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 - and -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.