Synthesis and Structural Characterization of Pyrrole Heterocyclic Systems Bearing Amino Acid Units: Novel Pyrrol‐3‐ones, Pyrrolo[1,2‐ a ][3,1]benzoxazines, and Pyrrolo[2,1‐ b ][1,3]oxazoles

Furan‐3‐one derivatives 1 were converted into 2‐hydroxy‐pyrrole‐3‐ones 4 by reacting with various α‐ and β‐amino acids. In contrast, the reaction of furan‐3‐ones and 1‐aminocyclobutanecarboxylic acid afforded spiro‐pyrrolo[2,1‐ b ][1,3]oxazoles 5 via the pyrrole‐3‐one intermediate under the same reaction conditions. Some of 2‐hydroxy‐pyrrole‐3‐ones 3 derived from anthranilic acids were transformed to pyrrolo[1,2‐ a ][3,1]benzoxazines via intramolecular esterification .