Elimination results

The resulting macrocyclic ligand was then metallated with nickel(II) acetate. Hydride abstraction by the strongly electrophilic trityl cation and proton elimination resulted in the formation of carbon-carbon double bonds (T.J. Truex, 1972). 

According to these conclusions, it is possible to propose a catalytic cycle (Fig. 20) involving no radical species, but a copper(I) complex with the classical oxidative addition, nucleophilic substitution and reductive elimination resulting lastly in the arylated nucleophile. 

Oxidative addition of a silyl-protected 4-(bromomethyl)phenol precursor to (tme-da)Pd(II)Me2 (tmeda = tetramethylethylenediamine), followed by ethane reductive elimination, resulted in formation of the benzylic complex 16 (Scheme 3.10). Exchange of tmeda for a diphosphine ligand (which is better suited for stabilizing the ultimate Pd(0) QM complex), followed by removal of the protecting silyl group with fluoride anion, resulted in the expected p-QM Pd(0) complex, 17, via intermediacy of the zwitterionic Pd(II) benzyl complex. In this way a stable complex of p-BHT-QM, 17b, the very important metabolite of the widely used food antioxidant BHT20 (BHT = butylated hydroxytoluene) was prepared. Similarly, a Pd(0) complex of the elusive, simplest /)-QM, 17a, was obtained (Scheme 3.10). 

Monitor serum creatinine because patients with renal insufficiency (CrCl less than 50 mL/minute) may have reduced ribavirin elimination resulting in increased drug accumulation and toxicity (e.g., hemolytic anemia). 

These compounds contain a furan ring fused to a benzene moiety in the 2,3-position. This synthesis was also described by Flynn et al. [73] and is shown in Scheme 25 involved the coupling of 2-iodo-5-methoxyphenol 104, 4-methoxyphenylethyne 105 to form the intermediate o-alkynylphenolate 106. Aryl iodide 107 was added to the phenolate in DMSO with heat. Oxidative addition, palladium(II)-induced cyclization and reductive elimination resulted in the product 108 with an 88% yield. 

The higher catalytic activity of the cluster compound [Pd4(dppm)4(H2)](BPh4)2 [21] (20 in Scheme 4.12) in DMF with respect to less coordinating solvents (e.g., THF, acetone, acetonitrile), combined with a kinetic analysis, led to the mechanism depicted in Scheme 4.12. Initially, 20 dissociates into the less sterically demanding d9-d9 solvento-dimer 21, which is the active catalyst An alkyne molecule then inserts into the Pd-Pd bond to yield 22 and, after migratory insertion into the Pd-H bond, the d9-d9 intermediate 23 forms. Now, H2 can oxidatively add to 23 giving rise to 24 which, upon reductive elimination, results in the formation of the alkene and regenerates 21. 

The values of y are tabulated with the data. There are 5 constants and S equations. The solution of the linear equatioons by Gaussian elimination results in the rate equation... 

Out of the above the P elimination is most common. These eliminations result in the formation of alkenes and alkynes. When P phenylethyl bromide is heated with an alcoholic solution of an alkali first a carbanion is formed by the loss of a proton followed by the loss of a halide ion and simultaneous formation of a double bond. 

With the paraboloid method followed by the maximum-likelihood refinement of the exit-wave function, the inherent effects of the microscope on the exit wave function due to spherical aberration and defocus are eliminated resulting in a complex-valued wave function with the delocalization removed. However, the electron wave function frequently suffers from residual aberrations due to insufficient microscope alignment. In a single image, it is not possible to remove these aberrations, but, with the reconstructed complex wave function, one can use a numerical phase plate to compensate the effect of aberrations by applying appropriate phase shifts (Thustetal. 1996b). 

Some patients show a hypersensitivity to succinylcholine, which is related to an acquired or inherited dysfunction of unspecific esterases. The reduced rate of elimination results in a more effective and longer duration of action. 

