Enantioselective Organo-SOMO Cycloadditions: A Catalytic Approach to Complex Pyrrolidines from Olefins and Aldehydes

A new method to rapidly generate pyrrolidines via a SOMO-activated
enantioselective (3 + 2) coupling of aldehydes and conjugated olefins
has been accomplished. A radical-polar crossover mechanism is proposed
wherein olefin addition to a transient enamine radical cation and
oxidation of the resulting radical furnish a cationic intermediate
which is vulnerable to nucleophilic addition of a tethered amine group.
A range of olefins, including styrenes and dienes, are shown to provide
stereochemically complex pyrrolidine products with high chemical efficiency
and enantiocontrol.