Catalytic σ-Bond Annulation with Ambiphilic Organohalides Enabled by β-X Elimination

Palladium Catalysis: Dependence of the Efficiency of C-N Bond Formation on Carboxylate Ligand and Metal Carboxylate or Carboxylic Acid Additive

The Pd-catalyzed inter- and intramolecular reactions of nitrogen compounds are often carried out with palladium carboxylates, sometimes in the presence of carboxylic acids or alkali metal carboxylates. This Mini-Review highlights the dependence of the reaction efficiency on the nature of the ligand and the carboxylate additives. The proposed reaction mechanisms are presented with, as far as possible, personal comments.

A Three-Component Arene Difunctionalization: Merger of C(sp3 )/(sp2 )-H Bond Addition

A tandem three-component C-H bond addition involving the activation of an inert C(sp3 )-H bond is reported. The process enables the direct regioselective synthesis of 1,2-difunctionalized arenes with the formation of C(sp3 )- and C(sp2 )-C(arene) bonds. 2-Iodobenzoic acid derivatives behave as masked bifunctional reagent (BFR) and react with 2-pyridyl-methyl sulfoximine (MPyS) protected aliphatic acids bearing α,α-disubstituted groups, and alkenes to produce β-aryl-δ-alkenyl amide derivatives in a single operation. The transformation involves Pd(II)/Pd(IV) and Pd(II)/Pd(0) catalytic systems. Detailed mechanistic studies, including density functional theory (DFT) calculations, reveal the formation of large T-shaped palladacycles and the onset of a 1,2-palladium migration via decarboxylation.

Catalytic Asymmetric Ring-Opening Reactions of Unstrained Heterocycles Using Cobalt Vinylidenes

Cobalt catalysts promote highly enantioselective ring-opening reactions of 2,5-dihydrofurans using vinylidenes. The products are acyclic organozinc compounds that can be functionalized with an electrophile. The proposed mechanism involves the generation of a cobalt vinylidene species that adds to the alkene by a [2+2]-cycloaddition pathway. Ring-opening then occurs via outer-sphere β-O elimination assisted by coordination of a ZnX2 Lewis acid to the alkoxide leaving group. DFT models reveal that competing inner-sphere syn β-H and β-O elimination pathways are suppressed by the geometric constraints of the metallacycle intermediate. These models rationalize the observed stereochemical outcome of the reaction.