Abstract: The alkyl phosphorchloridisocyanatidate(2) is a kind of bifunctional compound which has a high reactivity.We have reported a new efficient method to prepare a new kind of fused phosphorus heterocyclic compounds using the reaction of the bifunctional compound─alkyl phosphorchloridisocyanatidate(2)with 5-amino-3-benzylthio-1,2,4-triazole and its analogues(1).In this paper,the cyclization reaction of aryl phosphonochloridisocyanatidate(2) with 5-amino-3-benzylthio-1,2,4-triazole and its analogues 1 was described. Twelve 2-benzylthio-7-aryl(alkoxyl)-7-phospha-5,7-dioxo-4,5,6,7-tetrahydro-1,2,4-triazolo[1,5a]triazines were synthesized. The structures were assigned on the basis of ¹H NMR,³¹P NMR,IRsupported by satisfactory elemental analysis.The ¹H NMRspectrum of 2-benzylthio-7-phenyl-7-phospha-5,7-dioxo-4,5,6,7-tetrahydro-1,2,4-triazolo[1,5a ]triazine(3_c) shows doublet at δ8.72 with the coupling constant ²J_PCH=8.9 Hz, single peak at δ10.84 for NHadjacent to the heterocyclic moiety.In NMRof 3_c, one singlet at δ 4.2,appearing in the lower field than in that of 2-benzylthio-7-alkoxyl-7-phospha-5,7-dioxo-4,5,6,7-tetrahydro-1,2,4-triazolo[1,5a]triazines(3_a,3_b,3_c,3_f,3_i, 3_j) which could be attributed to the deshielding effect of the phenyl substituent, indicated one isomer.The strong(C=O) stretching absorption band at 1681 cm^-1 indicated that 3_c existed in the keto form instead of enolic form.The most probable mechanism of the cyclization reaction was proposed.Initially nucleophilic addition of NH₂ group to the isocyanate group of 2 gives an intermediate 4,which undergoes cyclization by nucleophilic attack of 1-NHgroup on Pwith the cleavage of P-Cl bond.The cyclization yield of aryl phosphonochloridisocyanatidate is lower than that of alkyl phosphorchloridisocyanatidate which might be due to the steric influence of the aryl group.On the basis of ¹H NMR,³²P NMR,IRspectra,Z-configuration could be proposed.The preliminary biological tests show that some compounds have herbicidal activities.

Key words: Fused phosphorus heterocylic compounds, ALS enzyme inhibitor, Cyclization reaction