Oxygen donors hypochlorite

In summary, the reaction of osmium tetroxide with alkenes is a reliable and selective transformation. Chiral diamines and cinchona alkakoid are most frequently used as chiral auxiliaries. Complexes derived from osmium tetroxide with diamines do not undergo catalytic turnover, whereas dihydroquinidine and dihydroquinine derivatives have been found to be very effective catalysts for the oxidation of a variety of alkenes. OsC>4 can be used catalytically in the presence of a secondary oxygen donor (e.g., H202, TBHP, A -methylmorpholine-/V-oxide, sodium periodate, 02, sodium hypochlorite, potassium ferricyanide). Furthermore, a remarkable rate enhancement occurs with the addition of a nucleophilic ligand such as pyridine or a tertiary amine. Table 4-11 lists the preferred chiral ligands for the dihydroxylation of a variety of olefins.61 Table 4-12 lists the recommended ligands for each class of olefins. 

There are various alternatives for reoxidizing the hydroxylamine back to TEMPO to complete the catalytic cycle. It can be oxidized by dioxygen, laccase or the oxoammonium cation. The active oxidant is the same as that in the TEMPO catalyzed oxidations of alcohols with hypochlorite (or other single oxygen donors), a method which is widely used in the oxidation of a broad range of alcohols using low catalyst loadings (1 mol % or less) (59). 

This is similar to the oxenoid species proposed earlier as the active intermediate of enzymatic oxidations. It has been made accessible for mechanistic studies via the reaction of metalloporphyrins (Fe,Mn) with single oxygen donors, such as iodosylbenzene, hypochlorite, etc. This concept helped design efficient and selective epoxidation systems. Selective epoxidizing catalysts utilizing dioxygen are based on ruthenium porphyrins. 

Metal complexes combined with a suitable oxygen atom donor can often act as versatile and selective oxidation catalysts. The oxygen atom donors commonly used are N-methyl morpholine oxide 8.27 (see reaction 8.30), organic hydroperoxides, sodium hypochlorite, hydrogen peroxide, etc. Three such reactions of industrial relevance are shown by 8.30, 8.31, and 8.32. Obviously these reactions are catalytic with respect to the metal complex but stoichiometric with respect to the oxygen atom donor. 

With a Mn3+ Schiff base complex as the epoxidation catalyst, from the point of view of selectivity, would an organic hydroperoxide or sodium hypochlorite be a better oxygen atom donor ... 

Taking into account the hint cited above, the fact that a proton donor is essential, and that the ideal final intermediate would be an unstable a-halo a-hy-droxy species, H20 would seem to be the obvious candidate combining the roles of general acid providing the proton needed to activate the f-butyloxy leaving group of f-butyl hypochlorite, and the nucleophilic oxygen source. 

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