Advances in Stereoselective Palladium(ΙΙ)-Catalyzed Oxidative Transformations of Allenes

Sammanfattning: Palladium(ΙΙ)-catalyzed carbon-carbon and carbon-heteroatom bond formation via selective C-H bond oxidation constitutes a step-economical and versatile approach towards complex target molecules. This thesis has been focused on the development of new selective palladium(ΙΙ)-catalyzed transformations of allenes under oxidative conditions catalyzed by either homogenous or heterogeneous palladium(ΙΙ) catalysts.The first part of this thesis describes carbocyclization-borylation of bisallenes, alkynylation of enallenes and preparation of [3]dendralenes from readily available allene starting materials. These homogenous palladium(ΙΙ)-catalyzed transformations involve selective allenic C-H cleavage under oxidative conditions. The aforementioned reactions can be carried out under aerobic biomimetic conditions by using electron transfer mediators (ETMs) and oxygen gas as the stoichiometric oxidant.The second part deals with highly diastereoselective palladium-catalyzed oxidative carbocyclization reactions of enallenes assisted by weakly coordinating functional groups, such as hydroxyl or sulfonamide groups. It was demonstrated, that this weak coordination is sufficient to trigger the allene attack on the metal center enabling formation of (vinyl)Pd(II) intermediates, previously achievable by the directing effect of unsaturated hydrocarbon groups. A broad range of borylated cyclohexanol derivatives, as well as cis-fused [5,5] bicyclic γ-lactones and γ-lactams were obtained with superb diastereoselectivity via palladium(ΙΙ)-catalyzed carbocyclization-functionalization reactions of enallenols.The final part of the thesis describes applications of the heterogenous catalyst Pd-AmP-MCF in oxidation reactions of allenes. Chemodivergent oxidative cascade reactions of enallenols were realized by switching between heterogeneous (Pd-AmP-MCF) and homogeneous (Pd(OAc)2) palladium catalysts. In separate cases, the heterogeneous catalyst Pd-AmP-MCF showed improved performance over its homogeneous counterpart, accompanied by high recyclability and no detectable metal leaching. Synthetically important cyclic skeletons such as cyclobutenols, furanes, oxaboroles, and fused γ-lactones/lactams were obtained via borylative or carbonylative carbocyclization reactions of enallenols in high yields and with excellent stereoselectivity.