Conformational studies of some 5,9-dimethyl-6,7-benzomorphan diastereoisomers and related compounds

The proton magnetic resonance characteristics of some α/β diastereoisomeric 5,9-dimethyl-6,7-benzomorphans are reported for free base, hydrohalide, and methiodide forms, and differences between α- and β-signals are interpreted in terms of the piperidine ring fragment of the β-salts adopting skew-boat conformations. The steric course of quaternization of benzomorphan isomers is discussed from results of alkylations using trideuteriomethyl iodide and other experiments. A possible correlation between conformational and potency differences in analgesically active benzomorphan diastereoisomers and related compounds is discussed.