Yangxin Jin,Predrag V. Petrovic,Shuquan Huang,Shibdas Banerjee,Abhijit Nandy,Paul T. Anastas,Jason Chun-Ho Lam
Dehydrogenative aromatization (DA) of cyclic ketones is central to the development of functionalized aromatic precursors and hydrogen transfer–related technologies. Traditional DA strategies require precious metals with oxidants and are typically performed at high temperatures (100–150 °C) to overcome the high energy barrier of aliphatic C–H bond activation. Recently, a mild alternative approach based on I2 has been proposed to realize DA on substituted unsaturated cyclic ketones under ambient conditions. However, depending on the solvent, the product selectivity may vary between phenol ether and phenol, and the reaction mechanisms remain unclear. Herein, based on time-resolved proton nuclear magnetic resonance, DFT calculation, and mass spectrometric analyses, we established a unified mechanism to account for the product distribution. Through substrate scope and desorption electrospray ionization–mass spectrometry, we discovered the formation of a carbocation, which has been overlooked in previous studies. An expanded substrate scope study coupled with spectroscopic observation provided strong evidence to elucidate the formation mechanism and the location of the carbocation. With a renewed understanding of the mechanism, we achieved a phenolic product yield of 17–96% while controlling the selectivity. Moreover, some reactants could undergo DA in H2O, achieving 95–96% yield at below water-boiling temperature.
Disproportionation of alcohols to the corresponding alkanes and aldehydes/ketones is an important reaction, especially for biomass valorisation. Previously, we reported for the first time that hydroiodic acid can be used as an efficient catalyst for the alcohol disproportionation reaction, and the interconversion between hydroiodic acid and iodine is the key step for hydrogen transfer. As a continuation of our previous work, this work mainly focused on the mechanistic study involved and studied the difference between hydroiodic acid or molecular iodine as the catalyst for the disproportionation of alcohols. Density Functional Theoretical calculation indicated the oxidation step was a synergistic reaction process through the iodine effect on oxygen-hydrogen bond, which was proved by the characteristic oxygen-iodine bond captured by in-situ Attenuated Total Reflectance Fourier Transform Infrared. A non-polar solvent was preferable for the reaction with iodine. Addition of small amount of water was shown to be beneficial for the reaction, because water promoted Brønsted acidity of hydroiodic acid and accelerated the rate-determining step. Finally, we showed that the system was also applicable to various benzyl, allyl alcohols, and some heterocyclic alcohols. Graphical Abstract
An intramolecular aryl C−H amination reaction has been achieved using molecular iodine as the sole oxidant for the synthesis of benzimidazole derivatives. The required substrates were readily prepared by addition or coupling of arylamines with the corresponding nitriles or aryl iodides. Iodine-mediated oxidative cyclization of these substrates in the presence of potassium carbonate (K 2 CO 3 ) as base afforded the corresponding products in moderate to good yields. The transition metal-free protocol presented here is insensitive to air and operationally simple. This versatile and eco-friendly synthetic methodology is broadly applicable to a variety of N -aryl-substituted amidines and pyridin-2-amines, and provides direct access to both 1 H -benzo[ d ]imidazole and pyrido[1,2- a ]benzimidazole derivatives from the corresponding precursors.
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