Friedel-Crafts Alkylations of Arenes with Mono- and Bis(trifluoro-methyl)oxiranes in Superacid Medium: Facile Synthesis of α-(Trifluoro-methyl)- and α,α-Bis(Trifluoromethyl)-β-Arylethanols

摘要

Triflic acid catalyzed Friedel-Crafts alkylation of aromatics with mono- and bis(trifluoromethyl)oxiranes through ring opening afforded α-(trifluoromethyl) and α,α-bis(trifluoromethyl)-β-phenylethanols in excellent yields. The regioselectivity of the -oxirane ring opening and subsequent Friedel-Crafts alkylation have been found to depend on the electronic and steric effects of the -substituents in the oxirane ring. DFT studies show that C2-O bond is longer than C1-O bond due to high electron-withdrawing effect of CF3 groups effecting C2-O cleavage resulting in a C2 electrophilic center promoting electrophilic substitution with the C2 center on aromatics.