2-, 3-, and 4-(Trifluoromethoxy)phenyllithiums: Versatile Intermediates Offering Access to a Variety of New Organofluorine Compounds

Consecutive treatment of (trifluoromethoxy)benzene with sec-butyllithium and electrophilic reagents affords previously inaccessible ortho-substituted derivatives in generally excellent yields. 2-(Trifluoromethoxy)phenyllithium acts as the key intermediate. The 3- and 4-isomers can readily be generated from the corresponding 3- and 4-bromo precursors by halogen-metal interconversion with butyllithium or tert-butyllithium. Upon trapping of the 2-, 3- and 4-(trifluoromethoxy)phenyllithiums with 11 different electrophiles the expected products were formed in generally high yields. Only the attempted nucleophilic addition of 2-(trifluoromethoxy)phenyllithium to oxirane did not succeed. This failure is tentatively attributed to a lowering of the nucleophilicity by fluorine-lithium interactions. Conformationally restricted analogs — i.e., 2,2-difluoro-1,3-benzodioxol-4-phenyllithium and its 5-fluoro- and 5-bromo-substituted congeners — did indeed react smoothly with oxirane, affording the adducts in ordinary yields.