Multicomponent Diversity-Oriented Synthesis of Symmetrical and Unsymmetrical 1,4-dihydropyridines in Recyclable Glycine Nitrate (GlyNO3) Ionic Liquid: A Mechanistic Insight Using Q-TOF, ESI-MS/MS**

Abstract

Multicomponent reactions are eye-catching strategies to generate chemically diverse set of multifunctionalized heterocyclic motifs with high atom economy manner which render the transformations green. These strategies can further become more prolific if catalyst recyclability, compatibility and exploration of exact mechanistic pathway are taken into account. To this end, an inexpensive and recyclable glycine nitrate (GlyNO3) ionic liquid has been efficiently employed to access diversely substituted symmetrical and unsymmetrical 1,4-dihydropyridines up to 93% yields via three and four components respectively. The catalyst recyclability and compatibility to access both symmetrical and unsymmetrical 1,4 DHPs under identical reaction conditions, are added benefits to its practical utility. Furthermore, progress of the reaction was monitored by Q-TOF, direct infusion electrospray ionization mass spectrometry (ESI-MS) and key cationic intermediate involved in reaction have been further identified by tandem MS experiment (Q-TOF, ESI-MS/MS) which served as proof-of-concept to the mechanistic model. This is the first report which revealed that the Hantzsch reaction predominately follow diketone path way among four competing reaction pathways.