A(1,3) interaction and conformational preference in some N-acetyl-2-phenyl-trans-decahydroquinolin-4-ones

A(1,3) type strain is demonstrated directly by the nuclear magnetic resonan ce studies (H-1 and C-13 NMR) on the N-acetyl derivatives of 2-phenyl-trans -decahydroquinolin-4-ones 5-8. In compounds 5-8 the bulky phenyl group is f orced to assume axial orientation due to a severe A(1,3) interaction in equ atorial position. The ring torsional angles about C-(2)-C-(3) bond and Karp lus constants have been determined using DAERM method. The calculated torsi onal 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 a nd alkyl groups in N-acetyl derivatives.