A Broadly Applicable Synthesis of Fluorescent Condensed α-Pyrones

Article abstract of DOI:10.1007/BF00938720

In a two step procedure and in usually good yield an α-pyrone ring can be annelated to (enolized) cyclic β-dicarbonyl compounds like 4-hydroxy-2-pyrones, 4-hydroxycoumarins, 4-hydroxy-2-quinolones and more complex malonylheterocycles, but also to β-naphthole. In a first step the combined action of triethyl orthoformate and arylamines upon the dicarbonyl system affords the anilinomethylene derivatives B in usually high yields.B is reacted with an active methylene nitrile (like alkyl cyano-acetates) and one equivalent of a strong base (like sodium methoxide or potassium hydroxide) in a polar aprotic solvent (like dimethylformamide).Subsequent acidification with dilute aqueous acid gives the corresponding α-pyrone D with yields from 18 to 84percent. The reaction sequence is broadly applicable, which is demonstrated by the synthesis of a series of known (3, 7, 16, 31) and novel (10, 19, 22, 25, 28, 34) heterocyclic systems.Most of them exhibit strong fluorescence in the visible with emission maxima between 450 and 510 nm. - Keywords: Enamines; Fluorescence; α-Pyrone, synthesis