Abstract: The research enterprise in our laboratory is based on the premise that many conceptually simple chemical transformations can be envisioned which have not yet been reduced to practice. This account presents the discovery and current state of optimization of a new reaction which was recently discovered in our laboratories, namely the tungsten carbonyl-catalyzed endo-selective cycloisomerization of alkynyl alcohols to dihydropyrans, and applications to the stereoselective synthesis of disaccharide substructures of digitoxin, landomycin, and mithramycin natural products.