Nucleophilic Addition of Silyl Enol Ethers to Aromatic Nitro Compounds: Scope and Mechanism of Reaction

Article abstract of DOI:10.1021/ja00305a024

In sharp contrast to alkali-metal enolates, silyl enol ethers and ketene silyl acetals add to aromatic nitro compounds in the presence of a fluoride ion source to give the intermediate dihydroaromatic nitronates, which can be observed by NMR.In situ oxidation of the intermediate with bromine or DDQ yields α-nitroaryl carbonyl compounds in moderate-to-high yields.The reaction is applicable to alkyl-, alkoxy-, and halogen-substituted nitrobenzenes as well as to heterocyclic and condensed nitroaromatic compounds.While substitution ortho to the nitro group predominates with sterically undemanding silyl reagents, para-substitution products are exclusively obtained with bulky reagents.However, by blocking the para position with an appropriate group such as chlorine, the addition can be directed to the ortho position.Halogen atoms of halogenated nitroaromatics and p-nitrocumenyl chloride are not displaced in the reaction, suggesting the absence of radical ion intermediates.Dihydroaromatic nitro derivatives ca be isolated in some cases, such as anthracene and naphthalene systems which are less prone to rearomatize.