formaldehyd
methyl 3,4-cis-N-methyl-4-phenylpiperidine-3-carboxylate
(+/-)-6-oxo-4t-phenyl-piperidine-3r-carboxylic acid ethyl ester
methyl 3,4-trans-N-methyl-4-phenylpiperidine-3-carboxylate
(+/-)-1-methyl-4t-phenyl-piperidine-3r-carboxylic acid ethyl ester