No abstract

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...

A catalytic hypervalent iodine oxidation of p-dialkoxybenzenes using 4-iodophenoxyacetic acid (1) and 2KHSO 5 · KHSO 4 · K 2 SO 4 (Oxone ® ) was developed. Reaction of p-dialkoxybenzenes (2) with a catalytic amount of 1 in the presence of Oxone ® as a co-oxidant in 2,2,2-trifluoroethanol-water (1 : 2) gave the corresponding p-quinones (3) in excellent yields without purification. This procedure was applied to synthesis of blattellaquinone (9), the sex pheromone of the German cockroach, Blattella germanica.

Quinones Q 0390Catalytic Hypervalent Iodine Oxidation Using 4-Iodophenoxyacetic Acid and Oxone ® : Oxidation of p-Alkoxyphenols to p-Benzoquinones. -(YAKURA*, T.; TIAN, Y.; YAMAUCHI, Y.; OMOTO, M.; KONISHI, T.; Chem. Pharm. Bull. 57 (2009) 3, 252-256; Grad. Sch. Med. Pharm. Sci., Univ. Toyama, Toyama 930, Japan; Eng.) -D. Singer 35-083

The title reaction provides an efficient and practical method for the preparation of p-quinols and p-quinones. The quinone synthesis is applied to the synthesis of blattellaquinone (VIe), the sex pheromone of the German cockroach. -(YAKURA*, T.; OMOTO, M.; YAMAUCHI, Y.; TIAN, Y.; OZONO, A.; Tetrahedron 66 (2010) 31, 5833-5840,