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.