Novel Tandem Hydration/Cyclodehydration of α-Thiocyanatoketones to 2-Oxo-3-thiazolines. Application to Thiazolo[5,4-<i>c</i>]quinoline-2,4(3a<i>H</i>,5<i>H</i>)-dione Synthesis

Novel tandem hydration of α-thiocyanatoketones to thiocarbamates followed by in situ cyclodehydration to fused 2-oxo-3-thiazolines is described. The reaction is applied to the synthesis of [1,3]thiazolo[5,4-c]quinoline-2,4(3aH,5H)-diones (4). Concentrated sulfuric acid was found to be critical for the reaction as both corresponding 2,3-dioxo-1,2,3,4-tetrahydroquinolin-3-yl thiocyanates (2) and S-(2,4-dioxo-1,2,3,4-tetrahydroquinolin-3-yl) thiocarbamates (3) rapidly hydrolyze in the presence of water to 4-hydroxyquinolin-2(1H)-ones (1).