Nucleophilic Aromatic Substitutions of Unactivated Aryl Halides by Methyl Selenide Anions. Synthesis and Selective Dealkylations of Aryl Alkyl Selenides

Article abstract of DOI:10.1021/jo00171a027

Lithium methyl selenide, easily prepared from powdered gray selenium and MeLi, reacts with unactivated aryl halides, in DMF, to afford the aryl methyl selenides as a result of a nucleophilic aromatic substitution.The aryl methyl selenides are rapidly dealkylated in the reaction medium by MeSeLi to give the aryl selenide anions.Addition of an alkyl halide or of cyanogen iodide gives rise to the formation of aryl alkyl selenides or aryl selenocyanates in good yields.From competitive experiments, carried out on compounds of the type ArClSeR and ArClSR, it has been shown that an RSe group is as efficient as an RS group in activating the nucleophilic aromatic substitution of a chlorine atom by MeS or MeSe anions in DMF. (Alkylthio)phenyl and alkoxyphenyl alkyl selenides can be selectively dealkylated by nucleophilic aliphatic substitution with MeSNa or MeSeLi in DMF or by electron transfer with sodium in HMPA.In the first case the easiness with which the dealkylation occurs follows the order ArSeMe > ArOMe > ArSMe, whereas in the second case the order is ArSeR > ArSR > ArOR.The synthetic utility of these reactions is exemplified and discussed.