Flash Communication: Clarifying the Synthesis of 4,5-Dibromo-9,9-dimethyl-9 <i>H</i> -xanthene: A Scaffold for Organometallic Ligands and Frustrated Lewis Pairs

Xanthene-derived ligands, such as Xantphos, and related scaffolds are pivotal in contemporary organometallic chemistry, delivering wide-bite-angle diphosphines and frustrated Lewis pairs (FLPs) with applications in catalysis and main-group reactivity. 4,5-Dibromo-9,9-dimethyl-9H-xanthene serves as a common gateway intermediate for perisubstitution, yet literature reports on its synthesis are inconsistent. In our hands, direct bromination of 9,9-dimethylxanthene afforded exclusively the 2,7-dibromo regioisomer in 72% yield, as confirmed by single-crystal X-ray diffraction. A modified literature procedure employing an ortho-lithiation protocol with n-BuLi/TMEDA followed by bromination yielded the desired 4,5-dibrominated product in 65% on gram scale. This work resolves ambiguities in prior reports, providing a reliable, reproducible protocol to facilitate access to xanthene-based frameworks.