The Multicomponent Hantzsch Reaction: Comprehensive Mass Spectrometry Monitoring Using Charge‐Tagged Reagents

A novel strategy for the ESI-MS monitoring of re- action solutions involving the alternate use of permanently charge-tagged reagents has been used for comprehensive mass spectrometry monitoring of the multicomponent Hantzsch 1,4-dihydropyridine reaction. By placing a charge tag on either, or both, of the two key reactants, ion suppres- sion effects for ESI were eliminated or minimized, and com- prehensive detection of charge-tagged intermediates was achieved. The strategy allowed the trapping and characteri- zation of the important intermediates in the mechanism for 1,4-dihydropyridine formation.