Premium
Electron ionisation induced fragmentation of ethyl 5(1 H )‐oxo‐ and 7(1 H )‐oxo‐1‐aryl‐2,3‐dihydroimidazo[1,2‐ a ]‐pyrimidine‐6‐carboxylates: evidence for an unusually regioselective rearrangement of M +• ions
Author(s) -
Ovcharenko Vladimir V.,
Pihlaja Kalevi,
Matosiuk Dariusz
Publication year - 2001
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.535
Subject(s) - chemistry , fragmentation (computing) , electron ionization , aryl , mass spectrum , mass spectrometry , ion , medicinal chemistry , metastability , ionization , polyatomic ion , stereochemistry , computational chemistry , photochemistry , organic chemistry , chromatography , alkyl , operating system , computer science
The 70‐eV electron ionisation (EI) mass spectra of the title compounds show clear differences between the 5‐oxo and 7‐oxo isomers due to regioselective fragmentations involving the ester function. Exceptionally abundant metastable peaks due to molecular ions fragmenting to [M −CO 2 ] +· were observed exclusively for the 7‐oxo isomers, suggesting that the sufficiently long‐lived molecular ions undergo a slow rearrangement preceding this fragmentation reaction. The results are contrasted to the available literature data on the ester group fragmentations involving the loss of CO 2 and the EI mass spectrometry of pyrimidone β‐oxo esters. A reaction mechanism is proposed for the elimination of CO 2 following ethyl group migration to the pyrimidone carbonyl oxygen. Copyright © 2001 John Wiley & Sons, Ltd.