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ABSTRACT: Efficient and selective: Two lipophilic catalysts were used for Baeyer-Villiger (BV) oxidations to give lactones in high yields. Cascade reactions involving this BV oxidation were used to selectively obtain either unsaturated carboxylic acids or hydroxylactones in high yields from β-silyl cyclohexanones.
Angewandte Chemie International Edition 08/2012; 51(36):9093-6. · 13.45 Impact Factor
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ABSTRACT: We have developed the first example of hypervalent iodine(V)-catalyzed regioselective oxidation of phenols to o-quinones. Various phenols could be oxidized to the corresponding o-quinones in good to excellent yields using catalytic amounts of sodium salts of 2-iodobenzenesulfonic acids (pre-IBSes) and stoichiometric amounts of Oxone® as a co-oxidant under mild conditions. The reaction rate of IBS-catalyzed oxidation under nonaqueous conditions was further accelerated in the presence of an inorganic base such as potassium carbonate (K₂CO₃), a phase transfer catalyst such as tetrabutylammonium hydrogen sulfate (nBu₄NHSO₄), and a dehydrating agent such as anhydrous sodium sulfate (Na₂SO₄).
Molecules 01/2012; 17(7):8604-16. · 2.39 Impact Factor
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Angewandte Chemie International Edition 05/2011; 50(23):5331-4. · 13.45 Impact Factor
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ABSTRACT: It is desirable to minimize the use of rare or toxic metals for oxidative reactions in the synthesis of pharmaceutical products. Hypervalent iodine compounds are environmentally benign alternatives, but their catalytic use, particularly for asymmetric transformations, has been quite limited. We report here an enantioselective oxidative cycloetherification of ketophenols to 2-acyl-2,3-dihydrobenzofuran derivatives, catalyzed by in situ-generated chiral quaternary ammonium (hypo)iodite salts, with hydrogen peroxide as an environmentally benign oxidant. The optically active 2-acyl 2,3-dihydrobenzofuran skeleton is a key structure in several biologically active compounds.
Science 06/2010; 328(5984):1376-9. · 31.20 Impact Factor
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Angewandte Chemie International Edition 03/2010; 49(12):2175-7. · 13.45 Impact Factor
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Angewandte Chemie International Edition 03/2010; · 13.45 Impact Factor
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Chemistry - An Asian Journal 03/2010; 5(3):456-60. · 4.50 Impact Factor
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ABSTRACT: A 2-iodoxybenzenesulfonic acid (IBS)-catalyzed oxidative rearrangement of tertiary allylic alcohols to enones with powdered Oxone in the presence of potassium carbonate and tetrabutylammonium hydrogen sulfate has been developed.
Organic Letters 08/2009; 11(15):3470-3. · 5.86 Impact Factor
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ABSTRACT: The hypervalent iodine-catalyzed oxylactonization of ketocarboxylic acids to ketolactones was achieved in the presence of iodobenzene (10 mol%), p-toluenesulfonic acid monohydrate (20 mol%) and meta-chloroperbenzoic acid as a stoichiometric co-oxidant.
Bioorganic & medicinal chemistry letters 05/2009; 19(14):3848-51. · 2.65 Impact Factor
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ABSTRACT: Over the past two decades there has been a dramatic increse in the use of hypervalent iodine compounds in synthetic organic chemistry due to their mild and selective oxidizing properties. Hypervalent iodine compounds catalyze various oxidation reactions such as the oxidation of alcohols, alpha-oxidation of ketones, oxidative spirocyclization of phenols, etc. Very recently, we found that 2-iodoxybenzensulfonic acid (IBS, ), which was generated from 2-iodobenzenesulfonic acid in situ, is an extremely active and mild catalyst for the highly chemoselective oxidation of various alcohols with powdered Oxone(R) to carbonyl compounds such as aldehydes, carboxylic acids, ketones and cycloalkenones under non-aqueous conditions. In this review, we focus on the design of hypervalent iodine catalysts and review the discovery and development of the oxidation of alcohols with the stoichiometric or catalytic use of hypervalent iodine compounds.
