- Benzylic Ammonium Ylide Mediated Epoxidations
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A high yielding synthesis of stilbene oxides using ammonium ylides has been developed. It turned out that the amine leaving group plays a crucial role as trimethylamine gives higher yields than DABCO or quinuclidine. The amine group also influences the diastereoselectivity, and detailed DFT calculations to understand the key parameters of these reactions have been carried out.
- Roiser, Lukas,Robiette, Rapha?l,Waser, Mario
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supporting information
p. 1963 - 1968
(2016/08/10)
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- Gas-phase chemistry of benzyl cations in dissociation of N-Benzylammonium and N-benzyliminium ions studied by mass spectrometry
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In this study, the fragmentation reactions of various N-benzylammonium and N-benzyliminium ions were investigated by electrospray ionization mass spectrometry. In general, the dissociation of N-benzylated cations generates benzyl cations easily. Formation of ion/neutral complex intermediates consisting of the benzyl cations and the neutral fragments was observed. The intra-complex reactions included electrophilic aromatic substitution, hydride transfer, electron transfer, proton transfer, and nucleophilic aromatic substitution. These five types of reactions almost covered all the potential reactivities of benzyl cations in chemical reactions. Benzyl cations are well-known as Lewis acid and electrophile in reactions, but the present study showed that the gas-phase reactivities of some suitably ring-substituted benzyl cations were far richer. The 4-methylbenzyl cation was found to react as a Bronsted acid, benzyl cations bearing a strong electron-withdrawing group were found to react as electron acceptors, and parahalogen- substituted benzyl cations could react as substrates for nucleophilic attack at the phenyl ring. The reactions of benzyl cations were also related to the neutral counterparts. For example, in electron transfer reaction, the neutral counterpart should have low ionization energy and in nucleophilic aromatic substitution reaction, the neutral counterpart should be piperazine or analogues. This study provided a panoramic view of the reactions of benzyl cations with neutral N-containing species in the gas phase. American Society for Mass Spectrometry, 2012.
- Chai, Yunfeng,Wang, Lin,Sun, Hezhi,Guo, Cheng,Pan, Yuanjiang
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experimental part
p. 823 - 833
(2012/09/07)
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- EFFECTS OF SUBSTITUENTS IN THE BENZYL BROMIDE ON THE KINETICS OF THE BENZYLATION OF AMINES
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The kinetics of the reactions of 3- and 4-substituted benzyl bromides with amines having various structures in nitrobenzene at 40 deg C were investigated.The 4-substituted benzyl bromides have higher reactivity compared with that calculated on the basis of the linear correlations according to the Hammett-Taft equation for unsubstituted and 3-substituted benzyl bromides containing electron-withdrawning substituents.The reactivity of benzyl bromides containing electron-donating substituents obeys a linear correlation with the ?+ constants.The effects of structural changes in the substrate and the nucleophile on the character of the transition states of the investigated reactions is discussed.
- Shpan'ko, I. V.,Korostylev, A. P.,Rusu, L. N.
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p. 1715 - 1723
(2007/10/02)
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- α-Deuterium Isotope Effects in Benzyl Halides. 2. Reaction of Nucleophiles with Substituted Benzyl Bromides. Evidence for a Change in Transition-State Structure with Electron-Donating Substituents
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Rates and α-D isotope effects have been determined for the following substrates and nucleophiles: p-methoxybenzyl bromide (Et3N, SCN-, N3-, OH-, S2O32-) benzyl bromide (Et3N, SCN-, N3-, OH-, S2O32-), and p-nitrobenzyl bromide (Et3N, SCN-, N3-, S2O32-).In nearly all cases the second-order rate constant for each nucleophile goes though a minimum for the unsubstituted compound while the α-D isotope increases monotonically in the sequence p-NO2>p-H>p-OCH3.These results are consistent with an increasing "looseness" of the SN2 transition state as the substituent on the aromatic ring becomes more electron donating.
- Vitullo, V.P.,Grabowski, J.,Sridharan, S.
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p. 6463 - 6465
(2007/10/02)
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