The condensation of 3-acetyl-4-hydroxy-6-methyl-2H-pyran-2-one (I) with 2,4-dimethoxybenzaldehyde (II) by means of piperidine in refluxing ethanol gives the acryloyl derivative (III), which is finally cyclized with 2-aminoethanethiol (IV) in refluxing ethanol to afford the target thiazepine derivative.