Arylidene Pyruvic Acids Motif in the Synthesis of New 2<i>H</i>,5<i>H</i>-Chromeno[4′,3′:4,5]thiopyrano[2,3-<i>d</i>]thiazoles via Tandem Hetero-Diels–Alder-Hemiacetal Reaction

<div><p></p><p>We have developed a tandem hetero-Diels–Alder-hemiacetal reaction using arylidene pyruvic acids with 5-(<i>ortho</i>-hydroxybenzylidene)-substituted 4-thioxo-2-thiazolidinones, leading to 6-hydroxy-2-oxo-5-phenyl-3,5a,6,11b-tetrahydro-2<i>H</i>,5<i>H</i>-chromeno[4′,3′:4,5]thiopyrano[2,3-<i>d</i>][1,3]thiazole-6-carboxylic acids. The stereochemistry of cycloaddition was confirmed by NMR spectra and a single-crystal x-ray diffraction analysis.</p></div