Synthese quartärer Kohlenstoffzentren durch palladiumkatalysierte Dicarbofunktionalisierung

Palladium-Catalyzed Defluorinative Coupling of Difluoroalkenes and Aryl Boronic Acids for Ketone Synthesis

The transition-metal-catalyzed carbonylation reaction is a useful approach for ketone synthesis. However, it is often problematic to use exogenous carbonyl reagents, such as gaseous carbon monoxide. In this manuscript, we report a novel palladium-catalyzed coupling reaction of gem-difluoroalkenes and aryl boronic acids that yields bioactive indane-type ketones with an all-carbon α-quaternary center. Characterization and stoichiometric reactions of the key intermediates RCF₂ Pd^II support a water-induced defluorination and cross-coupling cascade mechanism. The vinyl difluoromethylene motif serves as an in situ carbonyl precursor which is unprecedented in transition-metal-catalyzed coupling reactions. It is expected to raise broad research interest from the perspectives of ketone synthesis, fluoroalkene functionalization, and rational design of new synthetic protocols based on the unique reactivity of difluoroalkyl palladium(II) species.

Visible Light Induced Brønsted Acid Assisted Pd-Catalyzed Alkyl Heck Reaction of Diazo Compounds and N-Tosylhydrazones

A mild visible light-induced palladium-catalyzed alkyl Heck reaction of diazo compounds and N-tosylhydrazones is reported. A broad range of vinyl arenes and heteroarenes with high functional group tolerance, as well as a range of different diazo compounds, can efficiently undergo this transformation. This method features Brønsted acid-assisted generation of hybrid palladium C(sp3 )-centered radical intermediate, which allowed for new selective C-H functionalization protocol.

Ni-Catalyzed Arylbenzylation of Alkenylarenes: Kinetic Studies Reveal Autocatalysis by ZnX2 *

We report a Ni-catalyzed regioselective arylbenzylation of alkenylarenes with benzyl halides and arylzinc reagents. The reaction furnishes differently substituted 1,1,3-triarylpropyl structures that are reminiscent of the cores of oligoresveratrol natural products. The reaction is also compatible for the coupling of internal alkenes, secondary benzyl halides and variously substituted arylzinc reagents. Kinetic studies reveal that the reaction proceeds with a rate-limiting single-electron-transfer process and is autocatalyzed by in-situ-generated ZnX2 . The reaction rate is amplified by a factor of three through autocatalysis upon addition of ZnX2 .

Nickel-Catalyzed Regioselective Alkenylarylation of γ,δ-Alkenyl Ketones via Carbonyl Coordination

We disclose a nickel-catalyzed reaction, which enabled us to difunctionalize unactivated γ,δ-alkenes in ketones with alkenyl triflates and arylboronic esters. The reaction was made feasible by the use of 5-chloro-8-hydroxyquinoline as a ligand along with NiBr2 ⋅DME as a catalyst and LiOtBu as base. The reaction proceeded with a wide range of cyclic, acyclic, endocyclic and exocyclic alkenyl ketones, and electron-rich and electron-deficient arylboronate esters. The reaction also worked with both cyclic and acyclic alkenyl triflates. Control experiments indicate that carbonyl coordination is required for the reaction to proceed.

Selective Alkynylallylation of the C-C σ Bond of Cyclopropenes

A Pd-catalyzed regio- and stereoselective alkynylallylation of a specific C-C σ bond in cyclopropenes, using allyl propiolates as both allylation and alkynylation reagents, has been achieved for the first time. By merging selective C(sp² )-C(sp³ ) bond scission with conjunctive cross-couplings, this decarboxylative reorganization reaction features fascinating atom and step economy and provides an efficient approach to highly functionalized dienynes from readily available substrates. Without further optimization, gram-scale products can be easily obtained by such a simple, neutral, and low-cost catalytic system with high TONs. DFT calculations afford a rationale toward the formation of the products and indicate that the selective insertion of the double bond of cyclopropenes into the C-Pd bond of ambidentate Pd complex and the subsequent nonclassical β-C elimination promoted by 1,4-palladium migration are critical for the success of the reaction.

Visible-Light-Induced Palladium-Catalyzed Generation of Aryl Radicals from Aryl Triflates

A mild visible-light-induced Pd-catalyzed intramolecular C-H arylation of amides is reported. The method operates by cleavage of a C(sp2 )-O bond, leading to hybrid aryl Pd-radical intermediates. The following 1,5-hydrogen atom translocation, intramolecular cyclization, and rearomatization steps lead to valuable oxindole and isoindoline-1-one motifs. Notably, this method provides access to products with readily enolizable functional groups that are incompatible with traditional Pd-catalyzed conditions.