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.