Catalytic Hypervalent Iodine Oxidation of p-Dialkoxybenzenes to p-Quinones Using 4-Iodophenoxyacetic Acid and Oxone

Tian

Yamauchi

et al. 2009

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Hypervalent iodine compounds, trivalent iodine compounds such as phenyliodine(III) diacetate (PIDA) and phenyliodine(III) trifluoroacetate (PIFA) and pentavalent iodine reagents such as Dess-Martin periodinane (DMP) and o-iodoxybenzoic acid (IBX), have been used extensively in recent organic synthesis because of their low toxicity, ready availability and easy handling. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] However, these reagents are highly expensive. And stoichiometric amounts of iodine reagents are required to produce equimolar amounts of organic iodine waste. Moreover, pentavalent iodine reagents are potentially explosive. To overcome these disadvantages, catalytic hypervalent iodine oxidations [16][17][18] using mchloroperbenzoic acid (m-CPBA), [19][20][21][22][23][24][25][26][27] Oxone ® (2KHSO 5 · KHSO 4 · K 2 SO 4 ), 28,29) and H 2 O 2 30) as a co-oxidant have been reported recently.Development of efficient methods for synthesis of pquinone and p-quinone derivatives is an important subject in synthetic organic chemistry because they are structural components of numerous natural products and useful synthetic intermediates. [31][32][33][34][35][36] A convenient procedure for p-quinones was hypervalent iodine oxidation of p-alkoxyphenols using PIFA.37) Reactions of p-alkoxyphenols with an equimolar amount of PIFA in a 2 : 1 mixture of acetonitrile and water at room temperature gave the corresponding p-quinones in excellent yield.As part of our study for development of practical and environmentally benign oxidation, we report a mild, efficient and practical procedure for catalytic hypervalent iodine oxidation of p-alkoxyphenols to p-quinones using a catalytic amount of 4-iodophenoxyacetic acid (1a) and Oxone ® as a co-oxidant 38) in 2,2,2-trifluoroethanol-water. Results and DiscussionWe chose Oxone ® as an environmentally safe co-oxidant for a catalytic hypervalent iodine oxidation of p-alkoxyphenols because Oxone ® is an inorganic and water-soluble oxidant with a low order of toxicity, moreover, it is commercially available and inexpensive. 39) Oxone ® has been already used as a co-oxidant under heating conditions in the catalytic IBX oxidation by Vinod 28) and Giannis 29) groups, independently. Because alkoxyphenols have high reactivity under oxidation conditions, we first investigated the oxidative ability of Oxone ® itself. 40) A mixture of 2-pivaloyloxymethyl-4-methoxyphenol (2a) and an equimolar amount of Oxone ® in acetonitrile-water (2 : 1) at room temperature gave the corresponding p-benzoquinone (3a), but the reaction was sluggish and the yield of 3a was only 13% along with 78% of recovered starting 2a after 24 h. Next, we examined reactions of 2a in the presence of several iodoarenes as a catalyst (Chart 1). Table 1 presents the results. According to the procedure reported by Vinod, 28) a mixture of 2a, 0.2 equivalents (eq) of 2-iodobenzoic acid, and 1 eq of Oxone ® in acetonitrile-water was heated at 70°C for 19 h to give a complicated mixture (entry 2). However, a similar reactio...

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Section: Resultsmentioning

confidence: 77%

Section: Resultsmentioning

confidence: 99%

Catalytic Hypervalent Iodine Oxidation Using 4-Iodophenoxyacetic Acid and Oxone: Oxidation of p-Alkoxyphenols to p-Benzoquinones

Tian

Yamauchi

et al. 2009

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“…However, oxidation of electron-poor phenols such as 3 did not work. The reactions of p-methylphenol (4), and pdimethoxybenzene (5) gave complex mixtures due to bromination of the aromatic ring, in contrast to the catalytic hypervalent iodine oxidations [19][20][21] (Fig. 1).…”

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confidence: 99%

An Efficient Catalytic Oxidation of p-Alkoxypenols to p-Quinones Using Tetrabutylammonium Bromide and Oxone

Ozono

Morimoto

2011

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“…30) Moreover, the solubility of 3 in alkaline solution makes its separation and recovery steps easier to carry out without a purification step. As part of our study for development of catalytic hypervalent iodine oxidations, [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45] we report herein an efficient synthesis of p-quinols directly from 4-arylphenols using catalytic amount of 3 and Oxone ® in tetrahydrofuran (or 1,4-dioxane)-water (Chart 2). We first examined 4-phenylphenol (1a) as a model substrate ( Table 1).…”

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confidence: 99%

“…A similar reaction of 1a in acetone-water (1 : 2) gave an almost identical result to that in acetonitrile-water (entry 4). Use of 2,2,2-trifluoroethanol (TFE), which is known to be an efficient solvent in catalytic hypervalent iodine reactions, 29,31,38) gave high yield (76%) of 2a, but needed a longer reaction time (entry 5). However, it is interesting that an unfamiliar solvent in hypervalent iodine chemistry, tetrahydrofuran (THF) gave a better result than TFE did (entry 6).…”

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confidence: 99%

Efficient Synthesis of p-Quinols Using Catalytic Hypervalent Iodine Oxidation of 4-Arylphenols with 4-Iodophenoxyacetic Acid and Oxone

Omoto

2009

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