Asymmetric Annulation of 3‑Alkynylacrylaldehydes with Styrene-Type Olefins by Synergetic Relay Catalysis from AgOAc and Chiral Phosphoric Acid

Asymmetric
annulation of 3-alkynylacrylaldehydes with 2-hydroxystyrenes
has been studied and achieved by synergetic catalysis from AgOAc and
chiral phosphoric acid, providing the corresponding multiring products
with decent total yields and moderate to excellent enantioselectivities
(up to 95% ee). The developed mild multibond-formation cascade reaction
involves in situ generation of pyrylium intermediate by Ag­(I)-catalyzed
alkyne/carbonyl cycloisomerization, counteranion-directed asymmetric
oxa [4 + 2]-cycloaddition, and intramolecular nucleophilic substitution.