Synthesis of 2-Difluoroethylated 2H-1,3-Benzoxazines via Proton-Mediated Ring Opening/Interrupted Ritter Reaction of 1,1-Difluorocyclopropanes

2-(1,1-Difluoroethyl)-2H-1,3-benzoxazines were synthesized by (i) the regioselective ring opening of 1,1-difluorocyclopropanes bearing an aryloxy group and (ii) the Ritter reaction followed by a Friedel–Crafts-type ring closure. When 2-aryloxy-1,1-difluorocyclopropanes were treated with triflic acid, the C–C bond distal to the CF2 moiety was cleaved regioselectively via protonation to generate the corresponding oxocarbenium ions. These intermediates readily underwent nucleophilic attack by nitriles, followed by a carbocationic cyclization to afford the 2-difluoroethylated benzoxazines.