Abstract
The first enantioselective total synthesis of the hexacyclopropane natural product U-106305, which is produced by Streptomyces sp. UC 11136, is described in full detail. Considerations on the biosynthesis of U-106305 and its close resemblance to the pentacyclopropane bacterial metabolite FR-900848 (10) led to the proposal that its previously unknown stereostructure should be represented as 11. The central C2-symmetrical quinquecyclopropane unit of 11 was assembled by repeatedly using a three-step cyclopropane “homologation” sequence in an efficient bidirectional approach. Desymmetrized quinquecyclopropane 23 was converted to dienol 13 which was monocyclopropanated stereo- and regioselectively to provide hexacyclopropane 25. Deoxygenation was achieved by conversion to thioether 29 and desulfurization. The synthesis was completed by a one-pot deprotection−oxidation−Wittig olefination sequence to give 11. The synthetically derived material was found to be identical in all respects to an authentic sample of U...
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