Elimination equations

These precursors are generally prepared by alkane elimination (Equation (7a)) or—especially useful with bulkier substituents—the coupling of metal chlorides with lithium pnictides or silyl arsines (Equation (7b)) or salt elimination or silyl halide elimination reactions (Equation (7c)) ... 

The last entry in this table, the results obtained from eliminating equation 5-4, represents of course the results obtained from the original set of three equations, since eliminating equation 5-4 from the set leaves us with exactly that same set. However, even though there does not seem to be much difference between the various equations represented by equations 2a -2d/, it is clear that the fitting equation depends very strongly upon which subset of these equations we choose to keep in our calculations. 

Eliminating equation 7-1 Eliminating equation 7-2 Eliminating equation 7-3 Eliminating equation 7-4... 

Oxidative addition of dihalomethanes CH2X2 to cyclic gold(i) ylide compounds yields bicyclic compounds with a methylene bridge between two gold(m) centers.2 The two halogens can also be replaced by diphenyl-dithiophosphinate groups to give products which are kinetically stable toward reductive elimination (Equation (38)).191... 

Selenoaldehydes,2 In the presence of 5-10 mole% of butyllithium, this disilyl selenide converts aldehydes into selenoaldehydes with formation of the disiloxane [(CH,)3SiOSi(CH3),]. The active reagent is presumed to be lithium trimethylsilyl-selenide, (CH3)3SiSeLi, which can be regenerated by a Peterson-type elimination (equation I). 

The influence of hydration on the reactivity of anions is much more evident in the case of OH. In the chlorobenzene-aqueous NaOH system the hydration sphere of tetrahexylammonium hydroxide dissolved in the organic phase progressively decreases from 11 to 3.3 water molecules when the base concentration is raised from 15 to 63%. This leads to an enhanced reactivity of OH which was measured in the Hofmann elimination (Equation 3). In the examined ranges of NaOH concentrations the reactivity increased up to more than four orders of magnitude (Table I). Although the dehydration of OH is... 

One of the most important side reactions often observed with the [1,2]-Wittig rearrangement is the a,/3 -elimination (equation 3). In fact, treatment of benzyl ether 3 with n-BuLi afforded predominantly the elimination product 4 (equation A f. 

Other 0-aUcylation methods are exploited less frequently. 0-Allylation of Af-substituted hydroxamic acids of type 25 with allyl carbonates such as 26 and related compounds has been achieved through palladium catalyzed addition-elimination (equation 16). 

Trost and Tanoury found an interesting skeletal reorganization of enynes using a palladium catalyst.In this reaction, the second product is derived from a metathesis reaction (Equation (5)). It was speculated that the reaction would proceed by oxidative cyclization of enynes with the palladium complex followed by reductive elimination and then ring opening. To confirm this reaction mechanism, they obtained a compound having a cyclobutene ring, which was considered to be formed by the reductive elimination (Equation (6)). 

Mg+" reacts with alcohols via either condensation or via elimination. The ontcome is snbstrate dependent. Thns while n-BnOH reacts via condensation (eqnation 24), f-BnOH reacts via elimination (equation 25). No oxidative reactions (cf equations 21-23) are observed. Armentront and coworkers have examined the CID reactions of methanol addncts of Mg using Xe as the collision gas and fonnd competition between ligand loss (eqnation 26), ligand switching (equation 27) and C—O bond activation (eqnations 28 and 29). 

The first practical approach applying this strategy consisted of a carbocupration of an alkynyl sulfoxide 47 followed by methylene homologation of 48 with a zinc carbenoid and /3-elimination (equation 20)25. Yields of 1,1-disubstituted allenes 50 are good to high as outlined in Table 4. 

C of the acetal and the Lewis acid. Enantiomerically pure cyclic acetals 49 deriving from chiral diols open a route to adducts 50, which can be successively elaborated to chiral /9-hydroxyesters upon oxidation of the alcoholic group followed by alkaline elimination (equation 33). 

Condensation with enolntes of carbonyl compounds (r/. T richloroethylene, 9,479-480). The reagent can react in two ways with carbonyl enolates. The first one evidently is a direct addition-elimination (equation I) the second one is considered to involve perchlorobutenync (a) as an intermediate (equation II).1... 

