Hetaryl Thioketones: Synthesis and Selected Reactions

A series of phenyl/hetaryl and bishetaryl thioketones have been prepared via oxygen/sulfur exchange of the corresponding ketones by treatment with Lawesson's reagent. The nonsymmetrical ketones were conveniently accessible via the reactions of lithiated furan, thiophene, and selenophene with N,N‐dimethylbenzamide and hetarylcarboxamides, respectively, whereas the symmetrical ketones were obtained by treatment of ethyl N,N‐dimethylcarbamate with 2 equiv of lithiated heterocycles. Under typical conditions, selected examples of the hetaryl thioketones were oxidized selectively to give thiocarbonyl S‐oxides (sulfines). Reactions with diazomethane at –65°C yielded 1,3‐dithiolanes in a regioselective manner and hetero‐Diels–Alder reactions of 2‐thienyl substituted thioketones with dimethyl acetylenedicarboxylate yielded the corresponding 7H‐thieno[2,3‐c]thiopyran‐4,5‐dicarboxylates.