The title compounds are the 3-ethyl, (I), and 3-isopropyl, (II), derivatives of (1-methyl-2,6-diphenylpiperidin-4-ylidene)amino phenyl carbonate. The main difference in the conformation of the two compounds is the angle of inclination of the phenoxycarbonyl ring with respect to the piperidine ring mean plane, with a dihedral angle of 2.05 (8)° in (I) and 45.24 (13)° in (II).