APPLICATION OF THE REICH IODOSO SYN-ELIMINATION FOR THE PREPARATION OF AN INTERMEDIATE APPROPRIATE FOR THE SYNTHESIS OF BOTH HEXACYCLIC STEROIDAL UNITS OF CEPHALOSTATIN-7

Hecogenin acetate 5 was converted to an intermediate suitable for cons truction of both ''North'' and ''South'' hexacyclic spiroketals presen t in cephalostatin 7. The key chemical transformations involved are: ( I)the Reich iodoso syn-elimination of iodide 18; (2) Rhodium [II] cata lyzed intermolecular oxygen alkylation of secondary neopentyl alcohol 21; and (3) Intramolecular Wadsworth-Emmons reaction to provide the es ter precursor of aldehyde 4.