A Rapid, Large-Scale Synthesis of a Potent Cholecystokinin (CCK) 1R Receptor Agonist

General Method for the Amination of Aryl Halides with Primary and Secondary Alkyl Amines via Nickel Photocatalysis

The Buchwald-Hartwig C-N coupling reaction has been ranked as one of the 20 most frequently used reactions in medicinal chemistry. Owing to its much lower cost and higher reactivity toward less reactive aryl chlorides than palladium, the C-N coupling reaction catalyzed by Ni-based catalysts has received a great deal of attention. However, there appear to be no universal, practical Ni catalytic systems so far that could enable the coupling of electron-rich and electron-poor aryl halides with both primary and secondary alkyl amines. In this study, it is reported that a Ni(II)-bipyridine complex catalyzes efficient C-N coupling of aryl chlorides and bromides with various primary and secondary alkyl amines under direct excitation with light. Intramolecular C-N coupling is also demonstrated. The feasibility and applicability of the protocol in organic synthesis is attested by more than 200 examples.

The Quest for the Ideal Base: Rational Design of a Nickel Precatalyst Enables Mild, Homogeneous C-N Cross-Coupling

Palladium-catalyzed amination reactions using soluble organic bases have provided a solution to the many issues associated with heterogeneous reaction conditions. Still, homogeneous C-N cross-coupling approaches cannot yet employ bases as weak and economical as trialkylamines. Furthermore, organic base-mediated methods have not been developed for Ni(0/II) catalysis, despite some advantages of such systems over those employing Pd-based catalysts. We designed a new air-stable and easily prepared Ni(II) precatalyst bearing an electron-deficient bidentate phosphine ligand that enables the cross-coupling of aryl triflates with aryl amines using triethylamine (TEA) as base. The method is tolerant of sterically congested coupling partners, as well as those bearing base- and nucleophile-sensitive functional groups. With the aid of density functional theory (DFT) calculations, we determined that the electron-deficient auxiliary ligands decrease both the pK_a of the Ni-bound amine and the barrier to reductive elimination from the resultant Ni(II)-amido complex. Moreover, we determined that the preclusion of Lewis acid-base complexation between the Ni catalyst and the base, due to steric factors, is important for avoiding catalyst inhibition.

Discovery and Development of Metal-Catalyzed Coupling Reactions in the Synthesis of Dasabuvir, an HCV-Polymerase Inhibitor

Dasabuvir (1) is an HCV polymerase inhibitor which has been developed as a part of a three-component direct-acting antiviral combination therapy. During the course of the development of the synthetic route, two novel coupling reactions were developed. First, the copper-catalyzed coupling of uracil with aryl iodides, employing picolinamide 16 as the ligand, was discovered. Later, the palladium-catalyzed sulfonamidation of aryl nonaflate 33 was developed, promoted by electron-rich palladium complexes, including the novel phosphine ligand, VincePhos (50). This made possible a convergent, highly efficient synthesis of dasabuvir that significantly reduced the mutagenic impurity burden of the process.

Breaking the Base Barrier: An Electron-Deficient Palladium Catalyst Enables the Use of a Common Soluble Base in C-N Coupling

Due to the low intrinsic acidity of amines, palladium-catalyzed C-N cross-coupling has been plagued continuously by the necessity to employ strong, inorganic, or insoluble bases. To surmount the many practical obstacles associated with these reagents, we utilized a commercially available dialkyl triarylmonophosphine-supported palladium catalyst that facilitates a broad range of C-N coupling reactions in the presence of weak, soluble bases. The mild and general reaction conditions show extraordinary tolerance for even highly base-sensitive functional groups. Additionally, insightful heteronuclear NMR studies using 15N-labeled amine complexes provide evidence for the key acidifying effect of the cationic palladium center.

Real-time analysis of Pd2(dba)3 activation by phosphine ligands

Real-time UV-Vis/ESI-MS monitoring of Pd₂(dba)₃ activation provides insight into active species and the effect of activation protocol on their formation.

Synthesis of quinazolines and quinazolinones via palladium-mediated approach

Quinazoline derivatives have drawn attention in the field of heterocyclic chemistry because of their unique skeleton and interesting biological applications. This review summarizes the recent palladium-catalyzed reactions used to construct quinazoline and its related 4(3H)-quinazolinone analogues. The mechanisms of some Pd-catalyzed reactions are also discussed.

N-heterocyclic carbene-assisted, bis(phosphine)nickel-catalyzed cross-couplings of diarylborinic acids with aryl chlorides, tosylates, and sulfamates

Efficient bis(phosphine)nickel-catalyzed cross-couplings of diarylborinic acids with aryl chlorides, tosylates, and sulfamates have been effected with an assistance of N-heterocyclic carbene (NHC) generated in situ from N,N'-dialkylimidazoliums, e.g., N-butyl-N'-methylimidazolium bromide ([Bmim]Br), in toluene using K3PO4·3H2O as base. In contrast to bis(NHC)nickel-catalyzed conventional Suzuki coupling of arylboronic acids, mono(NHC)bis(phosphine)nickel species generated in situ from Ni(PPh3)2Cl2/[Bmim]Br displayed high catalytic activities in the cross-couplings of diarylborinic acids. The structural influences from diarylborinic acids were found to be rather small, while electronic factors from aryl chlorides, tosylates, and sulfamates affected the couplings remarkably. The couplings of electronically activated aryl chlorides, tosylates, and sulfamates could be efficiently effected with 1.5 mol % NiCl2(PPh3)2/[Bmim]Br as catalyst precursor to give the biaryl products in excellent yields, while 3-5 mol % loadings had to be used for the couplings of non- and deactivated ones. A small ortho-substitutent on the aromatic ring of aryl chlorides, tosylates, and sulfamates was tolerable. Applicability of the nickel-catalyzed cross-couplings in practical synthesis of fine chemicals has been demonstrated in process development for a third-generation topical retinoid, Adapalene.

Efficient synthesis of 3H-indoles enabled by the lead-mediated α-arylation of β-ketoesters or γ-lactams using aryl azides

The development of a lead-mediated α-arylation reaction between aryl azides and β-ketoesters or γ-lactams that facilitates the formation of 3H-indoles is disclosed. Twenty-five examples are included which demonstrate the generality of this reaction to access aryl azides bearing tetrasubstituted o-alkyl substituents. When paired with a Staudinger reduction, this reaction streamlines the synthesis of functionalized 3H-indoles.

Palladium-catalyzed N-monoarylation of amidines and a one-pot synthesis of quinazoline derivatives

A method for the Pd-catalyzed N-arylation of both aryl and alkyl amidines with a wide range of aryl bromides, chlorides, and triflates is described. The reactions proceed in short reaction times and with excellent selectivity for monoarylation. A one-pot synthesis of quinazoline derivatives, via addition of an aldehyde to the crude reaction mixture following Pd-catalyzed N-arylation, is also demonstrated.

Dialkylbiaryl Phosphines in Pd-Catalyzed Amination: A User's Guide

Dialkylbiaryl phosphines are a valuable class of ligand for Pd-catalyzed amination reactions and have been applied in a range of contexts. This review attempts to aid the reader in the selection of the best choice of reaction conditions and ligand of this class for the most commonly encountered and practically important substrate combinations.