A novel rearrangement in the gas phase under electron ionization for 3-glycosyl-5-aryl-2-isoxazolines

Some 3-glycosyl-5-aryl-2-isoxazolines were studied in the gas phase under e lectron ionization (EI) conditions in order to elucidate their behavior. Th ese derivatives showed an interesting rearrangement involving opening of th e heterocyclic ring with a concomitant ring closing to afford a new isoxazo line derivative. The first step of this reaction was the less common cleava ge of the heterocyclic C(5)-O bond. The 5-aryl substituent was responsible for the pseudobenzylic stabilization of the new isoxazoline derivative. EI tandem mass spectrometry and EI high-resolution mass spectrometry allowed t he elucidation of fragmentation pathways. Copyright (C) 1999 John Wiley & S ons, Ltd.