Dehydrogenative aromatization (DA) of cyclic ketones to form aromatic phenol or phenol ether is central to the development of functionalized aromatic precursors and hydrogen transfer-related technologies. Traditional DA strategies require precious metals, such as Pd, Au, and Pt, with oxidants or ligands and are typically performed at high temperatures (100–150 °C) to overcome the high energy barrier of aliphatic carbon-hydrogen (C–H) bond activation. Even though metal-based catalytic systems have attracted much attention due to their high efficiency, the cost and environmental impact are significant drawbacks in most cases. In this work, a mild, green, and low-cost alternative approach based on I₂ mediation has been developed to implement DA on substituted unsaturated cyclic ketones under ambient conditions (1 atm and 60 °C). It was demonstrated that the reaction mechanism is significantly influenced by the solvent. Briefly, product selectivity could vary between alkyl phenol ether or phenol depending on the choice of solvent, which usually occurred in alcohols. Additionally, the reaction efficiency of the DA reaction also differs due to the varying polarity of the applied polar or non-polar solvents, which affects the yield of phenol. It should be noted that the reaction mechanism associated with product selectivity has been different in existing studies and remains unclear.

Even though solvent choice is an essential factor in the field of organic synthesis, its role, apart from being a medium, has often been neglected, especially in iodine catalysis. Iodine chemistry has developed as an important branch of organic chemistry, but many researchers have habitually overlooked the interaction between solvent and iodine. Meanwhile, the dehydrogenation of cyclic unsaturated ketones to aromatics is highly significant for the development of value-added chemicals; however, the core mechanism remains a mystery since the reaction was first proposed. In this research project, we made numerous efforts through experiments, characterizations, and theoretical simulations to elucidate the mechanism. The solvent effect was investigated via UV-Vis observations, which confirmed the reactive iodine species. Moreover, based on time-resolved proton nuclear magnetic resonance (¹H-NMR), DFT calculations, and mass spectrometric analyses, we established a unified mechanism to account for the differences in product selectivity in various common solvents, including alcohols, polar solvents, and water.

Through substrate scope examination and desorption electrospray ionization–mass spectrometry (DESI-MS), we discovered the formation of a carbocation intermediate, which has been overlooked in previous studies for many years. Specifically, we observed a carbon shift for certain substrates during the DA reaction, leading us to hypothesize the formation of a carbocation, which is a short-lived intermediate during the reaction. We successfully captured the carbocation using a positively charged microdroplet produced by electrospraying H₂O at high voltage. The expanded substrate scope study coupled with spectroscopic observation provided strong evidence to elucidate the formation mechanism and location of the carbocation. Based on this valid evidence, we confirmed the dehydrogenation site on the cyclic ketones and elucidated the most stable carbocation structure that should form during the DA reaction, marking a breakthrough for the aromatization of cyclic ketones. With a renewed understanding of the reaction mechanism, we achieved the DA of several substituted cyclic ketones, realizing a phenolic product yield of 17–96% and a phenol ether product yield of 34-80% while controlling the selectivity. Moreover, some aqueous-friendly reactants could undergo DA in H₂O, achieving 95–96% aromatized product yield at temperatures below the boiling point of water.