cis-Selective, Enantiospecific Addition of Donor-Acceptor Cyclopropanes to Activated Alkenes: An Iodination/Michael-Cyclization Cascade.

We present a versatile method for the enantiospecific, cis-diastereoselective intermolecular and intramolecular cycloaddition of donor-acceptor cyclopropanes to electron-poor alkenes with cyclic acceptor groups to afford highly substituted spirocyclopentanes in good to excellent yields. The reaction can be applied to biologically interesting scaffolds, including barbiturates and isoxazolones. Mechanistic investigations were undertaken to explain the unusual diastereoselectivity and enantiospecificity; these suggest an iodination/Michael-cyclization cascade.