Transfer C–H borylation of alkenes under Rh(I) catalysis: Insight into the synthetic capacity, mechanism, and selectivity control

Transfer C–H borylation of alkenes bears the potential to unlock a range of attractive transformations for modular synthesis and late-stage derivatization of complex molecules. However, its scarce precedence and a limited mechanistic understanding hinders the development of practical synthetic protocols. Here, we report a Rh(I)-catalyzed transfer C–H borylation that is applicable to various terminal and internal alkenes and compatible with a plethora of functional groups, including often problematic motifs. The successful late-stage borylation of bioactive molecules, including derivatives of macrocyclic zearalenol and the drug brompheniramine, underscores its synthetic capacity. A thorough mechanistic investigation involving a series of catalytic and stoichiometric experiments as well as computational studies gave insight into the full catalytic cycle employing a β-boryl elimination, which is unprecedented for Rh-catalysis, and elucidated the features controlling the activity and the selectivity. This work sets the stage for the development of other hydrogen-for-functional group exchange reactions undergoing similar pathways.