Chemical Communications 05/2009; · 6.17 Impact Factor
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ABSTRACT: Electron-donating group-substituted 2-iodoxybenzoic acids (IBXs) such as 5-Me-IBX (1g), 5-MeO-IBX (1h), and 4,5-Me(2)-IBX (1i) were superior to IBX 1a as catalysts for the oxidation of alcohols with Oxone (a trademark of DuPont) under nonaqueous conditions, although Oxone was almost insoluble in most organic solvents. The catalytic oxidation proceeded more rapidly and cleanly in nitromethane. Furthermore, 2-iodoxybenzenesulfonic acid (IBS, 6a) was much more active than modified IBXs. Thus, we established a highly efficient and selective method for the oxidation of primary and secondary alcohols to carbonyl compounds such as aldehydes, carboxylic acids, and ketones with Oxone in nonaqueous nitromethane, acetonitrile, or ethyl acetate in the presence of 0.05-5 mol % of 6a, which was generated in situ from 2-iodobenzenesulfonic acid (7a) or its sodium salt. Cycloalkanones could be further oxidized to alpha,beta-cycloalkenones or lactones by controlling the amounts of Oxone under the same conditions as above. When Oxone was used under nonaqueous conditions, Oxone wastes could be removed by simple filtration. Based on theoretical calculations, we considered that the relatively ionic character of the intramolecular hypervalent iodine-OSO(2) bond of IBS might lower the twisting barrier of the alkoxyperiodinane intermediate 16.
Journal of the American Chemical Society 01/2009; 131(1):251-62. · 9.91 Impact Factor
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ABSTRACT: Highly diastereoselective polycyclization of homo(polyprenyl)arene analogues bearing terminal siloxyvinyl groups was catalyzed by tin(IV) chloride (10 mol %). The cyclizations of tert-butyldiphenylsilyl and triisopropylsilyl polyenol ethers gave 4alpha(equatorial)- and 4beta(axial)-siloxypolycycles as major isomers, respectively. The strong nucleophilicity of pro-C(9), a (6E) geometry, and a bulky silyl group effectively favored the alpha-preference, whereas the weak nucleophilicity of pro-C(9), a (6Z)-geometry, and less steric hindrance of a silyl group favored the beta-preference. [reaction: see text].
Organic Letters 12/2006; 8(24):5649-52. · 5.86 Impact Factor
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ABSTRACT: Asymmetric total syntheses of acid-sensitive (-)- and (+)-caparrapi oxides (1) and (+)-8-epicaparrapi oxide (2) from farnesol (10) are achieved using Sharpless-Katsuki epoxidation and Lewis acid-assisted chiral Brønsted acid (chiral LBA)-induced polyene cyclization as key steps. The relative configuration of (+)-dysifragin (4) is determined by a single-crystal X-ray diffraction and its total synthesis is accomplished by the diastereoselective epoxidation of (+)-1. Furthermore, (-)-1 can be directly synthesized from (S)-nerolidol (3) and (R)-LBA with 88% ds by reagent control, which overcame substrate control, while (-)-2 is obtained from (R)-3 and (R)-LBA with >99% ds by the double asymmetric induction.
Bioorganic & Medicinal Chemistry 10/2005; 13(17):5055-65. · 2.92 Impact Factor
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ABSTRACT: [reaction: see text] Asymmetric total syntheses of acid-sensitive (-)-caparrapi oxide (1) and (+)-8-epicaparrapi oxide (2) from farnesol (9) were achieved using Sharpless-Katsuki epoxidation and Lewis acid-assisted chiral Bronsted acid (chiral LBA)-induced polyene cyclization as key steps. Furthermore, (-)-1 could be directly synthesized from (S)-nerolidol (3) and (R)-LBA with 88% ds by reagent control which overcame substrate control, while (-)-2 was obtained from (R)-3 and (R)-LBA with >99% ds by the double-asymmetric induction.
Organic Letters 05/2005; 7(8):1601-4. · 5.86 Impact Factor