Selenoxide elimination.3 A short synthesis of royal jelly acid (2) from a commercially available starting material (1) involves phenylselenenylalion followed by concurrent ozonation of a double bond and selenoxide elimination (equation I). 

Enamines. In the presence of alumina (Woelm 200 neutral) cw-a,p-epoxy-silanes can be opened by pyrrolidine or morpholine to give a-amino-p-hydroxy-silanes, from which the pure as-enamine can be obtained by KH-induced syn p-elimination (equation I). The isomeric trans-a,p-epoxysilane is inert to this ring... 

A second process that has been invoked is heterolytic fission of H2.49 Examples are shown in equations (15) and (16). Although the overall process certainly involves heterolysis, some or all of these reactions may well go via initial oxidative addition followed by fast deprotonation or reductive elimination (equation 17). A third variant closely related to heterolytic fission is the addition of hydrogen across a metal-ligand or metal-metal bond. Examples are shown in equations (18) and (19). Here too, homolytic addition via equation (1) followed by fast reductive elimination may be taking place in some cases. In d° systems, the homolytic fission reaction of equation (1) is unlikely as the metal is already at its maximum valency, so examples of heterolytic fission and addition to... 

Elimination. Two kinds of elimination reaction are important in homogeneous catalysis. A catalytic cycle which has involved an oxidative addition generally ends with the reverse process of reductive elimination (equation 6). Rhodium-catalyzed hydrogenations end with this step. 

The other common elimination is the /3-elimination (equation 7). This is a vital step in many palladium-catalyzed reactions, such as alkene arylation, and occurs as a side reaction leading to isomerization in other alkene reactions such as hydrogenation and hydroformylation. 

The mechanism of this transformation presumably involves palladium alkoxide formation followed by jS-hydride elimination (equation 191). 

Pyrolyses of esters (60) and xanthate esters (61), either in the gas phase or in solution, give 1,2-elimination (Equations 7.46 and 7.47). These reactions are... 

A special example is the replacement of a nitro group on [(Tj6-nitrobenzene)FeCp]+.78,79 Reaction with O-, S-, N- and stabilized C-nucleophiles gives overall addition-elimination (equation 25). The nitroarene complexes are prepared by oxidation of the corresponding aniline complexes and are readily available.78,79... 

Attack by nucleophiles on the electrophilic ir-allylpalladium complex can take place by two distinct mechanisms, which have opposite stereochemical consequences. Stereochemical inversion is achieved by attack of the nucleophile directly on the allyl ligand on the face opposite the palladium (equation 148). Retention is achieved by attack of the nucleophile at the metal center, followed by reductive elimination (equation 149). The reductive elimination step could proceed through an V-allylpalladium-Nuc species or directly from an i)3-allylpalladium-Nuc complex. Recent evidence strongly suggests the latter pathway.384... 

Conversion of allylic acetates of allylstannanes by treatment with Et2AlSnBus and Pd° catalysts proceeds by addition of the tin to the metal, followed by reductive elimination (equation 204).309 The corresponding ally phosphonate, however, showed some loss of stereochemical integrity (equation 205).310 The Pd°-catalyzed reaction of allylic acetates, trialkyltin chlorides and Smh produced allylstannanes with no stereospecificity.311... 

The /i-effect was first noted by Ushakov and Itenberg in 193734, and in 1946 Sommer, Whitmore and coworkers reported the high reactivity of /f-chlorosilyl systems to elimination (equation 14), compared to the corresponding a- and y-systems35,36. 

Two different mechanisms have been proposed for this dehydrogenative silylation process. The first mechanism proposed by Oro, Esteruelas and coworkers includes the oxidative addition of 1-alkyne to the Ir—Si bond, followed by the reductive elimination of 151 (equation 61)117,118. The proposed mechanism is supported by the identification of [IrH(C=CPh)( j2-( -Pr)2PCH2CH20Me)]BF4 in stoichiometric as well as catalytic conditions by 31P 1H NMR analyses118. The other mechanism proposed by Jun and Crabtree includes the insertion of 1-alkyne into the Ir—Si bond, followed by isomerization and /J-hydride elimination (equation 62)113, which is consistent with the mechanism proposed for the highly selective formation of (Z)-l-silyl-l-alkenes (see Section IILB)115. 

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