Olefin osmium-catalyzed dihydroxylation

Dapprich, S., Ujaque, G., Maseras, F., Lledos, A., Musaev, D. G., Morokuma, K., 1996, Theory Does Not Support an Osmaoxetane Intermediate in the Osmium-Catalyzed Dihydroxylation of Olefins , J. Am, Chem. Soc., 118, 11660. 

A photo-induced dihydroxylation of methacryamide by chromium (VI) reagent in aqueous solution was recently reported and may have potential synthetic applications in the syn-dihydroxylation of electron-deficient olefins.63 Recently, Minato et al. demonstrated that K3Fe(CN)6 in the presence of K2C03 in aqueous rm-butyl alcohol provides a powerful system for the osmium-catalyzed dihydroxylation of olefins.64 This combination overcomes the disadvantages of overoxidation and low reactivity on hindered olefins related to previous processes (Eq. 3.14). 

The osmium-catalyzed dihydroxylation reaction, that is, the addition of osmium tetr-oxide to alkenes producing a vicinal diol, is one of the most selective and reliable of organic transformations. Work by Sharpless, Fokin, and coworkers has revealed that electron-deficient alkenes can be converted to the corresponding diols much more efficiently when the pH of the reaction medium is maintained on the acidic side [199]. One of the most useful additives in this context has proved to be citric acid (2 equivalents), which, in combination with 4-methylmorpholine N-oxide (NMO) as a reoxidant for osmium(VI) and potassium osmate [K20s02(0H)4] (0.2 mol%) as a stable, non-volatile substitute for osmium tetroxide, allows the conversion of many olefinic substrates to their corresponding diols at ambient temperatures. In specific cases, such as with extremely electron-deficient alkenes (Scheme 6.96), the reaction has to be carried out under microwave irradiation at 120 °C, to produce in the illustrated case an 81% isolated yield of the pure diol [199]. 

After their leading publication on the osmium-catalyzed dihydroxylation of olefins in the presence of dioxygen [208], Beller et al. [209] recently reported that alcohol oxidations could also be performed using the same conditions. The reactions were carried out in a buffered two-phase system with a constant pH of 10.4. Under these conditions a remarkable catalyst productivity (TON up to 16 600 for acetophenone) was observed. The pH value is critical in order to ensure the reoxidation of Os(VI) to Os(VIII). The scope of this system seems to be limited to benzylic and secondary alcohols. 

An interesting offshoot of the work on osmium-catalyzed dihydroxylations is vicinal hydroxyamination [24]. Here, imido analogs of OSO4 react with olefins to produce /5-aminoalcohols by a cw-addition process. The oxyamination reaction can be made catalytic in OSO4 by employing chloramine salts of arylsulfonamides (ArS02NClNa) or carbamates. 

The enormous synthetic utility of AD depends on the one hand on the broad applicability of the osmium-catalyzed dihydroxylation for nearly every class of olefins, and on the other hand on the high selectivities which can be reached with optimized catalyst-ligand systems. 

Torrent, M., Deng, L., Duran, M., Sola, M., Ziegler, T. Density Functional Study of the [2+2]- and [2+3]-Cycloaddition Mechanisms forthe Osmium-Catalyzed Dihydroxylation of Olefins. Organometallics 1997,16,13-19. 

Osmium-catalyzed dihydroxylation of olefins involves an Os(VIII)/Os(VI) substrate-selective redox system [36c-gj. In this system, N-methylmorpholine N-oxide (NMMO) can be used for the reoxidation of Os(VI) to Os(VIII), with NMMO being reduced to NMM. In cyclohexene oxidation catalyzed by Os with HP, the yield to cis-1,2-cyclohexandiol can be improved remarkably by the use of specific mediators for NMM oxidation to NMMO, for instance by means of catalytic fiavin/HP. In this case, a yield to the cis-diol of 91% was obtained, as compared to 50% with the OSO4/HP system alone [36hj. Mixtures of aqueous HP and acetic acid or formic acid are also effective reagents for the dihydroxylation of olefins, but neutralization of the acid solvent is necessary for the recovery of the product. 

C. Dobler, G. M. Mehltretter, U. Sundermeier, M. Beller, Osmium-catalyzed dihydroxylation of olefins using dioxygen or air as the terminal oxidant, ]. Am. Chem. Soc. 122 (2000) 10289. 

