Palladium-Catalyzed Intramolecular Asymmetric C–H Functionalization/Cyclization Reaction of Metallocenes: An Efficient Approach toward the Synthesis of Planar Chiral Metallocene Compounds

Enantioselective Synthesis of Planar Chiral Ferrocifens that Show Chiral Discrimination in Antiproliferative Activity on Breast Cancer Cells

The design and first enantioselective synthesis of a series of chiral ferrocifens and ferrociphenols was realised by enantioselective palladium-catalysed intramolecular direct C-H bond activation followed by McMurry coupling. Biological evaluation revealed moderate anticancer activities on breast cancer cells and evidence of chiral discrimination between enantiomers. Treatment of the novel ferrocifens with Ag₂ O revealed that these systems are unable to form a neutral quinone methide, yet still demonstrate marked antiproliferative properties against both the hormone-dependent MCF-7 and hormone-independent MDA-MB-231 cell lines. This bioactivity arises from two mechanisms: Fenton-type chemistry and the anti-estrogenic activity associated with the tamoxifen-like structure.

Synthesis of planar chiral ferrocenes via a Pd(0)-catalyzed syn-carbopalladation/asymmetric C–H alkenylation process

The Pd(0)-catalyzed tandem intermolecular syn-carbopalladation/asymmetric C–H alkenylation reaction of N-ferrocenyl propiolamides with aryl iodides has been realized, generating planar chiral ferrocene[1,2-d] pyrrolinones in good yields.

Recent developments in the synthesis and applications of chiral ferrocene ligands and organocatalysts in asymmetric catalysis

This review highlights recent advances in the synthesis and application of ferrocene-containing chiral ligands and organocatalysts in asymmetric catalysis.

Palladium-Catalyzed C-H Diarylation of Ferrocenecarboxylic Acids with Aryl Iodides

Palladium-catalyzed C-H diarylation of ferrocenes is described. In the presence of 10 mol % Pd(OAc)₂, direct C-H diarylation reactions of commercially available ferrocenecarboxylic acid with aryl iodides proceeded smoothly to afford diarylated ferrocenes bearing a variety of functional groups in moderate to good yields. The carboxylic group could also act as a remote directing group to result in the third arylation on the other Cp ring of ferrocene.

Thioketone-directed rhodium(I) catalyzed enantioselective C-H bond arylation of ferrocenes

Planar chiral ferrocenes have received great attention in both academia and industry. Although remarkable progresses have been made over the past decade, the development of efficient and straightforward methods for the synthesis of enantiopure  planar chiral  ferrocenes remains highly challenging. Herein, we report a rhodium(I)/phosphonite catalyzed thioketone-directed enantioselective C-H bond arylation of ferrocenes. Readily available aryl iodides are used as the coupling partners in this transformation, leading to a series of planar chiral ferrocenes in good yields and excellent enantioselectivities (up to 86% yield, 99% ee). Of particular note, heteroaryl coupled ferrocenes, which are difficult to access with previous approaches, can be obtained in satisfactory results.

Catalytic Asymmetric C-H Arylation of (η6-Arene)Chromium Complexes: Facile Access to Planar-Chiral Phosphines

A catalytic asymmetric direct C-H arylation of (η6-arene)chromium complexes to obtain planar-chiral compounds is reported. The use of the hemilabile ligand H8-BINAP(O) is key to providing high enantioselectivity in this transformation. We show that this methodology opens the door to the synthesis of a variety of planar-chiral chromium derivatives which can be easily transformed into planar chiral mono- or diphosphines. Mechanistic studies, including synthesis and characterization of Pd and Ag complexes and their detection in the reaction mixture, suggest a Pd-catalyzed/Ag-promoted catalytic system where Ag carries out the C-H activation step.

Micellar Catalysis for Ruthenium(II)-Catalyzed C-H Arylation: Weak-Coordination-Enabled C-H Activation in H2 O

Chemoselective C-H arylations were accomplished through micellar catalysis by a versatile single-component ruthenium catalyst. The strategy provided expedient access to C-H-arylated ferrocenes with wide functional-group tolerance and ample scope through weak chelation assistance. The sustainability of the C-H arylation was demonstrated by outstanding atom-economy and recycling studies. Detailed computational studies provided support for a facile C-H activation through thioketone assistance.

Simultaneous Construction of Planar and Central Chiralities as Well as Unprecedented Axial Chirality on and around a Ferrocene Backbone

Simultaneous generation of planar, central and axial chiralities on and around a ferrocene backbone via a d-phenylglycinol-induced intramolecular iminium cyclization was disclosed, which is rare and differs from known methods. A series of chiral spiro[cyclopentadienyl-1,2,3,3a-tetrahydropentalenyliron(II)-1,2'-pyrrolidine] derivatives were prepared acording to the new method, and their structures were characterized unambiguously. The axial chirality caused by the ferrocene backbone and the rigid spiral structure was verified by NOESY and variable-temperature NMR experiments and single-crystal XRD analyses. Mechanism for the stereoselective iminium cyclization reaction was suggested, which was influenced by steric hindrance and hydrogen bonding.

