ChemInform Abstract: Ambivalent Role of Metal Chlorides in Ring Opening Reactions of 2H-Azirines: Synthesis of Imidazoles, Pyrroles and Pyrrolinones.

2H-Azirines were found to react with imines, enaminones and enaminoesters in the presence of metal salts. Imidazoles, pyrroles and new pyrrolinones derivatives are isolated in good overall yields. The role of metal salts was investigated as they can act as Lewis acids or electron donors. Mechanisms are proposed suggesting that imidazoles arise from addition of azirine to imines via radical or ionic mechanism; pyrroles and pyrrolinones are obtained from azirines with enamino derivatives when the salt acts as a Lewis acid. In the latter case the properties of the metallic compound influence the reaction regioselectivity

Ambivalent role of metal chlorides in ring opening reactions of 2H-azirines: synthesis of imidazoles, pyrroles and pyrrolinones.

2H-Azirines were found to react with imines, enaminones and enaminoesters in the presence of metal salts. Imidazoles, pyrroles and new pyrrolinones derivatives are isolated in good overall yields. The role of metal salts was investigated as they can act as Lewis acids or electron donors. Mechanisms are proposed suggesting that imidazoles arise from addition of azirine to imines via radical or ionic mechanism; pyrroles and pyrrolinones are obtained from azirines with enamino derivatives when the salt acts as a Lewis acid. In the latter case the properties of the metallic compound influence the reaction regioselectivity

Synthesis of Functionalized Aromatic Carboxylic Acids from Biosourced 3Hydroxy-2-pyrones through a Base-Promoted Domino Reaction

Nowadays, the use of biomass derived synthons as precursor of aromatic products is an important research topic in green chemistry. In particular, Diels–Alder protocol has been applied in the construction of valuable aromatic derivatives such as terephthalic acid and esters using muconic acid and 2-pyrones as diene components. In this context, we now propose the use of 3-hydroxy-2-pyrones, prepared from galactaric acid, as building block for the synthesis of functionalized aromatic carboxylic acids. Our protocol consists in a base promoted domino reaction in which 2-pyrones and electron-poor alkenes lead directly to the aromatic derivatives preserving all the carbon atoms. High yields are obtained by using small amounts of solvent, in neat conditions and in a water biphasic system, typically at 50 °C. The reaction proceeds through a Diels–Alder cycloaddition followed by aromatization reaction with elimination of water. The aromatization represents a key step and a possible reaction mechanism is propose

Synthesis of Functionalized Aromatic Carboxylic Acids from Biosourced 3-Hydroxy-2-pyrones Through a Base Promoted Domino Reaction

Nowadays, the use of biomass derived synthons as precursor of aromatic products is an important research topic in green chemistry. In particular, Diels–Alder protocol has been applied in the construction of valuable aromatic derivatives such as terephthalic acid and esters using muconic acid and 2-pyrones as diene components. In this context, we now propose the use of 3-hydroxy-2-pyrones, prepared from galactaric acid, as building block for the synthesis of functionalized aromatic carboxylic acids. Our protocol consists in a base promoted domino reaction in which 2-pyrones and electron-poor alkenes lead directly to the aromatic derivatives preserving all the carbon atoms. High yields are obtained by using small amounts of solvent, in neat conditions and in a water biphasic system, typically at 50 °C. The reaction proceeds through a Diels–Alder cycloaddition followed by aromatization reaction with elimination of water. The aromatization represents a key step and a possible reaction mechanism is propose