摘要

An efficient, one-pot tandem reaction of pyridine, an alpha-haloacetate, an aromatic aldehyde and cyclohexane-1,3-dione, dimedone or 4-hydrocoumarin in acetonitrile using 1,4-diazabicyclo[2.2.2]octane as a basic catalyst is described. The products, 2,3,6,7-tetrahydro-4(5H)-benzofuranones and 2,3-dihydrofurocoumarins, are obtained in a diastereoselective manner via a mechanism involving in situ formation of a pyridinium ylide. H-1 NMR spectroscopy and single crystal X-ray analysis indicates that the products are formed exclusively as the trans isomers.