Catalytic, Enantioselective [4 + 2]-Cycloadditions of Ketene Enolates and o-Quinones:  Efficient Entry to Chiral, α-Oxygenated Carboxylic Acid Derivatives

We report catalytic, enantioselective [4 + 2]-cycloadditions of o-quinones with ketene enolates (derived from readily available acid chlorides) using cinchona alkaloid derivatives as catalysts to produce products in high enantiomeric excess (ee) and good to excellent yields. The thermodynamic driving force for these reactions is due in part to the restoration of aromaticity to the products. The resulting chiral, bicycloadducts can be synthetically manipulated in a variety of useful ways, for example to provide a flexible synthesis of alpha-oxygenated carboxylic acid derivatives.