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]

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Hetaryl-substituted thiochalcones react with acetylenic mono-and diesters in the THF solution in the presence of LiClO4 at 65°C to give, after 24h, 4H-thiopyran carboxylates and dicarboxylates, respectively, in moderate to good yields. The same reactions were performed also in the THF solution without a catalyst under microwave irradiation. In that case, the reaction time was reduced to three minutes and, in most cases, an improvement in the yield of the [4+2]-cycloadduct was observed. The reactions with methyl propiolate occurred regioselectively and the 3-carboxylates were formed exclusively.

The in situ-generated reactive thiocarbonyl S-methanides were reacted with fluorinated enones. The type of the obtained [3+2]-cycloadduct depends strongly on the location of the activating CF3 group. In the case of enones containing the CF3CH=CH moiety, the [3+2]-cycloaddition occurs chemoand regioselectively onto the C=C bond to give trifluoromethylated tetrahydrothiophene derivatives. On the other hand, enones containing the CF3-C=O unit react as carbonyl dipolarophiles leading to trifluoromethylated 1,3-oxathiolanes also in a chemo-and regioselective manner. These are the first reported reactions of thiocarbonyl S-methanides with ,-unsaturated ketones.

Dihetaryl thioketones possessing thiophen-2-yl and selenophen-2-yl rings react as "superdienophilic" reagents with nonactivated 1,3-dienes such as 2,3-dimethylbuta-1,3-diene, cyclopentadiene, and mixtures of isomeric hexa-2,4-dienes to produce the expected 2H-thiopyrans in moderate to excellent yields. In the latter case, the corresponding cis-2,2-dihetaryl-3,6-dimethyl-3,6-dihydro-2H-thiopyrans are formed as the sole products in a stereoconvergent thia-Diels-Alder reaction. A stepwise mechanism via delocalized diradical intermediates is postulated to rationalize the observed reaction course. Treatment of 4,5-dimethyl-2,2-di(thiophen-2-yl)-3,6-dihydro-2H-thiopyran with excess of m-CPBA at room temperature leads to the oxidation of the C=C bond and the sulfur atom in the six-membered ring.

Pyrazole 10a 28 Exemplary 1 H NMR data of thiochalcone 2f (mixture of dimers) 30 X-ray data of pyrazole 10a 31 Attempted reaction of thiochalcone 2a with the non-fluorinated nitrile imine 12 33

SummarySelected hetaryl and aryl thioketones react with acetylenecarboxylates under thermal conditions in the presence of LiClO4 or, alternatively, under high-pressure conditions (5 kbar) at room temperature yielding thiopyran derivatives. The hetero-Diels–Alder reaction occurs in a chemo- and regioselective manner. The initially formed [4 + 2] cycloadducts rearrange via a 1,3-hydrogen shift sequence to give the final products. The latter were smoothly oxidized by treatment with mCPBA to the corresponding sulfones.

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