Addition of iodine to dimethyl norbornadiene-2,3-dicarboxylate: nuclear magnetic resonance (1H and 13C) spectra and stereochemistry of nortricyclenes

Abstract

The free radical addition of iodine to dimethyl bicyclo[2.2.1]hepta-2,5-diene-2,3-dicarboxylate (3a)yields three stereoisomeric dimethyl 3,5-diiodotricyclo[2.2.1.02,6]heptane-2,3-dicarboxylates (nortricyclenes 4–6), as well as dimethyl 5,6-diiodobicyclo[2.2.1]hept-2-ene-2,3-dicarboxylate (9). By-products are two dimethyl 3-hydroxy-5-iodotricyclo[2.2.1.02,6]heptane-2,3-dicarboxylates (nortricyclenes 7, 8). Compounds 4 and 5 are also obtained as major products of addition of iodine to dimethyl tetracyclo[2.2.1.02,603,5]heptane-2,3-dicarboxylate (quadricyclane 10a). The structures of these various products were elucidated with the aid of 1H and 13C nmr and high-resolution mass spectroscopy.