Synthesis of 3,7-dimethyl-1,9-dioxo-1H,9H,10H-pyrano[3,2-c:5,6-c′]dipyran-10-ylacetic acid and its ethyl ester

Abstract

3,7-Dimethyl-1,9-dioxo-1H,9H,10H-pyrano[3,2-c:5,6-c′]dipyran-10-ylacetic acid (Ia) and its ethyl ester (Ib) have been synthesized by a double Michael addition of two molecules of triacetic acid lactone (4-hydroxy-6-methylpyran-2-one) to one of ethyl propiolate followed by intramolecular etherification. An intermediate Michael adduct, ethyl trans-β-(6-methyl-2,4-dioxopyran-3-yl)acrylate (II), was isolated from the reaction under milder conditions. The ¹H n.m.r. spectra of these products are discussed.