Benzyl chloride and its derivatives are efficiently deprotonated with strong bases to form αchlorocarbanions. These anions are long-lived enough to enter VNS reactions with nitroarenes or nitroheteroarenes to give a variety of unsymmetrical o-and p-nitrodiarylmethanes. Selectivity of the reaction can be controlled to some extent by changing metal counterions of the base.
Readily available α,α-dichlorotoluenes enter a vicarious nucleophilic substitution (VNS) reaction with electron-deficient arenes to give α-chlorobenzylated nitrobenzenes, as well as six- and five-membered heterocycles. Oxidation of the initially formed α-chlorobenzylic carbanions instead of protonation results in formation of diaryl ketones, providing a means for overall nucleophilic C-H benzoylation of electron-deficient aromatic rings. Alternatively, benzoylated nitroarenes can be obtained via the reaction of isolated α-chlorodiarylmethanes with sodium azide.
Palladium‐catalyzed activation of C(sp2)−H bond in a readily E,Z‐isomerizable aldonitrone, bearing an ester group at the C terminus, enabled its cross‐coupling with a variety of aryl and heteroaryl bromides to give ketonitrones, including products with functional groups not compatible with the classical nitrone synthesis via condensation with hydroxylamines. The reactions proceeded with very high (usually complete) E selectivity. The key to obtaining good yields of the cross‐coupling products was the use of sterically hindered carboxylic acid as additive and non‐polar solvent (toluene), in which the starting nitrone exists mainly as E isomer. Further use of the obtained ketonitrones in dipolar cycloaddition or nucleophilic addition has also been demonstrated.
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