Selective ion-molecule reactions of 2,5-dimethylpyrrole-γ-butyrolactone with dimethyl ether ions

The use of bimolecular reactions as selective and sensitive diagnostic probes of analytically relevant molcules has undergone rapid development, especially with the increasing availability of ion trapping techniques which allow detailed examination of ion-molecule reactions. In this report, selective ion-molecule reactions of 2,5-dimethylpyrrole-γ-butyrolactone with protonated dimethyl ether and methoxymethylene cations (CH3OCH2 +) are described. A quadrupole ion trap and a triple-quadrupole mass spectrometer are used to examine the bimolecular and dissociation reactions of γ-butyrolactone and 2,5-dimethylpyrrole, both of which are the building blocks of a more complex bicyclic substrate, 2,5-dimethylpyrrole-γ-butyrolactone. All three compounds are protonated by ion-molecule reactions with dimethyl ether ions. The γ-butyrolactone also reacts with CH3OCH2+ to produce [M + 15]+ ions (by methyl cation attachment), whereas 2,5-dimethylpyrrole reacts to form [M + 13]+ ions (by methylene substitution). The bicyclic substrate reacts with CH3OCH2+ to form only the [M + 13]+ adduct, which indicates that the pyrrole ring mediates the reaction chemistry. By comparing the reactions of model compounds and by using collisional-activated dissociation techniques, the site of the methylene substitution reaction was determined to be a double bond of the pyrrole ring.