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Concise and stereocontrolled total syntheses of (+)-castanospermine and N-acetylneuraminic acid methyl ester were achieved from diastereomerically enriched anti,syn,syn-1,3-oxazine and anti,syn,anti-1,3-oxazine, respectively. The key step in this strategy was the stereoselective BF3·OEt2-mediated allylation.

We report the first total synthesis of (−)-kopsifoline A and (+)-kopsifoline E. Our synthetic strategy features a biogenetically inspired regioselective C17-functionalization of a versatile intermediate containing the pentacyclic core of aspidosperma alkaloids. The vinylogous urethane substructure of this intermediate affords (−)-kopsifoline D via C3−C21 bond formation under the Mitsunobu reaction conditions, while it enables selective C17-functionalization en route to (−)-kopsifoline A and (+)-kopsifoline E.

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Total syntheses of (–)-7-epi-alexine and (+)-alexine were achieved by using stereoselective allylation via a functionalized pyrrolidine obtained from an extended chiral 1,3-oxazine. The synthetic strategies include pyrrolidine formation via oxazine cleavage and diastereoselective allylations of a pyrrolidine aldehyde. (–)-7-epi-Alexine and (+)-alexine were synthesized from anti,syn,anti-oxazine in 12 steps.