Synthetic studies on furanoheliangolides. Stereocontrolled construction of the oxygen-bridged tricyclic framework

Abstract

The heavily functionalized 6,9-epoxycyclodeca[b]furan-11-ones 34 and 37 have been prepared in 13 steps from 4-methyl-2-[(phenylmethoxy)methyl]furan. The key elements of the scheme include a high-pressure Diels-Alder cycloaddition to 1-cyanovinyl acetate, highly regiselective hydroboration, controlled stepwise oxidation to give keto aldehyde 20, and thermal oxy-Cope rearrangement of both 32 and 36b. The prior introduction of a phenylthio substituent provides for the accommodation of different levels of unsaturation at a more advanced stage of furanoheliangolide construction