Oxazolines are five-membered heterocyclic compounds with one double bond. The double bond may be in one of three positions, so there may be three different oxazoline rings. The 2-oxazoline structure is the most common, and 3-oxazoline and 4-oxazoline exist mainly as laboratory research compounds. Oxazolines exist between oxazole and oxazolidine in terms of saturation.
Tetrahydropyran is an organic compound consisting of a saturated six-membered ring containing five carbon atoms and one oxygen atom. Tetrahydropyrans are common structural motifs in natural products and synthetic therapeutic molecules. In nature, these six-membered oxygen heterocycles are usually assembled by intramolecular reactions, including oxygen Michael addition or ring opening of epoxy alcohols. In fact, polyether natural products have been particularly extensively studied for their fascinating structures and important biological properties; these are often formed through endoselective epoxy open cascades.