Bioinspired Synthesis of Alstoscholarinoids A and B

Biomimetic synthesis can be an attractive approach to
access complex
natural products by addressing challenging structural features through
cascade reactions, which are inferred through tangible biosynthetic
hypotheses. In some instances, the originally proposed structure or
biosynthetic path might be revised through synthesis. In this communication
we report a short and efficient bioinspired synthesis of Alstoscholarinoids
A and B, rearranged triterpenes from the Alstonia scholaris tree. Salient features of the synthesis include a transannular aldol
addition as well as a cascade consisting of a Schenck–Ene reaction,
Hock rearrangement, and aldol addition. This culminated in a revision
of the likely biosynthetic origin of Alstoscholarinoid A and a thorough
exploration of the previously proposed intermediates.