2-Thio 3 alkyl 5 phenylmethylidene 4 imidazolidinones were synthesized via tandem aza Wittig reaction of vinyliminophosphorane, carbon disufide and aliphatic primary amines. A possible mechanism for the cyclization reaction was put forward, and the spectral properties and the condition for cyclization of the synthesized compounds were researched. All the cyclized products are new, and their structures are c...