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

Beyond Tertiary Amines: Introducing Secondary Amines by Palladium/Norbornene-Catalyzed Ortho Amination

Since the discovery of the palladium/norbornene (Pd/NBE)-catalyzed ortho amination in 2013, escaping the limitation of only yielding tertiary anilines has been a long-standing challenge. Here, we describe that, by carefully choosing the phosphine ligand and NBE mediator, the installation of a N-mono-alkylamino group becomes feasible. The reaction tolerates a wide range of aryl iodide substrates and various N-mono-tertiary alkylamine-derived electrophiles. Both ipso alkenylation and alkynylation can be realized. The synthetic utility of this method is exemplified by the formation of primary amino group via selective deprotection and streamlined access to N-heterocycles. Preliminary success of installing a bulky N-secondary alkylamino group and a mechanistic understanding of the decomposition pathways of mono N-alkylamine electrophiles have been obtained.

Palladium-catalyzed interannular C-H amination of biaryl amines

A palladium-catalyzed interannular C-H amination of biaryl amines with O-benzoylhydroxylamines is reported. This reaction undergoes smoothly with operational practicality and good tolerance of functional groups, thereby providing a concise synthesis of 2,2'-diaminobiaryls. Moreover, the readily accessible scale-up synthesis and the ability to transform the products into structurally diverse N-containing heterocycles demonstrate the synthetic potential of this catalytic protocol.

Synthesis of C3,C4-Disubstituted Indoles via the Palladium/Norbornene-Catalyzed ortho-Amination/ipso-Heck Cyclization

Herein, we report the synthesis of C3,C4-disubstituted indoles via the palladium/norbornene cooperative catalysis. Utilizing N-benzoyloxy allylamines as the coupling partner, a cascade process involving ortho-amination and ipso-Heck cyclization takes place with ortho-substituted aryl iodides to afford diverse indole products. The reaction exhibits good functional group tolerance, in addition to tolerating a removable protecting group on the indole nitrogen. Divergent reactivity has been observed using the allylamine coupling partner containing more substituted olefins. Construction of the core framework of mitomycin has also been attempted with this strategy.

Alkylation-Terminated Catellani Reactions by Cyclobutanol C-C Cleavage

This report describes the first application of a cyclobutanol ring-opening procedure in the Catellani termination reaction, which includes two β-carbon elimination processes. This tandem reaction features mild conditions, high yields, good functional group tolerance, and a broad substrate scope. Meanwhile, four types of electrophiles (N-benzoyloxyamines, alkyl iodides, aryl bromides, and benzyl chlorides) are quite compatible with this termination reaction for the construction of various types of polysubstituted aromatic hydrocarbons.

A Catellani and retro-Diels–Alder strategy to access 1-amino phenanthrenes via ortho- and interannular C–H activation of 2-iodobiphenyls

A palladium-catalyzed three-component domino reaction for the construction of 1-amino phenanthrene derivatives by ortho- and interannular C–H activation of 2-iodobiphenyls has been developed.

C–H hetero-functionalization of arenes through palladacyclopentane-type intermediates

In this review article, we summarized recent advances in C–H hetero-functionalization of arenes through palladacyclopentane-type intermediates.

A carboxylate-assisted amination/unactivated C(sp2)–H arylation reaction via a palladium/norbornene cooperative catalysis

A carboxylate-assisted palladium-catalysed Catellani reaction, which is compatible with ortho-amination and unactivated C(sp²)–H arylation, synthesized a series of 1-amino substituted dihydrophenanthridines, phenanthridines and 6H-benzo[c]chromenes.

A denitrogenative palladium-catalyzed cascade for regioselective synthesis of fluorenes

We herein report a denitrogenative palladium-catalyzed cascade for the modular and regioselective synthesis of polysubstituted fluorenes. Hydrazone facilitates the Pd(ii) to Pd(iv) oxidative addition in a Catellani pathway and is also the methylene synthon in the proposed reaction. Aryl iodides and 2-bromoarylaldehyde hydrazones undergo a norbornene-controlled tandem reaction sequence to give a broad scope of fluorenes in the presence of a palladium catalyst. The method described is scalable and adaptable to a three-component reaction with in situ generation of the hydrazone group. Preliminary mechanistic investigations have been conducted.

