Phosphate esters as activators of decarboxylation catalytic reactions

Summary The possibilities for increasing the catalytic activity of magnesium and calcium in the decarboxylation of oxaloacetic acid was studied. The alkyl and aryl esters of phosphoric acid were used as activators of the reactions. The application of TBP as activator in 50% ethanolic medium permits the determination of 50g of magnesium.

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Zusammenfassung Möglichkeiten zur Erhöhung der katalytischen Wirksamkeit von Mg und Ca bei der Decarboxylierung von Oxalessigsäure wurden geprüft. Alkyl- und Arylester der Phosphorsäure wurden als Aktivatoren verwendet. Tributylphosphat als Aktivator in 50%ig äthanolischem Medium ermöglicht die Bestimmung von 50g Magnesium.

     

Catalytic reactions involving the cleavage of carbon-cyano and carbon-carbon triple bonds

The catalytic reactions that involve the cleavage of C-CN bonds and carbon-carbon triple bonds are described in this tutorial review. Regarding the cleavage of a C-CN bond, the catalytic reaction can proceed by two different mechanisms: oxidative addition and deinsertion of silyl isocyanide. A carbon-carbon triple bond can be cleaved in the absence of an organic promoter via the formation of unique organometallic species, such as allenylidene and cyclopropyl carbenoid complexes.     

Ligand-free Ni-catalyzed reductive cleavage of inert carbon-sulfur bonds

A catalytic reductive cleavage of C(sp(2))- and C(sp(3))-SMe bonds under ligandless conditions is presented. The method is characterized by its wide scope and high chemoselectivity profile including challenging substrate combinations, allowing the design of orthogonal and site-selectivity approaches.     

Catalytic cross-coupling reaction of esters with organoboron compounds and decarbonylative reduction of esters with HCOONH4: a new route to acyl transition metal complexes through the cleavage of acyl-oxygen bonds in esters

The Ru3(CO)12-catalyed cross-coupling reaction of esters with organoboron compounds leading to ketones is described. A wide variety of functional groups can be tolerated under the reaction conditions. Aromatic boronates function as a coupling partner to give aryl ketones. Acyl-alkyl coupling to dialkyl ketones is also achieved by the use of 9-alkyl-9-BBN in place of boronates. The Ru3(CO)12-catalyzed decarbonylative reduction of esters with ammonium formate (HCOONH4) leading to hydrocarbons is also described. No expected aldehydes are produced, and controlled experiments indicate that aldehydes are not intermediate for the transformation. A hydrosilane can also be used as a reducing reagent in place of HCOONH4. A wide variety of functional groups are compatible for both reactions. The key step for both catalytic reactions is the directing group-promoted cleavage of an acyl carbon-oxygen bond in esters, leading to the generation of acyl transition metal alkoxo complexes.     

Organocuprate reactions of enone lactones. II. Regiochemical effect on reductive cleavage.

The course of organocuprate conjugate addition and reduction in cyclohexenones made conformationally rigid by attachment of a 1,3-lactone is shown to depend on the regiochemistry of such enones.     

Application of decarboxylation reactions in catalytic analysis determination of aluminium

Summary The activation of the catalytic decarboxylation of oxaloacetic acid with some pyridine derivatives was studied in order to select suitable activators for increasing the sensitivity of this type of analytical catalytic reactions. The catalytic activity of some bivalent metal ions (Cu²⁺, Zn^2s+, Cd²⁺, Pb²⁺) as well as that of Al³⁺ was also studied. On that ground a catalytic method for determination of aluminium was developed. The sensitivity of the method is 0.5g of aluminium in the sample.

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Zusammenfassung Die Aktivierung der katalytischen Decarboxylierung von Oxalessigsäure durch einige Pyridinderivate wurde untersucht, um geeignete Aktivatoren zur Steigerung der Empfindlichkeit dieser analytisch auswertbaren Reaktion zu finden. Die katalytische Aktivität einiger zweiwertiger Metallionen (Cu, Zn, Cd, Pb) sowie von Al wurde ebenfalls geprüft. Auf dieser Grundlage wurde eine Methode zur Aluminiumbestimmung entwickelt, deren Empfindlichkeit zur Bestimmung von 0,5g Al je Einwaage ausreicht.

     

Factors influencing the reductive cleavage of C-x multiple bonds in their reactions with meal-meal multiple bonds (X = C, N, O, S)

Though metal-metal multiple bonds of the transition elements are redox active, their reactivity towards C-X multiple bonds (X = C, N, O, S) vary greatly depending principally on: 1. The coordination geometry of the metal. 2. The oxidation state of the metal and the electronic configuration of the M-M bond. 3. The nature of the attendant ligands. Specific examples of C-X multiple bond activation at dimolybdenum and ditungsten centers are presented that illustrate the importance of these factors. Evidence is presented to support the view that reductive cleavage of a C-X multiple bond can be considered to be equivalent to an intramolecular redox reaction within a [M2CX] "cluster complex," for which the frontier orbital energies of the C-X and M-M multiple bonds are of paramount importance. Some applications of these C-X reductive cleavage reactions toward organic synthesis are described.     

