Erlenmeyer–Plöchl azlactone and amino-acid synthesis

The Erlenmeyer–Plöchl azlactone and amino acid synthesis, named after Friedrich Gustav Carl Emil Erlenmeyer who partly discovered the reaction, is a series of chemical reactions which transform an N-acyl glycine to various other amino acids via an oxazolone (also known as an azlactone).

[1][2] Hippuric acid, the benzamide derivative of glycine, cyclizes in the presence of acetic anhydride, condensing to give 2-phenyl-oxazolone.

This compound on reduction gives access to phenylalanine.

Hydantoin (in Bergmann modification), thiohydantoin and rhodanine have each been employed as the enolate-forming component of the condensation.

[5][6] 2,5-Diketopiperazine can be used as a methylene component as well; its condensation products with aromatic aldehydes, on reduction and hydrolysis give the corresponding amino acids.