Iminophosphorane‐mediated synthesis of mesoionic 1,3,4‐Oxadiazolo‐[3,2‐ a ]pyridinylium‐2‐aminides

Reaction of iminophosphorane 2 with methyl isocyanate yields the mesoionic 1,3,4‐oxadiazolo[3,2‐ a ]pyridinylium‐2‐methylamindie 3 , which undergoes N ‐methylation with CF 3 SO 3 CH 3 to give the 1,3,4‐oxadiazolo[3,2‐ a ]pyridinium cation 4 . The structure of compound 4 has been established by means of X‐ray crystallography. Mesoionic aminide 3 undergoes rearrangement by the action of base to give the isomeric mesoionic compound 1,3,4‐triazolo[3,2‐ a ]pyridinylium‐2‐olate 11 . Compound 3 by the action of (arylimino)triphenylphosphoranes is converted into the corresponding 1,3,4‐oxadiazolo[3,2‐ a ]pyridinylium‐2‐arylaminides 12 , which can be also prepared from iminophosphorane 2 and hydroximoyl chlorides.