P,N-Coordinating Ylide-Functionalized Phosphines (NYPhos): A Ligand Platform for the Selective Monoarylation of Small Nucleophiles

Palladium-catalyzed coupling reactions of small nucleophiles are of great interest, but challenging due to difficulties in selectivity control. Herein, we report the development of a new platform of P,N-ligands consisting of ylide-functionalized phosphines with aminophosphonium groups (NYPhos) to address this challenge. These phosphine ligands are easily accessible in a wide structural diversity with highly modular electronic and steric properties. Based on a family of 14 ligands the selective monoarylation of acetone as well as other challenging ketones and amides was accomplished with record-setting activities even for aryl chlorides at room temperature including late-stage functionalizations of drug molecules. Moreover, ammonia and other small primary amines could be coupled at mild conditions. Isolation and structure analyses of palladium complexes within the catalytic cycle confirmed that the P,N-coordination mode is necessary to achieve the observed selectivities. It also demonstrated the facile adjustability of the N-donor strength, which is beneficial for the targeted design of tailored P,N-ligands for future applications.

Photo-Catalyzed Acyl Azolium Promoted Selective α-C(sp3 )-H Acylation of Acetone via HAT: Access to Thermodynamically Less Favoured (Z)-α,β-Unsaturated Ketones

Mono α-acylation of acetone has been achieved for the first time by reacting with bench-stable acyl azolium salts under violet-LED light at room temperature. The intermolecular hydrogen atom transfer (HAT) from acetone to triplet state of azolium salts under violet LED irradiation resulted in thermodynamically less favourable (Z)-α,β-unsaturated ketones with up to 99 : 1 selectivity via C-C bond formation. This compelling protocol access the desired α-C(sp3 )-H acylation product under metal-, ligand- and oxidant-free conditions on a wide range of substrates.

From Academia to the Market - Air-stable Ni(ii)/Josiphos Catalysts

The design, synthesis, commercialization and application of air-stable Ni(II)/Josiphos complexes has been realized in a collaboration between Solvias and ICBMS (University Lyon 1). The Ni-complexes are utilized as versatile precatalysts for diverse cross-coupling reactions. Apart from being active in established C-C and C-N couplings at low catalyst loadings, the novel Ni-precatalysts enabled the development of the challenging monoarylation of ammonia, ammonia surrogates and even alkylammonium chlorides with aryl carbamates. Finally, the α-arylation of acetone with aryl chlorides, carbamates and pivalates was demonstrated using the Ni(II)/Josiphos precatalysts.

An Efficient Palladium-Catalyzed α-Arylation of Acetone Below its Boiling Point

The monoarylation of acetone is a powerful transformation, but is typically performed at temperatures significantly in excess of its boiling point. Conditions described for performing the reaction at ambient temperatures led to significant dehalogenation when applied to a complex aryl halide. We describe our attempts to overcome both issues in the context of our drug-discovery program.

Nickel-Catalyzed Mono-Selective α-Arylation of Acetone with Aryl Chlorides and Phenol Derivatives

The challenging nickel-catalyzed mono-α-arylation of acetone with aryl chlorides, pivalates, and carbamates has been achieved for the first time. A nickel/Josiphos-based catalytic system is shown to feature unique catalytic behavior, allowing the highly selective formation of the desired mono-α-arylated acetone. The developed methodology was applied to a variety of (hetero)aryl chlorides including biologically relevant derivatives. The methodology has been extended to the unprecedented coupling of acetone with phenol derivatives. Mechanistic studies allowed the isolation and characterization of key Ni⁰ and Ni^II catalytic intermediates. The Josiphos ligand is shown to play a key role in the stabilization of Ni^II intermediates to allow a Ni⁰ /Ni^II catalytic pathway. Mechanistic understanding was then leveraged to improve the protocol using an air-stable Ni^II pre-catalyst.

Vinyl Cation Stabilization by Silicon Enables a Formal Metal-Free α-Arylation of Alkyl Ketones

The ability of silicon to stabilize vinyl cationic species leads to a redox arylation of alkynes whereby the stringent limitations of reactivity and regioselectivity of alkyl-substituted alkynes are lifted. This allows the synthesis of a range of α-silyl-α'-arylketones under mild conditions in good to excellent yields and with high functional group tolerance, whereby the silicon moiety in the final products can either be removed for a formal acetone monoarylation transform, or capitalized upon for subsequent electrophilic substitutions at either side of the carbonyl group.

Cascade Amination and Acetone Monoarylation with Aryl Iodides by Palladium/Norbornene Cooperative Catalysis

A palladium/norbornene cocatalyzed three-component reaction of aryl iodides, O-benzoylhydroxylamines, and acetone is reported. o'-Aminoaryl acetones or o,o'-diaminoaryl acetones are efficiently prepared via tandem ortho-C-H amination/ipso-C-I α-arylation sequence, and the regiospecificity has been confirmed by X-ray analysis. The proposed method addresses the condensation/amination of free-N-H-bearing substrates in acetone monoarylations and the synthesis of extremely congested 2,6-disubstituted aryl acetones.

A simple synthetic entryway into palladium cross-coupling catalysis

The simple synthesis of a family of palladates containing an imidazolium counterion is presented. These “ate” complexes can be easily converted into well-defined palladium–N-heterocyclic carbene (NHC) complexes.

Exploiting Aryl Mesylates and Tosylates in Catalytic Mono-α-arylation of Aryl- and Heteroarylketones

The first general palladium catalyst for the catalytic mono-α-arylation of aryl- and heteroarylketones with aryl mesylates and tosylates is described. The newly developed indolyl-derived phosphine ligand L7 has been identified to promote this reaction efficiently. The key to success is attributed to the enhanced steric congestion of the catalyst and effective oxidative addition of the C(Ar)-OMs bond. In the presence of Pd(OAc)2 (0.25-2.5 mol %) and L7, selective monoarylations are achieved with ample reaction scope and product yields up to 95%. Importantly, we demonstrated the applicability of this protocol with the modification of biological phenolic compounds, rendering it amenable for functionalization of phenolic (pro)drugs.