Abstract
Electrophilic and nucleophilic substitutions of aromatic substrates share common mechanistic
pathways. In both scenarios reacting species attack rings at the unsubstituted (C–H)
positions, giving cationic Wheland intermediates or anionic Meisenheimer complexes.
However, the following step of rearomatization breaks the intrinsic symmetry, due
to different leaving group ability of proton and hydride anion, respectively. In effect,
electron-deficient arenes are prone to transformations unparalleled in electrophilic
chemistry. In our article, we present transformations of anionic σH-adducts, formed between nitroarenes and carbanions of the Corey–Chaykovsky reagents.
Depending on structure of the substrates and reaction conditions, the intermediates
undergo cyclization to cyclopropanes (norcaradienes) or base-induced elimination to
the alkylated products. Mechanistic studies reveal that order of the carbanions controls
competition between the processes, due to steric hindrance developing at the β-elimination
step.
1 Introduction
2 Cyclopropanation of Nitronaphthalenes
3 Alkylation of Nitropyridines
4 Mechanistic Studies
5 Summary and Outlook
Key words
nitroarenes - sulfones - selenones - sulfonium salts - cyclopropanation - alkylation
- carbanions - Meisenheimer complex
