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IJC-B Vol.45B [2006] >
IJC-B Vol.45B(09) [September 2006] >


Title: Stereochemistry of N-acyltetrahydro-1,5-benzodiazepines using NMR spectra, X-ray crystallography and semiempirical MO calculations
Authors: Ponnuswamy, S
Murugadoss, R
Jeyaraman, R
Keywords: 1,5-Benzodiazepine
diformyl
major conformers
minor conformers
benzoyl
phenylcarbamoyl
diacetyl
interconversions
X-ray
energy barrier
semiempirical MO calculations
Issue Date: Sep-2006
Publisher: CSIR
IPC CodeInt. Cl.8 C07D
Abstract: The preferred conformations of N-acyl derivatives of 2,2,4-trimethyl-1H-tetrahydro-1,5-benzodiazepines 6-9 have been studied using NMR spectral techniques. In the case of N1,N5-diformyl derivative 9, there is an equilibrium between the boat BE and chair CE conformations in which the two N-CO groups at N1 and N5 adopt endo and exo orientation, respectively. The average energy barrier for the interconversion between the major (BE) and minor (CE) conformers of 9 has been found to be 79.7 kJ/mol on the basis of the dynamic 1H NMR spectral studies. The N5-benzoyl- and N5-phenylcarbamoyltetrahydrobenzodiazepines 6 and 7 prefer boat conformations BE with exo orientation of the N-CO groups. The X-ray crystal structure of 7 also shows the boat conformation BE with the exo orientation of the N-CO group. The diacetyl derivative 8 prefers a boat conformation BE in which the N-acetyl group at N1 is predominantly at the endo position while that of N5 is at exo orientation. The semiempirical molecular orbital calculations (AM1 and PM3) support the conformational preferences derived from the NMR results.
Page(s): 2059-2070
ISSN: 0975-0983(Online); 0376-4699(Print)
Source:IJC-B Vol.45B(09) [September 2006]

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