One‐Pot, Four‐Component Synthesis of Fully Substituted 1,3,4‐Oxadiazole Derivatives from (Isocyanoimino)triphenylphosphorane, a Primary Amine, an Aromatic Carboxylic Acid, and Chloroacetone

The 1 : 1 imine intermediate 7 generated by the addition of a primary amine 2 to chloroacetone (1) is trapped by (isocyanoimino)triphenylphosphorane (4) in the presence of an aromatic carboxylic acid 3 and leads to the formation of the corresponding iminophosphorane intermediate 9 (Scheme 2). The 1,3,4‐oxadiazole derivatives 5 are then formed via an intramolecular aza‐Wittig reaction of the iminophosphorane intermediate 9. The reactions were completed under neutral conditions at room temperature. The fully substituted 1,3,4‐oxadiazole derivatives 5 were produced in high yields (Table).