Acyl derivatives reductive elimination reactions

In all these reactions, the acylating reagent reacts with the active Pd(0) catalyst to give an acyl Pd(II) intermediate. Transmetallation by the organoboron derivative and reductive elimination generate the ketone. 

If the reaction mixture also contains a nucleophile, then the acyl-palladium complex might undergo displacement of the metal, which usually leads to the formation of a carboxylic acid derivative. The side product in this process is a palladium(II) complex that undergoes reductive elimination to regenerate the catalytically active palladium(O) complex. 

Nucleophilic attack occurs at C(2) of the diene. The 1,3-cyclohexadiene complex 66 is converted to the homoallyl anionic complex 67 by nucleophilic attack, and the 3-alkyl-1-cyclohexene 68 is obtained by protonation. Insertion of CO to 67 generates the acyl complex 69, and its protonation and reductive elimination afford the aldehyde 70 [20]. Reaction of the butadiene complex 56 with an anion derived from ester 71 under CO atmosphere generates the homoallyl complex 72 and then the acyl complex 73 by CO insertion. The cyclopentanone complex 74 is formed by intramolecular insertion of alkene, and the 3-substituted cyclopentanone 75 is obtained by reductive elimination. The intramolecular version, when applied to the 1,3-cyclohexadiene complex 76 bearing an ester chain at C(5), offers a good synthetic route to the bicyclo[3.3.1]nonane system 78 via intermediate 77 [21]. 

The dibutyl derivative Ti(r7 -C5H5)2Bu2 decomposes upon treatment with CO, but the dibenzyl compound gives dibenzylketone, suggesting that the relatively slow carbon monoxide insertion reaction [reaction (b)] is followed by fast reductive elimination from the intermediate alkyl-acyl complex. 

Side reactions such as double-bond migration and others are observed, similar to hydroformylation. Mechanistically, hydrocarboxylation is related to hydroformylation up until the metal acyl formation stage13. The presence of an acidic compound shifts the reaction towards formation of carboxylic acid derivatives and suppresses reductive elimination which forms aldehydes. The mechanism of the final steps is unclear13. 

Migratory insertion reactions allow the generation of different kinds of Ni-G bonds. GO insertion is a classic example that has received much attention due to its involvement in catalytic and stoichiometric G-G bond formation processes.Although the carbonylation of cr-organonickel complexes is often followed by reductive elimination processes, many stable Ni-acyl complexes have been isolated. Recent examples of such reactions are shown in Equations (68) and (69). " Their formation is usually reversible, as demonstrated by the equilibrium shown in Equation (70), which indicates that the insertion of GO into Ni-aryl bonds is thermodynamically favored over the insertion into Ni-alkyl bonds. Acyl complexes containing Bp or Tp ligands have been prepared by carbonylation of the corresponding alkyl or aryl precursors. The ready carbonylation of the Tp derivative 137 (Equation (71))... 

The ortfro-acylation of IV-benzyltriflamides with benzylic and aliphatic alcohols has been reported using palladiiun catalysis with t-butyl hydroperoxide (TBHP) as an oxidant. The reaction is likely to involve formation of acyl radicals from the alcohols and their reaction with a cyclopalladated intermediate to produce (149). Reductive elimination yields the acylated product. A similar pathway is probable in the palladium-catalysed ortfro-acylation of 2-arylbenzothiazoles to give derivatives (150). There has been an investigation involving both kinetic and DFT studies of the factors affecting the reactivity of aminoesters in cyclopalladation reactions carbonylation may yield products such as (151). 

Azanickelacycle formation with partial replacement of the heterocyclic moiety substance by the nickel catalyst was also employed for the synthesis of indoles, an important class of heterocycles found in natural products and pharmaceuticals. Maizum et al. demonstrated a nickel-catalyzed decarbonylative cycloaddition by which anthranilic acid derivatives 39, which are readily available, react with alkynes to afford substituted indoles 41 (Scheme 12.17) [20]. The reaction is supposed to proceed via oxidative addition and decarbonylation to afford azanickelacycle 40, followed by alkyne insertion, 1,3-acyl migration, and reductive elimination, to afford A-pivaloyl-protected indole 41. Deprotected indole 42 was obtained as the final product upon workup, that is, treatment of the reaction crude reaction mixture with NaSMe in MeOH. 

Under ruthenium-catalyzed ortho-C-H activation and intramolecular C-N bond formation, the condensation of iminophosphoranes (in situ generated from acyl azides and triphenylphosphine) with internal alkynes afforded a variety of isoquinolinone derivatives (Eq. (7.43)) [53]. The regioselective insertion of unsymmetrical alkynes led to an (aryl)C-N bond formation. Thiophene and indole-based acyl azides were also compatible for this transformation. A domino reaction sequence via coordination of ruthenium with Af-atom of iminophosphoranes, ort/zo-cyclometalation, alkyne insertion, protonation, and reductive elimination was proposed for the catalytic cycle. Based on and NMR experiments, the involvement of benzamide during the reaction process was ruled out. 

The 2-methylenecyclopentanone initially formed presumably rearranges into 2-methyl-2-cyclopentenone under the reaction conditions. The final step of the mechanism, elimination of the cobalt carbonyl group, is not well understood but the same kind of elimination and reduction reactions occur with known 3-ketocobalt complexes. As mentioned above, crotonaldehyde, acrolein (27), and glyddaldehyde (38) react rapidly with cobalt hydrocarbonvl under similar conditions to give reduction products, rather than forming stable alkyl- or acyl-cobalt tetracarbonyl derivatives. 

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