Epoxidation methyltrioxorhenium -catalyzed

Several general reviews describe the state of the art of peroxide epoxidation catalyzed by TM compounds at about a decade ago [2A. Later on, specialized reviews dealt with particular peroxides ofCr, Mo, andW [5], V [6], and with epoxidation reactions catalyzed by methyltrioxorhenium (MTO) [7] that involve Re peroxo complexes as species responsible for the oxygen transfer. 

G. S. Owens, M. M. Abu-Omar, Methyltrioxorhenium-catalyzed epoxidations in ionic liquids, Chem. Commun. 1165-1166 (2000). 

A. Goti, F. Cardona, G. Soldaini, C. Crestini, C. Fiani, R. Saladino, Methyltrioxorhenium-catalyzed epoxidation-methanolysis of glycals under homogeneous and heterogeneous conditions, Adv. Synth. Catal. 348,476 86 (2006). 

A Pt salt, [(dppe)Pt(C6F5)(H20)]0Tf, is able to catalyze selective epoxidation of a monosubstituted (terminal) aUcene with H2O2, without affecting an internal double bond. As catalysts for epoxidation, methyltrioxorhenium is modified by converting into the more stable 2 °... 

Methyltrioxorhenium, supported on silica functionalized with polyether tethers, catalyzed the epoxidation of alkenes with 30% aq H2O2 in high selectivity compared to the ring opening products observed in homogeneous media in the absence of an organic solvent.46... 

Hi. Epoxidation of allylic alcohols with special synthetic utility or academic interest. In 1999, Adam and coworkers reported on the methyltrioxorhenium (MTO) catalyzed... 

MTO [methyltrioxorhenium(VII), cf. Chapter 3.3.13] can be used as a catalyst for the epoxidation of olefins with urea hydroperoxide in [EMIMJBF4 [19]. The activity is reported to be comparable with the reaction in organic solvents but side reactions are suppressed. The use of an ionic liquid as a co-solvent in CH2CI2 for the enantioselective Mn-salen complex-catalyzed epoxidation of olefins with Na(OCl) was reported to result in enhanced reaction rates at no loss of enantioselectivity [20]. Cr-salen complexes can further be used for the asymmetric kinetic resolution of epoxides by ring-opening with azide [21]. 

Catalytic oxidation of 239 to the quinone 240 was also effected with H2O2 catalyzed by methyltrioxorhenium(VII) (McRcOb) (Scheme 60)", where a small amount of hydroxy-substituted quinone 280 was produced in addition to 240 (70%). In this reaction, MeRe03 is stepwise converted by H2O2 into the mono- and bis(peroxo)rhenium complex MeRe(02)20-H20 (281). This active oxidant then reacts with the phenol to give the epoxide 282, which is further converted to the two quinones (240 and 280). 

W. M. Adam, C. M. Mitchell, Methyltrioxorhenium(VII)-catalyzed epoxidation of alkenes with the urea/hydrogen peroxide adduct, Angew. Chem. Int. Ed. Engl. 35, 533— 535 (1996). 

H. Adolfsson, C. Coperet, J. P. Chiang, A. K. Yudin, Efficient epoxidation of alkenes with aqueous hydrogen peroxide catalyzed by methyltrioxorhenium and 3-cyano-pyridine, J. Org. Chem. 65, 8651-8658 (2000). 

O. A. Bouh, J. H. Espenson, Epoxidation reactions with urea-hydrogen peroxide catalyzed by methyltrioxorhenium(VII) on niobia. J. Mol. Cat. A Chem. 200, 43 7 (2003). 

Methyltrioxorhenium (MTO) supported on silica functionalized with polyether tethers (prepared by a sol-gel procedure) was shown to catalyze epoxidations with 30% H2O2 in the absence of solvent [69]. The silica-attached polyether phase is assumed to act as a solvent for the MTO (see Figure 3). The hydropho-... 

An example of using deuterated reactants for detailed kinetic studies of transition metal catalyzed reactions in ionic hquids vras contributed by Abu-Omar and coworkers. They studied the Rh-catalyzed epoxidation of olefins at ambient temperatures using [Dglstyrene and [Dio]-cylcohexene [71]. They also applied H-NMR experiments of [D3]-diperoxorhenium, formed in situ by reaction of [D3]-methyltrioxorhenium and urea hydrogen peroxide (UHP) to determine rate constants in single turnover experiments. 

Adam, W., A. Corma, A. Martinez, C.M. Mitchell, T.I. Reddy, M. Renz, and A.K. Smerz, Diastereoselective Epoxidation of Allyhc Alcohols with Hydrogen Peroxide Catalyzed by Ttitanium-Containing Zeohtes or Methyltrioxorhenium Versus Stoichiometric Oxidation with Dimethyldioxirane Clues on the Active Species in the Zeolite Lattice, J. Mol Catal A Chem. 117 357-366 (1997). 

Hydrogen peroxide is a particularly attractive oxidant and holds a prominent position in the development of benign catalytic oxidation procedures. In recent years a number of highly versatile catalytic oxidation methods based on, for example, polyoxometalates [154], methyltrioxorhenium [155] or tungstate [4, 156] complexes in the presence of phase transfer catalysts, all using hydrogen peroxide as the terminal oxidant, have been introduced. Mn-catalyzed epoxidations, aldehyde... 

Figure 10 Methyltrioxorhenium (MTO)-catalyzed epoxidation of PBD in CH2CI2/H2O2 biphasic system.

---