Diiodo Acetals and Unsaturated Lactones From Dihydropyran

Abstract

Reaction of dihydropyran with propiolic acid and N- iodosuccinimide gave an iodo ester which was cyclized under free-radical conditions to form an (E) iodomethylene lactone. Photolysis of this lactone could be controlled to generate mixtures of (E) and (Z) iodomethylene lactones, or alternatively the iodine-free methylene lactone. The structures of some by-products of the iodo ester formation have been shown to be a succinimide derivative and two stereoisomers of a diiodo acetal. X-Ray determination of the structure of one of the diiodo acetal isomers is described.