Spirastrellolide B: construction of the C(26)-C(40) northern hemisphere and a related [5,5,7]-bis-spiroketal analogue

Differential synthetic access to an advanced C26-C40 northern hemisphere fragment of spirastrellolide B and to a related [5,5,7]-bis-spiroketal analogue from a common intermediate has been achieved. Central to this venture is the regiocontrolled functionalization of a C(31-32) alkyne, exploiting different transition metal catalysts (cf. Pt(II) and Au(I)).