Three Component Cascade Processes Involving Palladium Catalyzed Transformations/Dipolar Cycloadditions for the Synthesis of Angular Heterotriquinane Derivatives

Abstract

Combining chemical reactivities of allenes and oximes created a methodology for the preparation of heterocyclic triquinane-type skeletons via a cascade process constructing four bonds in a single step. The initial reaction of allene moiety promoted by Pd-catalysis, affording π-allyl Pd-species, was followed by two additional transformations - nucleophilic displacement and dipolar cycloaddition - to furnish the product highly stereoselectively in moderate to good yields. For the process to be efficient, it was necessary to use a dipolarophilic component as a solvent. Intriguingly, while the reaction with cyclopentanone derived oxime progressed through the whole cascade, with cyclohexanone analogue it stopped at the nitrone stage, requiring an additional step to yield similar type of products. Some aspects of the studied cascade were examined by DFT.