2‐Hydroxypyridines as N‐ and O‐Nucleophiles in Organic Synthesis

2‐Hydroxypyridines have emerged as versatile nucleophiles in organic synthesis. The N ‐ and O ‐functionalization of 2‐hydroxypyridines affords straightforward and practical methods for the construction of N ‐substituted 2‐pyridones and O ‐substituted 2‐hydroxypyridines, which are important structural motifs in numerous natural products, pharmaceuticals and biologically active compounds. Nonetheless, the competition between N ‐ and O ‐functionalization of 2‐hydroxypyridines presents an inevitable and formidable challenge. In the past few decades, chemoselective N ‐ and/or O ‐functionalization of 2‐hydroxypyridines has received extensive attention from the synthetic community, resulting in the development of elegant and effective strategies to address this chemoselectivity. This review provides a summary of recent advancements in the realm of transition‐metal and organo‐catalyzed, as well as visible‐light promoted chemoselective functionalization of 2‐hydroxypyridines, including N ‐alkylation, N ‐allylation, N ‐arylation, N ‐alkenylation, O ‐alkylation, O ‐allylation, O ‐arylation, and O ‐alkenylation.