Synthesis of novel series of 7,7′-(substituted methylene)bis-imidazo[1,2-b]pyrazoles via an acid catalyzed one-pot three-component reaction†
An efficient and rapid synthesis of new series of N-alkyl-2-aryl-5H-imidazo[1,2-b]pyrazoles has been achieved in high yields through a three-component reaction of 3-amino-4-substituted pyrazoles, aromatic aldehydes and isocyanides mediated by acid catalysts. In addition, a novel and straightforward approach to a sequential one-pot multicomponent reaction has been developed for the synthesis of hitherto undescribed 7,7′-(substituted methylene)bis-imidazo[1,2-b]pyrazoles, starting from 3-amino-5-substituted (or unsubstituted) pyrazoles, various aldehydes and isocyanides. The reaction was performed under mild conditions in the presence of inexpensive zirconium(IV) chloride as a catalyst. A library of 22 products was obtained in moderate to good yields.