Synthesis of benzofurans from the cyclodehydration of α-phenoxy ketones mediated by Eaton’s reagent

Abstract

Cyclodehydration of α-phenoxy ketones promoted by Eaton’s reagent (phosphorus pentoxide–methanesulfonic acid) is used to prepare 3-substituted or 2,3-disubstituted benzofurans with moderate to excellent yields under mild conditions. The method provides a facile access to benzofurans from readily available starting materials such as phenols and α-bromo ketones. The reaction is highly efficient, which is attributed to the good reactivity and fluidity of Eaton’s reagent. The reaction can be applied to prepare naphthofurans, furanocoumarins, benzothiophenes, and benzopyrans.

An Easy Access to Furan-Fused Polyheterocyclic Systems

“… Literature-reported methods [ 15 , 17 , 18 , 19 , 21 ] ( a) , ( b ) and the approach of the present work ( c ). …”

“…Due to their wide range of applications, many synthetic methods for the preparation of naphtho- and dihydronaphthofuran derivatives have been reported ( Scheme 1 )—the most common involving either the cyclization of a properly functionalized naphthol [ 15 , 16 , 17 ] or the two-step intermolecular reaction of a naphthol with a suitable reagent, followed by cyclization to give the final heterocyclic system. More often, basic conditions are employed to improve the reactivity of naphthol as double nucleophile, as, for instance, in the classical approach of the annulation of 2-naphthol with dihalo compounds [ 18 ].…”