Copper-Catalyzed Diastereoselective [3+2] Cycloaddition

Significance

This report of a cobalt-catalyzed intermolecular reductive [3+2] cycloaddition of allenes and enones affords carbocycles in good yields and high diastereoselectivities. Both cyclic and acyclic vinyl ketones can be used with a variety of aromatic, alkyl, cycloalkyl, and heteroaromatic allenes. All of the products were isolated as single diastereomers with the exception of the products from 1-naphthyl and o-tolyl allenes. These allenes are sterically hindered, which could affect the equilibrium and rates for forming one carbonyl insertion isomer over another. When 2-allenyl benzoates are used in the reaction, lactonization occurs following the formation of the cyclopentanol, yielding benzopyran derivatives as single diastereomers.