Oxidative annulation of <scp>l</scp> -phenylalanine using I ₂ /DMSO: an easy approach for chemoselective synthesis of 2,3,5-trisubstituted pyridines and 2,5-disubstituted oxazoles

A facile approach for chemoselective synthesis of 2,3,5-trisubstituted pyridines and 2,5-disubstituted oxazoles from L-phenylalanine and aryl methyl ketone using I₂/DMSO has been developed. Two equivalents of L-phenylalanine reacted with aryl methyl ketone and I₂/DMSO giving 2,3,5-trisubstituted pyridines and interestingly one equivalent of L-phenylalanine afforded 2,5-disubstituted oxazoles. This chemo-divergent approach has features of being transition metal-free, free from expensive ligands, additives and starting materials, and having a less toxic nitrogen source and broad substrate scope.