identical methyl groups remain inequivalent in the course of an n-propyl⇄isopropyl isomerization operative in Fe+ -mediated dehydration of propanols. The reversibility of the β-hydrogen transfer steps is addressed by examination of the H/D equilibration in metastable complexes of Fe+ with a set of selectively deuterated propanols by using tandem mass spectrometry.
Lithium Hexamethyldisilazide-Mediated Enolization of Acylated Oxazolidinones: Solvent, Cosolvent, and Isotope Effects on Competing Monomer- and Dimer-Based Pathways
作者:Gabriel J. Reyes-Rodríguez、Russell F. Algera、David B. Collum
DOI:10.1021/jacs.6b11354
日期:2017.1.25
hydrocarbon cosolvent (hexane versus toluene) and to isotopic labeling. Four mechanisms corresponding to monosolvated monomers, trisolvated dimers, octasolvated monomers, and octasolvated dimers were identified. Even under conditions in which the LiHMDS monomer was the dominant observable form, dimer-based metalation was significant. The mechanism-dependent isotope and cosolvent effects are discussed in the
A practical and environmentally friendly protocol for synthesis of α‐deuterated carboxylic acids
作者:Johan Wennerberg、Klaus Dreisch
DOI:10.1002/jlcr.4021
日期:——
α-deuterated carboxylicacids have been synthesized from the corresponding malonic acids via hydrogen/deuteriumexchange and decarboxylation in presence of D2O. The method is general, mild and efficient and does not require organic solvents or other additives. Yields range between 83% and 94% and purification was not necessary. Starting materials were easy accessible and the α-deuterated carboxylicacids may
1,3,5-Cycloheptatriene (1) and various 7-alkyl-1,3,5-cycloheptatrienes (3, 6, 9, 13, and 16-19) were subjected to gas-phase protonation under Cl(CH4) and Cl(iC(4)H(10)) conditions and the MIKE spectra of their [M + H](+) ions were measured Loss of CH, from the parent ion [1 + H](+) and almost exclusive loss of C2H4 from the methyl derivative [3 + H](+) indicate ring contraction of the dihydrotopylium ions to protonated toluene (toluenium ions) and protonated ethylbenzene (ethylbenzenium ions), respectively, prior to fragmentation. With increased exothermicity of protonation, ions [3 + H](+) also isomerize to xylenium ions. Similarly, higher protonated n-alkylcycloheptatrienes undergo skeletal isomerization to the corresponding "chain-elongated" (n + 1)-alkylbenzenium and to the corresponding n-alkyltoluennium ions. Starting with ethyldihydrotropylium ions, a competing isomerization channel is opened giving rise to expulsion of C2H4 from the constituents of the seven-membered ring, as evidenced bg deuterium labelling and an unusually high kinetic energy release, Isoalkyl analogues behave in a similar manner with increased hydrogen exchange between the alpha position of the side chain and the ring. Copyright (C) 1999 John Wiley & Sons, Ltd.