Toward the synthesis of spirastrellolide A:: Construction of a tetracyclic C26-C40 subunit containing the DEF-Bis-Spiroacetal

A stereocontrolled synthesis of the fully elaborated C-26-C-40 tricyclic [5,6,6]-bis-spiroacetal of spirastrellolide A containing the C-28 chlorine substituent is reported, exploiting asymmetric Sharpless dihydroxylation and boron-mediated allylation methodology.