Biomimetic Total Synthesis of Santalin Y

A biomimetic total synthesis of santalin Y, a structurally complex but racemic natural product, is described. The key step is proposed to be a (3+2) cycloaddition of a benzylstyrene to a vinylogous oxidopyrylium, which is followed by an intramolecular Friedel-Crafts reaction. This cascade generates the unique oxafenestrane framework of the target molecule and sets its five stereocenters in one operation. Our work provides rapid access to santalin Y and clarifies its biosynthetic relationship with other colorants isolated from red sandalwood.