Esters of 2,3-Dihydro-3-oxobenzofuran-2-acetic Acid and 3,4-Dihydro-4-oxo-2H-1-benzopyran-3-acetic Acid by Intramolecular Stetter Reactions
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Abstract
Intramolecular Stetter reaction of methyl 3-(2-formylphenoxy)-prop-2-enoate catalyzed by 3-benzyl-5-(2-hydroxyethyl)-4-methyl-1,3-thiazolium chloride in refluxing dimethylformamide gave methyl 2,3-dihydro-3-oxobenzofuran-2-acetate in 39% yield. The presence of a tertiary amine, which in this case caused destruction of the product, is thus not necessary for the success of the Stetter reaction. When sodium cyanide was used as the catalyst, methyl 2-cyano-2,3-dihydro-4-hydroxy-2H-1-benzopyran-3-carboxylate was formed in 58% yield. Methyl 4-(2-formylphenoxy)but-2-enoate underwent intramolecular Stetter reaction to give methyl 3,4-dihydro-4-oxo-2H-1-benzopyran-3-acetate in 86% yield. Base-catalyzed cyclization of methyl 4-(2-formylphenoxy)but-2-enoate gave methyl-1-benzoxepin-4-carboxylate in 52% yield.