Reactions of Alkyl -Nitroacrylates with Arenes in Triflic Acid: Synthesis of Oximes of Alkyl 2,3-Diaryl-3-oxopropanoates

Methyl or ethyl 3-nitropropenoates (beta-nitroacrylates) AlkO(O)C1-C2H=C3H-NO2 in reaction with arenes ArH in triflic acid CF3SO3H (TfOH) at room temperature in 1 h give rise to oximes of alkyl 2,3-diaryl-3-oxopropanoates AlkO(O)C-CH(Ar)-C(Ar)=NOH in yields of 42-92 %. The obtained oximes bearing ortho-methyl substituents in the aryl ring exist as atropoisomers in solutions. The study of protonated forms of beta-nitroacrylates by NMR and DFT calculations has revealed that the reactive electrophiles are species AlkO(HO+)C1-C2H=C3H-N+(O)(OH) protosolvated on the acceptor groups NO2 and CO2R. Plausible reaction mechanism is based on the primary interaction of aromatic nucleophiles with these electrophilic species onto their carbon C2.