Following a known procedure, 4-(benzylthio)-1,3-oxazol-5(2H)-one (4a) was synthesized starting from sodium cyanodithioformate (1) and cyclohexanone (Scheme 1). The structure of the intermediate4-(benzylthio)-1,3-thiazol-5(2H)-one (3a) was established by X-ray crystallography. An alternative route was developed for the synthesisof 4-(arylthio)-1,3-oxazol-5(2H)-ones which are not accessible by the former reaction. Treatment of ethyl cyanoformate (5) with a thiophenol in the presence of catalytic amounts of Et3NH andTiCI4, followed by addition of a ketone and BF3.Et2O in a one-pot-reaction, gave 4f-i in low-to-fair yields (Scheme 3). Both synthetic pathways -complementary as for benzyl-S and aryl-S derivatives - seem to be limited with respect to variation of substituents of the ketone.