Methyltrioxorhenium oxidation catalyst

The BaeyerVilliger oxidation of flavanones 407 using methyltrioxorhenium (MTO) catalyst affords 1,5-benzodiox-epin-2-ones 408 in excellent yields (Scheme 214) . 

W. A. Hemnaim, R. W. Fischer, D. W. Marz, Multiple bonding between main group elements and transition metals. 100. Part 2. Methyltrioxorhenium as catalyst for olefin oxidation, Angew. Chem. Int. Ed. Engl. 30, 1638-1641 (1991). 

Hermann WA, Fischer RW, Marz DW. Methyltrioxorhenium as catalyst for olefin oxidation. Angew Chem Int Ed 1991 30 1638-1641. 

Oxidation of Primary Amines. Goti and coworkers described a one-pot condensation/oxidation of primary amines and aldehydes (eq 46) using UHP as stoichiometric oxidant in the presence of methyltrioxorhenium as catalyst. This reaction leads to nitrones in a simple and regioselective manner. From a sustainability point of view, this one-pot synthesis is simple to perform, takes place under mild conditions, and releases water as the only byproduct. ... 

Activation of hydrogen peroxide has been achieved by the use of methyltrioxorhe-nium (MTO) [322]. Strukul and coworkers employed cationic platinum complexes as catalysts and hydrogen peroxide as the oxidant in the conversion of cyclohexanones into caprolactones [323]. A niobiocene complex has been applied giving esters with a regioselectivity opposite to that generally observed [324]. Some supported platinum [325], nickel [326] and methyltrioxorhenium [327] catalysts have also been used in reactions with hydrogen peroxide. 

The oxidation of alkenes and allylic alcohols with the urea-EL202 adduct (UELP) as oxidant and methyltrioxorhenium (MTO) dissolved in [EMIM][BF4] as catalyst was described by Abu-Omar et al. [61]. Both MTO and UHP dissolved completely in the ionic liquid. Conversions were found to depend on the reactivity of the olefin and the solubility of the olefinic substrate in the reactive layer. In general, the reaction rates of the epoxidation reaction were found to be comparable to those obtained in classical solvents. 

Methyltrioxorhenium (MTO) is now well established as a catalyst in a number of oxidations employing hydrogen peroxide. Two groups have now reported,... 

Methyltrioxorhenium 41 has been established as a good catalyst for the selective oxidation of sulfides to sulfoxides by H2O2319 320. Both mono 42 and diperoxo species 1 (equation 30) are reactive in this oxidation. High selectivity of sulfoxide over sulfone has been reported, except in the presence of large contents of water in the reaction mixture319. 

In methyltrioxorhenium-catalysed reactions, residual pyridine, pyrazole or imidazole may deactivate the active catalyst and the ionic liquid should be purified accordingly.118 191 The nature of the ionic liquid may decide the success or failure of a given reaction and, for example, Ru-catalysed alcohol oxidations appear to be very sensitive to the type and quality of ionic liquid used. 

A novel family of catalysts [6], highly useful for the purpose described above, are organometallic as well as inorganic rhenium oxides such as methyltrioxorhenium [CHsReOa] (MTO), ReOj, or RcjOv. 

Under the name Oxone an oxidation agent has been introduced, consisting of KHSO4-K2SO4-2KHSO5. Solid Oxone converts methylenic functions under anhydrous, biphasic conditions to carbonyl compounds under the catalytic influence of ligand-modified Mn porphyrins and phase-transfer catalysts (e. g., acetophenone is obtained from ethylbenzene). In the case of cyelohexane, e-caprolactone results as well as cyclohexanol and -one ([219 b, 241] cf. also Baeyer-Villiger oxidation). Biphasic oxidations with methyltrioxorhenium (e. g., to epoxides) are reviewed in Section 3.3.13 [244 i]. 

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