Organocatalytic Oxy-Michael Addition

Significance

The authors report an enantioselective organocatalytic oxy-Michael addition to γ/δ-hydroxy-α,β-unsaturated ketones 1 and 2. Bifunctional thiourea catalysts 5 or 6 in combination with PhB(OH)₂ were found to be effective for the reaction. After basic H₂O₂ workup, chiral diols 3 and 4 were obtained from the dioxaborolane intermediates. While catalyst 5 was the best catalyst for the γ-hydroxy-α,β-enones, catalyst 6 was found to be highly enantioselective for δ-hydroxy-α,β-enones. With 10-20 mol% of the catalysts, good to high yields (71-95%) and excellent enantio­selectivities (er = 94:6 to >99:1) are obtained for different enones.