Enantio- and Diastereoselective Spiroketalization Catalyzed by Chiral Iridium Complex

Iridium–(P,olefin)
complex-catalyzed enantio- and diastereoselective formation of substituted
spiroketals from racemic, allylic carbonates is reported, which enables
the installation of multiple stereogenic centers in a single operation.
The protocol was effective for the preparation of a collection of
spiroketals of various ring sizes and substituents, including heteroatoms
with high enantio- and diastereoselectivity. Furthermore, cascade
reactions that couple this enantio- and diastereoselective transformation
to additional reversible processes have been achieved to exert concomitant
stereocontrol over additional stereogenic centers.