Synthesis, functionalization, and isolation of planar-chiral pillar[5]arenes with bulky substituents using a chiral derivatization agent

Bulky perneopentyloxy-pillar[5]arene (Pillar-1) was synthesized and its conformational mobility was investigated using variable-temperature ¹H NMR spectroscopy. The host–guest interactions between Pillar-1 and n-octyltrimethylammonium hexafluorophosphate (OMA) were investigated, and the formation of a 1 : 1 complex was revealed via¹H NMR. Planar-chiral isomers were synthesized via the reaction of a hydroxy-functionalized pillar[5]arene with chiral derivatization agent (S)-(+)-MTPA-Cl. The (Sp, R)-and (Rp, R)-forms of the pillar[5]arene diastereomers were isolated by HPLC, and their structures were analyzed by ¹⁹F NMR. HPLC measurements indicated that racemization did not take place at 40 °C for 72 h.

Bulky perneopentyloxy-pillar[5]arene was synthesized. Complexation behavior and conformational mobility were investigated using ¹H NMR spectroscopy. Isolation of planar-chiral pillar[5]arenes using a chiral derivatization agent were carried out.

Chiral discrimination of 2-heptlyaminium salt by planar-chiral monohydroxy-functionalized pillar[5]arenes

A chiral receptor was synthesized based on monohydroxy-functionalized pillar[5]arenes and its ability to discriminate alkyl aminium salts is demonstrated.

Assembling a Hybrid Pd Catalyst from a Chiral Anionic CoIII Complex and Ligand for Asymmetric C(sp3 )-H Functionalization

An unusual hybrid palladium catalyst containing an anionic chiral Co^III complex and a chiral phosphoramidite ligand shows a high capacity for catalyzing asymmetric thioamide-directed C(sp³ )-H arylation and delivers excellent yield and enantioselectivity (up to 99 % yield, 99 % ee). Significant synergy between the chiral ligand and the anion in terms of stereochemical control was observed. Mechanistic investigations have revealed both the nature of the C-H activation and the origin of the enantioselectivity.

Synthesis of Indoles through Palladium-Catalyzed Three-Component Reaction of Aryl Iodides, Alkynes, and Diaziridinone

The three-component reaction of aryl iodides, alkynes, and diaziridinone is described. The reaction provides an innovative synthetic approach for indoles. The approach features high efficiency, broad substrate scope, and excellent regioselectivity. C, C-Palladacycles should act as the intermediates. The C, C-palladacycles are obtained from simple aryl halides and alkynes and then reacted with diaziridinone to afford indoles.

Thiocarbonyl-enabled ferrocene C-H nitrogenation by cobalt(III) catalysis: thermal and mechanochemical

Versatile C–H amidations of synthetically useful ferrocenes were accomplished by weakly-coordinating thiocarbonyl-assisted cobalt catalysis. Thus, carboxylates enabled ferrocene C–H nitrogenations with dioxazolones, featuring ample substrate scope and robust functional group tolerance. Mechanistic studies provided strong support for a facile organometallic C–H activation manifold.

Enantioselective Synthesis of Chiral-at-Cage o-Carboranes via Pd-Catalyzed Asymmetric B-H Substitution

Carborane cage chirality is an outstanding issue of great interest as the icosahedral carboranes have wide applications in medicinal and materials chemistry. The synthesis of optically active carborane derivatives, whose chirality is associated with the substitution patterns on the polyhedron, will open new avenues to carborane chemistry. We report herein an efficient method to achieve chiral-at-cage arylation of o-carboranes with high regio- and enantioselectivities by a strategy of palladium-catalyzed asymmetric intramolecular B-H arylation and cyclization. This represents the first example of the enantioselective reaction on carboranes, providing an efficient way for the construction of chiral-at-cage compounds with new skeletons.

Enantioselective Synthesis of Planar Chiral Pyridoferrocenes via Palladium-Catalyzed Imidoylative Cyclization Reactions

A highly efficient synthesis of planar chiral pyrido[3,4- b] ferrocenes by a palladium-catalyzed enantioselective isocyanide insertion/desymmetric C(sp²)-H bond activation reaction was developed. Various planar chiral pyridoferrocenes were obtained in high yields with good to excellent enantioselectivity under mild conditions (up to 99% yield, 99% ee), enabled by a unique SPINOL-derived phosphoramidite ligand.

nBu4NOTf-promoted radical self-hydrogen transferring isomerization under transition metal-free conditions

We report the first allylic isomerization of alcohols catalyzed by ⁿBu₄NOTf generated in situ from tetrabutylammonium triflate and potassium tert-butoxide.

Palladium-catalyzed enantioselective C(sp2)–H arylation of ferrocenyl ketones enabled by a chiral transient directing group

A carboxylate-assisted palladium-catalyzed enantioselective C(sp²)–H arylation of ferrocenyl ketones is achieved through utilizing catalyticl-tert-leucine as a chiral transient directing group.