Synthesis, spectral and computational studies of some N-acyl-t(3)-isopropyl-r(2),c(6)-bis-2′-furylpiperidin-4-one oximes

Four N-acyl-t(3)-isopropyl-r(2),c(6)-bis-2′-furylpiperidin-4-one oximes 1-4 were synthesized and the high resolution 1H and 13C NMR spectra have been recorded at various temperatures and analyzed. The spectra reveal the presence of two rotameric forms (syn and anti) in solution. 1H-1H COSY and 1H-13C COSY spectra have been recorded to assist the assignment of the signals for the syn and anti 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 and at C(4) on the 1H and 13C chemical shifts has been analyzed in detail. The molecular structures of the N-acyl derivatives 1-4 were also determined using AM1 Hamiltonian and the results have been compared to the results derived from spectral studies. Mass spectra have also been recorded for 1-4.