Base-promoted cascade recyclization of allomaltol derivatives containing an amide fragment into substituted 3-(1-hydroxyethylidene)tetronic acids.

For the first time, recyclization of allomaltol derivatives with an amide fragment in the side chain were investigated. It was shown that the studied process leads to substituted tetronic acids bearing a pyrrolidinone moiety. The application of 1,1'-carbonyldiimidazole and DBU is necessary for implementation of the considered reaction. Based on the performed research a general method for the synthesis of a wide range of (3E,5E)-3-(1-hydroxyethylidene)-5-(5-oxopyrrolidin-2-ylidene)furan-2,4(3H,5H)-diones was elaborated. The advantages of the presented protocol are easily available starting compounds and simple isolation of the target products without chromatographic purification. The synthetic utility of the prepared tetronic acids was demonstrated by further transformations at the hydroxyethylidene fragment. The structures of one obtained tetronic acid and one product of derivatization were confirmed by X-ray analysis.