Synthesis of a C n –C n +6 Building Block Common to Important Polyol,Polyene Antibiotics from a Divinylcarbinol by a Desymmetrizing Sharpless Epoxidation

A stereocontrolled synthesis of the enantiomerically pure epoxide 7b from propargyl ether 15 has been realized in 15 steps. Epoxide 7b represents a building block for the “eastern” moieties of the title compounds. Key steps in our approach were a desymmetrizing Sharpless epoxidation (→  anti , cis ‐ 16 ), the selective processing of the bis‐enolate of the bis( tert ‐butyl alkoxyacetate) 11 through a diastereoselective [2,3]‐Wittig rearrangement (→  syn , syn ‐ 9 ), and a stereo‐ and chemoselective iodolactonization (→  35 ). The CO 2 H groups of dicarboxylic acid 37 were differentiated in a one‐pot bis‐oxidation reaction. The latter entailed the novel transformation of HO 2 CCH 2 ‐ O ‐alkyl into AcOCH 2 ‐ O ‐alkyl.