C—O bond activation

Lactones reduce more easily than acyclic esters. Lactone 2 with an activated C—O bond is hydrogenolyzed to dimethyl 2-methyl-terephthalate over Pd ... 

A sequential C-C bcuid activation/C-O bond cleavage reaction was subsequently reported by the same group [30], It was discovered that alternative reaction... 

Studies of reaction mechanisms ia O-enriched water show the foUowiag cleavage of dialkyl sulfates is primarily at the C—O bond under alkaline and acid conditions, and monoalkyl sulfates cleave at the C—O bond under alkaline conditions and at the S—O bond under acid conditions (45,54). An optically active half ester (j -butyl sulfate [3004-76-0]) hydroly2es at 100°C with iaversion under alkaline conditions and with retention plus some racemization under acid conditions (55). Effects of solvent and substituted stmcture have been studied, with moist dioxane giving marked rate enhancement (44,56,57). Hydrolysis of monophenyl sulfate [4074-56-0] has been similarly examined (58). 

Hen egg-white lysozyme catalyzes the hydrolysis of various oligosaccharides, especially those of bacterial cell walls. The elucidation of the X-ray structure of this enzyme by David Phillips and co-workers (Ref. 1) provided the first glimpse of the structure of an enzyme-active site. The determination of the structure of this enzyme with trisaccharide competitive inhibitors and biochemical studies led to a detailed model for lysozyme and its hexa N-acetyl glucoseamine (hexa-NAG) substrate (Fig. 6.1). These studies identified the C-O bond between the D and E residues of the substrate as the bond which is being specifically cleaved by the enzyme and located the residues Glu 37 and Asp 52 as the major catalytic residues. The initial structural studies led to various proposals of how catalysis might take place. Here we consider these proposals and show how to examine their validity by computer modeling approaches. 

Lin Y-S, Yamamoto A (1999) Activation of C-O Bonds Stoichiometric and Catalytic Reactions. 3 161-192... 

SPECTROSCOPY OF THE POTENTIAL ENERGY SURFACES FOR C-H AND C-O BOND ACTIVATION BY TRANSITION METAL AND METAL OXIDE CATIONS... 

Spectroscopy of the Potential Energy Surfaces for C-H AND C-O Bond Activation by Transition Metal and Metal Oxide Cations 331 By R. B. Metz... 

With the more active RNi cathode, the electrohydrogenation is much less selective and hydrogenolysis of the benzylic C-O bond of 26 occurs to an appreciable extent to give / -aminophcnethyl alcohol (28) and cyclohexanol (30) in 70% yield (30% yield of aminodioxolane 28) after 8.9 F/mol (15). The hydrogenolysis of the benzylic C-O bond gives the intermediate hemiketal 27 which cleaves to p-aminophenethyl alcohol (30) and cyclohexanone (29) (Scheme 9). Cyclohexanone is electiohydrogenated further to cyclohexanol (30). 

The deoxygenation of cyclic ethers means the cleavage of both C-O bonds and leads to alkenes or alkanes depending on the hydrogenating activity of the catalyst (Scheme 4.2). 

All of the compounds in the previous sections containing C-O bonds to be hydrogenolyzed easily were activated at the carbon atom. However, O-alkyl-N,N -dicyclohexylisoureas (11), which can be prepared by the reaction of alcohols with dicyclohexylcarbodiimide, can also be hydrogenolyzed but they are activated on the oxygen atom (Scheme 4.61).273... 

Hydrogenolytic cleavage of the C-N bond takes place more easily than that of the C-C bond but with more difficulty than that of the C-O bond. Activation... 

The most important contributions in this area, however, directly related to bond activation chemistry, and, undoubtedly triggered by theoretical considerations along the lines of Figure 1, were reported by Whitesides and coworkers in 1986 and 1988 [11]. It was shown that the bent, bisphosphine-coordinated platinum chelate complex [(dcpe)Pt(O)] (9) (dcpe = bis(dicyclohexylphosphino)ethane), which could be generated thermally as a "hot" reactive intermediate by reductive elimination of neopentane from its ris-neopentylhydride Pt(II) precursor at around 60-70°C in solution, was able to activate C-H bonds, even of unactivated alkanes. 

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