Terminating Catalytic Asymmetric Heck Cyclizations by Stereoselective Intramolecular Capture of η-Allylpalladium Intermediates: Total Synthesis of (-)-Spirotryprostatin B and Three Stereoisomers.

A catalytic intramolecular Heck reaction, followed by capture of the resulting η(3)-allylpalladium intermediate by a tethered diketopiperazine, is the central step in a concise synthetic route to (-)-spirotryprostatin B and three stereoisomers. This study demonstrates that an acyclic, chiral η(3)-allylpalladium fragment generated in a catalytic asymmetric Heck cyclization can be trapped by even a weakly nucleophilic diketopiperazine more rapidly than it undergoes diastereomeric equilibration.