- The role of ion/neutral complexes in the fragmentation of N-benzyl-(alkylpyridinium) ions
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N-Benzylpyridinium ions bearing an alkyl group at the pyridine nucleus were studied as potential precursors of gaseous ion/neutral complexes. The occurrence of I/N complexes [C6H5CH2 + ? alkylpyridine] was probed by the reactivity of the potential benzylic hydride donor sites present in the ortho-, meta- and para-alkyl groups (R = methyl, ethyl, isopropyl and benzyl). Collision-induced dissociation of the ions, carried out in an electrical ion cage mass spectrometer, revealed that hydride transfer strongly depends both on the energy requirements of the hydride transfer but also on the position of the hydride donor. Hydride transfer, giving rise to the loss of toluene, was found to occur exclusively with those N-benzylpyridinium ions which bear an isopropyl or a benzyl substituent in the ortho position of the pyridine ring, thus reflecting the intermediacy of I/N complexes. All of the putative hydride donor alkyl groups were found to be non-reactive in the meta and para positions, as were methyl and ethyl groups even in the ortho positions. Density functional calculations (B3LYP/6-311+G/3d,2p)//(B3LYP/6-31+G(d)) on the hydride-transfer and simple-cleavage channels were carried out to help rationalizing these observations. The results suggest that the intra-complex hydride abstraction from the 3- and 4-isopropyl- and from the 3- and 4-benzylpyridine neutrals, although being thermodynamically favorable, is suppressed by substantial intra-complex rotational (or reorientation) barriers.
- Kuck, Dietmar,Grützmacher, Hans-Friedrich,Barth, Dieter,Heitkamp, Sandra,Letzel, Matthias C.
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body text
p. 159 - 166
(2012/07/13)
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- Synthesis of 2,3-disubstituted indoles by radical cyclization with hypophosphorous acid and its application to total synthesis of (±)-catharanthine
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Radical cyclization of o-alkenylthioanilides using hypophosphorous acid and AIBN in the presence of Et3N proceeded smoothly to furnish the corresponding 2,3-disubstituted indoles in high yields. Utilizing the newly developed cyciization condition, a stereocontrolled total synthesis of (±)-catharanthine has been completed.
- Reding, Matthew T.,Kaburagi, Yosuke,Tokuyama, Hidetoshi,Fukuyama, Tohru
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p. 313 - 330
(2007/10/03)
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- Stereocontrolled total synthesis of (±)-catharanthine via radical-mediated indole formation
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(matrix presented) A stereocontrolled total synthesis of (±)-catharanthine, 1, has been completed. The key step involves the radical-mediated cyclization of a highly functionalized intermediate to furnish the corresponding indole. The cyclization utilizes
- Reding, Matthew T.,Fukuyama, Tohru
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p. 973 - 976
(2008/02/09)
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- On the preparation of amine N-oxides by using dioxiranes
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The reaction of heterocyclic aromatic amines, anilines and tertiary amines with dimethyldioxirane (DMD) was examined. Treatment of heterocyclic aromatic amines and anilines with a slight excess of DMD at 0°C afforded the corresponding N-oxides in quantitative conversion yields. In addition, the oxidation was chemoselective in the presence of carbon-carbon double bonds. On the other hand, most of the tertiary amines assayed did afford also quantitative yields of the corresponding N. oxides, although reaction conditions, in particular regarding the amount of DMD required, depended on each substrate. Additional studies carried out on selected substrates suggested that certain N-oxides derived from tertiary amines deactivate DMD.
- Ferrer, Marta,Sanchez-Baeza, Francisco,Messeguer, Angel
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p. 15877 - 15888
(2007/10/03)
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- 2-Cyano-Δ3-piperideines. 12. Stereochemistry of Formation of N-Benzyl-2-cyano-Δ3-piperideines and Facile Isomerization on Alumina to 2-Cyano-Δ4-piperideines. A Potentially General Route to the Synthesis of 2,6-Disubstitute
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The reaction of the piperideine N-oxides 1a-f with trifluoroacetic anhydride in CH2Cl2 at 0 deg C (Polonovski-Potier reaction) led to the formation of the N-benzyl-2-cyano-Δ3-piperideines 3a-f.Epimeric mixtures were obtained for the amino nitri
- Bonin, Martine,Romero, Jose Ricardo,Grierson, David S.,Husson, Henri-Philippe
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p. 2392 - 2400
(2007/10/02)
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