- Development of highly regioselective amidyl radical cyclization based on lone pair-lone pair repulsion
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(Chemical Equation Presented) The substituent effect on the reactivity and regioselectivity of N-(4-pentenyl)amidyl radical cyclization was investigated. Exclusive 6-endo cyclization was observed for N-(4-pentenyl)amidyl radicals with internal vinylic heteroatom substitution (Cl, Br, I, OMe, SEt). The substituent on the carbonyl group also showed a significant influence on the reactivity of amidyl radicals, which increases in the order of Ph a result, the photostimulated reactions of N-(4-halopent-4-enyl)amides and carbamates (X = Cl, Br, I) with DIB/I2 or Pb(OAc)4/I 2 led to the efficient and exclusive formation of the corresponding piperidines while those of N-(5-halopent-4-enyl)amides afforded the pyrrolidine products only. The halogen-substitution effect also allowed the 6-exo and 7-endo amidyl radical cyclization to proceed in a highly regioselective manner. The above experimental results, in combination with theoretical analyses, revealed that the lone pair-lone pair repulsion between the nitrogen radical and the vinylic heteroatom played an important role in controlling the regioselectivity of cyclization.
- Yuan, Xinting,Liu, Kun,Li, Chaozhong
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p. 6166 - 6171
(2008/12/22)
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- Eclipsed Conformation of the Exocyclic N-CH2 Bond in N-Neopentylpiperidines and the Stereodynamic Consequences As Studied by Dynamic NMR Spectroscopy and Molecular Mechanics Calculations
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The dynamic stereochemistry of a range of N-neopentylpiperidines 1 with an eclipsed N-CH2-t-Bu bond is compared with that of the corresponding range of N-ethylpiperidines 2 with a gauche N-CH2Me bond. By using dynamic NMR spectroscopy, the relative importance of ring inversion, exocyclic bond rotation, and nitrogen inversion are elucidated and barriers are reported and discussed. Minor populations of the neopentyl-axial-eclipsed conformation are detected directly and identified with the help of molecular mechanics calculations. The corresponding N-alkylpyrrolidines are also reported.
- Anderson, J. Edgar,Ijeh, Anthony I.,Storch, Christine,Casarini, Daniele,Lunazzi, Lodovico
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p. 3310 - 3317
(2007/10/03)
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- NMR Spectra and Stereochemistry of N-Acetyl and N-Benzoyl Derivatives of Solasodine
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N-Acetylation of solasodine gives only one rotameric N-acetyl derivative compared with N-acetyl-3-methylpiperidine, which exists in solution as two equally populated rotamers.The 1H and 13C NMR spectra (CDCl3) of O,N-diacetyl- and O-acetyl-N-benzoylsolasodine indicate significant deviations from F-ring chair geometry.Opening of the F ring of these derivatives in CDCl3 solution at 25 deg C, to give the corresponding furosta-5,20(22)-diene derivatives, was ascertained by NMR spectroscopy.Key Words: Solasodine O,N-Diacetylsolasodine O-Acetyl-N-benzoylsolasodine 3β-Acetoxy-26-acetamidofurosta-5,20(22)-diene 3β-Acetoxy-26-benzamidofurosta-5,20(22)-diene
- Patel, Asmita V.,Blunden, Gerald,Crabb, Trevor A.
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p. 794 - 800
(2007/10/02)
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