Conformational studies of some N-acyl-t(3)-isopropyl-r(2), c(6)-bis-(2'-furyl)piperidin-4-ones

Abstract

The high resolution ¹H and ¹³C NMR spectra of four N-acyl-t(3)-isopropyl-r(2),c(6)-bis(2¢-furyl)piperidin-4-ones 1-4 have been recorded at various temperatures and analysed. The spectra reveal the presence of two rotameric forms (E and Z) in solution. ¹H-¹H COSY spectra for 1-4 and ¹H-¹³C COSY spectrum for 4 have been recorded to assist the assignment of the signals for the E and Z isomers of 1-4. Coupling constants predict an equilibrium mixture of boat form B₁ and alternate chair form CA for 1-4. The effect of varying the substituents at nitrogen on the ¹H and ¹³C chemical shifts have been analysed in detail. Mass spectra have also been recorded for 1-5.