Abstract Authentic samples of 1, 3, 3-trimethyl-2-(3, 4, 5-trimethoxyphenyl)-4- methylenepiperidine (Ia) and 2-(p-chlorophenyl)-1, 3, 3-trimethyl-4-methylenepiperidine (Ib) are prepared by Mannich condensation between 4-methyl-1-methylamino-3-pentanone hydrochloride (VI) and an aromatic aldehyde, followed by a Wittig reaction on the resulting 4- piperidone. Comparing the physical and spectroscopic properties of Ia and Ib with those of ...