Sterically Controlled Late‐Stage Functionalization of Bulky Phosphines

The fine‐tuning of metal‐phosphine‐catalyzed reactions relies largely on accessing ever more precisely tuned phosphine ligands by de‐novo synthesis. Late‐stage C−H functionalization and diversification of commercial phosphines offers rapid access to entire libraries of derivatives based on privileged scaffolds. But existing routes, relying on phosphorus‐directed transformations, only yield functionalization of C [Formula: see text] −H bonds in a specific position relative to phosphorus. In contrast to phosphorus‐directed strategies, herein we disclose an orthogonal functionalization strategy capable of introducing a range of substituents into previously inaccessible positions on arylphosphines. The strongly coordinating phosphine group acts solely as a bystander in the sterically controlled borylation of bulky phosphines, and the resulting borylated phosphines serve as the supporting ligands for palladium during diversification through phosphine self‐assisted Suzuki‐Miyaura reactions.