New Solutions to the C‐12,13 Stereoproblem of Epothilones B and D; Synthesis of a 12,13‐Diol‐Acetonide Epothilone B Analog

New approaches are described to the synthesis of epothilone B and a 12,13‐diol‐acetonide derivative. Specifically the (12Z) double bond is formed quantitatively by a silicon‐tethered ring‐closing metathesis (RCM) reaction with 85 % selectivity. Alternatively, a direct route to the 12,13‐epoxide by cyclization of a 12,13‐diol has been developed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)