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1. A highly efficient metal-free protocol for the synthesis of linear polydicyclopentadiene

   https://doi.org/10.1039/D1PY00191D  

   Yang, Xuejin; Murphy, Laura M.; Haque, Farihah M.; Grayson, Scott M.; Boydston, Andrew J. (May 2021, Polymer Chemistry)

   We have developed a highly efficient synthesis of linear polydicyclopentadiene (pDCPD)viaphotoredox mediated metal-free ring-opening metathesis polymerization (MF-ROMP) and investigated theT_g–M_ndependence of linear pDCPD. 

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2. A droplet microfluidic platform for high-throughput photochemical reaction discovery

   https://doi.org/10.1038/s41467-020-19926-z  

   Sun, Alexandra C.; Steyer, Daniel J.; Allen, Anthony R.; Payne, Emory M.; Kennedy, Robert T.; Stephenson, Corey R. (December 2020, Nature Communications)

   null (Ed.)

   Abstract The implementation of continuous flow technology is critical towards enhancing the application of photochemical reactions for industrial process development. However, there are significant time and resource constraints associated with translating discovery scale vial-based batch reactions to continuous flow scale-up conditions. Herein we report the development of a droplet microfluidic platform, which enables high-throughput reaction discovery in flow to generate pharmaceutically relevant compound libraries. This platform allows for enhanced material efficiency, as reactions can be performed on picomole scale. Furthermore, high-throughput data collection via on-line ESI mass spectrometry facilitates the rapid analysis of individual, nanoliter-sized reaction droplets at acquisition rates of 0.3 samples/s. We envision this high-throughput screening platform to expand upon the robust capabilities and impact of photochemical reactions in drug discovery and development. 

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3. Nickel nanoparticles supported on multi-walled carbon nanotubes; versatile catalyst for Suzuki cross-coupling reactions in batch and continuous flow

   Coker, Katherine A; Winkleman, Harlee; Siamaki, Ali R (October 2023, American Chemical Society (ACS))

   NA (Ed.)

   Metal catalyzed carbon-carbon bond forming reactions have rapidly become one of the most effective tools in organic synthesis for the assembly of highly functionalized molecules. These reactions have typically been carried out under homogeneous reaction conditions, which require the use of ligands to solubilize the catalyst and broaden its window of reactivity. However, the use of these catalysts under homogeneous conditions has limited their commercial viability due to product contamination as a direct result of inability to effectively separate the catalyst from the reaction product. Ligand-free heterogeneous catalysis presents a promising option to address this problem as evidenced by the significant increase in research activity in this area. We have recently developed a simple, one-step method for the preparation nickel nanoparticles supported on multi-walled carbon nanotubes (Ni/MWCNTs) under mechanical shaking in a ball-mill. The preparation method is very fast and straightforward which does not require any chemicals, solvents, or additional ligands. The as-prepared nanoparticles demonstrated remarkable catalytic activities in Suzuki cross-coupling reactions of the functionalized aryl halides and phenylboronic acids in batch with high turnover number in a single catalytic reaction. Batch operations have several inherent limitations that include reproducibility, scalability, and reactor productivity. Continuous flow chemistry has been considered as an alternative approach in academic and industrial processes due to its efficient and innovative synthetic design. Due to the low level of leaching observed in batch reactions as well as remarkable recyclability, the Ni/MWCNTs nanoparticles demonstrated remarkable catalytic activity in Suzuki coupling reactions with a diverse range of functionalized aryl halides and phenyl boronic acids under continuous flow conditions. Further optimization of the method including the reaction time, temperature, required solvents, flow rate, and minimum residence time will be discussed in this presentation. 

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4. An Ion‐Pairing Approach to Stereoselective Metal‐Free Ring‐Opening Metathesis Polymerization

   https://doi.org/10.1002/anie.202016393  

   Yang, Xuejin; Gitter, Sean R.; Roessler, Allison G.; Zimmerman, Paul M.; Boydston, Andrew J. (June 2021, Angewandte Chemie International Edition)

   Abstract Stereochemistry can have a profound impact on polymer and materials properties. Unfortunately, straightforward methods for realizing high levels of stereocontrolled polymerizations are often challenging to achieve. In a departure from traditional metal‐mediated ring‐opening metathesis polymerization (ROMP), we discovered a remarkably simple method for controlling alkene stereochemistry in photoredox mediated metal‐free ROMP. Ion‐pairing, initiator sterics, and solvation effects each had profound impact on the stereochemistry of polynorbornene (PNB). Simple modifications to the reaction conditions produced PNB withtransalkene content of 25 to >98 %. Highciscontent was obtained from relatively larger counterions, toluene as solvent, low temperatures (−78 °C), and initiators with low Charton values. Conversely, smaller counterions, dichloromethane as solvent, and enol ethers with higher Charton values enabled production of PNB with hightranscontent. Data from a combined experimental and computational investigation are consistent with the stereocontrolling step of the radical cationic mechanism proceeding under thermodynamic control. 

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5. Asymmetric Transfer Hydrogenation of Heterocyclic Compounds in Continuous Flow Using an Immobilized Chiral Phosphoric Acid as the Catalyst

   https://doi.org/10.1055/a-2085-5256  

   Zhelavskyi, Oleksii; Jhang, Yin-Jia; Nagorny, Pavel (July 2023, Synthesis)

   Abstract This manuscript describes transfer hydrogenation of bicyclic nitrogen-containing heterocyclic compounds using the immobilized chiral phosphoric acid catalyst (R)-PS-AdTRIP in batch and continuous flow. A significant improvement in enantioselectivities is achieved in continuous flow with a fluidized bed reactor packed with (R)-PS-AdTRIP when the flow rate is increased from 0.2 mL/min to 2.0–2.5 mL/min. The optimized continuous flow conditions consistently provide 4–6% ee higher selectivity than transfer hydrogenation in batch with 2 mol% of (R)-PS-AdTRIP, and are used to generate multiple chiral products with the same fluidized bed reactor. 

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