Stereochemistry of isomeric 1,2,5-trimethyl-4-phenylpiperidin-4-ols: a 1H nuclear magnetic resonance study

Abstract

Some ¹H n.m.r. spectral features of three diastereoisomeric 1,2,5-trimethyl-4-phenylpiperidin-4-ols are reported and shown to provide evidence of the configurations t-2-Me,c-5-Me,r-4-OH (γ-isomer), t-2-Me,t-5-Me-r-4-OH (β-isomer), and c-2-Me,t-5-Me,r-4-OH (α-isomer). Evidence is given that significant skew-boat populations (with the 4-phenyl group pseudoequatorial) arise in the case of the α-alcohol as solute in deuteriochloroform, while preferred conformations of the γ- and β-isomers are piperidine chairs with the 4-phenyl group equatorial. Stable epimeric conjugate acids of the β-hydrochloride were detected in deuterium oxide. Present findings are compared with those of previous studies.