Reinvestigation of the reaction between 2-furancarboxaldehyde and 4-hydroxy-5-methyl-3(2H)-furanone

The reaction between 2-furancarboxaldehyde and 4-hydroxy-5-methyl-3(2H)-fur anone was reinvestigated as a part of a systematic study on low molecular w eight colored compounds from the Maillard reaction. In acetic acid/piperidi ne, besides 2-(2-furanylmethylene)-4-hydroxy-5-methyl-3-(2H)-furanone(1) an d 5-[2-(2-furanyl)ethenyl]-2-(2-furanylmethylene)4-hydroxy-5-methyl-3(2H)-f uranone (2), four novel compounds, 15a, 15b, 16a, and 16b, were isolated an d characterized. These compounds are produced from two molecules of furanon e 1 and one molecule of 2-furancarboxaldehyde, and a mechanism is proposed for their formation. Compounds 1, 15a, 15b, 16a, and 16b are formed also by reacting 2-furancarboxaldehyde and 4-hydroxy-5-methyl-3(2H)-furanone in wa ter at pH 3 and 2, whereas 2 was never detected. The formation of these com pounds was studied also in xylose/lysine and xylose/glycine model systems.