Elimination alkylative

Historically, the rhodium catalyzed carbonylation of methanol to acetic acid required large quantities of methyl iodide co-catalyst (1) and the related hydrocarboxylation of olefins required the presence of an alkyl iodide or hydrogen iodide (2). Unfortunately, the alkyl halides pose several significant difficulties since they are highly toxic, lead to iodine contamination of the final product, are highly corrosive, and are expensive to purchase and handle. Attempts to eliminate alkyl halides or their precursors have proven futile to date (1). 

Termination Reactions / -Hydrogen Elimination, Alkyl Chain End Transfer, and fi-Methyl Elimination... 

A broad spectrum of chemical reactions can be catalyzed by enzymes Hydrolysis, esterification, isomerization, addition and elimination, alkylation and dealkylation, halogenation and dehalogenation, and oxidation and reduction. The last reactions are catalyzed by redox enzymes, which are classified as oxidoreductases and divided into four categories according to the oxidant they utilize and the reactions they catalyze 1) dehydrogenases (reductases), 2) oxidases, 3) oxygenases (mono- and dioxygenases), and 4) peroxidases. The latter enzymes have received extensive attention in the last years as bio catalysts for synthetic applications. Peroxidases catalyze the oxidation of aromatic compounds, oxidation of heteroatom compounds, epoxidation, and the enantio-selective reduction of racemic hydroperoxides. In this article, a short overview... 

However, when the salt anion is susceptible to hydrolysis by trace moisture (such as BF4 or PFe ), the generated HE eliminates alkyl carbonate as a surface species and only LiF can be observed as the overwhelming species in the SEI ... 

By contrast with the structurally congeneric telluronium salts R3Te + X that readily eliminate alkyl or aryl halides RX upon heating either in the solid or in pyridine solution (74MI1 83MI2), benzoxatelluroles 29 exhibit enhanced thermal stability and do not eliminate butyl halides even under prolonged heating. 

Eliminative alkylation of dithioacetals.1 The reaction of CH3MgI with ally lie dithioacetals in the presence of this Ni-phosphine catalyst (3 mole %) effects gem-dimethylation. A substituent at C2 favors formation of a 1,3-diene. 

These results, opposite to those observed for the cyclopentadienyl early transition metal systems, can be accounted for in terms of the known influence of the cocatalyst concentration on the possible eliminations, alkyl transfer pathways, and other deactivation processes [45,46]. Under similar conditions, the polymerization of ethylene at high pressure leads to a considerable increase in activity and produces polymers of higher molecular weight than at atmospheric pressure (entries 6 and 3). This effect is a consequence of the rate of insertion, which is proportional to the monomer concentration in solution. 

Triamino-halogenophosphonium halides, [(R2N)3PX]+ X , on heating eliminate alkyl halides with formation of phosphinoamioimines, which in turn dimerize to cyclic derivatives containing the tetraazaphosphonium moiety [PN4]+ moiety (R = Et, X = Br) (Scheme 25). ... 

The relative rates of chain transfer to monomer (briefly transfer), termination and propagation, determine molecular weights and ultimate conversions in most cationic olefin polymerizations. The corresponding model reactions are proton elimination, alkylation by the counteranion and formation of Cfg and higher fractions. Thus, a quantitative analysis of [Cfa]. [C13 or C14] and [Cj ] could give clues as to the relative rates of these competing reactions. The following equations further illustrate the concept ... 

The counter anion strongly affects the relative rates of elimination/ alkylation (transfer/termination). 

Telluroxide elimination, Alkyl phenyl tellurides on oxidation with CIC6H4CO3H in ether afford alkenes as the major product. In some cases a stable Te(IV) compound is formed, which undergoes elimination on pyrolysis. Examples ... 

The reaction of iminium chloride with alcohols affords imidoyl ester hydrochlorides LXXXVI as intermediates, which eliminate alkyl halides upon heating, thereby regenerating the corresponding carboxylic acid amide... 

The reactivity of the C—Pd bond is very diverse. In addition to the previously discussed j8-elimination and reductive elimination, alkyl-, benzyl-, aryl-, alkenyl-, and alkynyl-Pd complexes can undergo syn addition of the C—Pd bond across the C—C bond of alkenes and alkynes, that is, carbopalladation. This reaction can generate alkyl- or alkenyl-Pd complexes and is occasionally used as a preparative method, as exemplified in Scheme 31.Closely related is the hydropalladation of alkenes and alkynes. However, these processes are mostly observed under catalytic conditions. 

Alkenylboronic acids and esters are also very useful substrates (Equation 71, Figure 1.38) [405], in particular to access substituted olefins and dienyl moieties commonly encountered in several classes of bioactive natural products [282, 406]. To this end, Kishi and co-workers examined the influence of the base, and developed an optimal variant using thallium hydroxide [281]. Recently, allylic alcohols were found to couple directly with alkyl and alkenyl boronic acids without the aid of a base [407]. In rare cases, the Suzuki reaction has been applied to the use of alkylboronic acids [296, 408], including cyclopropylboronic acids [409]. Hitherto notorious for their tendency to undergo [3-hydride elimination, alkyl bromides are now suitable as electrophiles under carefully optimized conditions that even allow Csp -Csp couplings with alkylboronic acids (Equation 72) [410]. The Suzuki reaction has also been applied very successfully in solid-phase chemistry and combinatorial library synthesis [411]. It has been applied industrially [412], especially in medicinal chemistry, e.g. in the production of the antihypertensive drug losartan [195]. 

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