(HFIP) as solvent is described. By tuning the reaction time and temperature,
the obtained allenes rearrange to 1,3-biaryl-1-trifluoromethyl-1H-indenes. By tuning the structure of the propargylic alcohol
substrates, a range of trifluoromethylated 2H-chromenes
were successfully synthesized with the use of catalytic quantities
of strong Brønsted acid in HFIP. The present method is therefore
highly potent for the synthesis of a number of potentially pharmaceutically
interesting new trifluoromethylated compounds and produces water as
the only stoichiometric byproduct.