Reactions of Alkyl β-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.

Automated summary

Methyl or ethyl 3-nitropropenoates react with arenes in triflic acid tetrahydrofuran solution to form oximes of alkyl 2,3-diaryl-3-oxopropanoates in good yields. The obtained oximes exhibit atropoisomerism due to the presence of ortho-methyl substituents in the aryl ring. The reactive electrophiles in this reaction are AlkO(HO+)C1-C2H=C3H-N+(O)(OH) species protosolvated on the NO2 and CO2R acceptor groups.