On-surface multicomponent Povarov reaction examined by paper spray mass spectrometry

Abstract

Povarov multicomponent reaction (MCR) is an acid-catalyzed process that uses three distinct classes of reactants. i. e. an aldehyde, aniline, and activated alkene. We employ paper spray ionization mass spectrometry (PS-MS) as a convenient platform for investigating the on-surface Povarov reaction using the following suitable prototype starting reactants: the tag-charged aldehyde 1, 4-bromoaniline, 2,3-dihydrofuran, and formic acid. The PS(+)-MS revealed, besides the formation of the Povarov product (a tetrahydroquinoline compound), the transitional imine. Moreover, the oxonium intermediate was also detected as the water and formic acid adducts. Other alkenes (2,3-dihydropyran and styrene), acid catalysts (acetic acid and p-sulfonic acid calix[4]arene), and aldehydes (4-nitrobenzaldehyde, 4-anisaldehyde, 4-methoxycinnamaldehyde, citronellal, and valeraldehyde) were employed to verify the reaction generality. We observed that styrene (an unactivated alkene), p-sulfonic acid calix [4] arene (an acid with a non-nucleophilic conjugated base), and aromatic aldehydes (4-nitrobenzaldehyde and 4-anisaldehyde) showed lower reactivity than the other reactants. In conclusion, an exciting possibility emerges as PS-MS can be widely employed to investigate similar on-surface organic reactions to verify the connections between the on-surface and condensed phase processes.