Total synthesis of (-)-ebelactone A and B

Article abstract of DOI:10.1021/jo00116a010

The β-lactone enzyme inhibitors (-)-ebelactone A (1) and (-)-ebelactone B (2) have been prepared in 12 steps from diethyl ketone (4 and 3% overall yield, respectively). The synthetic strategy adopted for the ebelactones demonstrates the use of reagent- and substrate-derived stereocontrol and requires the minimal use of protecting groups. The stereocenters at C₂, C₃, C₈, C₁₀, and C₁₁ were constructed using boron aldol methodology. An asymmetric syn aldol addition of diethyl ketone to 2-ethylacrolein gave adduct 8 in 86% ee, followed by a diastereoselective syn aldol reaction to give 11. Subsequently, an Ireland-Claisen rearrangement was used to relay 1,2-syn into 1,5-syn relative stereochemistry, as in 12 → 14. In the anti aldol construction of the C₂-C₃ bond, the use of either a propionate or butyrate thioester enolate allowed for a divergent approach from aldehyde 17 to both (-)-ebelactone A and B. Several novel analogues of ebelactone A and B were also prepared with inverted stereochemistry at C₂, C₃, or C₁₂.