By elimination

The other important route to silenes via eliminations has been studied by Jones el al. through addition of /-butyllithium to vinylchloro- or fluorosi-lanes followed by 1,2-elimination of the LiX [Eq. (11)]. While silenes... 

In contrast, exposure of 14-VE (diene)MCp Cl complexes (M = Zr, Hf) to CO (1 atm) results in the formation of cyclopentadienes70. The mechanism proposed for this transformation was elucidated with a carbon labeled CO ( CO) as requiring an initial coordination of CO to generate a (diene)MCp (CO)Cl complex 153 (Scheme 37). For the hafnium complex, the intermediate 153 (M = Hf) was observed by infrared spectroscopy. Insertion of CO into the a2, jt diene generates a metallacyclohexenone, which undergoes reductive elimination to generate the dimeric metallaoxirane species 154. -Hydride elimination from 154 (M = Zr, Hf) followed by 1,2-elimination produces substituted cyclopentadienes and the polymeric metal-oxide 155. Treatment of (diene)TiCp Cl with CO leads to isolation of the metallaoxirane complex 154 (M = Ti). 

The most straightforward synthesis of unsaturated Si=C compounds is the formation of the double bond by 1,2-elimination of a salt. This method has been widely used by N. Wiberg s and N. Auner s groups in recent years to produce a variety of different silenes. 

Alternatively, it may occur by 1,2-elimination of HPdCl followed by reverse readdition and reductive elimination. Moiseev and Vargaftik533 prepared the o-bonded complex independently by reaction of PdCl2 with 3-chloromercuri-ethanol and showed that it afforded acetaldehyde on decomposition ... 

The iV-methyl group is the source of one of the eliminated hydrogen. The subsequent loss of water by 1,2-elimination gives rise to the formation of the nitrile structure. Mass spectra of mono-, di-, and trideuterated nitroimidazoles were investigated in order to prove the fragmentation mechanism [1307],... 

Fischer carbyne complexes are usually generated from carbene complexes by 1,2-elimination of an alcohol under the influence of boron trihalides204 or other Lewis acids.205... 

Although the Cossee mechanism accounted for much of the experimental data related to Z-N polymerization, it was a bold proposal because 1,2-inser-tions into M-C bonds of early transition metal complexes were unknown at the time. Metal alkyls, should they form by 1,2-insertion into an M-C bond, ought to have a high propensity to undergo loss of a (3-hydrogen by 1,2-elimination. Thus,... 

The effect of chromium on the formation of CFC-1113 is proportional to the Cr loading thus, it appears that the support is the main (or sole) responsible for the dehalogenation reaction (by 1,2 elimination), which is repressed when the chromium phase covers the support surfece and blocks the access to the dehalogenation sites. 

Direct evidence in favor of the involvement of the free silene 54 in the trapping reactions is provided by the observation that trapping with 2,3-dimethylbutadiene yields a 4 1 mixture of the 4 + 2 adduct and the ene product, exactly the ratio in which the same two products are found when 54 is generated by 1,2-elimination from Me2SiX-CLi(SiMe3)2. 

A soln. of startg. chlorosulfone in DMF added via syringe to a stirred soln. of KOBu-/ in the same solvent at —40° under argon, after 5 min tropylium fluoroborate in DMF added dropwise during ca. 5 min below —40°, and stirred for a further 5 min - chloro(7-cycloheptatrienyl)phenyl(phenylsulfonyl)methane. Y 65%. F.e. and hepta-fulvenes by 1,2-elimination s. S. Ostrowski, M. Makosza, Ann. Chem. 1989, 95-7. 

Vinylketenes have been prepared by 1,4-elimination from the acid chloride (114) or by 1,2-elimination from (115), with triethylamine. The [2+2] adducts (116), (117), and (118) were formed with cyclopentadiene in the ratio indicated with vinyl-ketene from either source. In the presence of excess base equilibration of the isomers took place to give more (117) at the expense of (116) and (118). 

This rule deals with the structural orientation of the alkenes formed by 1, 2 -elimination reactions. The rule states that the least substituted product is the predominant product in a 1,2 - elimination reaction involving alkene formation. For example, when sec - butyl trimethyl ammonium hydroxide is heated, 1-butene will be formed predominantly. 

Usually ammonium, sulphonium and phosphonium compounds give the Hofmann products by 1, 2 elimination reactions. 

With TBHP, it is easy to remove the oxygen as it is formed by passing a slow current of argon. The main products formed were cyclooctene (minor) and cyclooctyl-/.-butyl mi. ed peroxide (major). We consider that these products arise from the postulated Fe -carton bond by 1,2-elimination to give cyclooctene and Fe or by ligand coupling of bound TBHP to give the mi. ed pero.xide and Fe. ... 

Many addition-elimination reactions at carbonyl centers involve a nucleophilic attack on the carbonyl carbon, followed by an elimination that restores the double bond. We first explore addition followed by 1,2-elimination, one of many types of reactions referred to as condensations. Strictly speaking, a condensation occurs when two large molecules combine to create a more complex molecule with the loss of a small molecule, such as water or an alcohol. Therefore, a condensation is a form of substitution. We will also examine condensation reactions that form polymers (see Chapter 13). One of the more complex condensations is the formation of an imine or enamine from a carbonyl and an amine. In both of these cases an oxygen is replaced by a nitrogen with loss of water (Eq 10.105 and 10.106). 

In a recent application of benzyne click chemistry [505], a variety of 1-substituted benzotriazoles (6, R = alkyl, aryl) was prepared by 1,3-dipolar cycloaddition of alkyl or aryl azides to benzyne generated from (2-TMS)phenyltriflate (7) by 1,2-elimination with CsF as fluoride source. This methodology tolerates a wide range of functional groups. 

Synthesis of Vinylsilanes. Lithiated reagent (2) reacts with a-trimethylsilyloxiranes to yield vinylsilanes (eq 8). The reaction involves nucleophilic opening of the oxirane ring by (2), followed by 1,2-elimination of a silyl and a phenylthio group. ... 

Compound (557) has been hydrolysed with the hope that, by analogy with the formation of trishomocyclopropenyl from cis-bicyclo[3,l,0]hex-3-yl tosylate, products from heptahomotropylium cation would be found. This was not realized and 97 % of the products arise by 1,2-elimination. In contrast to these negative results, a cyclopropyl substituent in arenes causes a large increase in... 

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