Oxidation of styrene by 2,3-dichloro-5,6-dicyano-p-benzoquinone

Abstract

Styrene is oxidized by 2,3-diclaloro-5,6-dicyano-p-benzoquinone (DDQ), affording hydroquinune mono(2-phenylethyl) ether. Kinetic studies (50~ in CHCI3) show that the reaction is faster under N2 than under air and takes place via intramolecular H-atom transfer within the 1:1 and 1:2 DDQ -styrene chargetransfer complexes. The semiquinone radical intermediate is reoxidized to DDQ by O2 when the latter is present, therefore, the apparent rate of DDQ reduction is lower. Stability constants of the CT-complexes and kinetic parameters for the oxidation are reported.

Green and Efficient: Iron-Catalyzed Selective Oxidation of Olefins to Carbonyls with O2

“…Moreover, the presence of the radical initiator benzoyl peroxide did not alter the oxidative cleavage of 1b or induce the formation of other products, suggesting that freely diffusing carbon-based radicals are not generated during the oxidation reaction (Figure b). Indeed, catalytic oxidation of styrenes that proceeds via benzyl radical intermediates generates polymerization or dimer byproducts; however, polymers and dimer byproducts were not observed in the Fe­(OTf) 3 - L1 -catalyzed oxidations. In addition, catalysts that initiate radical species are substantially less efficient or inactive toward the oxidation of electron-deficient styrenes. ,, In contrast, the Fe­(OTf) 3 - L1 catalyst promotes the oxidation of both electron-rich and -deficient styrenes with high yields (Table ).…”

“…Indeed, catalytic oxidation of styrenes that proceeds via benzyl radical intermediates generates polymerization or dimer byproducts; however, polymers and dimer byproducts were not observed in the Fe­(OTf) 3 - L1 -catalyzed oxidations. In addition, catalysts that initiate radical species are substantially less efficient or inactive toward the oxidation of electron-deficient styrenes. ,, In contrast, the Fe­(OTf) 3 - L1 catalyst promotes the oxidation of both electron-rich and -deficient styrenes with high yields (Table ).…”

“…And under visible light irradiation, a Pt­(II) polypyridyl complex was found to promote the aerobic oxidation of aminopent-3-en-2-ones to diketones, affording 1,2-acyl migration in the presence of an alcohol . Cheaper cobalt-based catalysts enabled the scission of styrenes under mild aerobic conditions; however, a low selectivity was achieved due to the formation of undesired diols or radical-derived byproducts . More easily available copper salts also catalyzed the aerobic cleavage of electron-rich enamines and enol ethers and styrene under electrocatalytic conditions .…”

Observations on the DDQ Oxidation of 1-Acyldihydropyridines - A Synthetic Application

“…13 In addition, the oxidation of styrene mainly affords the hydroquinone 2-phenylethyl ether. 14 The favored mechanism for these transformations is considered to be a single electron transfer from the charge transfer complex, rather than hydride transfer. While DDQ hydride abstraction from benzylic positions is clearly a known transformation, significant activation is usually required in the aromatic ring (e.g.…”

Iron-assisted, base-catalyzed biomimetic activation of dioxygen by dioximatoiron(II) complexes

“…Our earlier work was concerned with the biomimetic catalytic oxidation of 3,5-di-tert-butylcatechol (3,5-H 2 dtbc), using the functional catecholase models [bis(dimethyl-glyoximato) cobalt(II)] [12][13][14][15] and [bis(dimethylglyoximato)iron(II)] [16,17] complexes (also known as cobaloxime(II) and ferroxime(II) derivatives, respectively). Kinetic investigations of these models were carried out to help elucidate the mechanism of the underlying biological catecholase reaction.…”