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

Intramolecular Stetter reaction of methyl 3-(2-formylphenoxy)prop-2-en oate catalyzed by -benzyl-5-(2-hydroxyethyl)-4-methyl-1,3-thiazolium c hloride in refluxing dimethylformamide gave methyl 2,3-dihydro-3-oxobe nzofuran-2-acetate in 39% yield. The presence of a tertiary amine, whi ch in this case caused destruction of the product, is thus not necessa ry for the success of the Stetter reaction. When sodium cyanide was us ed as the catalyst, methyl 2-cyano-2,3-dihydro-4-hydroxy-2H- 1-benzopy ran-3-carboxylate was formed in 58% yield. Methyl 4-(2-formylphenoxy)b ut-2-enoate underwent intramolecular Stetter reaction to give methyl 3 ,4-dihydro-4-oxo-2H-1-benzopyran-3-acetate in 86% yield. Base-catalyze d cyclization of methyl 4-(2-formylphenoxy)but-2-enoate gave methyl 1- benzoxepin-4-carboxylate in 52% yield.