摘要:
[GRAPHICS]A diene transmissive cycloaddition strategy for the synthesis of tetracyclic skeletons is described, Initially both L-gulonolactone and L-arabinose were converted independently to related acetal aldehydes 13 and 14, A pentadienyl indium reagent supplied the triene unit for 16. The cisisopropylidene acetal controlled the initial intramolecular [4 + 2] cycloaddition to the decalin 21, and a second (tandem) intermolecular cyclization afforded highly oxygenated nor-steroid and triterpenoid skeletons as chiral nonracemic compounds.