Regiospecific N-Arylation of Aliphatic Amines under Mild and Metal-Free Reaction Conditions

Recent synthetic strategies for N-arylation of pyrrolidines: a potential template for biologically active molecules

The chemistry of nitrogen-containing heterocyclic compounds has been a multifaceted area of research for an extended period due to their varied therapeutic and biological significance. N-Aryl pyrrolidine formed by condensation of aryl group with nitrogen atom of pyrrolidine is present in a wide array of compounds. Various significant activities shown by N-arylated pyrrolidine include anti-Alzheimer, antihypoxic, anticancer, plant activator, analgesic effect, and hepatitis C inhibitor. This review summarizes different synthetic approaches, e.g., transition-metal catalyzed and transition-metal-free synthesis, decarboxylation reaction, reductive amination, nucleophilic cyclization, Ullmann-Goldberg amidation, Buchwald-Hartwig reaction, Chan-Evans-Lam coupling, addition to benzyne, multistep reaction, green synthesis, rearrangement reaction, and multicomponent reaction, to afford the derivatives of N-aryl pyrrolidine. It encompasses synthetic strategies documented from 2015 to 2023.

Organohypervalent heterocycles

This review summarizes the structural and synthetic aspects of heterocyclic molecules incorporating an atom of a hypervalent main-group element. The term "hypervalent" has been suggested for derivatives of main-group elements with more than eight valence electrons, and the concept of hypervalency is commonly used despite some criticism from theoretical chemists. The significantly higher thermal stability of hypervalent heterocycles compared to their acyclic analogs adds special features to their chemistry, particularly for bromine and iodine. Heterocyclic compounds of elements with double bonds are not categorized as hypervalent molecules owing to the zwitterionic nature of these bonds, resulting in the conventional 8-electron species. This review is focused on hypervalent heterocyclic derivatives of nonmetal main-group elements, such as boron, silicon, nitrogen, carbon, phosphorus, sulfur, selenium, bromine, chlorine, iodine(III) and iodine(V).

Utilization of Aryl(TMP)iodonium Salts for Copper-Catalyzed N-Arylation of Isatoic Anhydrides: An Avenue to Fenamic Acid Derivatives and N,N'-Diarylindazol-3-ones

Herein, we report a general method for copper-catalyzed N-arylation of isatoic anhydrides with unsymmetrical iodonium salts at room temperature. The developed catalytic protocol is mild and operationally simple, and aryl(TMP)iodonium trifluoroacetate is employed as the arylating partner. The methodology offers the broad applicability of both structurally and electronically diverse aryl groups from aryl(TMP)iodonium salts to access N-arylated isatoic anhydrides in moderate to excellent yields (53-92%). Moreover, the substituted isatoic anhydrides are equally compatible with the protocol too. To demonstrate the synthetic utilities of the N-arylation process, we also report an alternative approach for biologically relevant fenamic acid derivatives and N,N'-diarylindazol-3-ones in a one-pot step economical system. In addition, the scale-up synthesis of flufenamic acid is also illustrated.

Ligand-free Ullmann-type arylation of oxazolidinones by diaryliodonium salts

The arylation of azaheterocycles can be considered as one of the most important processes for the preparation of various biologically active compounds. In the present work, we describe a method for the copper-catalyzed N-arylation of hindered oxazolidinones using diaryliodonium salts. The method succeeds in good to excellent yields for the arylation of 4-alkyloxazolidinones, including sterically hindered isopropyl- and tert-butyl-substituted. The efficiency of the method was demonstrated for a wide range of diaryliodonium salts - symmetric and unsymmetric as well as ortho-substituted derivatives. The developed approach will provide an important contribution in the development and preparation of novel drugs and bioactive molecules containing oxazolidinone moieties.

Metal-free S-arylation of 5-mercaptotetrazoles and 2-mercaptopyridine with unsymmetrical diaryliodonium salts

Herein, we demonstrate the application of unsymmetrical iodonium salts towards S-arylation of heterocyclic thiols (especially tetrazole-5-thiols and pyridine-2-thiol) under metal-free conditions, affording a diverse range of di(hetero)aryl thioethers in moderate to good yields. A detailed study on the effects of counter-anions and the auxiliary of iodonium salts was conducted. Suitable auxiliary selection of the unsymmetrical iodonium salt offers flexibility for a wide range of aryl moieties and its incorporation into S-arylation. The DFT study supports the experimental observations of chemoselective arylation.

Transition Metal-Free N-Arylation of Amino Acid Esters with Diaryliodonium Salts

A transition metal-free approach for the N-arylation of amino acid derivatives has been developed. Key to this method is the use of unsymmetric diaryliodonium salts with anisyl ligands, which proved important to obtain high chemoselectivity and yields. The scope includes the transfer of both electron deficient, electron rich and sterically hindered aryl groups with a variety of different functional groups. Furthermore, a cyclic diaryliodonium salt was successfully employed in the arylation. The N-arylated products were obtained with retained enantiomeric excess.

Enantioselective Synthesis of N-C Axially Chiral Compounds by Cu-Catalyzed Atroposelective Aryl Amination

N-C axially chiral compounds have emerged recently as appealing motifs for drug design. However, the enantioselective synthesis of such molecules is still poorly developed and surprisingly no metal-catalyzed atroposelective N-arylations have been described. Herein, we disclose an unprecedented Cu-catalyzed atroposelective N-C coupling that proceeds at room temperature. Such mild reaction conditions, which are a crucial parameter for atropostability of the newly generated products, are operative thanks to the use of hypervalent iodine reagents as a highly reactive coupling partners. A large panel of the N-C axially chiral compounds was afforded with very high enantioselectivity (up to >99 % ee) and good yields (up to 76 %). Post-modifications of thus accessed atropisomeric compounds allows further expansion of the diversity of these appealing compounds.

Cascade π-Extended Decarboxylative Annulation Involving Cyclic Diaryliodonium Salts: Site-Selective Synthesis of Phenanthridines and Benzocarbazoles via a Traceless Directing Group Strategy

A novel cascade π-extended decarboxylative annulation (PEDA) involved with cyclic diaryliodonium salts is described. Via fine-tuning of the reaction conditions, the Pd(II)-catalyzed site-selective N1/C2 or C2/C3 annulation of commercially available indole-2-carboxylic acids can be achieved, affording valuable phenanthridines or benzocarbazoles, respectively. The key strategy is the carboxylic acid functionality being employed as both a traceless directing group for the ortho C-N or C-C coupling and a reactive group for the cascade π-extended decarboxylative annulation in a highly step economical manner.

Concerted Nucleophilic Aromatic Substitution Reactions

Recent developments in experimental and computational chemistry have identified a rapidly growing class of nucleophilic aromatic substitutions that proceed by concerted (cSN Ar) rather than classical, two-step, SN Ar mechanisms. Whereas traditional SN Ar reactions require substantial activation of the aromatic ring by electron-withdrawing substituents, such activating groups are not mandatory in the concerted pathways.