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1.4.1.3 Reduction of Pyridine Derivatives

DOI: 10.1055/sos-SD-226-00082

Chen, Z.-P.; Zhou, Y.-G.Science of Synthesis: Catalytic Reduction in Organic Synthesis, (20171157.

As an approach for the synthesis of important piperidine products, the reduction of pyridines has attracted considerable interest for a long time. In general, heterogeneous catalytic hydrogenation of pyridine derivatives is usually carried out in acidic media, as protonation activates the pyridine toward hydrogenation and suppresses catalyst poisoning by the resulting products. Adamsʼ catalyst [platinum(IV) oxide] and palladium on carbon are most frequently employed, exhibiting broad substrate scope under low hydrogen pressure, although rhodium on carbon is effective for pyridin-3-ol and nicotinamide.[‌19‌] As shown in Table 1, pyridines bearing pyrazole (entry 1)[‌20‌] or indole moieties (entry 2)[‌21‌] are selectively hydrogenated to the piperidine derivatives using Adamsʼ catalyst either in acidic media or through prior conversion of the pyridines into their hydrochloride salts. Reducible functionalities such as alkynes (entry 3)[‌22‌] or nitro groups (entry 4)[‌23‌] are reduced during the hydrogenation, whereas a more resistant functionality such as an ester (entry 5)[‌24‌] remains intact.

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References