Novel Routes to Nonsymmetric Cephalostatin Analogous

Having demonstrated that nonsymmetric cephalostatin analogues are superior in biological activity to their symmetric counterparts we here report on further possibilities for desymmetrization of the readily available diketone 4.Since monoenolates had been prepared at an earlier stage, we describe here the selectivity of phenyl-iodosyldiacetate oxidations under basic conditions and as an example of selective nucleophilic attack, the Wittigmethylenation at the 12-ketogroup followed by a hydroboration is documented.