Oxygen bearing complexes

From a stereochemical point of view, compound 35 is rather complex, for it possesses four contiguous oxygen-bearing stereocenters. Nonetheless, compound 35 is amenable to a very productive retro-synthetic maneuver. Indeed, removal of the epoxide oxygen from 35 furnishes trans allylic alcohol 36 as a potential precursor. In the synthetic direction, SAE of 36 with the (+)-dialkyl tartrate ligand would be expected to afford epoxy alcohol 35, thus introducing two of the four contiguous stereocenters in one step. 

It has been shown that olefins that are electron rich, such as enol ethers, give products formed via an olefin complex. An olefin complex between an enol ether and a trivalent cobalt complex should in the presence of a nucleophile (such as an alcohol) undergo addition of the nuclephile to the oxygen-bearing carbon, forming a cr-bonded acetal. 

Hine et al. [6] approached the complex structures of bisphenol (dibenzocyclobutane-1,8-diol) and sp oxygen bearing partners using X-ray crystallographic analysis the two... 

A first aluminum derivative is complexed between the two oxygen atoms of 57, which have to be in an appropriate configuration to allow this chelation. A second aluminum reagent is then complexed by the oxygen bearing the most available electron lone pair. This second complexation directs the reaction of de-O-alkylation, and rationalizes the observed regioselectivity leading to 58 as the sole product (Scheme 9.27). The mechanism involves two aluminum derivatives, one as a Lewis acid, which activates the alkyl ether, the other as a hydride donor, which reacts with the activated position [63]. 

A second separation technique is leaching, which uses solubility properties to separate the components of an ore. For example, modem gold production depends on the extraction of tiny particles of gold from gold-bearing rock deposits. After the rock is crushed, it is treated with an aerated aqueous basic solution of sodium cyanide. Molecular oxygen oxidizes the metal, which forms a soluble coordination complex with the cyanide anion ... 

A similar system, but with a more hindered porphyrin (tetramesitylporphyrin = tetraphenylporphyrin bearing three methyl substituents in ortho and para positions on each phenyl group), was tested for P-carotene oxidation by molecular oxygen. This system was chosen to slow the oxidation process and thus make it possible to identify possible intermediates by HPLC-DAD-MS analysis. The system yielded the same product families as with lycopene, i.e., (Z)-isomers, epoxides, and P-apo-carotenals, together with new products tentatively attributed to diapocarotene-dials and 5,6- and/or 5,8-epoxides of P-apo-carotenals. The oxidation mechanism appeared more complex in this set-up. 

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