The fragmentation mechanism of beta-(N-alkyl/arylamino)-alpha,beta-unsaturated carboxylates under electrospray ionization conditions.

The positive ion mass spectrometric behavior of six beta-(N-alkyl/arylamino)-alpha,beta-unsaturated carboxylates, alpha-(1-alkyl/arylaminoethylidene)-gamma-lactones, has been studied under electrospray ionization conditions. Their fragmentation pathways are described and supported by tandem mass spectrometry. The protonated compounds are apt to eliminate a water, and a water plus a oxacyclopent-2-yne molecule. Some of the compounds show a tendency to undergo a four-membered ring contraction rearrangement to lose a carbon dioxide. The fragmentation patterns of these compounds exhibit a strong substituent dependency.