Unlocking the Friedel-Crafts arylation of primary aliphatic alcohols and epoxides driven by hexafluoroisopropanol
Shaofei Zhang, Marie Vayer, Florent Noël, Vuk D. Vuković, Andrei A. Golushko, Nazanin Rezajooei, Christopher N. Rowley, David Lebœuf, Joseph Moran
Abstract
Alcohols and epoxides are arguably ideal electrophiles for the Friedel-Crafts alkylation, since they are widely available, require no pre-activation, and produce no stoichiometric waste beyond water. However, neither primary aliphatic alcohols nor most classes of terminal epoxides are compatible with existing intermolecular Friedel-Crafts methodologies, and sequential Friedel-Crafts reactions starting from epoxides consequently remain underexplored. Here, we report that these limitations are easily overcome using Brønsted acid catalysis in hexafluoroisopropanol (HFIP) as a solvent. Electron-poor aromatic epoxides and aliphatic epoxides undergo stereospecific arylation to give an alcohol which, depending on the reaction conditions, can partake in a second nucleophilic substitution with a different arene in one pot. Phenyl ethanols react through a phenonium intermediate, whereas simple aliphatic alcohols participate in a rare intermolecular S N 2 Friedel-Crafts process, delivering linear products exclusively. This work provides an alternative to metal-catalyzed cross-couplings for accessing important scaffolds, widening the range of applications of the Friedel-Crafts reaction.