Synthesis of highly substituted pyranonaphthalene spiroketals related to the griseusins using a Hauser–Kraus annulation strategy

The synthesis of an advanced pyranonaphthalene spiroketal as an intermediate for the total synthesis of griseusin B is described. A one-pot Hauser–Kraus annulation–methylation via reaction of a highly-substituted enone with a cyanophthalide was employed to construct the naphthalene framework. Other key steps include Sharpless asymmetric dihydroxylation of a (Z)-alkene and an HF-pyridine mediated double TBS deprotection-spirocyclisation.