Stereodynamics of 9,11-Diphenyl-10-azatetracyclo[6.3.0.0.4,110.5,9]undecanes. Highly Restricted Nitrogen Inversion and Isolated Phenyl Rotation. X-ray Crystallographic, Dynamic NMR, and Molecular Mechanics Studies

Stereodynamics of 9,11-Diphenyl-10-azatetracyclo[6.3.0.0.4,110.5,9]undecanes. Highly Restricted Nitrogen Inversion and Isolated Phenyl Rotation. X-ray Crystallographic, Dynamic NMR, and Molecular Mechanics Studies

The 1H NMR spectra of 10-benzyl-9,11-diphenyl-10-azatetracyclo[6.3.0.0.4,110.5,9]undecane (BnPh 2 ) and 10-methyl-9,11-diphenyl-10-azatetracyclo[6.3.0.0.4,110.5,9]undecane (MePh 2 ) decoalesce due to slowing inversion at nitrogen and to slowing isolated bridgehead phenyl rotation. The high nitrogen...

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Published in:Journal of organic chemistry Vol. 61; no. 13; pp. 4319 - 4327
Main Authors: Gribble, Gordon W, Switzer, Frank L, Bushweller, John H, Jewett, John G, Brown, Jay H, Dion, Jessica L, Bushweller, C. Hackett, Byrn, Marianne P, Strouse, Charles E
Format: Journal Article
Language:English
Published: United States American Chemical Society 26-06-1996
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Summary:The 1H NMR spectra of 10-benzyl-9,11-diphenyl-10-azatetracyclo[6.3.0.0.4,110.5,9]undecane (BnPh 2 ) and 10-methyl-9,11-diphenyl-10-azatetracyclo[6.3.0.0.4,110.5,9]undecane (MePh 2 ) decoalesce due to slowing inversion at nitrogen and to slowing isolated bridgehead phenyl rotation. The high nitrogen inversion barriers in MePh 2 (ΔG ⧧ = 12.2 ± 0.1 kcal/mol at 250 K) and BnPh 2 (ΔG ⧧ = 10.6 ± 0.1 kcal/mol at 215 K) are typical of tertiary amines in which at least one C−N−C bond angle is constrained to a small value. Compared to the minuscule rotation barriers about sp2−sp3 carbon−carbon bonds in simple molecular systems, the bridgehead phenyl rotation barriers in MePh 2 (ΔG ⧧ = 9.8 ± 0.1 kcal/mol at 210 K) and BnPh 2 (ΔG ⧧ = 9.8 ± 0.1 kcal/mol at 210 K) are unusually high. Molecular mechanics calculations (MMX force field) suggest that the origin of the high phenyl rotation barriers lies in the close passage of an o-phenyl proton and a methyl (or benzylmethylene) proton in the transition state. BnPh 2 crystallized from hexane as white needles in the monoclinic system Pn. Unit cell dimensions are as follows:  a = 12.198(1) Å, b = 6.1399(6) Å, c = 14.938(2) Å, β = 107.470(4)°, V = 1067.1(2) Å3, Z = 2. In the crystal molecular structure, the imine bridge CNC bond angle in BnPh 2 is constrained to a small value (96°). The benzylic phenyl group is oriented gauche to the nitrogen lone pair.
Bibliography:istex:ADA706602C94552B6580F5A6C3A77284EC5126AB
Abstract published in Advance ACS Abstracts, June 1, 1996.
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ObjectType-Article-1
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content type line 23
ISSN:0022-3263
1520-6904
DOI:10.1021/jo952185b