Application of biphasic reaction procedure using ferric chloride dissolved in an imidazolium salt and benzotrifluoride (FeIm-BTF procedure) to aza-Prins cyclization reaction

Aza-Prins cyclization reaction of N -tosyl-3-butenylamine with aliphatic and aromatic aldehydes was performed using a combination of FeCl 3 and 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF 6 ) or 1-butyl-3-methylimidazolium tetrachloroferrate (BmimFeCl 4 ) in benzotrifluoride (BTF). The desired N -tosyl-4-chloro-2-substituted piperidines were obtained from aliphatic aldehydes in comparable yields to those for the previously reported reactions in which FeCl 3 was used in CH 2 Cl 2 . On the other hand, significant progress for the piperidine synthesis from aromatic aldehydes has been achieved, particularly when BmimFeCl 4 was used with FeCl 3 in BTF.