Mt. Crimmins et al., SYNTHETIC STUDIES ON THE GINKGOLIDES - TOTAL SYNTHESIS OF (+ -)-BILOBALIDE/, Journal of the American Chemical Society, 115(8), 1993, pp. 3146-3155
Two syntheses of the C15 ginkgolide, bilobalide, are presented. One ap
proach results in a formal synthesis by intersecting an intermediate i
n the Corey synthesis, while a second approach results in a completed
total synthesis which is considerably shorter than the first. Both app
roaches rely on a stereoselective intramolecular [2 + 2] photocycloadd
ition to control much of the stereochemistry. A diastereoselective ald
ol condensation serves to establish the relative stereochemical relati
onship between the secondary and tertiary alcohols in the second appro
ach. This circumvents problems of incorporation of the tertiary carbin
ol which were encountered in both previous approaches.