Synthesis of functionalized 3-hydroxy-thiophenes from α,β-unsaturated enones and 1,4-dithiane-2,5-diol (dimer of α-mercaptoacetaldehyde) | Poster Board #230

In a continuation of our studies of Michael addition to endo- and exo-cyclic enones^1,2 we decided to study the reaction of α,β-unsaturated ketones with 1,4-dithiane-2,5-diol³ (1,4-DTD) as illustrated in the scheme below. We selected three structurally different reactants belonging to either the exo- or endo-cyclic enone category. In the case of exo-cyclic enones the adduct was identified as a spiro-cyclic derivative. In the case of 4-methoxy-aurone the addition product was identified as spiro-adduct to double bond of exo-cyclic aurone. In contrast, the addition reaction of 1,4-DTD to levoglucosenone proceeds via a stereoselective Michael addition at the C-4 position.
The products were isolated in good yield (58-65%) and characterized by ¹H and ¹³C NMR spectroscopy. A plausible reaction mechanism of stereoselective addition will be presented.