Alkene derivatives mechanisms

In contrast, the ultrasonic irradiation of organic Hquids has been less studied. SusHck and co-workers estabHshed that virtually all organic Hquids wiU generate free radicals upon ultrasonic irradiation, as long as the total vapor pressure is low enough to allow effective bubble coUapse (49). The sonolysis of simple hydrocarbons (for example, alkanes) creates the same kinds of products associated with very high temperature pyrolysis (50). Most of these products (H2, CH4, and the smaller 1-alkenes) derive from a weU-understood radical chain mechanism. 

The suggestion that a metal carbene was the active metal-containing species involved in the reaction inspired an impressive number of elegant experiments, designed to test the vahdity of this mechanism. The results of double crossover experiments as well as isotopic labeling experiments showed conclusively that a pairwise mechanism could not account for the observed data. The reaction shown in equation (5) shows the possible products of the metathesis of two isotopically labeled dienes, and these products include a cyclic alkene derived from the closing of the diene as well as a series of deuterated ethylenes. At very low conversions, the observed ratio of ethylenes was 1 2 1 dQ d.2.d ). A detailed analysis of these results demonstrated that the pairwise mechanism could not possibly account for this result, while the carbene mechanism could. 

Simple amines in the presence of Oxone oxidize alkenes to oxiranes. For example, Oxone, pyridine, and a 2-pyrrolidine derivative in a medium of aqueous acetonitrile selectively converts the triene in Equation (72) to a single epoxide. This process also proceeds using noncyclic alkenes. The mechanism is believed to proceed via a single-electron transfer (SET) process involving radical cation intermediates <2000JA8317>. 

Tosylhydrazones of aliphatic aldehydes and ketones react with a base in an aprotic solvent at 90-180 C to give diazo compounds which undergo thermal decomposition with loss of nitrogen to yield alkenes derived from hydrogen migration and cyclopropanes from intramolecular insertion. In proton donor solvents decomposition of y-tosylhydrazones by base occurs primarily by a cationic mechanism involving diazonium and/or carbenium ion intermediates. 

Treatment of an alkyne/alkene mixture with ruthenium carbene complexes results in the formation of diene derivatives without the evolution of byproducts this process is known as enyne cross-metathesis (Scheme 22). An intramolecular version of this reaction has also been demonstrated, sometimes referred to as enyne RCM. The yield of this reaction is frequently higher when ethylene is added to the reaction mixture. The preferred regiochemistry is opposite for enyne cross-metathesis and enyne RCM. The complex mechanistic pathways of Scheme 22 have been employed to account for the observed products of the enyne RCM reaction. Several experiments have shown that initial reaction is at the alkene and not the alkyne. The regiochemistry of enyne RCM can be attributed to the inability to form highly strained intermediate B from intermediate carbene complex A in the alkene-first mechanism. Enyne metathesis is a thermodynamically favorable process, and thus is not a subject to the equilibrium constraints facing alkene cross-metathesis and RCM. In a simple bond energy analysis, the 7r-bond of an alkyne is... 

Loss of pyridine from 349 and trans-cis isomerization should give an intermediate accounting for the oxidative addition of the hydrocarbon and the H/D isotopic exchange between CsDs and hydrocarbons catalyzed by 349 (for cyclohexane/CsDg, measurements yielded TON = 240). The related phenyl derivative [IrPh(re -0,0-acac)2(py)] 352 catalyzes the anti-Markovnikov hydroarylation of unactivated alkenes. ° The mechanism of the alkene hydroarylation catalyzed by 352 was theoretically analyzed by DFT methods. ... 

Rahman and Clapp decomposed dinitromethane derivatives in DMF in the presence of alkenes to obtain 2-isoxazolines. Without any alkene present, an acid and KNO2 were obtained. They proposed a mechanism which proceeded via a three-membered ring or a nitrocarbene which rearranged to a nitrile oxide (76JOC122, 75MI41612). 

Electrophilic attack on the sulfur atom of thiiranes by alkyl halides does not give thiiranium salts but rather products derived from attack of the halide ion on the intermediate cyclic salt (B-81MI50602). Treatment of a s-2,3-dimethylthiirane with methyl iodide yields cis-2-butene by two possible mechanisms (Scheme 31). A stereoselective isomerization of alkenes is accomplished by conversion to a thiirane of opposite stereochemistry followed by desulfurization by methyl iodide (75TL2709). Treatment of thiiranes with alkyl chlorides and bromides gives 2-chloro- or 2-bromo-ethyl sulfides (Scheme 32). Intramolecular alkylation of the sulfur atom of a thiirane may occur if the geometry is favorable the intermediate sulfonium ions are unstable to nucleophilic attack and rearrangement may occur (Scheme 33). 

Photochemical reaction of the ester 114 afforded the alkene 115 and three products derived from 115. A mechanism, involving dimerization of 114 leading to a dithietane intermediate 116, was proposed. Trapping of active sulfur species, generated from 116, with dienes was also described (75CB630). 

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