Synthesis of Both Enantiomers of Conduritol C Tetraacetate and of meso‐Conduritol D Tetraacetate by Oxidation of Benzoquinone Bis(ethylene acetal)

Epoxidation of p ‐benzoquinone bis(ethylene acetal) ( 1 ) with m ‐chloroperbenzoic acid or hydrogen peroxide/benzonitrile afforded corresponding monoepoxide 2 , which was converted into p ‐benzoquinone mono(ethylene acetal) monoepoxide 5 with perchloric acid. Dihydroxylation of 1 with osmium tetroxide or ruthenium trichloride/sodium periodate afforded corresponding cis ‐diol 6 , which was subsequently acetylated to give diacetate 7 . One ethyleneacetal moiety in 7 could be selectively hydrolyzed with silica gel/ferric chloride under solvent‐free conditions to give ketone 8 , which, upon reduction with sodium borohydride and subsequent acetylation of the formed alcohol group, afforded two diastereomeric triacetates 10 . Hydrolysis of the remaining acetal functions in the two diastereomers 10 , followed by reduction of the second carbonyl group as described above, afforded racemic conduritol C and meso ‐conduritol D tetraacetates 12 and 13 , respectively. Enzymatic resolution of the racemic arabino ‐configured triacetate 10 with Lipozym failed, while the ribo ‐configured counterpart reacted smoothly to give enantiomerically pure D ‐ ribo ‐ and L ‐ ribo ‐configured triacetates 10 . The latter pair of enantiomerically pure triacetates were converted into both enantiomers of conduritol C tetraacetate 13 as described for the racemic compounds. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)