Aryl carbonyls and carbinols as proelectrophiles for Friedel–Crafts benzylation and alkylation

Abstract

Friedel–Crafts benzylation/alkylation using benzylic, tertiary, and homobenzylic alcohols; aryl aldehydes, aryl ketones, and the highly challenging aryl carboxylic acids and esters as proelectrophiles has been achieved using borane-ammonia and TiCl₄, greatly broadening the scope of useable substrates. Incorporation of deactivated aromatic proelectrophiles and specificity for substitution at the benzylic position are demonstrated in the synthesis of various di- and triarylalkane products. Dual protocols allow for the use of standard nucleophilic solvents (benzene, toluene, etc.) or for stoichiometric addition of more valuable nucleophiles including furans, thiophenes, and benzodioxoles.