Carbamic acid, N-[(3S,5S,6R)-6-methyl-2-oxo-5-phenyl-3-piperidinyl]-, 1,1-dimethylethyl ester Carbamic acid, N-[(3R,5S,6R)-6-methyl-2-oxo-5-phenyl-3-piperidinyl]-, 1,1-dimethylethyl ester