The 1, 2-thiazoles obtained from 3-chloroalk-2-enals and ammonium thiocyanate (7+ 9, Scheme I) are easily transformed to 1, 2-thiazol-3 (2H)-one 1, l-dioxides 10 on treatment with H202 in AcOH at 80. Hydrogenation of 10 in AcOH yields the corresponding saturated I, 2- thiazolidin-3-one 1, I-dioxides 16 (Scheme 3). Cycloalka [c]-l, 2-thiazoles 18 are prepared from 2-[(thiocyanato) methyliden] cycloalkan-l-ones and ammonia (Scheme 4). ...