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Volumn 125, Issue 49, 2003, Pages 15191-15199

An Evaluation of Amide Group Planarity in 7-Azabicyclo[2.2.1]heptane Amides. Low Amide Bond Rotation Barrier in Solution

Author keywords

[No Author keywords available]

Indexed keywords

DENSITY FUNCTIONAL THEORY;

EID: 0344236075     PISSN: 00027863     EISSN: None     Source Type: Journal    
DOI: 10.1021/ja036644z     Document Type: Article
Times cited : (111)

References (89)
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    • note
    • Some of the data have been presented in ref 12a.
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    • note
    • The two angle parameters, θ and α, are not independent. On the basis of the structural data shown in Table 1, θ showed a high correlation with α (regression coefficient, r = 0.92).
  • 45
    • 0345471161 scopus 로고    scopus 로고
    • note
    • -3.
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    • note
    • The parameters of the single-crystal X-ray diffraction structure of the monocyclic piperidine amide 8d (X = Cl) were also determined: θ = 358.1°, α = 168.2°, and \τ\ = 9.5° (see ref 31). The magnitudes of deviation of θ and α are similar to those of pyrrolidine amides. As indicated by the magnitudes of the α and \τ\ values, the piperidine amide (8d) is a pyramidal amide with enhanced twisting (see ref 35). The B3LYP/6-31G* optimized structure of N-benzoylpiperidine 8a also exhibited slight nitrogen-pyramidalization and apparent twisting of the amide bond: θ = 356.3°, α = 162.0°, and \τ\ = 15.7°.
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    • note
    • -3.
  • 62
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    • note
    • The significantly low rotational barrier of the six-membered piperidine N-benzoylamide (8a, 15.3 kcal/mol, the coalescence temperature method) is consistent with values previously obtained (see ref 36a). As proposed previously (see ref 36b-d), this small rotational barrier is likely to be due to 1,3-allylic strain between equatorial protons of the piperidine ring and ortho-protons of the phenyl ring or the oxygen atom of the amide in the ground state: this strain destabilizes the ground-state structure, leading to a reduction of the energy gap with the rotational TS. This allylic strain leads to twisting of the amide bond, resulting in nitrogen-pyramidalization (see ref 30).
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    • ≠ for 5e in this method is consistent with that previously obtained by a different line shape analysis (see ref 27).
  • 73
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    • note
    • p + constants (Figure 6) are as follows: 1a-g, 0.94: 2a-e, 0.95; 4a-e, 0.97; 5a-g, 0.98; 6a-e, 0.98; 7a-e, 0.89.
  • 75
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    • In the case of aziridine amides, the inversion barrier exceeds the amide rotational barrier in magnitude. (a) Anet, F. A. L.; Osyany, J. M. J. Am. Chem. Soc. 1967, 89, 352-356.
    • (1967) J. Am. Chem. Soc. , vol.89 , pp. 352-356
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    • note
    • We also studied single-crystal X-ray diffraction structures (Supporting Information) of two N-acetyl-7-azabicyclo[2.2.1]heptane derivatives, N-acetyl-endo-2,3-di(methoxycarbonyl)-7-azabicyclo[2.2.1]heptane (K), and N-acetyldibenzo-7-azabicyclo[2.2.1]heptadiene (L). The structural parameters are as follows: θ = 344.2(3)°, α = 146.7°, and \τ\ = 4.2(5)° for K; θ = 357.8-(3)°, α = 168.0°, and \τ\ = 0.2(8)° for L (see Supporting Information). We thus confirmed that these compounds exhibit nitrogen-pyramidalization in the solid state.
  • 80
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    • note
    • The calculated (B3LYP/6-31G*) twist angles \τ\ were as follows: 1a, 18.3°; 1h, 6.2°; 1i, 4.0°; 5a, 8.6°; 5h, 0.5°; 5i, 0.2°; 7a, 11.0°; 7h, 2.5°; 7i, 1.5°. This reduction of the \τ\ values depending on the N-substituent can be interpreted in terms of relief of the allylic strain with decrease in the size of the substituent.
  • 81
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    • The combination of the effects of twisting of the amide bond and nitrogen pyramidalization would modulate the reactivities of the amide. For example, the acceleration of hydrolysis of amides was recently computationally studied: Lopez, X.; Mujika, J. I.; Blackburn, G. M.; Karplus, M. J. Phys. Chem. A 2003, 107, 2304-2315.
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    • Lopez, X.1    Mujika, J.I.2    Blackburn, G.M.3    Karplus, M.4
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    • Bond Model for Molecules and Transition States Program. Inagaki, S.; Ikeda, H. J. Org. Chem. 1998, 63, 7820-7824. See also: (a) Inagaki, S.; Kawata, H.; Hirabayashi, Y. Bull. Chem. Soc. Jpn. 1982, 55, 3724-3732.
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    • Bond Model for Molecules and Transition States Program. Inagaki, S.; Ikeda, H. J. Org. Chem. 1998, 63, 7820-7824. See also: (a) Inagaki, S.; Kawata, H.; Hirabayashi, Y. Bull. Chem. Soc. Jpn. 1982, 55, 3724-3732.
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    • note
    • T values, and is optimized to give the maximum value of the coefficient of the ground configuration.


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.