Double ‐ action haloketones: A super silyl group enabled the first highly diastereoselective Mukaiyama aldol reactions of α ‐ chloro ‐ and α ‐ fluoroketones with a wide range of aldehydes, providing anti ‐ β ‐ siloxy ‐ α ‐ haloketones. This process is compatible with one ‐ pot double ‐ aldol methodology and allows for rapid access to new halogen ‐ modified polyketide fragments bearing up to four contiguous stereocenters (see scheme).