Total synthesis of natural (-)- and ent-(+)-4-desacetoxy-6,7-dihydrovindorosine and natural and ent-minovine: Oxadiazole tandem intramolecular Diels-Alder/1,3-dipolar cycloaddition reaction

摘要

[GRAPHICS]Efficient and unusually concise total syntheses of both enantiomers of the Aspidosperma alkaloids 4-desacetoxy-6,7-dihydrovindorosine (12) and minovine (1) are detailed. A tandem intramolecular Diels-Alder/1,3-dipolar cycloaddition reaction of the 1,3,4-oxadiazole 8, in which three new rings, four new C-C bonds, and five stereocenters are formed, is a key step in the sequence. The availability of optically active material permitted an assessment of the enantiomeric integrity of minovine and the source of its reported unusual optical rotation.