Syntheses of cis- and trans-Jamtine and Their N-Oxides via a Benzyl Configuration-Inversion Approach

A novel synthesis of the tetrahydroisoquinoline alkaloid jamtine and its epimer is reported. The synthetic strategy hinges on a one-pot conjugate reduction/Robinson cyclization sequence and an efficient benzyl configuration inversion by an oxidation/reduction approach. The N-oxide derivatives of the jamtine isomers were also synthesized and identified by X-ray crystallographic analysis. Additionally, a density functional theory calculation for the four possible N-oxide structures was exploited to gain further insight into the structure of the natural product in comparison to those of the synthetic N-oxides, because the NMR data of the synthetic derivatives did not match those reported for natural jamtine N-oxide.