Further studies of an approach to a total synthesis of phomactins

The bicyclic sulfone 28, which has the intact carbon skeleton of phomactins, was prepared using a stereoselective [2,3]-Wittig Still rearrangement, a ytterbium triflate-mediated addition of a vinyllithium reagent to an aldehyde and macrocyclisation via an intramolecular sulfone alkylation, as key steps. During studies into the conversion of this intermediate into phomactin A, it was found that oxidation of homoallylic alcohols using TPAP can give unsaturated keto-aldehydes, and the stereoselectivity of reduction of a ketone at C(14) is influenced by the presence of a remote sulfonyl group at C(10).