- Unraveling the Dynamic Network in the Reactions of an Alkyl Aryl Ether Catalyzed by Ni/γ-Al2O3 in 2-Propanol
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The reductive cleavage of aryl ether linkages is a key step in the disassembly of lignin to its monolignol components, where selectivity is determined by the kinetics of multiple parallel and consecutive liquid-phase reactions. Triphasic hydrogenolysis of
- Qi, Long,Chamas, Ali,Jones, Zachary R.,Walter, Eric D.,Hoyt, David W.,Washton, Nancy M.,Scott, Susannah L.
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p. 17370 - 17381
(2019/11/03)
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- An asymmetric synthesis of L-[3-13C]phenylalanine and L-[3- 13C]tyrosine from [13C]carbon monoxide
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L-[3-13C]Phenylalanine and L-[3-13C]tyrosine were synthesized. [α- 13C]Benzyl bromides were prepared from [13C]carbon monoxide via the palladium-catalyzed carboalkoxylation of aryl halides. The asymmetric carbon corresponding to the 2-position in phenylalanine was introduced by the diastereoselective alkylation of Dellaria's oxazinone with [α-13C]benzyl bromides. Finally, ethanolysis, deprotection, hydrogenolysis and acid hydrolysis of the resulting alkylated oxazinones gave L-[3- 13C]phenylalanine and L-[3-13C]tyrosine in high optical purity.
- Takatori, Kazuhiko,Nishihara, Mikiko,Nishiyama, Yukie,Kajiwara, Masahiro
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p. 15861 - 15869
(2007/10/03)
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- Shapes of dendrimers from rotational-echo double-resonance NMR
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The solid-state shape, size, and intermolecular packing of a fifth-generation dendritic macromolecule were determined by a combination of site-specific stable-isotope-labeling, rotational-echo double-resonance (REDOR) NMR and distance-constrained molecula
- Wooley, Karen L.,Klug, Christopher A.,Tasaki, Kenzabu,Schaefer, Jacob
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- Aromatic Rearrangements in the Benzene Series. Part 4. Intramolecularity of both the ortho- and para-Rearrangements of Benzyl Phenyl Ether as shown by Labelling Experiments
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The rearrangement of a mixture of Ph13CH2OPh and PhCH218OPh (with some unlabelled ether) catalysed by AlBr3 in homogeneous solution in 1,2,4-trichlorobenzene and in nitrobenzene has been examined.The literature report of this reaction was shown to be substantially correct: the reaction is very rapid, and ortho-migration of the benzyl group predominates, but does not (in contrast to the earlier report) occur exclusively.The ortho : para ratio of the rearrangement products is ca. 11 in 1,2,4-trichlorobenzene and ca. 4.7 in nitrobenzene.The ether undergoes rearrangement in both solvents without prior scrambling of isotopic labels.In trichlorobenzene, the reaction appears to be almost completely intramolecular, even for para-rearrangement: o-benzylphenol is unscrambled, the para-isomer almost so.In nitrobenzene, o-benzylphenol is virtually unscrambled, the para-isomer ca. 25percent so.A mechanism involving a tight ion-pair (from which some leakage occurs in nitrobenzene) is proposed, and possible explanations of the high ortho : para ratios are considered.
- Hart, Lionel S.,Waddington, Catherine R.
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p. 1607 - 1612
(2007/10/02)
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- Degenerate Carbon Skeleton Isomerization of the Cyclopentyl Cation in the Gas Phase. Experimental and Theoretical Evidence for the Existence of a Pyramidal C5H9(+) Cation as an Intermediate in the Unimolecular Ethylene Elimination
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The investigation of 13C2-labelled isotopomeric bromocyclopentanes (5a, b), cyclobutylmethyl bromide (6a) and 5-bromo-1-pentenes (7a, b) clearly demonstrates, that unimolecular ethylene loss from the gaseous + ions generated from both the cyclic and acyclic precursors is preceded by complete carbon scrambling.Whereas the degenerate isomerization 8a 8b can, in principle, proceed either via the bisected cyclobutylmethyl cation 9 or via the non-classical, pyramidal cation 3, the MINDO/3 calculations reveal, that ethylene loss from C5H9+ involves 3 as an intermediate.From 3 a transition state is reached which can be regarded as a partially opened cyclopropyl cation "solvated" by interaction with C2H4.Descriptions of the syntheses of the 13C2-labelled bromides are given.
- Franke, Wilfried,Schwarz, Helmut,Thies, Helga,Chandrasekhar, Jayaraman,Raque' Schleyer, Paul von,et al.
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p. 2808 - 2824
(2007/10/02)
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