Chemoselective Oxidative Esterification and Iodocyclization of Hydroxyalkynyl Aldehydes

We have described the chemoselective behavior of iodine in the oxidative esterification and electrophilic iodocyclization of hydroxyalkynyl aldehydes that contain a primary alcohol moiety. In the presence of an alcohol, which serves as the nucleophile and solvent, the reaction of the hydroxyalkynyl aldehydes and I₂ proceeds through a hemiacetal species to give alkyl 4-(3-hydroxyalkynyl)benzoate esters. In CH₂Cl₂, these substrates undergo an electrophilic iodocyclization through a cyclic iodonium ion to provide a synthetic route for the formation of the bioactive dihydrofuran/pyran ring system.