<i>syn</i> ‐Selective Michael Reaction of α‐Branched Aryl Acetaldehydes with Nitroolefins Promoted by Squaric Amino Acid Derived Bifunctional Brønsted Bases

Here we describe a direct access to 2,2,3-trisubstituted syn γ-nitroaldehydes by addition of α-branched aryl acetaldehydes nitroolefins promoted cinchona based squaric acid-derived amino acid peptide. Different α-methyl arylacetaldehydes react with β-aromatic and β-alkyl afford the Michael adducts in high enantioselectivity syn-selectivity. NMR experiments DFT calculations predict reaction occur through intermediacy E-enolate. The interaction between substrates catalyst follows Pápai's model, wherein an intramolecular H-bond NH group one tert-leucines squaramide oxygen seems be key for discrimination corresponding transition states.