Complementary Synthetic Approaches toward 9‑Phosphatriptycene and Structure–Reactivity Investigations of Its Association with Sterically Hindered Lewis Acids

Two practical and high-yielding syntheses of 9-phosphatriptycene are reported. In both approaches, the key step is based on the cyclization of a (tris)­lithio-triphenylmethane or a (tris)­lithio-triphenylphosphine intermediate on a phosphorus or a carbon electrophile, respectively. The association of 9-phosphatriptycene with representative boron- and carbon-centered Lewis acids was investigated by IR, NMR, and UV–vis titration experiments and by computational methods, shedding light on its steric hindrance, σ-donating ability, and Brønsted and Lewis basicities.