Indium triflate-catalyzed Friedel-Crafts alkylation of weakly reactive benzenes by 1-bromoadamantane

Indium triflate (at ca. 5 mol%) efficiently catalyzed the Friedel–Crafts reaction of 1-bromoadamantane with some weakly reactive benzenes such as 1,2-dichlorobenzene, 1,2-dibromobenzene, and acetanilide to give monosubstituted 1-adamantyl benzenes. Addition of metallic indium enabled removal of all HBr which was produced to give indium bromide and afforded a noticeably improved reactivity in the case of acetanilide. It proved also beneficial for another type of substrate having sensitive groups to HBr such as methoxy. Thus, 2,4-dimethoxybenzoic acid was cleanly adamantylated to 5-(adamantan-1-yl)-2,4-dimethoxybenzoic acid.