Dienediones as Building Blocks of an Unfused Polyaromatic Furan Ring System with Tunable Regioselectivity
作者:Chi Wi Ong、Chong-Ming Chen、Shyh Shiaan Juang
DOI:10.1021/jo00115a032
日期:1995.5
The 1,6-dioxo (E,E)-diene has two available sites for isomerization td 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 substituents and the acid conditions.