The and 13C NMR spectra of cocaine (1), pseudococaine (2), allococaine (3), allopseudococaine (4), and the hydrochloride salts of 1, 2, and 4 have been recorded. The conformation of the piperidine ring in all four isomers, including the orientation of the IV-methyl substituent, was determined from analysis of the data. Vicinal, geminal, and long-range coupling constants strongly suggest a chair conformation for the piperidine ring of all the compounds studied. Comparison of the and 13C chemical shift data suggests that 2 and 4 have a larger population of axial IV-methyl substituents than 1 and 3, respectively. Improved procedures for the synthesis of 2, 3, and 4 are reported. In particular, a stereoselective route to 4 is presented.
Natural abundance carbon‐13 chemical shifts are reported for the hydrochloride salts of phencyclidine (1a) and twelve analogs substituted in the piperidine and aromatic rings. The signals are assigned on the basis of chemical shift theory, SFORD multiplicities, signal intensities, and comparisons with related compounds.
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