Δ6,7-Unsaturated 2-iodo ester 1a and 4-oxa esters 1b-d are cycloisomerized with catalytic amounts of chromium(II) acetate in high yield to substituted cyclopentanes 2 and tetrahydrofurans 3. An inter- and intramolecular radical addition of ethyl 2-iodoacetate (6) to a 1,6-diene 5 (diethyl diallylmalonate) gave in 88 % yield diethyl 3-[2-(ethoxycarbonyl)ethyl]-4-(iodomethyl)-1,1-cyclopentanedicarboxylate (7).