Diastereoselective Rhodium-Catalyzed Ene-Cycloisomerization Reactions of Alkenylidenecyclopropanes: Total Synthesis of (−)-α-Kainic Acid

The rhodium-catalyzed ene-cycloisomerization of alkenylidenecyclopropanes
provides an atom-economical approach to five-membered carbo- and heterocycles
that contain two new stereogenic centers. A key and striking feature
of this protocol is that the alkene geometry does not impact the efficiency
and diastereocontrol, which provides excellent synthetic versatility.
For instance, (E)- and (Z)-allylic
alcohols furnish the corresponding aldehydes with similar efficiency
and selectivity. This process facilitates the construction of a key
intermediate in an eight-step total synthesis of (−)-α-kainic
acid.