The expanding utility of continuous flow hydrogenation

• Peter J. Cossar ^a
• Lacey Hizartzidis ^a
• Michela I. Simone ^a
• Adam McCluskey ^*a
• Christopher P. Gordon ^*b

• ^* Corresponding authors ^a Centre for Chemical Biology, Chemistry Building, School of Environmental and Life Science, The University of Newcastle, University Drive, Callaghan, Australia
• ^b Nanoscale Organisation and Dynamics Group, School of Science and Health, University of Western Sydney, Locked Bag, Penrith, Australia

There has been an increasing body of evidence that flow hydrogenation enhances reduction outcomes across a wide range of synthetic transformations. Moreover flow reactors enhance laboratory safety with pyrophoric catalysts contained in sealed cartridges and hydrogen generated in situ from water. This mini-review focuses on recent applications of flow chemistry to mediate nitro, imine, nitrile, amide, azide, and azo reductions. Methodologies to effect de-aromatisation, hydrodehalogenation, in addition to olefin, alkyne, carbonyl, and benzyl reductions are also examined. Further, protocols to effect chemoselective reductions and enantioselective reductions are highlighted. Together these applications demonstrate the numerous advantages of performing hydrogenation under flow conditions which include enhanced reaction throughput, yields, simplified workup, and the potential applicability to multistep and cascade synthetic protocols.

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