γ-Spiroketal γ-Lactones from 2-(γ-Hydroxyalkyl)furans: Syntheses of epi-Pyrenolides D and Crassalactone D

Photooxygenation of 2(gamma-hydroxyalkyl)furans followed by dehydration affords, in one synthetic operation and in high yield, gamma-spiroketal gamma-lactones. This newly developed technology was successfully applied to the synthesis of three different epimers of pyrenolide D, as well as to the first synthesis of the anticancer natural product crassalactone D and its C4-epimer.