Oxygen atom transfer carbonyl oxides

D. Oxygen Atom Transfer from Dioxiranes and Carbonyl Oxides. 32... 

The decomposition of (18) in the presence of electron-deficient oxygen acceptors such as tetracyanoethylene forms the tetracyanoethylene oxide (19)51, with 60% yield. The oxygen atom transfer may be considered a general reaction of carbonyl oxides in ozonolysis of C=C double bonds when oxygen-accepting substrates are present. 

Oae and Numata proposed intermediate formation of a S-S dication 5 in order to explain migration of the oxygen occurred when 4 was treated with concentrated sulfuric acid. Similarly, Ruffato and Miotti proposed formation of a disulfonium dication as a result of intramolecular interaction during the oxygen atom transfer from arylmethylsulfoxide to dialkyl disulfide. In 1974, Simonet et al suggested transient formation of an extremely unstable S-S dication 7 (Scheme 3) during electrochemical oxidation of thioketals 6 to afford disulfides 9 and carbonyl compounds 8 after hydrolysis. 

Catalytic oxidation of alcohols by cis-dioxomolybdenum(VI) complexes, involving oxygen atom transfer from sulfoxides has been reported [1397]. Catalytic amounts of cis-dioxomolybdenum(Vl) complexes in association with sulfoxides can be used to oxidize alcohols to carbonyl compounds. For primary alcohols, the oxidation to the aldehyde is selective, and no further oxidation to the carboxyUc add is observed. The oxidation is most effective for benzylic and allylic alcohols. The mechanism... 

That specific hydride transfer from carbon to carbon does occur, was established by showing that use of labelled (Me2CDO)3Al led to the formation of RjCDOH. The reaction probably proceeds via a cyclic T.S. such as (47), though some cases have been observed in which two moles of alkoxide are involved—one to transfer hydride ion, while the other complexes with the carbonyl oxygen atom. The reaction has now been essentially superseded by MH reductions, but can sometimes be made to operate in the reverse direction (oxidation) by use of Al(OCMc3)3 catalyst, and with a large excess of propanone to drive the equilibrium over to the left. This reverse (oxidation) process is generally referred to as the Oppenauer reaction. 

The first class of reactions, direct transfer of an oxygen atom from the oxidant to carbon monoxide, has not been commonly observed as a reaction catalyzed by metal complexes in solution. One example, derived from a preparative procedure developed to substitute carbonyls with other ligands (90), is the reaction of trimethylamine oxide, Me3NO, with carbonyl clusters such as Os3(CO)12 in the presence of excess CO. The net reaction is shown as (27). 

Free-radical autoxidation of aldehydes with 02 is facile and affords the corresponding peradds, which are used as oxidants for carbonyl compounds. The peracid can transfer an oxygen atom to a substrate such as an olefin or ketone, resulting in the formation of one equivalent of epoxide or ester and add as a co-produd in the absence of metal catalysts [59]. Kaneda and coworkers have developed several HT materials that are active for heterogeneous Baeyer-Villiger reactions with 02/aldehyde [60]. Combination with Lewis addic metals improved the reaction by allowing coordination of the peracid and the intermediate. 

Metal (IV) species - Oxidation of the carbonyls to metal(IV) derivatives requires oxidants capable of transferring oxygen atoms. Best characterized are the p-oxobis[oxometal(IV)] complexes directly accessible with alkylhydroperoxides or dioxygen/2,3-dimethylindole (path e). Other metal(IV) derivatives, e.g. bis-alkoxides or oxometal(IV) complexes, are formed from the dioxometal(VI) porphyrins mentioned below. 

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