Substituted pyrans are a common structural motif of many natural products. The dihydropyran skeleton is a particularly attractive target since it both occurs in many natural products and furthermore the olefin function is a synthetically useful handle for further functionalisation, making it a key intermediate to many polysubstituted tetrahydropyrans. The literature now contains many versatile methods for the synthesis of dihydropyrans, 1., , , , , , and such as the hetero-Diels–Alder ...
