1, 3-Dipolar cycloaddition of imidazoline 3-oxides 1 with methylisothiocyanate proceeds regio-and diastereoselectively to give tetrahydroimidazo [1, 5-b][1, 2, 4] oxadiazol-2 (1 H)- thiones 3 in high yields. The cis configuration of the adducts were proved by our double cis elimination test as well as by NOESY experiments. The imidazooxadiazol-2-thiones 3a-e were treated with concentrated HCl in ethanol at 50°; C to give the corresponding 4 H-[1, 2 ...