Abstract: An efficient stereorational total synthesis of (f)-porantherine (l), the major alkaloid isolated from Poranthera corymbosa, is described. The synthesis features two stereospecific Mannich-type condensations. Novel dialkylpiperidine 20 is prepared by the addition of 2 equiv of 5-lithio-2-pentanone 2', 2'-dimethylpropylene ketal (19) to 0-methylvalerolactim. Porantherine is obtained in 31% overall yield.
