Synthesis of thiapyranoside precursors using the building-block approach from a phosphonodifluorodithioacetate

Phosphonodifluorodithioacetate 2 demonstrates high reactivity towards dienes due to the presence of the two fluorine atoms. A hetero Diels–Alder reaction afforded the corresponding dihydrothiapyrans in 60–90% yields. These adducts can be submitted to a selective dihydroxylation and desulfanylation to produce phosphonodifluorothiaglycoside precursors.