Novel Synthetic Access to Para-Quinones Via Direct Electrochemical Oxidation

Abstract

Equipped with unique and straightforward tunable redox properties quinones find manifold applications ranging from bio-active compounds to material science.[1] Current state of the art synthesis still resorts to stoichiometric amounts of problematic chemical oxidizing agents and noble catalysts adding to the growing environmental strain by depletion of scarce resources.[2] In order to overcome this challenge, we have developed novel and scalable protocols for the synthesis of para-quinones applicable to readily available, inexpensive phenols and benzaldehydes.[3] In advancement of previous methods, the oxidation is performed free of catalyst, mediator, or terminal oxidizing agent, effectively minimizing waste. Electricity serves as a sustainable, reagent-free oxidant and enables excellent selectivity. Effortless scalability is ensured by the development of a flow protocol, which is operable at mild, ambient conditions. The novel protocols provide quinones in yields up to 99% and possess high synthetical utility through tolerance of a wealth of functional groups, including halogens, fulfilling the prerequisite for facile late-stage modification. The scalability of the reaction was proven on a gram-scale without corrosion in yield. Moreover, the versatility of the method was demonstrated by successful extension of the protocol to generate value-added quinones from the biopolymer lignin.Literature:[1] a) E. J. Son, J. H. Kim, K. Kim, C. B. Park, J. Mater. Chem. A 2016, 4, 11179; b) L. A. Sazanov, Nat. Rev. Mol. Cell Bio. 2015, 16, 375.[2] a) R. Yoshida, K. Isozaki, T. Yokoi, N. Yasuda, K. Sadakane, T. Iwamoto, H. Takaya, M. Nakamura, Org. Biomol. Chem. 2016, 14, 7468; 19, b) K. Omura, Synthesis 1998, 1998, 1145.[3] F. Sprang, J. D. Herszman, S. R. Waldvogel, Green Chem. 2022, 24, 5116–5124. Figure 1