Abstract
A novel bis-iodurated polyether compound, based on an unprecedented tetra-THF backbone, has been isolated as a trace by-product of the oxidation of squalene with the catalytic system RuO2(cat.)/NaIO4. The double erythro configuration of the central portion of the molecule furnishes the first indirect support of the previously postulated pathway operating in the oxidative pentacyclization of the isoprenoid substrate. A bidirectional double oxidative bis-cyclization is invoked to explain the formation of this compound. The isolated substance was successfully subjected to a double rearrangement-ring expansion to give a novel bis-THF-bis-THP compound.
Highlights
Some years ago we discovered a novel cascade process catalysed by RuO4 generated in situ by the action of NaIO4 on RuO2, the pre-catalytic species employed to generate RuO4 [1]
Previous studies from our group had demonstrated that the oxidation of both linear and isoprenoid polyenes constantly furnishes poly-THF compounds possessing threo inter-THF
We have previously demonstrated that progressive structural simplification of compound 1 to small-sized poly-THF compounds can be achieved via an iterative PCC-mediated oxidative cleavage/reduction [7] sequence
Summary
Some years ago we discovered a novel cascade process catalysed by RuO4 generated in situ by the action of NaIO4 on RuO2, the pre-catalytic species employed to generate RuO4 [1]. This is a unique process by which a poly-THF backbone, made up of adjacently linked THF rings, can be built-up in a single step and in a stereoselective manner starting from polyenes characterized by a repetitive. Four new C30 isomeric heptacyclic polyether substances (compounds 2-5, Scheme 2) were obtained through a unique seven-step cascade process featuring a pentacyclization of squalene followed by a double oxidative spiroketalization at the two bis-THF termini of the first-formed penta-THF intermediates. Synthesis of polycyclic polyethers by one-step RuO4-catalysed oxidative polycyclization/oxidative spiroketalization of squalene
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