<p>Novel rel-(6R,7R)-2-oxo-7-phenyl-3,5,6,7-tetrahydro-2H-thiopyrano[2,3-d]thiazole-6-carbaldehydes were synthesized via regio- and diastereoselective hetero-Diels-Alder reaction of 5-arylidene-4-thioxo-2-thiazolidinones with acrolein. The synthesized compounds were evaluated for anticancer and antiviral activities by the National Institutes of Health (NIH) following US NCI and AACF protocols. Anticancer activity screening on NCI60 cell lines allowed identification of 7-phenyl-2-oxo-7-phenyl-3,5,6,7-tetrahydro-2H-thiopyrano[2,3-d]thiazole-6-carbaldehyde <b>3a</b> with the highest level of antimitotic activity against leukemia with mean GI<sub>50</sub>/TGI values 1.26/25.22 μM. The screening of antiviral activity lead to identification of 7-(4-methoxyphenyl)-2-oxo-3,5,6,7-tetrahydro-2H-thiopyrano[2,3-d]thiazole-6-carbaldehyde <b>3b</b> with a promising influence on EBV virus (EC<sub>50</sub> = 0.07 μM, SI = 3279) and moderate effect on Herpes simplex virus type 1 and Varicella zoster virus and 7-[4-(benzyloxy)phenyl]-2-oxo-3,5,6,7-tetrahydro-2H-thiopyrano[2,3-d][1,3]thiazole-6-carbaldehyde <b>3e</b> with a promising influence on Hepatitis C virus (EC<sub>50</sub> = 12.6 μM, SI = 43.1).</p
