Elimination reactions activation

BU3P. A rapid redox reaction takes place to yield the active Pd(0) species and tributylphosphine oxide. The Pd(0) thus generated is a phosphine-free cata-lyst[341]. Severe reaction conditions are necessary, or no reaction takes place, when Pd2(dba)3 is used in the elimination reaction of cyclic allylic compounds with an excess of -Bu3P[342]. 

The optically active 1,4-cyclohexenediol monoacetate 525, prepared by hydrolysis of the me.so-diacetate with lipase, was converted into the optically pure cyclohexenone 526 by an elimination reaction in the presence of ammonium formate. Optically active carvone (527) was prepared from 526[343],... 

Neutral alcohols, ROH, and ethers, ROR, do not undergo either substitution or elimination reactions, presumably because OH (OR ) is a poor leaving group. Acids can activate OH (OR) by converting it into a better leaving group. 

A 1,8-naphthyridine, nalidixic acid (39), shows clinically useful antibacterial activity against Gram-negative bacteria as such, the drug is used in the treatment of infections of the urinary tract. Condensation of ethoxymethylenemalonate with 2-amino-6-methylpyridine (36) proceeds directly to the naphthyri-dine (38) the first step in this transformation probably involves an addition-elimination reaction to afford the intermediate, 37. W-Ethylation with ethyl iodide and base followed by saponification then affords nalidixic acid (39). 

It has been shown that the imidoyl chloride moiety of 2(lff)-pyrazinones can imdergo an easy addition/elimination reaction with alkyl amines [24], while reactions with anilines proceed under harsher conditions. Ullmann coupling [109-113] of 2(lff)-pyrazinones with substituted anilines could open the way to the libraries of physiologically active compounds useful in inhibiting HIV replication [7]. Polymer-bound pyrazinone was successfully... 

This section describes reactions in which elimination to form a double bond or a new ring occurs as a result of thermal activation. There are several such thermal elimination reactions that are used syntheses, some of which are concerted processes. The... 

Another important family of elimination reactions has as its common mechanistic feature cyclic TSs in which an intramolecular hydrogen transfer accompanies elimination to form a new carbon-carbon double bond. Scheme 6.20 depicts examples of these reaction types. These are thermally activated unimolecular reactions that normally do not involve acidic or basic catalysts. There is, however, a wide variation in the temperature at which elimination proceeds at a convenient rate. The cyclic TS dictates that elimination occurs with syn stereochemistry. At least in a formal sense, all the reactions can proceed by a concerted mechanism. The reactions, as a group, are often referred to as thermal syn eliminations. 

Alkane activation by metal atoms by osmium atoms, 273-274 by rhenium atoms, 265-271 by tungsten atoms, 270-272 description, 265 Alkane elimination reactions, processes, 20,22... 

Fixation by formaldehyde virtually eliminates enzymatic activity in a process that is sometimes reversible (vide infra). Dehydration and embedding significantly reduces the reversibility of this process, suggesting that dehydration and embedding facilitate additional chemical reactions that are not observed in aqueous solution. 

Reactions leading to the formation of the catalytically active nickel hydride species from organonickel precursors (Section III) can be regarded as model reactions for olefin oligomerization reactions. The reactions described by Eq. (8) and Scheme 3 (Section III) show that RNiX compounds (R = methyl orallyl, X = halide or acetylacetonate) activated by Lewis acids add to double bonds under mild reaction conditions (-40° or 0°C). It follows further from these reactions that under conditions leading to olefin dimerization a rapid nickel hydride /3-hydrogen elimination reaction occurs. The fact that products resulting from olefin insertion into the nickel-carbon bond are only observed when /3-hydride... 

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