Author Spotlight of CCS Chemistry ——中科院上海有机化学研究所 刘国生研究员

Q1: Who helped you the most as you pursued your research career?

Prof. Liu:  My Ph.D. advisor, Prof. Xiyan Lu, introduced me to the world of organometallic chemistry, especially the field of OMCOS. My postdoc advisor, Prof. Shannon Stahl, has also been very important for my academic career. From him, I received solid training on mechanistic investigations and analysis. My study of carbonylative polymerization with Prof. Li Jia greatly broadened my horizons in chemistry. My experiences in different research areas not only provided me with valuable and indispensable tools to tackle important research problems, but also built up my confidence to move to research areas completely new to me.

Q2: What are some difficult challenges you have faced during your research career? How did you overcome them?

Prof. Liu:  In the early stage of my independent career, we explored amination-based difunctionalization of alkenes via hypervalent palladium chemistry. At the time, we wanted to develop the enantioselective version by employing different chiral ligands. To our disappointment, we found that these reactions were all inhibited by the added nitrogen-containing ligands, including pyridine-oxazoline (Pyox) ligands that are commonly used in oxidative amination. This issue troubled us for a long time. After our continuous efforts on mechanistic elucidation and reaction optimizations, we finally discovered that introducing sterically bulky groups to the C-6 position of the pyridine in Pyox could significantly improve the reactivity of palladium towards alkene activation, resulting in the development of a series of successful asymmetric intramolecular amination reactions. These newly designed Pyox ligands have been equally successful in palladium-catalyzed asymmetric intermolecular difunctionalizations of simple alkenes, including both terminal and internal alkenes. We are currently facing new challenges in the field of radical chemistry, such as site-selective hydrogen atom transfer and asymmetric radical control. Our research team will strive to address these challenges through our mechanism-guided approach.

Q3: Who is(are) scientist(s) you most respect or admire? Why?

Prof. Liu:  I have great respect to Prof. Jay K. Kochi. He was an incredibly talented physical organic chemist, and he made invaluable contributions to transition-metal-catalyzed cross-coupling transformations with electron-transfer processes and radical species as intermediates. Although many were largely overlooked by the synthetic community at the time, the fundamental reactivity of organic radicals in the transition-metal catalysts he examined has kept inspiring the development of innovative cross-couplings in modern research, including the research in my group.

Q4: What do you see as the biggest obstacles and most promising applications in your research area?

Prof. Liu: Site-selective and enantioselective functionalization of C–H bonds have been recognized as a long standing research problem which has great potential not only in direct transformation of simple hydrocarbons to fine chemicals, but also for the discovery of new organic materials and new drugs. Designing efficient, transition metal-based catalytic systems that are compatible with hydrogen atom transfer (HAT)-based radial processes is the biggest obstacle in the field, particular building catalytic systems with high efficiency and practical utility. It should be noted that enzymes are extremely effective in catalyzing these reactions. Perhaps we can take inspiration from the nature when it comes to catalyst design.

Q5: What advice do you have for younger students and researchers beginning their careers in chemistry, and in particular those interested in your field?

Prof. Liu: During the exploration of new catalytic methods, my younger students and coworkers often paid more attention to screening reaction conditions only to improve the yield, but seldom thought about the underlying principles for the observations. I often tell them that a detailed mechanistic analysis is the key to success, and checking the mass balance of starting materials is also necessary. Meanwhile, I encourage my young colleagues to tackle important and contemporary scientific problems.

Q6: Thank you for publishing your superb work in CCS Chemistry!  Could you provide a brief summary of your article and current research direction in a few sentences?

Prof. Liu: Our research interest focuses on the highly selective C(sp3)–H bond functionalization, particularly on the site-selectivity and enantioselectivity of the reactions. In this paper, we report an efficient catalytic system for benzylic C–H bond thiocyanation via copper-catalyzed radical relay. The reaction exhibits the exquisite benzylic selectivity with C–H substrates as limiting reagents. The resulting benzyl thiocyanates are readily converted to other pharmaceutically important motifs, including isothiocyanate, thiourea, and others, providing a new approach to covert simple alkylarenes into various valuable synthons with high efficiency.

Learn more： Chao Jiang, Pinhong Chen, and Guosheng Liu* (刘国生). Copper-Catalyzed Benzylic C–H Bond Thiocyanation: Enabling Late-Stage Diversifications. CCS Chem. 2020, 2, 1884–1893.

Link: https://doi.org/10.31635/ccschem.020.202000435

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