CoSalen-Catalyzed Radical Hydrofunctionalization of Unactivated Internal Olefins at Low Catalyst Loading: Method Development, Regioselectivity, and Applications in Post-Polymerization Modification

The past two decades witnessed the rapid development of CoSalen-catalyzed hydrofunctionalization reactions, mostly on terminal and conjugation-activated olefins. However, the use of 1,2-dialkylsubstituted alkenes continues to pose challenges. In this study, we revisit this substrate class in the context of Carreira-type hydrofunctionalization reactions and introduce a simple yet effective modification (over 250-fold-increase in TON). Near-quantitative yields can be achieved at a low catalyst loading, typically 0.05 mol%. The key lies in inhibiting the degradation of the Salen backbone using molecular sieves. This new protocol facilitates a study on the MHAT regioselectivity of this type of alkenes. We found that allylic electron-negative groups and hyperconjugation have profound effects, yielding regioisomeric ratios ranging from 6.5:1 to < 1:20. The high TON, mild conditions, and versatility of this method further enable its application in the post-polymerization modification of several olefin-rich, commodity-relevant polymers.