Study of short-lived and early reaction intermediates in organocatalytic asymmetric amination reactions by ion-mobility mass spectrometry†
Reactive solvent-assisted electrospray ionization coupled to ion-mobility mass spectrometry (reactive SAESI-IM-MS) was used to study the reactive intermediates in organocatalytic asymmetric amination reactions. The transient intermediates including two isomers of carbinolamine and iminium species in the early stage of enamine formation and previously unrecognized triazane species appearing before the formation of iminium intermediates 6 were successfully intercepted and characterized by reactive SAESI-IM-MS. Moreover, the ratio of Z- and E-enamine intermediates in situ was obtained rapidly and accurately by IM-MS. Thus, a more clear and detailed landscape for understanding the mechanisms of organocatalytic asymmetric amination reactions and the origin of enantioselectivity was given, which demonstrates the remarkably increased ability of reactive SAESI-IM-MS in detecting and characterizing reaction intermediates.