Diazotization of 2-(di-2-furylmethyl)anilines 255 gave the corresponding diazonium salts. Intramolecular attack of the diazonium functionality on the 7t-system of one of the electron-rich furan rings yielded 256. Subsequent elimination results in ring opening which yielded cinnolines 257 (Scheme 64) <1997MOL62, 2000T8933>. 

Bromination of the enol ether product with two equivalents of bromine followed by dehydrobromination afforded the Z-bromoenol ether (Eq. 79) which could be converted to the zinc reagent and cross-coupled with aryl halides [242]. Dehydrobromination in the presence of thiophenol followed by bromination/dehydrobromination affords an enol thioether [243]. Oxidation to the sulfone, followed by exposure to triethylamine in ether, resulted in dehydrobromination to the unstable alkynyl sulfone which could be trapped with dienes in situ. Alternatively, dehydrobromination of the sulfide in the presence of allylic alcohols results in the formation of allyl vinyl ethers which undergo Claisen rearrangements [244]. Further oxidation followed by sulfoxide elimination results in highly unsaturated trifluoromethyl ketonic products (Eq. 80). 

The ability of the Y group to be eliminated results apparently from the superposition of two factors on the one hand, the specific leaving ability of the Y group, and on the other, the possibility of intramolecular interactions between the Y group and the phosphorus atom. Further, the EHa mechanism is favoured by low hydroxide ion concentration680,719, since it is first order with respect to hydroxide ion, whereas the competitive mechanisms or p] are second order. 

This approach gave fair yields of Gly-based building units (R2=H). A similar approach was used 122 to prepare a variety of monomers (Scheme 18) used in the synthesis of Leu-enkephalin peptoids. In the case of substituted a-halocarboxylic acids or esters bearing R2 side chains the yields were lowered because of racemization and p-elimination resulting in the undesired a, 3-dehydrocarboxylic acids in addition to the desired chiral building unit. Another problem was polyalkylation. 

Selenothiolactonization Cycloalkenethiolcarboxylic acids react with 1 to form S-acyl phenylselenosulfides (2), which undergo cyclization to phenylseleno-thiolactones (3) when refluxed in benzene in the presence of AIBN. The C6H5Se group of 3 is selectively oxidized by m-C 1C6H4C03H, and subsequent selenoxide elimination results in thiolactones (4). 

The activated DMSO 9 can also suffer an elimination, resulting in the highly reactive H2C=S(+)-CH3 species that can react with the alcohol, yielding a methylthiomethyl ether 13 as a side compound. Fortunately, this elimination demands a higher temperature than the normal temperature of oxidation, and a proper control of the temperature minimizes the formation of the methylthiomethyl ether side compound. 

Diols are sometimes transformed with Fetizon s reagent into an intermediate (3-hydroxycarbonyl compound, which suffers water elimination resulting in the formation of an enone.6a... 

Stille coupling was also developed in tlie early 1980s and is similar to Suzuki coupling in its sequence. It is used to couple aryl or vinyl halides or triflates with organotin compounds via oxidative addition, transmetallation, and reductive elimination. The oxidative addition reaction has tlie same requirements and preferences as discussed earlier for tlie Heck and Suzuki reactions. The reductive elimination results in formation of tlie new carbon-carbon bond. The main difference is that tlie transmetallation reaction uses an organotin compound and occurs readily without the need for an oxygen base. Aryl, alkenyl, and alkyl stannanes are readily available. Usually only one of tlie groups on tin enters into... 

Unsaturated 1,5-dicarbonyl compounds. The phenylthioalkylation of silyl enol ethers of carbonyl compounds (9, 521-522) can be extended to the synthesis of unsaturated 1,5-dicarbonyl compounds. In a typical reaction the enol silyl ether of a ketone is alkylated with the unsaturated chloride 1 under ZnBr2 catalysis to give a homoallyl sulfide. Ozonolysis of the methylene group is accompanied by oxidation of the phenylthio group sulfoxide elimination results in an unsaturated 1,5-aldehydo ketone (equation I). Alkylation with 2 results in a methyl ketone (equation II). 

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