Synthesis of highly substituted tetrahydropyrans: preparation of the C20-C28 moiety of phorboxazoles

A propionate-derived polyketide building block A whose 2-methyl-1,3-diol moiety was built by a Ti(III)-mediated ring opening reaction of a trisubstituted 2,3-epoxy alcohol precursor was employed as a common starting material for the syntheses of highly substituted tetrahydropyrans 1-5, the first one being the C20-C28 fragment of cytotoxic natural products, phorboxazoles