Radical cascade reactions of unsaturated C–C bonds involving migration

During the past few years, with the rapid development of mild methods for the generation of radical species, great progress in radical cascade reactions of unsaturated C–C bonds has been made. Many radical cascade reactions involve functional groups migration, which leads structurally much more diverse, complex and valuable compounds not easily obtained through other methods. In this review, the recent achievements in unsaturated C–C bonds radical cascade reactions involving migration are summarized.     

Radical reactions involving esters of fumaric acid—I. Copolymerizations

¹⁴C-labelled samples of diethyl-, ethyl n-hexyl- and di-n-hexyl fumarates have been used in studies at 60° of their radical copolymerizations with styrene and with vinyl acetate. Changing the diluent from benzene to dimethylformamide in some of the copolymerizations had no effect on the compositions of the copolymers. Monomer reactivity ratios have been calculated for most of the systems; comparisons have been made of the reactivities of the fumarate esters towards the polyvinyl acetate radical.     

Electrochemical reductive cleavage of carbon-halogen bonds in 5-bromo-1,3-dichloro-2-iodobenzene

The electrochemical reduction of carbon-halogen bonds in 5-bromo-1,3-dichloro-2-iodobenzene follows quadratic activation-driving force relationship except in one of the carbon-chlorine bonds. The variation of the transfer coefficient with the electrode potential has been estimated using the voltammetric data coupled with the convolution analysis. The standard potentials pertaining to the reduction of carbon-halogen bonds are evaluated using the Marcus theory of outer sphere electron transfer.     

Smart cleavage reactions: the synthesis of benzimidazoles and benzothiazoles from polymer-bound esters

The preparation of an array of benzimidazoles and benzothiazoles from polymer-bound esters is described. Polymer-bound esters were treated with 2-aminothiophenols or 1,2-phenylenediamines in the presence of a Lewis acid to afford the corresponding benzothiazole or benzimidazole cleavage products. The reaction of 2-aminophenols with the polymer-bound esters failed to give the desired benzoxazole products using this procedure.     

Phosphate-phosphonate conversion: Nucleophilic displacement reactions involving phosphoric esters and methyllithium

The alkylation-metalation reaction of phosphoric esters depends on the way the lithium reagent has been prepared. With salt-containing methyllithium (LiBr or LiI), the alkylation is never complete. On the contrary, with salt-free methyllithium, the alkylation is completed at – 10°C. This reaction is performed independently of the substituents at the phosphoryl group.     

Radical reactions involving esters of fumaric acid—III. Chain transfer processes

Model compounds have been used in studies at 60° in connection with transfer to polymer during the copolymerization of vinyl acetate with esters of fumaric acid. Succinate esters were used to simulate the fumarate ester units and ethyl acetate the vinyl acetate units in the copolymers. The succinate esters are much more reactive than ethyl acetate in transfer reactions with polyvinyl acetate radicals. Methyl isobutyrate and methyl propionate were also examined to assess the difference in reactivity in transfer of tertiary and secondary hydrogen atoms. It is concluded that branching is a very important reaction in the preparation of high conversion copolymers of fumarate esters with vinyl acetate.     

Studies of reductive elimination reactions to form carbon-oxygen bonds from Pt(IV) complexes.

The platinum(IV) complexes fac-L(2)PtMe(3)(OR) (L(2) = bis(diphenylphosphino)ethane, o-bis(diphenylphosphino)benzene, R = carboxyl, aryl; L = PMe(3), R = aryl) undergo reductive elimination reactions to form carbon-oxygen bonds and/or carbon-carbon bonds. The carbon-oxygen reductive elimination reaction produces either methyl esters or methyl aryl ethers (anisoles) and L(2)PtMe(2), while the carbon-carbon reductive elimination reaction affords ethane and L(2)PtMe(OR). Choice of reaction conditions allows the selection of either type of coupling over the other. A detailed mechanistic study of the reductive elimination reactions supports dissociation of the OR(-) ligand as the initial step for the C-O bond formation reaction. This is followed by a nucleophilic attack of OR(-) upon a methyl group bound to the Pt(IV) cation to produce the products MeOR and L(2)PtMe(2). C-C reductive elimination proceeds from L(2)PtMe(3)(OR) by initial L (L = PMe(3)) or OR(-) (L(2) = dppe, dppbz) dissociation, followed by C-C coupling from the resulting five-coordinate intermediate. Our studies demonstrate that both C-C and C-O reductive elimination reactions from Pt(IV) are more facile in polar solvents, in the presence of Lewis acids, and for OR(-) groups that contain electron withdrawing substituents.     

Radical reactions initiated by the photochemical cleavage of carbon-indium bonds of organoindium compounds

Intra- and intermolecular reactions of carbon-centered radicals generated by photolysis of organoindium compounds were examined. The photolysis of vinylindium compounds and indium acetylides provided vinyl and alkynyl radicals, respectively, which were trapped with ethyl iodoacetate giving the corresponding β,γ-unsaturated esters. Allylic indium compounds, prepared from 8-bromo- or 8-iodooct-1,6-dienes and powdered indium metal, underwent an intramolecular radical cyclization to afford the 5-exo-trig product.