It is reported that an allene dienophilecan initiate a tandemintramolecular [4 + 2]/[3 + 2] cycloaddition cascade of 1,3,4-oxadiazoles,that the intermediate cross-conjugated 1,3-dipole (a carbonyl ylide)can participate in an ensuing [3 + 2] dipolar cycloaddition in a remarkablyeffective manner, and that the reaction can be implemented to providethe core pentacyclic ring system of vindoline. Its discovery improvesa previous total synthesis of (−)-vindoline and was used ina total synthesis of (+)-4-epi-vindoline and (+)-4-epi-vinblastine that additionally enlists an alternativeseries of late-stage transformations. [ABSTRACT FROM AUTHOR]