Assembly of Substituted 3-Aminoindazoles from 2-Bromobenzonitrile via a CuBr-Catalyzed Coupling/Condensation Cascade Process
摘要:
CuBr-catalyzed coupling reaction of 2-halobenzonitriles with hydrazine carboxylic esters and CuBr/4-hydroxy-L-proline-catalyzed coupling reaction of 2-bromobenzonitriles with N'-arylbenzohydrazides proceed smoothly at 60-90 degrees C to provide substituted 3-aminoindazoles through a cascade coupling/condensation (or coupling/deacylation/condensation) process. A wide range of 3-aminoindazoles with substituents at both the 1-position and the phenyl ring part can be prepared from the corresponding coupling partners.
A practical and efficient base mediated synthesis of free 3-aminoindazoles has been developed from the reaction of nitriles with hydrazines, which successfully overcomes the difficulty of using aromatic hydrazines as substrates and allows for the synthesis of a wide range of N-aryl substituted free 3-aminoindazoles in moderate to excellent yields under mild conditions in one-pot. This finding provides