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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
major conformers
minor conformers
energy barrier
semiempirical MO calculations
Issue Date: Sep-2006
Publisher: CSIR
Series/Report no.: Int. Cl.<sup>8</sup> C07D
Abstract: The preferred conformations of N-acyl derivatives of 2,2,4-trimethyl-1<i style="">H</i>-tetrahydro-1,5-benzodiazepines <b style="">6-9</b> have been studied using NMR spectral techniques. In the case of N<sub>1</sub>,N<sub>5</sub>-diformyl derivative <b style="">9,</b> there is an equilibrium between the boat <b style="">BE</b> and chair <b style="">CE</b> conformations in which the two N-CO groups at N<sub>1</sub> and N<sub>5</sub> adopt <i style="">endo</i> and <i style="">exo</i> orientation, respectively. The average energy barrier for the interconversion between the <i style="">major</i> (<b style="">BE</b>) and <i style="">minor</i> (<b style="">CE</b>) conformers of <b style="">9</b> has been found to be 79.7 kJ/mol on the basis of the dynamic <sup>1</sup>H NMR spectral studies. The N<sub>5</sub>-benzoyl- and N<sub>5</sub>-phenylcarbamoyltetrahydrobenzodiazepines <b style="">6</b> and <b style="">7</b> prefer boat conformations <b style="">BE</b> with <i style="">exo</i> orientation of the N-CO groups. The X-ray crystal structure of <b style="">7</b> also shows the boat conformation <b style="">BE</b> with the <i style="">exo</i> orientation of the N-CO group. The diacetyl derivative <b style="">8</b> prefers a boat conformation <b style="">BE</b> in which the N-acetyl group at N<sub>1</sub> is predominantly at the <i style="">endo</i> position while that of N<sub>5</sub> is at <i style="">exo</i> orientation. The semiempirical molecular orbital calculations (<b style="">AM1</b> and <b style="">PM3</b>) support the conformational preferences derived from the NMR results.
Description: 2059-2070
ISSN: 0975-0983(Online); 0376-4699(Print)
Appears in Collections:IJC-B Vol.45B(09) [September 2006]

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