Studies on Taxane Synthesis.I.Synthesis of 3, 8, 11, 11-Tetramethy1-4-oxobicyclo [5.3.1] undecane as a Model for Taxane Synthesis

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The bicyclo [5.3.1] undecanone 5 corresponding to the A and B rings in taxane diterpenes was synthesized from β-ionone.Reduction of the tosylhydrazone 11 with catecholborane afforded the trisubstituted olefin 12 having trans substituents at the C-1 and C-7 positions.The requisite cis-arrangement of these substituents for eight-membered ring formation was induced by epimerization of the aldehyde 13 to give the bicyclic hemiacetal 14.The lithium diisopropylamide-promoted intramolecular cyclization of the twelve-membered lactam sulfoxide 32 proceeded quite smoothly, affording the eight-membered keto sulfoxide 33 in quantitative yield.