Ring oxidative, preferential

Alkyl-substituted benzenes are oxidized both on the benzene ring and on the side chain. Additionally, some dimerization occurs.36 Alkylbenzenes containing linear alkyl groups are oxidized preferentially at the side chain33 nearest the benzene ring for example, ethylbenzene oxidizes first to 1-phenyl ethanol and then to acetophenone.36... 

Steric factors probably play a key role in determining the regiospecificity of the reactions leading to the phosphine oxides 4a and 4b. An intermediate involved in both cases is probably of type 5, in which ring closure preferentially occurs para rather than ortho to the bulky CF3 group. The preferential formation of 5b from the corresponding phosphoramidous dichloride is undoubtedly associated with the fact that... 

Thienylpyridazines were prepared from 2- or 3-thienyllithium and py-ridazine. In diethyl ether, the thienyl ring is attached at position 3 to give first the corresponding 2,3-dihydro derivatives accompanied by a small amount of 1,4-dihydro isomers, whereas in tetrahydrofuran and at low temperature, position 4 of the pyridazine ring is attacked. Aromatization can be achieved with various oxidants, preferentially with chloranil [81JCR(S)104 82CJC2668],... 

Fig. 3. A switchable rotaxane based on acceptor-donor complexes [24]. Before oxidation, the electron acceptor (ring) interacts preferentially with the benzidine nucleus (donor). After electrochemical oxidation of the latter, the ring is shifted towards the biphenol group. The process is reversible...

Zinc-chromium oxide and massive amounts of finely divided Ni (W4 or W6 Raney Ni) in ethanol are effective , but saturation of a benzene ring occurs preferentially. 

In the oxidation of dimethyl-bis-(5-trimethylsilyl-2-thienyl)silane, having two thiophene moieties, with one equivalent of m-CPBA, one thiophene ring was preferentially oxidized to afford only the mono-sulfone 52 in 36% yield. After further addition of m-CPBA, the corresponding mono-sulfone 52 and bis-sulfone 53 were obtained in 21 and 41% yields, respectively (Scheme 53) [64], In another example, the oxidation of 2,5 -bis(n-hexyl)-2,2 -bithiophene was found to be difficult the monodioxide 54 was obtained in low yield (10%), but no bis-6,6-dioxide was observed (Scheme 54) [61],... 

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