The conformational analysis of saturated heterocycles. Part XXXVIII. N-alkylpiperidine and N-alkylmorpholine N-oxides

Abstract

Some N-methyl- and N-t-butyl-piperidine and morpholine N-oxides are prepared. The N-oxide group shows a strong preference for the axial position compared with N-methyl as shown by n.m.r. chemical shifts and coupling constants. The N-oxides are highly hygroscopic and this hinders dipole-moment studies. The orientation of the N-oxidation of 1-methyl-4-p-nitrophenylpiperidine proceeds preferentially at the axial position in agreement with previous results.