Zwitterionic Imidazolium Salt: Recent Advances in Organocatalysis

Abstract

Imidazole-based zwitterionic-type molten salts have been explored as a new class of organocatalyst in various chemical transformations. It is known that imidazolium motifs provide an unconventional C–H bond for bonding. It is experimentally proven that C2–H of the imidazole moiety plays a crucial role in catalyzing the reaction via electrophilic activation. This review is based on the role of imidazole-based zwitterionic-type molten salts as an organocatalyst for some useful chemical transformations in organic synthesis. One of the most important features of this catalyst is that it can easily be recovered from the reaction media. The recovered catalyst can be reused for subsequent reactions without losing its catalytic activity significantly. 1 Introduction 2 Zwitterionic-type Molten Salt Catalyzed <i>syn</i>-Selective Aza-Henry Reaction 3 Synthesis of 1-(Amidoalkyl)- and 1-(Carbamatoalkyl)-2-naphthols 4 Synthesis of 3-Aminoalkylated Indoles 5 Synthesis of Highly Substituted Imidazoles 6 Synthesis of 5-Substituted 1<i>H</i>-Tetrazoles by the Cycloaddition of Arenecarbonitriles with Sodium Azide 7 Synthesis of 4-Arylidene-2-phenyloxazol-5(4<i>H</i>)-ones 8 Zwitterion-Promoted Ethylene Methoxycarbonylation 9 Synthesis of 5,6-Unsubstituted 1,4-Dihydropyridines 10 Regioselective Ring Opening of Aziridines 11 Conclusions