The stereoselective synthesis of heterocyclic compounds is a longstanding synthetic challenge. In recent years we have made several advances in this area by exploiting α-chloroaldehydes as versatile building blocks for the synthesis of tetrahydrofuran, tetrahydropyran, and pyrrolidine-containing natural products and therapeutic leads (including carbohydrate analogues, iminosugars). These efforts rely on highly diastereoselective aldol reactions of α-chloroaldehydes, affording β-ketochlorohydrins that can be rapidly converted into stereochemically rich heterocycles and natural products. We have also reported a one-pot organocatalytic aldehyde α-chlorination/aldol reaction that proceeds with dynamic kinetic resolution and provides direct entry to a new class of carbohydrate building blocks.