Kazuya Arima

Photochemical and electrochemical behavior of thiophene-S-oxides

The photochemical and electrochemical behavior of thiophene-S-oxides as a class was studied for the first time. It was shown that in both cases deoxygenation of the S—O functionality takes place. The outcome of the photoirradiation is very dependent on the substituent pattern of the starting material. Thiophene-S-oxides show different reduction behaviors in presence and absence of proton donors. In the absence of proton donors the reduction potential of the compounds is dependent on the substituents of the molecules. In the presence of proton donors, the substituents play a less significant role and a number of thiophene-S-oxides were reduced electrochemically to the corresponding thiophenes in presence of a 10-fold excess of benzoic acid. Copyright

Cycloaddition of thiophene S-oxides to allenes, alkynes and to benzyne

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.

Elongated phosphoranes by C–C coupling of haloaroylmethylidenetriphenylphosphoranes: synthesis and applications

Haloaroylmethylidenephosphoranes 3 can be subjected to Pd(0) mediated C–C coupling reactions to yield diaryl-, arylhetaryl-, dihetaryl, arylethenylaryl/hetaryl- and arylethynylaryl/hetaryl-carbonylmethylidenephosphoranes 4–9. Suzuki–Kumada reactions can also be run in a one-step procedure from (haloaroylmethyl)triphenylphosphonium bromides 2. Compounds 4–9 are air-stable phosphoranes which undergo formal Wittig-olefination reactions with aldehydes 10 under benzoic acid catalysis. C–C coupling reaction and Wittig olefination can also be performed in a one-step procedure. Preliminary experiments have been performed to carry out the synthesis on a solid support. Applications to the chain elongation and functionalisation of the chain terminus in a C-7 substituted estra-1,3,5(10)-triene 14 and a C-16 substituted estra-1,3,5(10),6-tetraene 12 are shown.

Photochemistry of substituted dibenzothiophene S-oxides and oxygenated bis-dibenzothiophenes

Substituted dibenzothiophene and bis-dibenzothiophene S-oxides were prepared and submitted to photolysis. The rate of deoxygenation of the molecules under photoirradiation was found to be highly dependent on their substitution pattern.