AN EFFECTIVE PROCEDURE TO PROMOTE AZA-PRINS CYCLIZATION REACTIONS EMPLOYING A COMBINATION OF FERRIC CHLORIDE AND AN IMIDAZOLIUM SALT IN BENZOTRIFLUORIDE

Aza–Prins cyclization reactions of N-tosyl-3-butenylamine with p-methoxybenzaldehyde, 1-naphthaldehyde and 2-naphthaldehyde take place efficiently using a combination of ferric chloride and 1-butyl-3-methylimidazolium hexafluorophosphate in benzotrifluoride (FeIm–BTF procedure). The new methodology, leading to formation of target N-tosyl-4-chloro-2-substituted piperidines, is superior to the one using 1-butyl-3-methylimidazolium tetrachloroferrate. The FeIm–BTF procedure was also applied to aza–Prins cyclization reactions of other aldehydes. Finally, the effects of imidazolium salts on aza–Prins cyclization reaction promoted by boranetrifluoride-diethyl ether complex, leading to formation of fluorinated piperidines, were explored