A new synthesis of 4‐cyano‐1,3‐dihydro‐2‐oxo‐2 H ‐imidazole‐5‐(N 1 ‐tosy1)carboxamide : reactive precursor for thiopurine analogues

N ‐[(5‐Cyano‐2‐oxoimidazolidin‐4‐yl)‐iminomethyl]‐ p ‐toluensulfonamide 3 was prepared in fairly good yield by the base catalyzed cyclisation of N ‐[(Z)‐2‐amino‐1,2‐dicycanovinylcarbamoyl]‐ p ‐toluenesulfon‐amide 2 . The N ‐[(Z)‐2‐amino‐1,2‐dicycanovinyl carbamoyl]‐ p ‐toluenesulfonamide 2 was reacted readily with two molar amount of p ‐nitrobenzaldehyde at room temperature in the presence of base to give 7,8‐dihy‐dro‐2‐(4‐nitrophenyl)‐8‐oxo‐9‐tosylpurine‐6‐carboxamide 8 . Thiation of compounds 3 and 8 using Lawesson's reagent in tetrahydrofuran gave novel thioimidazoles 4, 5 , and 6 and thiopurines 9, 10 , and 11 , which have been characterized spectroscopically.