GoId(I)-Catalyzed Cascade Cycloadditions between Allenamides and Carbonyl-Tethered Alkenes: An Enantioselective Approach to Oxa-Bridged Medium-Sized Carbocycles

摘要

During the last decade, research in homogeneous gold catalysis has experienced an extraordinary growth, resulting in the discovery of a variety of powerful transformations. Particularly relevant, in terms of versatility and synthetic potential, are those reactions involving the cycloaddition of two or more unsaturated components, as a variety of cyclic and polycyclic systems can be rapidly assembled in an efficient and usually stereoselective manner. In this context, we and others have reported several intramolecular gold-catalyzed cycloadditions involving allenes, as well as inter-molecular cycloadditions of allenamides to dienes, (4+2), or to alkenes, (2+2. The high regioselectivity observed in the (2+2) annulations, together with the intrinsic requirement of a carbocation-stabilizing group at the alkene, suggests that this reaction proceeds through a cationic pathway such as that depicted in the Scheme 1 (upper).