STUDIES DIRECTED TOWARD THE TOTAL SYNTHESIS OF CERORUBENIC ACID-III .4. EXPLORATION OF AN ORGANOMETALLIC APPROACH TO CONSTRUCTION OF THE EASTERN SECTOR

The concept of an intramolecular organometallic approach to the most i llustrious member of the cerorubenic acid family is outlined. Alkylati on of ketone 2 with the ethyl iodoacetate and conversion of the result ant intermediate into lactone 9 provided a ready means for attaching s ide chains carrying a vinyl iodide substituent. Arrival at the key iod o ketones was next realized by a three-step sequence involving sodium borohydride reduction, regiocontrolled silylation of the primary hydro xyl group in the diol, and Dess-Martin oxidation. The crucial six-memb ered cyclization of these intermediates is not favored kinetically, an d reductive deiodination was observed, if reaction occurred at all. At tempts to generate vinyl stannanes from these same substrates were als o ineffective. The failure of this approach demonstrates the difficult ies associated with closure of ring D, a phenomenon that has earlier b een observed in the context of other exploratory routes to cerorubenic acid-III.