Single C-F Bond Activation of the CF3 Group with a Lewis Acid: CF3 -Cyclopropanes as Versatile 4,4-Difluorohomoallylating Agents.

The selective activation of one C-F bond (single activation) of the CF3 group on cyclopropanes was achieved for the first time. When (trifluoromethyl)cyclopropanes were treated with arenes, allylsilanes, silyl enol ethers, or hydrosilanes in the presence of Me2 AlCl, fluoride elimination and the subsequent ring opening proceeded to afford 4,4-difluorohomoallylated products. In the absence of external nucleophiles, an alkyl group of AlR3 was effectively introduced to provide the corresponding 1,1-difluoroalkenes.

Lewis Acid Promoted Single C-F Bond Activation of the CF3 Group: SN 1'-Type 3,3-Difluoroallylation of Arenes with 2-Trifluoromethyl-1-alkenes.

Activation of the sp3 C-F bond in 2-trifluoromethyl-1-alkenes was accomplished through treatment with a Lewis acid. In the presence of an equimolar amount of EtAlCl2 , the (trifluoromethyl)alkenes readily underwent an SN 1'-type reaction with arenes through a Friedel-Crafts-type mechanism via elimination of a fluoride ion to afford 3,3-difluoroallylated arenes in good yields. This selective activation of one C-F bond of the CF3 group provides a synthetic method for accessing biologically and synthetically important 1,1-difluoro-1-alkenes.