A^1,3 interaction and conformational preference in some <i>N</i>-acetyl-2-phenyl-<i>trans</i>-decahydroquinolin-4-ones

Abstract

A^1,3 type strain is demonstrated directly by the nuclear magnetic resonance studies (¹H and ¹³C NMR) on the <i>N</i>-acetyl derivatives of 2-phenyl-<i>trans</i>-decahydroquinolin-4-ones <b>5-8</b>. In compounds <b>5-8</b> the bulky phenyl group is forced to assume axial orientation due to a severe A^1,3 interaction in equatorial position. The ring torsional angles about C₍₂₎<i> </i>–C₍₃₎ bond and Karplus constants have been determined using <b>DAERM</b> method. The calculated torsional angles in the N-acetyl derivatives are significantly higher than that in the normal chair conformation and thus confirm the nonchair (twist-boat) conformation of the heterocyclic ring with diaxial orientation of phenyl and alkyl groups in <i>N</i>-acetyl derivatives.