The Mukaiyama cross-aldol reaction of alpha-fluoro-, alpha-chloro-, and alpha-bromoacetaldehyde-derived (Z)tris(trimethylsilyl)silyl enol ethers is described, furnishing anti-beta-siloxy-alpha-haloaldehydes. A highly diastereoselective, one-pot, sequential double-aldol process is developed, affording novel beta,delta-bissiloxy-alpha,gamma-bishaloaldehydes. Reactions are catalyzed by C(6)F(5)CHTf(2) and C(6)F(5)CTf(2)AlMe(2) (0.5-1.5 mol %) and provide access to halogenated polyketide fragments.