TOTAL SYNTHESIS OF IONOPHORE ANTIBIOTIC X-14547A (INDANOMYCIN)

A convergent, enantioselective total synthesis of ionophore antibiotic X-14547A (indanomycin, 1) is described. The dioxanone-to-dihydropyran variant of the lactonic Ireland-Claisen rearrangement establishes the hydropyran nucleus of the ''left wing'' fragment 2. Elaboration to the target synthon utilizes a new methodology for the preparation of stereodefined vinylsilanes (24 --> 25 --> 26) via net S(N)2' coupling of [alpha-(mesyloxy)allyl]silanes with Grignard reagents catalyzed by CuCN. Salient features in the construction of the ''right wing'' subunit 3 include a modification of the Noyori three-component coupling procedure (32 --> 33) and the application,of a retro hetero Diels-Alder/intramolecular Diels-Alder (''mock Claisen'') process (5 --> 39), Palladium-mediated cross Coupling of ''left wing'' and ''right wing'' synthons using Stille's method tolerates a free carboxylic acid and an unprotected acyl pyrrole, affording indanomycin directly in its natural absolute configuration.