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

摘要

The concept of an intramolecular organometallic approach to the most illustrious member of the cerorubenic acid family is outlined. Alkylation of ketone 2 with the ethyl iodoacetate and conversion of the resultant intermediate into lactone 9 provided a ready means for attaching side chains carrying a vinyl iodide substituent. Arrival at the key iodo ketones was next realized by a three-step sequence involving sodium borohydride reduction, regiocontrolled silylation of the primary hydroxyl group in the diol, and Dess-Martin oxidation. The crucial six-membered cyclization of these intermediates is not favored kinetically, and reductive deiodination was observed, if reaction occurred at all. Attempts to generate vinyl stannanes from these same substrates were also ineffective. The failure of this approach demonstrates the difficulties associated with closure of ring D, a phenomenon that has earlier been observed in the context of other exploratory routes to cerorubenic acid-III. [References: 43]