Oxidation Epoxidation Ozonolysis

The location of the position of double bonds in alkenes or similar compounds is a difficult process when only very small amounts of sample are available [712,713]. Hass spectrometry is often unsuited for this purpose unless the position of the double bond is fixed by derivatization. Oxidation of the double bond to either an ozonide or cis-diol, or formation of a methoxy or epoxide derivative, can be carried out on micrograms to nanograms of sample [713-716]. Single peaks can be trapped in a cooled section of a capillary tube and derivatized within the trap for reinjection. Ozonolysis is simple to carry out and occurs sufficiently rapidly that reaction temperatures of -70 C are common [436,705,707,713-717]. Several micro-ozonolysis. apparatuses are commercially available or can be readily assembled in the laboratory using standard equipment and a Tesla coil (vacuum tester) to generate the ozone. Reaction yields of ozonolysis products are typically 70 to 95t, although structures such as... 

Compound 4 was epoxidized to give 15 (Scheme 3) and the MS fragmentation of 15 is given by the broken-line mlz (relative abundance). To ensure the location of the double bonds, the epoxidation and the MS of 15 was compared with the products of the ozonolysis identified by GC and MS (as marked by the broken lines)6. The use of the various derivatization products via oxidation, combined with other spectroscopic methods, is discussed in Section III. 

Cyelobutanone has been prepared by (1) reaction of diazomethane with ketene,4 (2) treatment of methylenecyclobutane with performic acid, followed by cleavage of the resulting glycol with lead tetraacetate,s (3) ozonolysis of methylenecyclobutane, (4) epoxidation of methylene-cyclopropane followed by acid-catalyzed ring expansion,7 and (5) oxidative cleavage of cyclobutane trimethylene thioketal, which in turn is prepared from 2-(co-chloropropyl)-l,3-dithiane.8... 

Chemical/Physical. Ozonolysis of acrylonitrile in the liquid phase yielded formaldehyde and the tentatively identified compound glyoxal, an epoxide of acrylonitrile and acetamide. The reported rate constant for the reaction of acrylonitrile and ozone in the gas phase is 1.38 x lO cm moFsec (Munshi et al., 1989). In the gas phase, cyanoethylene oxide was reported as an ozonolysis product... 

Different isomers of C qO have been prepared by photooxygenation [48], by MCPBA-oxidation [48], by ozonolysis [49] or they were extracted from fullerene soot [11, 50]. Isolation from fullerene soot and analysis of the product of photooxygenation and thermal ozonolysis yields only [6,6]-closed epoxide structures. As already observed for CgoO, ozonolysis and subsequent photolysis of the ozonide C7QO3 gives different [5,6]-open oxidoannulene structures [49]. 

Ozonolysis of pyrethroids generates ozonide products and epoxides which show mild levels of bacterial mutagenicity <86Mi 4i6-03>. This has possible implications for atmospheric oxidation of pesticides or ozonolytic treatment of waste water. 

Carbenes, dioxirane preparation, 1132 Carbocations, antimalarial endoperoxides, 1309 Carbohydrate hydroperoxides, Mo-catalyzed olefin epoxidation, 432, 436 Carbohydrates, TBARS assay, 669 Carbonate esters, oxidative ozonolysis, 737, 738... 

Hydrogenation/Reduction/Reductive Ring Cleavage of the N-0 Bond, 6.2 Hydroxylation of the Ring Carbon-Carbon Double Bond/Oxidation, 6.3 Ozonolysis. 6.4 Epoxidation... 

The trisubstituted alkene of 10 was more readily oxidized than was the congested tetrasubstituted alkene, so the more reactive alkene was temporarily epoxidized. After ozonolysis, the epoxide was reduced off using the Sharpless protocol. It is a tribute to the specificity of this reagent that the easily-reduced a-acetoxy ketone is not affected. Selective silylation of the more accessible ketone followed by melhylenation, hydrolysis and addition of methyl lithium to the outside face of the previously protected carbonyl then delivered 1. 

Silylation followed by selenium dioxide oxidation converted 13 into 14. Epoxidation of the derived TES ether proceeded by addition of oxygen to the more open face of the alkene, leading to 15. Ozonolysis followed by diastereoselective one-carbon homologation provided 17. This set the stage for intramolecular epoxide opening by the carboxylate, to give 2, in which all of the stereogenic centers of tetrodotoxin have been established. 

Dioxiranes (32) are isomeric with carbonyl oxides (33), one of the peroxidic intermediates involved in the ozonolysis process.9 Dimethyldioxirane (DMDO) (31) epoxidizes the double bond of the protected galactal favoring the Oepoxide 8 with a selectivity of 20 1.10,11 You can use 31 likewise to transform an aldehyde into a carboxylic acid. 

The activation of oxygen in oxygen transfer reactions is usually mediated by a suitable transition metal catalyst which has to be sufficiently stable under the reaction conditions needed. But also non-metal catalysts for homogeneous oxidations have recently been of broad interest and several of them have been compiled in a recent review.2 Other examples for well known alkene oxidation reactions are the ozonolysis, hydroboration reactions or all biological processes, where oxygen is activated and transferred to the substrate. Examples for these reactions might be cytochrome P450 or other oxotransferases. Of these reactions, this contribution will focus on transition-metal mediated epoxidation and dihydroxylation. 

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