Isomerization reactions stereochemistry

Palladium, (diammine)bis(thiocyanato)-isomerism, 1, 185 Palladium, dichlorobis(amine)-substitution reactions stereochemistry, 1, 318 Palladium, dichlorobis(pyridine)-substitution reactions, 1, 314 Palladium, dinitritobis(triisopropylphosphine)-substitution reactions, I, 314 Palladium, ethylene-synthesis... 

Hamed, O., Henry, P.M. and Thompson, C. (1999) Palladium(II)-catalyzed exchange and isomerization reactions. 17. Exchange of chiral allyl alcohols with hydroxide, methoxide, and phenyl at high [Cl-]. Stereochemistry of the Wacker reaction. J. Org. Chem., 64, 7745. 

The photochemical isomerization reaction has been shown" to be stereospecific following the disrotatory photochemically allowed cyclization path. Thus the stereochemistry of the nitrone is preserved in the oxaziridine. However, since some nitrones undergo trans-cis isomerization under the conditions of photolysis, mixtures of oxaziridines often result. 

If the X and Y ligands in the product are considered to be formally -1, then the metal center has increased its formal oxidation state by +2, and diis is the origin of the name oxidative addition. The reverse reaction is called reductive elimination. The various mechanisms have been reviewed by Rendina and Puddephat, with special reference to Pt(II) systems. The following reactions are examples of various types of oxidative additions. The stereochemistry of the products can be controlled by subsequent isomerization reactions and is not always indicative of the immediate oxidative addition product. 

Figure 5. Stereochemical effects of M4 isomerizations on stereochemistries of free radical oxidation Arbuzov, and substitution reactions...

These investigations are complicated by isomerization reactions which have to be considered. It is to be decided whetlier the stereochemistry observed is a result of the metathesis reaction or of isomerization reactions and whether the isomerization occurs via metathesis. 

In the first five chapters, we examined the most basic ideas of organic chemistry. We applied principles of general chemistry, such as orbital theory, thermodynamics, and kinetics, to organic molecules. We also introduced topics of particular relevance to organic chemistry, such as isomerism and stereochemistry. The properties and reactions of alkanes gave us an opportunity to observe many of these basic principles in action. 

Nitrile ylides derived from the photolysis of 1-azirines have also been found to undergo a novel intramolecular 1,1-cycloaddition reaction (75JA3862). Irradiation of (65) gave a 1 1 mixture of azabicyclohexenes (67) and (68). On further irradiation (67) was quantitatively isomerized to (68). Photolysis of (65) in the presence of excess dimethyl acetylenedicar-boxylate resulted in the 1,3-dipolar trapping of the normal nitrile ylide. Under these conditions, the formation of azabicyclohexenes (67) and (68) was entirely suppressed. The photoreaction of the closely related methyl-substituted azirine (65b) gave azabicyclohexene (68b) as the primary photoproduct. The formation of the thermodynamically less favored endo isomer, i.e. (68b), corresponds to a complete inversion of stereochemistry about the TT-system in the cycloaddition process. 

There appears to be no end to the structural ingenuity of boron and, whilst it is true that many regularities can now be discerned in its stereochemistry, much more work is still needed to unravel the reaction pathways by which the compounds are formed and to elucidate the mechanisms by which they isomerize and interconvert. 

The stereoisomers of olefin saturation are often those derived by cis addition of hydrogen to the least hindered side of the molecule (99). But there are many exceptions and complications (97), among which is the difficulty of determining which side of the molecule is the least hindered. Double-bond isomerization frequently occurs, and the hydrogenation product is the resultant of a number of competing reactions. Experimentally, stereochemistry has been found to vary, sometimes to a marked degree, with olefin purity, reaction parameters, solvent, and catalyst 30,100). Generalizing, it is expedient, when unwanted products arise as a result of prior isomerization, to avoid those catalysts and conditions that are known to favor isomerization. 

Nickel, methyltetrakis(trimethylphosphine)-tetraphenylborate stereochemistry, 1,44 Nickel, pentacyano-isomerism, 1, 206 structure, 1, 40 Nickel, tetracarbonyl-cxchangc reactions, 1,288 Nickel, tetracyano-, 5,67 Nickel, tetrahalo-, 5, 186 Nickel, tetrakis(dinitrogen)-syn thesis... 

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