Cationic Cyclopentannelation of Allene Ethers

The variant of the Nazarov cyclization that makes use of allenyl ethers is suitable for the preparation of diverse, highly functionalized cyclopentenones. Three variants of the basic reaction, differing in the nature of the electrophile that is combined with the allene to prepare the precursor for the pentadienyl cation, are described. One variant, which utilizes an α,β-unsaturated morpholino amide, has been successfully employed in an enantioselective version of the cyclopentannelation.