Quinolizidines. XIV. A racemic synthesis of 9-demethyltubulosine, an alkaloid isolated from Alangium vitiense

The first total synthesis of the Alangium vitiense alkaloid 9-demethyltubulosine (1) has been achieved in the form of a racemic modification through a"lactim ether route, " which included the intermediates (±)-7,(±)-8,(±)-10,and (±)-9. The 1\u27α-Hisomers (±)-12 and (±)-11 were also produced through this synthetic route. On the other hand, the nonconformity of synthetic (±)-1 with another (-)-demethyltubulosine from A. lamarckii indicated the alternative 10-demethyl structure (2) to be correct for the A. lamarckii alkaloid. The assignments of the configuration at C-1\u27 of (±)-1,(±)-9,(±)-11,and (±)-12 were based on four criteria, namely, the ratio of products from the catalytic reduction of (±)-10,thin-layer chromatographic mobility, and ^1H and ^C nuclear magnetic resonance spectral features