Redox-neutral ortho-C-H amination of pinacol arylborates via palladium(ii)/norbornene catalysis for aniline synthesis

A palladium(ii)/norbornene cooperative catalysis enabled redox-neutral ortho-C-H amination of pinacol aryl- or heteroarylborates for the synthesis of structurally diverse anilines is reported. This method is scalable, robust (tolerance of air and moisture), phosphine ligand-free, and compatible with a wide range of functionalities. These practical features make this reaction amenable for industry. A plethora of synthetically very useful halogenated anilines, which often cannot be prepared via other transition-metal-catalyzed aminations, are readily produced using this method. Particularly, the orthogonal reactivity between pinacol arylborates and aryl iodides is demonstrated. Preliminary deuterium-labeling studies reveal a redox-neutral ipso-protonation mechanism of this process, which will surely inspire the future development of this field. Overall, the exceptionally broad scope (47 examples) and reliability of this procedure, together with the wide availability of pinacol arylborates, make this chemistry a valuable addition to the existing methods for aniline synthesis.

Palladium/Norbornene Cooperative Catalysis

Palladium/norbornene cooperative catalysis has emerged as a distinct approach to construct polyfunctionalized arenes from readily available starting materials. This Review provides a comprehensive overview of this field, including the early stoichiometric investigations, catalytic reaction developments, as well as the applications in the syntheses of bioactive compounds and polymers. The section of catalytic reactions is divided into two parts according to the reaction initiation mode: Pd(0)-initiated reactions and Pd(II)-initiated reactions.

A palladium/norbornene cooperative catalysis to access N-containing bridged scaffolds

A palladium/norbornene cooperative catalysis promoted annulation involving an ortho-C-H amination and intramolecular Heck cascade between aryl iodides and functionalized amination reagents is reported, thereby providing a highly convergent access to the unique N-containing bridged scaffolds: hexahydro-2,6-methano-1-benzazocine. The salient features of the reaction include its broad substrate scope (with respect to aryl iodides), its high step economy, and good chemoselectivity. Preliminary studies underscore the future promise of rendering this Catellani-type annulation enantioselective.

Modular ipso/ ortho Difunctionalization of Aryl Bromides via Palladium/Norbornene Cooperative Catalysis

Palladium/norbornene (Pd/NBE) cooperative catalysis has emerged as a useful tool for preparing poly substituted arenes; however, its substrate scope has been largely restricted to aryl iodides. While aryl bromides are considered as standard substrates for Pd-catalyzed cross coupling reactions, their use in Pd/NBE catalysis remains elusive. Here we describe the development of general approaches for aryl bromide-mediated Pd/NBE cooperative catalysis. Through careful tuning the phosphine ligands and quenching nucleophiles, ortho amination, acylation and alkylation of aryl bromides have been realized in good efficiency. Importantly, various heteroarene substrates also work well and a wide range of functional groups are tolerated. In addition, the utility of these methods has been demonstrated in sequential cross coupling/ ortho functionalization reactions, consecutive Pd/NBE-catalyzed difunctionalization to construct penta-substituted aromatics and two-step meta functionalization reactions. Moreover, the origin of the ligand effect in ortho amination reactions has been explored through DFT studies. It is expected that this effort would significantly expand the reaction scope and enhance the synthetic potential for Pd/NBE catalysis in preparing complex aromatic compounds.

Direct Annulation between Aryl Iodides and Epoxides through Palladium/Norbornene Cooperative Catalysis

Herein we report a direct annulation between aryl iodides and epoxides through palladium/norbornene (Pd/NBE) cooperative catalysis. An iso-propyl ester substituted NBE was found to be most efficient to suppress the formation of multiple-NBE-insertion byproducts and affords the desired 2,3-dihydrobenzofuran derivatives in 44-99 % yields. The reaction is scalable and tolerates a range of functional groups. Asymmetric synthesis is realized using an enantiopure epoxide. Application of this method into a concise synthesis of insecticide fufenozide is demonstrated.

Synthesis of indolines via a palladium/norbornene-catalyzed reaction of aziridines with aryl iodides

A Pd- and norbornene-catalyzed domino procedure has been developed to synthesize indoline compounds.