Asymmetric Catalytic Conjugate Addition of Cyanide to Chromones and β‑Substituted Cyclohexenones

A highly
enantioselective conjugate cyanation of cyclic α,β-unsaturated
ketones was achieved with dual catalysis of chiral Lewis acids and
achiral organic bases. A variety of chromones and β-substituted
cyclohexenones were transformed into the desired β-cyano ketone
derivatives in good yields with high enantioselectivities under mild
conditions. The metal salts Ce­(OTf)3 and Ba­(OTf)2 in combination with chiral N,N′-dioxides facilitated the reaction well, revealing a close
connection between the outcome of the reaction and the Lewis acidity
with metal ion radii. The application of the methods was highlighted
by the facile synthesis of the bioactive compounds repinotan and sarizotan.