Dienediones as Building Blocks of an Unfused Polyaromatic Furan Ring System with Tunable Regioselectivity

Article abstract of DOI:10.1021/jo00115a032

The 1,6-dioxo (E,E)-diene has two available sites for isomerization to the (Z) configuration and can undergo an intramolecular acid-catalyzed cyclization to furanonium intermediates A and B, giving two distinct regioisomeric cyclized products.With unsubstituted aryl derivatives, unfused polyaromatic furans were obtained in good yield with HCl-AcOH.Aryl groups having electron-withdrawing substituents were found to give the opposite regioselectivity.In contrast, the reaction in p-TsOH-CH2Cl2 always resulted in a mixture of regioisomeric products, irrespective of the aryl substituents.Thus, the regioselectivity in the intramolecular cyclization of 1,6-dioxo 2,4-diene can be tuned by varying the aromatic aubstituents and the acid conditions.