We describe the total syntheses of (±)-phyllanthocin (1), the aglycon of the potent antineoplastic agent phyllanthoside (2a), and of (±)-chlorovulone II (3), a halogenated marine prostanoid with high antiproliferative and cytotoxic activity.* The key step of both syntheses is a novel carbonyl ene reaction, which occurs between ordinary aldehydes and vinyl ethers that display the oxygen functionality at the central carbon of an allylic system, e.g., 2-methoxypropene, under the catalytic influence of 0.5 mol% of the 1:1 complex of Yb(fod)\sb3 and acetic acid (Figure I).* ftn*Please refer to dissertation for diagrams.