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.