Details

Autor(en) / Beteiligte

• 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

Titel

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

Ist Teil von

• Journal of organic chemistry, 1996-06, Vol.61 (13), p.4319-4327

Ort / Verlag

United States: American Chemical Society

Erscheinungsjahr

1996

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• 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.