Filippo Maiolo

Selectivity of radical ipso attack. Alkyldeacylation reactions by dioxanyl radicals in unprotonated acetylpyri dines

Abstract Under neutral conditions the reaction of dioxanyl radicals with 2,5-diacetylpyridine gives the ipso substitution products; on the contrary, in the presence of sulphuric acid the substitution occurs at the 2- and 4- positions.

Selective cleavage of the carbon-sulphur and carbon-oxygen bonds in methoxythioanisoles

Abstract Selective cleavage of thioether of ether functions in methoxythioanisoles in hexamethylphosphoramide (HMPA) with sodium gives methoxythiophenols by cleavage of the carbon-sulphur bond. Reactions with sodium isopropanethiolate give instead the thiomethoxyphenols by dealkylation of the methoxy function. When the methoxythioanisoles were treated first with sodium isopropanethiolate and then with sodium complete dealkylation was achieved with formation of mercaptophenols. The present methods have considerable advantages over existing procedures for the synthesis of methoxythiophenols, thiomethoxyphenols and mercaptophenols. The mechanistic implications of the reactions investigated are also discussed.

Factors controlling the selectivity of ipso-attack in homolytic aromatic substitutions. Reactions of alkyl radicals with nitrothiophen derivatives

The reactions of the nearly electroneutral methyl and of the nucleophilic 1-adamantyl radical with some selected nitrothiophen derivatives have been investigated in order to elucidate the factors which control the positional selectivity of radical addition to an aromatic substrate. With 5-nitro-2-X-thiophens (II), (V), and (VI) and 3,5-dinitro-2-methoxycarbonylthiophen (III) the adamantyl radical gave exclusively the products of ipso-attack, whereas the methyl radical selectively added at the unsubstituted 4-position. On the other hand, with 4-nitro-2-methoxy-carbonylthiophen (I) both radicals added at the 5-position and with 4,5-dinitro-2-methoxycarbonylthiophen (IV) both radicals gave the products of ipso-substitution by displacing the nitro-group from the 5-position. These changes in positional selectivity are explained by assuming that the nature of the transition state of the addition step changes as a function of the polar character of the radical and of the electron deficiency of the aromatic substrates.