OXIDATION OF DIETHY OMEGA-PHENYLALKENYLMALONATES BY HIGH-VALENT METAL-SALTS

The oxidation of diethyl omega-phenylalkenylmalonates by Mn(III) aceta te in acetic acid and Fe(III) perchlorate nonahydrate in acetonitrile or acetonitrile/acetic anhydride is investigated. Diethyl cinnamylmalo nates 1, 2 and 3 afford intramolecular addition products to the double bond (cyclopropanes 10) and to the aromatic ring (tetrahydronaphthale nes 8 or 9). A mechanism based on a fast and reversible 3-exo-trig-add ition of malonyl radicals leading to cis-trans equilibration of the do uble bond, followed by competition between oxidation of benzyl radical s and intramolecular aromatic substitution, is suggested. Trapping exp eriments with styrene and metal ions elucidate some of the kinetic par ameters involved. Similarly, compounds 4 and 5 are oxidized by Mn(III) /AcOH and FEP/AN to 4- and 5-exo-trig- cyclization products. In contra st, an outer-sphere electron-transfer mechanism is suggested in the ox idation of 1, 4 and 5 at the styrenic double bond by FEP/AN-Ac2O and o f benzalketones 6 and 7 by Mn(III)/AcOH to alpha-oxygenation products 21-22.