Hydration hydride elimination

This combination of reagents h s been used to oxidize terminal vinyl groups to methyl ketones and is known as the Wacker oxidation. The nucleophile is simply water, which attacks the activated alkene at the more substituted end in an oxypalladation step. (3-Hydride elimination from the resulting a-alkyl palladium complex releases the enol, which is rapidly converted into the more stable keto form. Overall, the reaction is a hydration of a terminal alkene that can tolerate a range of functional groups. 

The last step, the release of acetaldehyde, can be interpreted as a reductive elimination to give the hydrate of acetaldehyde (Eqs. (9.19) and (9.20)) where Eq. (9.19) represents merely the completion of the complex ligation sphere at the central Pd by a solvent molecule. A reductive elimination is a common reaction of group 8 metal compounds. For this case, it has been first proposed in [20]. Keith etal. [21] derived such a pathway but chloride assisted from theoretical considerations. The barrier heights of the transition states for other pathways, for example, P-hydride elimination, were found to be too high. The route according to Eq. (9.20) would also be valid for chloride-free Pd compounds. 

Phthalyl alcohol, HOCH2CeH4CH20H-o. Mol. wt. 138.16, m.p. 64°. Prepared by reduction of phthalic anhydride with lithium aluminum hydride in ether (87% yield). In a novel and efficient synthesis of cyclopropanone hydrate, Grewe and Struve used the o-xylylene acetal protective group (1) and, after elimination of... 

The glycolytic pathway includes three such reactions glucose 6-phosphate isomer-ase (1,2-proton transfer), triose phosphate isomerase (1,2-proton transfer), and eno-lase (yS-elimination/dehydration). The tricarboxylic acid cycle includes four citrate synthase (Claisen condensation), aconitase (j5-elimination/dehydration followed by yS-addition/hydration), succinate dehydrogenase (hydride transfer initiated by a-proton abstraction), and fumarase (j5-elimination/dehydration). Many more reactions are found in diverse catabolic and anabolic pathways. Some enzyme-catalyzed proton abstraction reactions are facilitated by organic cofactors, e.g., pyridoxal phosphate-dependent enzymes such as amino acid racemases and transaminases and flavin cofactor-dependent enzymes such as acyl-C-A dehydrogenases others. 

Deamination of 2-amino-l,5-anhydro-2-deoxy-D-mannitol with nitrous acid gave principally l,5-anhydro-2-deoxy-D-e/ yt/fru-hex-3-ulose (68%), by migration of H-3, and some 2-deoxy-D-a/ a6/no-hexose (8%) and 1,5-anhydro-D-glucitol (6%). It was established that 2-deoxy-D-nrai>//in-hexose is formed via a hydride-shift mechanism, rather than by acid-catalysed hydration of D-glucal produced by an elimination pathway. 

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