Transannular Diels–Alder/1,3-Dipolar Cycloaddition Cascade of 1,3,4-Oxadiazoles: Total Synthesis of a Unique Set of Vinblastine Analogues

A powerful tandem [4 + 2]/[3 + 2] cycloaddition cascade of 1,3,4-oxadiazoles initiated by a transannular [4 + 2] cycloaddition is detailed. An impressive four rings, four carbon–carbon bonds, and six stereocenters are set on each site of the newly formed central six-membered ring in a cascade thermal reaction that proceeds at temperatures as low as 80 °C. The resulting cycloadducts provide the basis for the synthesis of unique analogues of vinblastine containing metabolically benign deep-seated cyclic modifications at the C3/C4 centers of the vindoline-derived subunit of the natural product.