Enantioselective [4+2] Cycloadditions of Ketenes with o-Quinones

Significance

Here the authors report a catalytic, enantioselective [4+2] cycloaddition of o-quinones with chiral 1-ammonium enolates generated in situ from the reaction of acid chlorides with a cinchona alkaloid based catalyst and Hünig’s base. The cycloadducts are converted into chiral α-hydroxyesters in a two-step alcoholysis/oxidation sequence with full preservation of optical purity. With 10 mol% of the catalyst 1, high yields and excellent enantioselectivities are obtained for different aliphatic and aromatic acid chlorides.