Cycloalkene budding: mass spectrometric studies of competitive and dual cycloalkene extrusion reactions from doubly unsaturated aldehyde N,N-dimethylhydrazones.
Mass spectral fragmentation pathways of four doubly unsaturated aldehyde N,N-dimethylhydrazones were investigated using EI-MS and tandem mass spectrometry (MS/MS) under electron ionization and collisionally activated decomposition (CAD) conditions. Cyclopentene extrusion was found to be slightly favored over cyclohexene loss in a hydrazone capable of losing either cycloalkene. Evidence for the regeneration of a chain-shortened iminium radical cation as a result of cycloalkene extrusion was provided by studying substrates capable of undergoing successive cycloalkene budding sequences. EI-MS of these compounds shows sequential loss of both cyclopentene and cyclohexene, in accord with expectations for a cascade mechanism. Although these MS/MS experimental results are also compatible with alternative mechanisms which would entail the simultaneous loss of both neutral cycloalkenes or of a macrocyclic diene, a rapid cascade of cycloalkene budding accounts best for the experimental observations.
Weibel
D B
DB
Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, USA.
Attygalle
A B
AB
Shevy
L E
LE
Meinwald
J
J
D000475:Alkenes / Q000737:chemistry*; D003500:Cyclization; D008401:Gas Chromatography-Mass Spectrometry; D006835:Hydrazones / Q000138:chemical synthesis* / Q000737:chemistry; D007202:Indicators and Reagents; D009682:Magnetic Resonance Spectroscopy
D000475:Alkenes; D006835:Hydrazones; D007202:Indicators and Reagents