A Formal Total Synthesis of (+)‐Frondosin A

An enantio- and stereoselective formal total synthesis of (+)-frondosin A was accomplished through an oxidopyrylium-ion-mediated [5+2] cycloaddition reaction. The cycloaddition reaction provided not only an efficient way of constructing the frondosin skeleton but also facial discrimination through an ether bridge for complete control of relative stereochemistry of the substituents in frondosin A.