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Thiophene S-oxides have been prepared and their photoreactivity has been studied. In many cases, the sulfur moiety of the thiophene S-oxides is deoxygenated. Here, the corresponding thiophenes or hydroxylated thiophenes are isolated. In the case of the photoirradiation of tert-butyl substituted thiophene S-oxides, the oxygen of the sulfoxy unit is incorporated into the heterocyclic ring system and the corresponding furans have been isolated. Also, structures with two thiophene cores have been oxidized to the respective thiophene S-oxides. These molecules undergo photodeoxygenation, a reaction, which is catalysed by (non-oxidized) thiophenes.

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Thiophenes have been treated with alkynes in the presence of m-chloroperoxybenzoic acid to give substituted arenes as cycloadducts. Alternatively, thiophene S-oxides have been prepared by oxidation from thiophenes and have been subjected to cycloaddition with alkynes in a subsequent step. The outcome of the reaction is dependent on the steric demand of the thiophene S-oxide. Some thiophene S-oxides can be reacted at temperatures as high as 140 C without decomposition. Thiophenes as deoxygenated products are the main by-products. Reactions of thiophene S-oxides with allenes give in part thiabicyclo[2.2.1]heptene S-oxides of type 12a and 13 along with aromatized products. Thiophene S-oxides also cycloadd to benzyne.

Cycloaddition reactions Cycloaddition reactions O 0070Cycloaddition of Thiophene S-Oxides to Allenes, Alkynes and to Benzyne. -Thiophene S-oxides react as diene components in [4 + 2] cycloaddition reactions. Best yields are obtained in reactions of donor substituted thiophene S-oxides with acceptor substituted alkynes. -(THIEMANN*, T.; FUJII, H.; OHIRA, D.; ARIMA, K.; LI, Y.; MATAKA, S.; New J. Chem. 27 (2003) 9, 1377-1384; Inst. Adv. Mater. Stud., Kyushu Univ., Kasuga, Fukuoka 816, Japan; Eng.) -Nuesgen 09-032 2004 Cycloaddition reactions

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