Nucleophilic addition to 1,2,2,6,6-pentamethyl-3,5-dimethylene-4-piperidone

Like branched primary amines, unbranched mercaptans react with 1,2,2,6,6-pentamethyl-3,5-dimethylene-4-piperidone to give products of ring opening. On the basis of the data obtained, a reaction scheme that includes the intermediate formation of 3,7-diazabicyclo(3.3.1)nonan-9-one seems less likely as compared with a scheme involving elimination from the monocyclic piperidene system. It is also shown that steric interaction of the vicinal substituents is one of the important factors that promote beta elimination. The PMR spectra of solutions of the compounds in CDCl3 were recorded with Varian T-60 and Varian HA-100 spectrometers with hexamethyldisiloxane (HMDS) as the standard. The chemical-ionization mass spectra were obtained with a Finnigan 4021 mass spectrometer.