One‐pot Synthesis of Substituted Pyrazoles from Propargyl Alcohols via Cyclocondensation of in situ‐Generated α‐Iodo Enones/Enals and Hydrazine Hydrate

An efficient Bi(OTf)3‐catalyzed transformation of unprotected propargylic alcohols has been developed, affording a general, one‐pot approach to access diverse pyrazoles via sequential iodo‐intercepted Meyer‐Schuster rearrangement, cyclocondensation of NH2NH2 ⋅ H2O and α‐iodo enones/enals generated in situ, and iodine elimination. This transformation tolerates a wide range of substrates and is reliable on a large scale. The high yields and convenient experimental operations make it a valuable method for the construction of pyrazole derivatives. A synthetic route to construct α‐iodo enones/enals and pyrazoles from propargyl alcohols was investigated. The method has the advantages of low catalyst loading, easily obtainable reactants, low cost, simple operation and scale‐up. In this reaction, neither ligands nor bases were used and various substituted pyrazoles could be conveniently obtained in a simple one‐pot process.