Biomimetic Synthesis of the Apoptosis-Inducing ThiazinoquinoneThiaplidiaquinone A

A concise total synthesis of the apoptosisinducing,marine metabolite thiaplidiaquinone A is described.The key ring forming steps are both based on biosyntheticconsiderations and involve the construction of the centralbenzo[c]chromene quinone unit by an extremely facile oxa-6π-electrocyclic ring closure reaction of an ortho-quinoneintermediate, derived by tautomerization of a bis-benzoquinone,readily accessed from two simple phenolic precursors.This is followed by the installation of the 1,4-thiazine-dioxidering by reaction of the benzo[c]chromene quinone with hypotaurine