A research team led by Ke-Yin Ye and Yuqi Lin at Fuzhou University developed an electrochemically mediated dearomatization saturation strategy, successfully achieving chemo, regio, and stereoselective multifunctionalization reactions of pyridine. This strategy provides an efficient synthetic route for the one-step construction of complex three-dimensional piperidine skeletons with four convertible functional groups. Mechanistic studies show that cyanogen bromide generated in situ by electrochemical processes can initiate the dearomatization of pyridine, thereby generating a dihydropyridine intermediate. This intermediate, through intramolecular anodic carbon effects and CH···π interactions, synergistically regulates the stereochemical selectivity of the subsequent electrochemical ortho-bifunctionalization process, thus achieving highly selective transformation. The article was published as an open access Research Article in CCS Chemistry , the flagship journal of the Chinese Chemical Society.
Background information:
The " escape from planarity " strategy is gaining increasing importance in contemporary drug development, as it can effectively improve the clinical success rate of candidate compounds. Pyridine, as one of the most common heterocyclic aromatic skeletons in drug molecules, can be transformed from a planar aromatic structure into a three-dimensional piperidine system. This not only significantly improves solubility and bioavailability but also enables specific recognition and binding to target proteins by introducing chiral centers, thereby enhancing the drug potential and therapeutic efficacy of the compound.
Transition metal-catalyzed hydrogenation is one of the most direct methods for synthesizing polysubstituted piperidines, but its harsh reduction conditions often make it incompatible with reduction-sensitive functional groups. In contrast, synthetic electrochemistry can achieve complex chemical transformations under mild conditions by precisely controlling potential and current, demonstrating significant synthetic potential. This technology uses electrons as clean redox reagents, generating and immediately consuming highly reactive intermediates in situ during the reaction, thus avoiding reagent accumulation and side reactions. This embodies the atom economy and precise process control emphasized in green synthesis.
Highlights of this article :
Under mild electrochemical reaction conditions, the authors successfully constructed a series of multi-substituted piperidine structures. Substrate suitability studies showed that both aryl and alkyl substituents participated readily in the reaction, yielding the target products in good to excellent yields with diastereoselectivity. By adjusting the current, the precise introduction of different halogen atoms, such as chlorine and bromine, could be achieved. Notably, bromine-substituted piperidine products typically exhibited a higher diastereomeric proportion than their corresponding chlorinated counterparts, and the bromination conditions showed good compatibility with various heterocyclic structures. All the obtained piperidine products possess the potential for further drug modification.
Furthermore, the authors experimented with other alcohol substrates, finding that only ethanol reacted successfully with an 88% yield and a 92:8 dr; the other alcohols failed to yield products. GC-MS analysis of the reaction system confirmed that the electrochemically generated BrCN was the key active species driving the dearomatization of pyridine. Further research showed that other alcohols were unable to effectively activate TMSCl/TMSBr and TMSCN in the system , thus failing to release sufficient Cl⁻/Br⁻ and CN⁻ to generate BrCN, leading to reaction failure. Based on this, by adding BrCN as a reagent, the efficient conversion of other alcohol substrates was successfully achieved.
Subsequently, the reaction proceeded smoothly at a scale of 10 mmol, yielding 2.12 g of product with a separation yield of 76%, demonstrating its good scalability. Based on this gram-level product, the authors further conducted functional group derivatization studies, successfully achieving selective transformation of multiple sites on the piperidine skeleton, including the C3 halogen, C6 methoxy group, and N-cyano group. The corresponding derivatized products all maintained high diastereoselectivity, showcasing the flexibility and practicality of this structure in medicinal chemical modification.
In terms of mechanistic studies, the authors first synthesized 1-methoxyisoquinoline-2(1H)-nitrile via a model reaction of isoquinoline and BrCN. This compound could be readily converted to the corresponding product under standard reaction conditions, thus confirming that the addition of pyridine to BrCN to form 1,2-dihydropyridine is the key intermediate in the reaction. Further density functional theory calculations showed that the intramolecular anodic effect and CH···π interaction synergistically regulated the attack orientation of the bromine radical. Subsequently, the intermediate underwent electro-oxidative single-electron transfer and methoxy nucleophilic attack steps, ultimately yielding a multi-substituted piperidine product with excellent stereoselectivity.
Summary and Outlook:
In summary, the team led by Ke-Yin Ye and Yuqi Lin at Fuzhou University developed an electrochemically mediated dearomatization saturation strategy for pyridine, achieving highly efficient multifunctional modification of pyridine. The functionalized three-dimensional piperidine structures obtained by this method carry multiple convertible functional groups and can be efficiently synthesized into various downstream compounds through subsequent derivatization. Mechanistic studies reveal that the addition reaction of pyridine with electrochemically generated in-situ cyanogen bromide to the dearomatization intermediate 1,2-dihydropyridine is the key step in this strategy; this intermediate exhibits excellent chemo, regio, and stereoselectivity in subsequent functionalization processes. This electrochemically driven dearomatization saturation strategy provides a new pathway for the synthesis of structurally complex nitrogen-containing heterocycles and drug-related molecules.
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About the journal: CCS Chemistry is the Chinese Chemical Society’s flagship publication, established to serve as the preeminent international chemistry journal published in China. It is an English language journal that covers all areas of chemistry and the chemical sciences, including groundbreaking concepts, mechanisms, methods, materials, reactions, and applications. All articles are diamond open access, with no fees for authors or readers. More information can be found at https://www.chinesechemsoc.org/journal/ccschem .
About the Chinese Chemical Society: The Chinese Chemical Society (CCS) is an academic organization formed by Chinese chemists of their own accord with the purpose of uniting Chinese chemists at home and abroad to promote the development of chemistry in China. The CCS was founded during a meeting of preeminent chemists in Nanjing on August 4, 1932. It currently has more than 120,000 individual members and 184 organizational members. There are 7 Divisions covering the major areas of chemistry: physical, inorganic, organic, polymer, analytical, applied and chemical education, as well as 31 Commissions, including catalysis, computational chemistry, photochemistry, electrochemistry, organic solid chemistry, environmental chemistry, and many other sub-fields of the chemical sciences. The CCS also has 10 committees, including the Woman’s Chemists Committee and Young Chemists Committee. More information can be found at https://www.chinesechemsoc.org/ .
CCS Chemistry
10.31635/ccschem.026.202507069
Experimental study
Not applicable
Chemo-, Regio-, and Stereoselective Electrochemical Dearomative Multifunctionalization of Pyridines
13-Feb-2026
There is no conflict of interest to report.