Salt, viii

Finally, compound (iv) is condensed with either trimethyl(6-methyl-3-pyridyl)tin or the boronate ester by means of Pd(PPh3)4 to afford etoricoxib. The metallated pyridine (vii) is obtained by esterification of 3-hydroxy-2-methylpyridine with triflic anhydride to give the corresponding triflate, which is treated with a tin reagent to yield the target tin intermediate. The boron lithium salt (viii) is prepared by treatment of 5-bromo-2-methylpyridine with butyllithium followed by addition of triisopropyl borate. 

Introduction of an alkyl group at the C-13 position of the protoberber-ine ring system is readily accomplished by direct alkylation of either the 8-acetonyl base 77) or the dihydro derivative (78) of the appropriate alkaloid. Reduction of the resulting salt, usually without isolation, affords the corresponding epimeric 13-methyltetrahydro bases. The conversion (79) of palmatine (V) to corydaline (VI) and mesocorydaline (VII) via the salt VIII exemplifies the use of this reaction which constitutes an early example of the now well-known C-alkylation of an enamine. 

The relative proportions of VI and VII obtained from the intermediate salt VIII (R = H) apparently vary with the nature of the reducing agent zinc-acid systems aiford corydaline predominantly 79) while boro-hydride reduction 80) is claimed to give corydaline exclusively. Products of types VI and VII may not originate exclusively from reduction of the imonium salt since a recent investigation (5i) of the reaction of methyl iodide with dihydroberine has indicated the imonium salt corresponding to VIII (R = H) readily disproportionates to berberine and tetrahydroberberine (IX). 

Quantitative Scales of Solvent Nucleophilicity. Solvolytic studies in solvents of low nucleophilicity led to renewed interest in quantitative measures of solvent nucleophilicity. Peterson and Waller (44) derived a scale of solvent nucleophilicity (Npw) from the rates of displacement by solvent of tetramethylenehalonium ions (VI) in liquid sulfur dioxide. The reaction is approximately half-order in carboxylic acid, possibly because dimer-monomer preequilibrium occurs (44). More recently, hydrolysis of the iodonium salt (VIII) in competition with anionic or solvent nucleophiles was studied. A scale of nucleophilicity relative to water was obtained by quan-... 

Another approach that has been reported for making water-processable resists is via polymeric quaternary pyridinium salts (VIII), which are made light sensitive by reaction with an aldehyde. ... 

The blsoxonlum Ion salt VIII decomposes on melting to give 1 mole of blsester V and 2 moles of THF (12). VIII Is sparingly soluble In THF at 25" and very slowly disappears over several hours by Initiating polymerization. It Is very soluble in nltromethane, In which solvent It has been found to polymerize THF as rapidly as (CF3S02)20 initiation. 

Chapters III to VII discuss the general properties of thiazoles having hydrocarbon and functional substituents, respectively. A special chapter (Chapter VIII) is devoted to mcso-ionic thiazoles, and Chapter IX describes the thiazolium salts and their numerous cyanine dyes derivatives. The last chapter concerns the monocyclic selenazoles. 

Dehalogenation of monochlorotoluenes can be readily effected with hydrogen and noble metal catalysts (34). Conversion of -chlorotoluene to Ncyanotoluene is accompHshed by reaction with tetraethyl ammonium cyanide and zero-valent Group (VIII) metal complexes, such as those of nickel or palladium (35). The reaction proceeds by initial oxidative addition of the aryl haHde to the zerovalent metal complex, followed by attack of cyanide ion on the metal and reductive elimination of the aryl cyanide. Methylstyrene is prepared from -chlorotoluene by a vinylation reaction using ethylene as the reagent and a catalyst derived from zinc, a triarylphosphine, and a nickel salt (36). 

The fact that the isomeric structure of azolides is thermodynamically controlled has been used by Olofson and Kendall to prepare 1-alkylazoles regioselectively (70JOC2246). An asymmetric pyrazole yields two alkylated derivatives (Scheme 21 see Section 4.04.2.1.3 (viii)), but the alkylation with a powerful alkylating agent of the acetylated derivative leads to the less abundant isomer via the salt (249), which is too unstable to be isolated. 

Proof of formula (VI) for dehydrolaudanosoline salts was provided by a study of its exhaustive methylation, the products at the first and second stages of the application of this process being 5 6-dimethoxy-2-(3 4 -dimethoxy-6 -vinylphenyl)-l-methyldihydroindole (VIII) and 6-dimethyl-amino-3 4 3 4 -tetramethoxy-6 -vinylstilbene (IX) respectively. 

SELECTIVE OXIDATIONS OF HYDROXY STEROIDS / 241 VIII. SILVER SALTS... 

Another way of replacing chloride trans to phosphine involves using silver salts reaction with AgPF6 and AgN03 introduces, respectively, a water molecule (XII) and a nitrate group (IX), which may in turn be replaced by a range of Lewis bases, giving (VIII), (X) and (XXV). 

Refs to nitrated materials, eg Cellulose Nitrate, Cyclonite etc., already described in this Encyclopedia will be found in Sections 11 111 In view of the definition of nitration presented above and the concepts to be developed in Section VIII, discussion of nitrate salts such as H2NNH2.HNG3 or CH3NH2.HN03 etc is not included in this article... 

High temperature coordination chemistry of group VIII. K. E. Johnson and J. R. Dickinson, Adv. Molten Salt Chem., 1973, 2, 83-198 (284). 

These oxidants have been used rarely. The kinetics of periodate oxidation of sulphoxides have been studied119,124. In an acid medium the reaction proceeds without catalysis but in alkali a catalyst such as an osmium(VIII) or ruthenium(III) salt is required124. Iodosylbenzene derivatives have also been used for the oxidation of sulphoxides to the sulphone level94,125 (equation 39). In order to use this reaction for the synthesis of sulphones, a ruthenium(III) complex should be used as a catalyst thus quantitative yields are obtained at room temperature in a few minutes. However, column chromatography is required to separate the sulphone from the other products of the reaction. 

Formation of mixtures of products in these reactions can be attributed largely to the properties of the acetate group. The reactions of a number of cycloalkenes with thallium(III) salts have been investigated in some detail and the results obtained have served both to elucidate the stereochemistry of oxythallation and to underline the important role assumed by the anion of the metal salt in these oxidations. The most unambiguous evidence as to the stereochemistry of oxythallation comes from studies by Winstein on the oxythallation of norbornene (VII) and norbornadiene (VIII) with thal-lium(III) acetate in chloroform, in which the adducts (IX) and (X) could be precipitated from the reaction mixture by addition of pentane 128) (Scheme 11). Both by chemical means and by analogy with the oxymercuration... 

The viscosity of the oxidized polymer (VIII) was determined using DMF as a solvent. Chloroform was not a good solvent because it was too volatile and resulted in poor reproducibility. The reduced viscosities are plotted against polymer concentration (Figure 6). Polymer VIII behaved like a polyelectrolyte, the reduced viscosities increased sharply on dilution in a salt free solution. The addition of 0.01 M KBr did not completely suppress the loss of mobile ions however, at 0.03 M KBr addition a linear relationship between the reduced viscosities and concentration was established. 

VIII. Polymer/Salt Hybrid Including Boron-Stabilized Imidoanion 190... 

VIII. POLYMER/SALT HYBRID INCLUDING BORON-STABILIZED IMIDOANION 190... 

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