Asymmetric Organocatalytic One-Pot, Two-Step Sequential Process to Synthesize Chiral Acetal-Containing Polycyclic Derivatives from Cyclic Hemiacetals and Enones

We have developed an efficient one-pot,
two-step sequential process
to synthesize biologically and synthetically important chiral acetal-containing
polycyclic derivatives. This novel protocol had been proved to proceed
via Michael-lactolization-oxocarbenium ion ring-closing sequence,
which was initiated by a key reactive enamine intermediate and interrupted
the previously established reaction pathway of two different enones
used in this work, and generated the corresponding cycloadducts with
excellent stereoselectivity bearing up to seven continuous stereocenters.
Both chiral and racemic starting cyclic hemiacetals worked well in
this strategy. The synthetic applications of the obtained polycyclic
products have also been demonstrated.