Thionyl Chloride-Mediated Synthesis of Erlenmeyer Azlactones from N -Acylated α-Amino Acids

A thionyl chloride-mediated synthesis of Erlenmeyer azlactones from N-acylated α-amino acids is described. The method relies on in situ activation of the carboxylic acid with SOCl₂ followed by base-promoted intramolecular cyclization, enabling direct access to diverse azlactones in moderate to good yields. Under microwave irradiation, the transformation proceeds efficiently and tolerates a range of N-acylated phenylalanine derivatives as well as selected aliphatic and aromatic amino acids. Control experiments highlight the unique role of thionyl chloride in promoting the cyclization. This protocol provides a straightforward route to azlactone scaffolds from readily available amino acid precursors.