The reaction of a-alkenoic acids with bis (sym-collidine) iodine (I) hexafluorophosphate led to (iodomethyl) 6-caprolactones in good yields (49-75%) and medium ring iodo lactones in low yields (44%). The latter compounds have been obtained after introduction of an oxygen atom in the carbon chain. The position of the oxygen appeared important. This oxygen effect was explained by the stabilization of the intermediate iodonium ion by the oxygen atom.
