16855-95-1Relevant academic research and scientific papers
Pyrylium salts in polyene natural product synthesis: organometallic additions to 4-methylpyrylium tetrafluoroborate
Taylor, Richard J. K.,Hemming, Karl,Medeiros, Edna Faria De
, p. 2385 - 2392 (2007/10/02)
The synthetic utility of organometallic additions to pyrylium salts as a procedure for the stereocontrolled preparation of 2Z,4E-dienals, and the use of these compounds in polyene natural product synthesis, is summarised.The extension of this methodology to 4-methylpyrylium tetrafluoroborate to give a new route to 3-methyl-2Z,4E-dienals via a six-carbon organometallic homologation procedure is then described.Finally, the utilisation of this methodology to provide a concise synthetic approach to 13Z-retinal, retinal and a range of retinal analogues is then elaborated.
Isomerization and Fragmentation of Methylfuran Ions and Pyran Ions in the Gas Phase
Spilker, Ruediger,Gruetzmacher, H.-F.
, p. 459 - 466 (2007/10/02)
The mutual interconversion of the molecular ions +. of 2-methylfuran (1), 3-methylfuran (2) and 4H-pyran (3) before fragmentation to + ions has been studied by collisional activation spectrometry, by deuterium labelling, by the kinetic energy release during the fragmentation, by appearance energies and by a MNDO calculation of the minimum energy reaction path.The electron impact and collisional activation mass spectra show clearly that the molecular ions of 1-3 do not equilibrate prior to fragmentation, but that mostly pyrylium ions + arise by the loss of a H atom.This implies an irreversible isomerization of methylfuran ions 1 and 2 into pyran ions before fragmentation, in contrast to the isomerization of the related systems toluene ions/cycloheptatriene ions.Complete H/D scrambling is observed in deuterated methylfuran ions prior to the H/D loss that is associated with an isotope effect kH/kD=1.67-2.16 for metastable ions.In contrast, no H/D scrambling has been observed in deuterated 4H-pyran ions.However, the loss of a H atom from all metastable +. ions gives rise to a flat-topped peak in the mass-analysed ion kinetic energy spectrum and a kinetic energy release (T50) of 26+/-1.5 kJ mol-1.The MNDO calculation of the minimum energy reaction path reveals that methylfuran ions 1+. and 2+. favour a rearrangement into pyran ions before fragmentation into furfuryl ions, but that the energy barrier of the first rearrangement step is at least of the same height as the barrier for the dissociation of pyran ions into pyrylium ions.This agrees with the experimental results.
