Oxidative transformation of phenols is of importance in view of its biological 1 and synthetic aspects. 2 However, the oxidation of phenols generally lacks selectivity because of coupling reactions caused by phenoxy radicals, 3 and hence a novel practical method for oxidation of phenols still waits to be explored. During the course of our systematic study on the simulation of the enzymatic function of cytochrome P-450 with low valent ruthenium complex catalysts, 4 we have found a biomimetic method for selective oxidation of phenols.The ruthenium-catalyzed oxidation of phenols 1 with tertbutyl hydroperoxide gives the corresponding (tert-butyldioxy)cyclohexadienones 2, which are versatile synthetic intermediates. As a typical example, the present oxidation provides a novel and convenient method for direct access to 2-substituted quinones 3 from phenols by Lewis acid promoted migration reactions of 2 (eq 1).Generally, metal-catalyzed oxidation of phenols with peroxides proceeds nonselectively, giving a variety of side products such as radical coupling products 3 and overoxidation products. 5 Selective oxidation of phenols is limited to those bearing substituents at their 2-and 6-positions. 6 The representative results of the oxidation of phenols with t-BuOOH are summarized in Table 1. Various phenols bearing para substituents can be converted into the corresponding tert-butyldioxy dienones selectively.The catalytic activity of various metal complexes was examined for the oxidation of p-cresol (1a) with t-BuOOH. RuCl 2 (PPh 3 ) 3 has proved to be the most effective catalyst for the selective formation of 4-(tert-butyldioxy)-4-methyl-2,5cyclohexadienone (2a). Other ruthenium catalysts such as RuCl 3 ‚nH 2 O gave satisfactory results. A typical experimental procedure is as follows. To a solution of 1a (0.652 g, 6.0 mmol) and RuCl 2 (PPh 3 ) 3 (0.173 g, 0.18 mmol) in ethyl acetate (6.0 mL) was added a 3.30 M solution of t-BuOOH in dry benzene (7.3 mL, 24.0 mmol) dropwise with stirring at room temperature over a period of 2 h. After stirring for an additional 3 h, removal of excess t-BuOOH upon treatment with a solution of sodium bisulfite, followed by short column chromatography (Florisil), gave the peroxide 2a (1.01 g, 85%).The oxidation can be rationalized by assuming hydrogen abstraction from phenol by the oxoruthenium intermediate 4 derived from RuCl 2 (PPh 3 ) 3 and t-BuOOH, to afford a phenoxy radical-Ru III (OH) intermediate. Electron transfer from the phenoxy radical to ruthenium gives a cationic intermediate, which undergoes nucleophilic reaction with the second molecule of t-BuOOH, to give tert-butyldioxy product 2, water, and the ruthenium(II) complex to complete the catalytic cycle. Selective formation of 2 is due to fast single electron transfer 7 to ruthenium from the phenoxy radical, to form the cationic intermediate before radical couplings can occur.4-(tert-Butyldioxy)cyclohexadienones 2 thus obtained are versatile synthetic intermediates. As an example, we want to show a novel, convenient method for T...

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The ruthenium-catalyzed oxidation of phenols with tert-butyl hydroperoxide efficiently gives the corresponding 4-(tert-butylperoxy)cyclohexadienones. The oxidation proceeds selectively because of ruthenium's ability for rapid single-electron transfer. This biomimetic oxidation reaction is highly useful to obtain the metabolic compounds desired for confirming the safety of medicines and related compounds. Typically, the first metabolic compound of the female hormone estrone is readily obtained by this biomimetic oxidation reaction. The resulting 4-(tert-butylperoxy)cyclohexadienones are versatile synthetic intermediates, which can be transformed into

Ruthenium-Catalyzed Oxidation of Tertiary Amines with HydrogenPeroxide in the Presence of Methanol.-The tertiary arylamines (I) and (IV) undergo α-methoxylation by ruthenium-catalyzed oxidation with hydrogen peroxide in methanol (II) to give selectively the corresponding methoxymethyl-or methylbenzylamines (III) and (V) without methoxylation of other alkyl groups. Subsequent treatment of (III) with an acid leads to the formation of the secondary amines (VI). Methoxymethylamines such as ( IIIa) react with electron-rich olefins such as (VII) in the presence of titanium tetrachloride to produce tetrahydroquinoline derivatives such as (VIII). (Mechanism). -(MURAHASHI, S.; NAOTA, T.; MIYAGUCHI, N.; NAKATO, T.; Tetrahedron Lett. 33 (1992) 46, 6991-6994; Dep. Chem., Fac. Sci., Osaka Univ.,

Phenols. -(MURAHASHI*, S.-I.; MIYAGUCHI, N.; NODA, S.; NAOTA, T.; FUJII, A.; INUBUSHI, Y.; KOMIYA, N.; Eur.