Harnessing Phenonium Ions in Synthesis

Whereas phenonium ions have been known for decades, their use in synthesis has been surprisingly scarce. This might be attributed to the difficulty in taming their formation and reactivity. However, by considering the physical-organic properties of phenonium species, through careful design of substrates, or the use of defined reagents/promoter systems, several applications have emerged in recent years to overcome those challenges. This minireview encompasses key recent strategies to generate those highly reactive cationic intermediates in line with their physicochemical properties, with special emphasis on mechanistic aspects, regioselectivity, and functional group compatibility.