An asymmetric multicatalytic reaction sequence of 2-hydroxycinnamaldehydes and enolic 1,3-dicarbonyl compounds to construct bridged bicyclic acetals

An efficient asymmetric multicatalytic system involving iminium catalysis and anion-binding catalysis has been developed, which exhibited high catalytic activity in a one-pot, two-step reaction sequence of 2-hydroxycinnamaldehydes and enolic 1,3-dicarbonyl nucleophiles to construct an enantioenriched 2,8-dioxabicyclo[3.3.1]nonane scaffold. The inherent phenolic hydroxyl group of 2-hydroxycinnamaldehyde played an important role in the catalytic process, which potentially provided a phenoxide anion to combine with the thiourea moiety of a bifunctional tertiary amine-thiourea catalyst via anion binding, thus making the developed multicatalytic system more economic and different from the previously reported catalytic mode.