Abstract
Tetrasubstituted 3-acylfuran derivatives were obtained by condensation of acetylacetone with alicyclic and heterocyclic α-hydroxy-β-oxo esters under acidic conditions [0.1 equiv. cerium(III) salt in AcOH]. With [b]-annulated 4-acyl-3-hydroxy-5-methylfuran-2-carboxylates as common intermediates, the reaction proceeded along different pathways depending on the starting materials used: Alicyclic α-hydroxy-β-oxo esters gave cycloalkane-annulated furans as products. The ester group was lost after saponification and decarboxylation at elevated temperature. A thiopyrano[3,4-b]-annulated 2H-furan was obtained when starting from a tetrahydrothiopyranone derivative. With piperidones or a tetrahydropyranone as starting materials, the heterocyclic six-membered ring was cleaved in a retro-Mannich type reaction and one carbon atom was lost. 4-Acetyl-5-methylfuran-2-carboxylates with a 2-amino or 2-hydroxyethyl substituent in the 3-position are obtained in these cases.
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