Add time:08/22/2019         Source:sciencedirect.com

The oxidation of diethyl ω-phenylalkenylmalonates by Mn(III) acetate in acetic acid and Fe(III) perchlorate nonahydrate in acetonitrile or acetonitrile/acetic anhydride is investigated. Diethyl cinnamylmalonates 1, 2 and 3 afford intramolecular addition products to the double bond (cyclopropanes 10) and to the aromatic ring (tetrahydronaphthalenes 8 or 9). A mechanism based on a fast and reversible 3-exo-trig-addition of malonyl radicals leading to cis-trans equilibration of the double bond, followed by competition between oxidation of benzyl radicals and intramolecular aromatic substitution, is suggested. Trapping experiments with styrene and metal ions elucidate some of the kinetic parameters involved. Similarly, compounds 4 and 5 are oxidized by Mn(III)/AcOH and FEP/AN to 4- and 5-exo-trig- cyclization products. In contrast, an outer-sphere electron-transfer mechanism is suggested in the oxidation of 1, 4 and 5 at the styrenic double bond by FEP/AN-Ac2O and of benzalketones 6 and 7 by Mn(III)/AcOH to α-oxygenation products 21–22.

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