[536-80-1]  · C6H5IO  · Iodosylbenzene-Dichlorotris(triphenylphosphine)ruthenium  · (MW 220.01) (RuCl2(Ph3P)3

[15529-49-4]  · C54H45Cl2P3Ru  · Iodosylbenzene-Dichlorotris(triphenylphosphine)ruthenium  · (MW 958.87)

(mild oxidant for selective catalytic transformation of alkynes and several functional groups)

Physical Data: see Iodosylbenzene and Dichlorotris(triphenylphosphine)ruthenium(II).

Oxidation of Alkynes.

This reagent combination oxidizes disubstituted alkynes to a-diketones.1 The reactions are carried out at rt by stirring the substrate in a CH2Cl2 suspension of PhIO (2-3 equiv) in the presence of the catalyst (1%) until the oxidant totally dissolves. The best results are obtained with aryl-substituted alkynes (eq 1), while alkynes with aliphatic substituents tend to undergo cleavage to carboxylic acids. Terminal alkynes react exclusively via cleavage (eq 2). Alkynyl ethers and amines afford a-keto esters and a-keto amides, respectively.2

Oxidation of Alcohols and Phenols.

Primary alcohols are oxidized by PhIO-RuCl2(Ph3P)3 to aldehydes which react further to form carboxylic acids (eq 3), while secondary alcohols afford ketones (eq 4).3 The scope and limitations of this system in alcohol oxidations are similar to the combination of N-Methylmorpholine N-Oxide and ruthenium catalysts described by Sharpless.4 The oxidation of primary alcohols may be stopped at the aldehyde stage when iodosyl diacetate5 or m-iodosylbenzoic acid6 is used instead of PhIO (eqs 5 and 6).

Hydroquinones are oxidized to quinones by PhIO (eq 7). In these transformations the reaction proceeds with similar yields in the presence or absence of catalyst. Catalysis, however, is required for oxidation of sterically hindered phenols to quinones (eq 8). Boron Trifluoride Etherate as catalyst affords higher yields than RuCl2(Ph3P)3,7 and m-iodosylbenzoic acid-RuCl2(Ph3P)3 or PhIO in AcOH lead to comparable results.

Oxidation of Sulfides and Selenides.

While the Ru-catalyzed oxidation of sulfides and selenides with PhIO proceeds to sulfones and selenones (eq 9), respectively, sulfoxides may be obtained selectively with m-iodosylbenzoic acid (eq 10).6

Oxidation of Amines.

Activated secondary amines are dehydrogenated to imines by PhIO alone or with Ru catalysis (eq 11).8

Other Variations of the System.

RuCl2(Ph3P)3 may be replaced by other Rh salts, such as Ruthenium(III) Chloride with practically no effect on the results. Other oxidants which have been used in combination with rhodium salts include N-methylmorpholine N-oxide (oxidation of alcohols),5 N-methylmorpholine/H2O2 (alcohols),9 t-Butyl Hydroperoxide (amines,10,11 hydroquinones,12 nitriles13), Hydrogen Peroxide (hydroquinones and phenols),14 Oxygen (alcohols,15 catechols,16 sulfides,17), Bis(trimethylsilyl) Peroxide (alcohols),18 Acetone (alcohols),19 and CCl4 (alcohols).20

1. Müller, P.; Godoy, J. HCA 1981, 64, 2531.
2. Müller, P.; Godoy, J. TL 1982, 23, 3661.
3. Müller, P.; Godoy, J. TL 1981, 22, 2361.
4. Sharpless, K. B.; Akashi, K.; Oshima, K. TL 1976, 2503.
5. Saltzman, H.; Sharefkin, J. G. OSC 1973, 5, 658.
6. Müller, P.; Godoy, J. HCA 1983, 66, 1790.
7. Müller, P.; Gilabert, D. M. C 1986, 40, 127.
8. Müller, P.; Gilabert, D. M. T 1988, 44, 7171.
9. Behr, A.; Eusterwiemann, K. JOM 1991, 403, 215.
10. Murahashi, S. I.; Naota, T.; Taki, H. CC 1985, 613.
11. Murahashi, S. I.; Yoshimura, N.; Tsumiyama, T.; Kojima, T. JACS 1983, 105, 5002.
12. Tsuji, Y.; Ohta, T.; Ido, T.; Minbu, H.; Watanabe, Y. JOM 1984, 270, 333.
13. Murahashi, S.; Naota, T.; Kuwabara, T. SL 1989, 62.
14. Ito, S.; Aihara, K.; Matsumoto, M. TL 1983, 24, 5249.
15. Bäckvall, J. E.; Chowdhury, R. L.; Karlsson, U. CC 1991, 473.
16. Matsumoto, M.; Kuroda, K. JACS 1982, 104, 1433.
17. Ledlie, M. A.; Allum, K. G.; Howell, I. V.; Pitkethly, R. C. JCS(P1) 1976, 1734.
18. Kanemoto, S.; Matsubara, S.; Takai, K.; Oshima, K.; Utimoto, K.; Nozaki, H. BCJ 1988, 61, 3607.
19. Wang, G. Z.; Bäckvall, J. E. CC 1992, 337.
20. Sasson, Y.; Wiener, H.; Bashir, S. CC 1987, 1574.

Paul Müller

University of Geneva, Switzerland

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