Palladium-catalyzed α-arylation of N-protected 2-piperidinones

Palladium-Catalyzed Direct α-Arylation of Indane-1,3-dione to 2-Substituted Indene-1,3-diones

A straightforward and feasible palladium-catalyzed direct α-arylation of indane-1,3-dione to 2-substituted aryl/heteroaryl indene-1,3-diones has been disclosed for the first time. Optimization of reaction conditions identified ^tBu-XPhos as a preferred ligand for the bis(acetonitrile)dichloropalladium(II) catalyst. A broad spectrum of aryl iodides and aryl triflates containing electron-donating, electron-withdrawing, and sterically hindered substituents gave an excellent yield for the quick access α-arylated 1,3-diones library.

α-C(sp3)-H Arylation of Cyclic Carbonyl Compounds

α-C(sp3)-H arylation is an important type of C-H functionalization. Various biologically significant natural products, chemical intermediates, and drugs have been effectively prepared via C-H functionalization. Cyclic carbonyl compounds comprise of cyclic ketones, enones, lactones, and lactams. The α-C(sp3)-H arylation of these compounds have been exhibited high efficiency in forming C(sp3)-C(sp2) bonds, played a crucial role in organic synthesis, and attracted majority of interests from organic and medicinal communities. This review focused on the most significant advances including methods, mechanism, and applications in total synthesis of natural products in the field of α-C(sp3)-H arylations of cyclic carbonyl compounds in recent years.

Palladium-Catalyzed Construction of Quaternary Stereocenters by Enantioselective Arylation of γ-Lactams with Aryl Chlorides and Bromides

Herein, we report the first Pd-catalyzed enantioselective arylation of α-substituted γ-lactams. Two sets of conditions were developed for this transformation, allowing for the use of either aryl chlorides or bromides as electrophiles. Utilizing a highly electron-rich dialkylphosphine ligand we have been able to construct α-quaternary centers in good yields (up to 91 % yield) and high enantioselectivities (up to 97 % ee).

Preparation and Application of Solid, Salt-Stabilized Zinc Amide Enolates with Enhanced Air and Moisture Stability

The treatment of various N-morpholino amides with TMPZnCl⋅LiCl (TMP=2,2,6,6-tetramethylpiperidyl) and Mg(OPiv)₂ in THF at 25 °C provides solid zinc enolates with enhanced air and moisture stability (t_1/2 in air: 1-3 h) after solvent evaporation. These enolates undergo Pd- and Cu-catalyzed cross-couplings with (hetero)aryl bromides as well as allylic and benzylic halides. The arylated N-morpholino amides were converted into various ketones by LaCl₃ ⋅2 LiCl mediated acylation with Grignard reagents. The new, solid enolates were used to prepare a potent anti-breast-cancer drug candidate in six steps and 23 % overall yield.

A General and Practical Palladium-Catalyzed Direct α-Arylation of Amides with Aryl Halides

An efficient system for the direct catalytic intermolecular α-arylation of acetamide derivatives with aryl bromides and chlorides is presented. The palladium catalyst is supported by Kwong's indole-based phosphine ligand and provides monoarylated amides in up to 95% yield. Excellent chemoselectivities (>10:1) in the mono- and diarylation with aryl bromides were achieved by careful selection of bases, solvents, and stoichiometry. Under the coupling conditions, the weakly acidic α-protons of amides (pKa up to 35) were reversibly depotonated by LiO t Bu, NaO t Bu, or NaN(SiMe3)2.

Chemoselective intramolecular alkylation of the Blaise reaction intermediates: tandem one-pot synthesis of exo-cyclic enaminoesters and their applications toward the synthesis of N-heterocyclic compounds

The intramolecular alkylative reactivity and N/C selectivity of the various Blaise reaction intermediates, which are formed from the reaction of the Reformatsky reagents with ω-chloroalkyl nitriles, did not reach the synthetic potential as an entry to exo-cyclic enaminoesters. To circumvent this issue, various additives were investigated, among which the addition of NaHMDS dramatically enhanced the reactivity and N/C selectivity. This modification provided a highly efficient route for the synthesis of various N-fused heterocyclic compounds, as it requires only two steps from nitriles.

Palladium-catalyzed intramolecular trapping of the Blaise reaction intermediate for tandem one-pot synthesis of indole derivatives

Palladium-catalyzed intramolecular N-arylative and N-alkylative/N-arylative trappings of the Blaise reaction intermediates could be a new route to construct the indole moiety in a tandem one-pot manner from nitriles.

Metal-catalyzed alpha-arylation of carbonyl and related molecules: novel trends in C-C bond formation by C-H bond functionalization

Alpha-arylated carbonyl compounds are commonly occurring motifs in biologically interesting molecules and are therefore of high interest to the pharmaceutical industry. Conventional procedures for their synthesis often result in complications in scale-up, such as the use of stoichiometric amounts of toxic reagents and harsh reaction conditions. Over the last decade, significant efforts have been directed towards the development of metal-catalyzed alpha-arylations of carbonyl compounds as an alternative synthetic approach that operates under milder conditions. This Review summarizes the developments in this area to date, with a focus on how the substrate scope has been expanded through selection of the most appropriate synthetic method, such as the careful choice of ligands, precatalysts, bases, and reaction conditions.

Palladium-catalyzed alpha-arylation of oxindoles

A catalyst generated from Pd(dba)2 and the bulky electron-rich phosphine ligand 2-(dicyclohexylphosphino)-2',4', 6'-tri-i-propyl-1-1'-biphenyl is effective for the alpha-arylation of oxindoles. Generation of the potassium-enolates of a range of oxindoles allows coupling with aryl chlorides, bromides, and triflates. Significant variation of the substitution pattern on both the oxindole and aryl halide is possible.

Palladium-Catalyzed Intermolecular α-Arylation of Zinc Amide Enolates under Mild Conditions

The intermolecular alpha-arylation and vinylation of amides by palladium-catalyzed coupling of aryl bromides and vinyl bromides with zinc enolates of amides is reported. Reactions of three different types of zinc enolates have been developed. The reactions of aryl halides occur in high yields with isolated Reformatsky reagents generated from alpha-bromo amides, with Reformatsky reagents generated in situ from alpha-bromo amides, and with zinc enolates generated by quenching lithium enolates of amides with zinc chloride. This use of zinc enolates, instead of alkali metal enolates, greatly expands the scope of amide arylation. The reactions occur at room temperature or 70 degrees C with bromoarenes containing cyano, nitro, ester, keto, fluoro, hydroxyl, or amino functionality and with bromopyridines. Moreover, the reaction has been developed with morpholine amides, the products of which are precursors to ketones and aldehydes. The arylation of zinc enolates of amides was conducted with catalysts bearing the hindered pentaphenylferrocenyl di-tert-butylphosphine (Q-phos) or the highly reactive, dimeric, Pd(I) complex [[P(t-Bu)3]PdBr]2.