Reactions p-elimination

Athene formation requires that X and Y be substituents on adjacent carbon atoms By mak mg X the reference atom and identifying the carbon attached to it as the a carbon we see that atom Y is a substituent on the p carbon Carbons succeedmgly more remote from the reference atom are designated 7 8 and so on Only p elimination reactions will be dis cussed m this chapter [Beta (p) elimination reactions are also known as i 2 eliminations ] You are already familiar with one type of p elimination having seen m Section 5 1 that ethylene and propene are prepared on an industrial scale by the high temperature dehydrogenation of ethane and propane Both reactions involve (3 elimination of H2... 

The E2 P-elimination reaction is a base-catalyzed concerted mechanism ... 

Fig. 1 Time-course of the P-elimination reaction of a 2.5 mg/ml pectin solution at 25 C in 0.2 M sodium hydrogenocaibonate carbonate buffer.

If a hydrogen atom is present in the p position of the halogen, a p-elimination reaction becomes possible. If the unsaturated compound obtained is particularly unstable, the reaction will be dangerous. 

ProLynx LLC has developed another type of releasable PEGylation technology based on the p-elimination reaction shown in Scheme 4. In this system, the release rate of the native drug is determined by the acidity of the proton adjacent to the... 

These P elimination reactions have been used in an olefine synthesis called the Peterson olefination reaction which is analogous (and sometimes superior) to the Wittig reaction. The Peterson olefination reaction involves the addition of an a-silyl carbanion to an aldehyde or ketone to give P-hydroxysilane, followed by P-elimination to give the olefine. 

FIGURE 7.5 Preparation of a protected dipeptide by the mixed-anhydride method, employing a chloroformate that generates a cleavable urethane.13 The urethane impurity is destroyed by a P-elimination reaction. NMM = A-methylmorpholine, Msc = methane-sulfonylethoxycarbonyl. 

A. Heterolysis of the Metal-Carbon a-Bond Homolysis of the Metal-Carbon a-Bond Oxidation of Lm iM +1-R Followed by Homolysis P-Hydride Shift Reactions P-Elimination Reactions P-Elimination of Carboxylates CO Insertion/Methyl Migration... 

The second important chain termination reaction characteristic of the catalysis of anionic polymerization of epoxy compounds by the TA consists in the abstraction of the hydrogen atom from the p-carbon atom in the tetraalkylammonium cation by the growing alkoxy anion (P-elimination reaction)I58 164). 

On esterification, the carboxyl group in uronic acid residues becomes a carboxylate that is electron-withdrawing, and, on subsequent treatment with base, / -elimination will occur. The p-elimination reaction for uronic acids and their derivatives has been reviewed in this Series, 6 and only its applications to structural polysaccharide chemistry will be discussed here. 

In addition to decomposition by loss of free radicals, Ga(C2H5)3 and Ga compounds with larger alkyl groups can undergo decomposition through a P-elimination reaction (118, 130). 

Starting from L-rhamnono-1,4- or 1,5-lactone, via p-elimination reactions, 3,5,6-trideoxy-a-DL-t/zra -hexose276 or 3,4,6-trideoxy-DL-t/zreo-hexose has been obtained.277... 

We studied the P-elimination and replacement reactions using our pyridoxamine analogs [43]. Initially, we examined the relative rates for the P-elimination reactions between chloropyruvic acid and small pyridoxamine analogs carrying a basic side chain (Table 2.2). In the dimethylamino series the HC1 elimination rates were fastest with the shorter chain of 4, as expected for a process that requires only proton removal from the pyridoxamine 4 -CH2 group. The contrast with the data for transamination... 

Bayer, Pan, and Kazmaier (7) proposed that labile sulfur originates from cysteinyl residues by a p-elimination reaction in the presence of... 

The migration reaction diminishes the total electron count of the complex by two, and creates a vacant site at the metal P-elimination does the opposite. P-Elimination requires a vacant site at the metal centre, and the electron count of the complex increases by two electrons during the process. The reaction resembles the P-elimination reaction occurring in many organic processes, but the difference lies in the intramolecular nature of the present process, as the eliminated alkene may be retained in the complex. In organic chemistry the reaction may well be a two-step process, e.g. proton elimination with a base followed by the leaving of the anion. In transition metal chemistry, however, it is the availability of d orbitals that greatly facilitates a concerted cis P-elimination. 

Figure 22.2. Enzymatic and chemical cleavage of DNA strand at the AP site. AP sites are chemically unstable, undergoing spontaneous P-elimination leading to DNA strand break at the 3 side of the AP site. Only the AP endonuclease generates a 3 terminus at the strand break that can be used by a DNA polymerase for DNA synthesis. The p-elimination reaction can also be catalyzed by AP lyases. The fate of the baseless deoxyribose is highlighted.

Scheme 5.62. Ab72D4 catalyzes the 4/( -selective p-elimination reaction and the 45-selective retroaldol reaction.

The reverse of the 1,3-migration of H from metal to coordinated olefin to form metal alkyls is the p-elimination reaction, where the hydrogen on the p-carbon migrates to the metal,... 

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