THREE-COMPONENT SYNTHESIS OF 2-ACYL-2,3-DIHYDRO-4<i>H</i>-THIOCHROMENO[4,3-<i>b</i>]FURAN-4-ONES AND THEIR REDUCTIVE REARRANGEMENT INTO 4<i>H</i>,5<i>H</i>-THIOCHROMENO[4,3-<i>b</i>]PYRAN-5-ONES
DOI:
https://doi.org/10.1007/6105Keywords:
2-acyl-2, 3-dihydro-4H-thiochromeno[4, 3-b]furan-4-ones, carbenes, 4-hydroxythiocoumarin, pyridinium ylides, 4H, 5H-thiochromeno[4, 3-b]pyran-5-ones, zirconium(IV) chloride, zinc, zinc carbenoids, multicomponent reactions, reductive rearrangement.Abstract
Three-component condensation of in situ generated pyridinium acyl methylides with aromatic aldehydes and 4-hydroxythiocoumarin led to a series of 2-acyl-2,3-dihydro-4H-thiochromeno[4,3-b]furan-4-ones. The reaction proceeds diastereoselectively with the formation of trans-isomers and represents a cascade process involving the Knoevenagel condensation, carbo-Michael reaction, and intramolecular nucleophilic substitution. The subsequent redox rearrangement of 2-acyl-2,3-dihydro-4H-thiochromeno[4,3-b]furan-4-ones by the action of Zn and ZrCl4 grants access to 4H,5H-thiochromeno[4,3-b]pyran-5-ones.