Sharpless asymmetric dihydroxylahon (AD) reaction or osmium-catalyzed dihydroxylation. Scheme 2.9, was initially developed in 1980s (1980 stoichiometric version, 1988 catalyhc version ) for the preparation of chiral diols from olefins. " The most popular standard set of reactants called as AD-mix-p or AD-mix-a has been developed for this reaction and is still intensively used for producing the chiral products with up to 99% ee.33/34 Commercially available AD-mix is composed of potassium osmate K20s02(0H)4 and powdered K3Fe(CN)g and K2CO3, respectively. P and... 

Recent Developments in the Osmium-catalyzed Dihydroxylation of Olefins... 

Scheme 1.2 Osmium-catalyzed dihydroxylation of olefins using...

In this multi-authored book selected authors in the field of oxidation provide the reader with an up to date of a number of important fields of modern oxidation methodology. Chapter 1 summarizes recent advances on the use of green oxidants such as H2O2 and O2 in the osmium-catalyzed dihydroxylation of olefins. Immobilization of osmium is also discussed and with these recent achievements industrial applications seem to be near. Another important transformation of olefins is epoxidation. In Chapter 2 transition metal-catalyzed epoxidations are reviewed and in Chapter 3 recent advances in organocatalytic ketone-catalyzed epoxidations are covered. Catalytic oxidations of alcohols with the use of environmentally benign oxidants have developed tremendously during the last decade and in Chapter 4 this area is reviewed. Aerobic oxidations catalyzed by N-hydroxyphtahmides (NHPI) are reviewed in Chapter 5. In particular oxidation of hydrocarbons via C-H activation are treated but also oxidations of aUcenes and alcohols are covered. 

Mono-, di-, and trisubstituted olefins undergo osmium-catalyzed enantioselective dihydroxylation in the presence of the (R)-proline-substituted hydroquinidine 3.9 to give diols in 67-95% yields and in 78-99% ee.75 Using potassium osmate(VI) as the catalyst and potassium carbonate as the base in a tm-butanol/water mixture as the solvent, olefins are dihydroxylated stereo- and enantioselectively in the presence of 3.9 and potassium ferricyanide with sodium chlorite as the stoichiometric oxidant the yields and enantiomeric excesses of the... 

SCHEME 178. Osmium-catalyzed catalytic asymmetric dihydroxylation of olefins by H2O2 as terminal oxidant... 

In September 1997, Chemical and Engineering News summarized the ongoing discussion about the precise mechanism of the initial steps of the osmium-catalyzed olefin dihydroxylation in an... 

Fig. 4.31 Mechanism of osmium-catalyzed vicinal dihydroxylation of olefins.

Examples include acetal hydrolysis, base-catalyzed aldol condensation, olefin hydroformylation catalyzed by phosphine-substituted cobalt hydrocarbonyls, phosphate transfer in biological systems, enzymatic transamination, adiponitrile synthesis via hydrocyanation, olefin hydrogenation with Wilkinson s catalyst, and osmium tetroxide-catalyzed asymmetric dihydroxylation of olefins. 

Osmium-tetroxide-catalyzed dihydroxylation of sterically hindered olefins proceeds more efficiently with trimethylamine AA-oxide in the presence of pyridine. The base appears to catalyze not only formation of the osmate ester, but also its hydrolysis. 

Because most olefins are prochiral starting materials, the dihydroxylation reaction creates one or two new stereogenic centers in the products. Since the discovery of the first stoichiometric asymmetric dihydroxylations [7], catalytic versions with considerable improvements in both scope and enantioselectivity have been developed [8]. From the standpoint of general applicability, scope, and limitations, the osmium-catalyzed asymmetric dihydroxylation (AD) of alkenes has reached a level of effectiveness which is unique among asymmetric catalytic methods. As there are recent reviews in this field [9], this section is primarily oriented toward a summary of aspects of fundamental understanding and interesting practical application of catalytic dihydroxylations. 

Norrby, P. O., Kolb, H. C., Sharpless, K. B. Calculations on the reaction of ruthenium tetroxide with olefins using density functional theory (DPT). Implications forthe possibility of intermediates in osmium-catalyzed asymmetric dihydroxylation. Organometallics 994,13, 344-347. 

Ogino, Y., Chen, H., Kwong, H. L., Sharpless, K. B. The timing of hydrolysis-reoxidation in the osmium-catalyzed asymmetric dihydroxylation of olefins using potassium ferricyanide as the reoxidant. Tetrahedron Lett. 1991, 32, 3965-3968. 

---