Cascade Reactions of α‐Phenylcinnamic Acid to Polycyclic Compounds Promoted by High Valent Transition Metal Halides

α‐Phenylcinnamic acid converts into polycyclic derivatives by interaction with high valent transition metal halides in chloroform at reflux temperature. Different products, featured by local structural differences depending on the nature of the metal halide system (i. e. WCl 6 , PCl 5 /NbF 5 or PCl 5 /NbCl 5 ), are easily isolable after treatment with water. In particular, WCl 6 configures as an efficient multitasking agent, working as 1) chlorinator of the carboxylic acid function, 2) catalytic precursor for intra‐ and intermolecular rearrangements, and 3) catalytic precursor for Baeyer‐Villiger lactonization in water at ambient temperature, exploiting air as oxidant. The products have been purified by alumina chromatography, and identified by analytical and spectroscopic (IR, NMR) techniques, and by single crystal X‐ray diffraction in three cases. Their formation probably involves a common reaction pathway which has been rationalized by DFT calculations.