Hypervalent Iodine Catalysis via Halogen‐Bonding Activation: Achieving Record Turnover Numbers

Comprehensive Summary Hypervalent iodine reagents have emerged as versatile and environmentally benign tools in modern organic synthesis, enabling diverse transformations under mild reaction conditions. Despite their remarkable synthetic utility, these reagents are typically employed in stoichiometric amounts, and catalytic versions using hypervalent iodine species remain underdeveloped. Herein, we report a hypervalent iodine(III) reagent, (phenyliodonio)sulfamate ( PISA ), that acts as an efficient halogen‐bond donor for the catalytic Knorr pyrazole synthesis. This method exhibits good functional group compatibility and allows for the efficient synthesis of a wide range of N‐ acyl‐ and N‐ sulfonyl‐substituted pyrazole derivatives under mild conditions. Mechanistic studies, including isolation and characterization of key intermediates, kinetic profiling, as well as DFT calculations, reveal that PISA plays a dual role in this reaction: it activates acetylacetone via halogen‐bonding interactions to accelerate cyclization, and critically facilitates the rate‐determining dehydrative aromatization step, ensuring high overall efficiency. Therefore, this catalytic reaction achieves an ultrahigh turnover number (TON) of 12685, which not only sets a new record for hypervalent iodine catalysts in this reaction, but also represents the highest TON value reported for all hypervalent iodine‐catalyzed reactions to date.