Exception to the ortho Effect in Palladium/Norbornene Catalysis

Modular One-Step Three-Component Synthesis of Tetrahydroisoquinolines Using a Catellani Strategy

Reported is a modular one-step three-component synthesis of tetrahydroisoquinolines using a Catellani strategy. This process exploits aziridines as the alkylating reagents, through palladium/norbornene cooperative catalysis, to enable a Catellani/Heck/aza-Michael addition cascade. This mild, chemoselective, and scalable protocol has broad substrate scope (43 examples, up to 90 % yield). The most striking feature of this protocol is the excellent regioselectivity and diastereoselectivity observed for 2-alkyl- and 2-aryl-substituted aziridines to access 1,3-cis-substituted and 1,4-cis-substituted tetrahydroisoquinolines, respectively. Moreover, this is a versatile process with high step and atom economy.

The Discovery of a Palladium(II)-Initiated Borono-Catellani Reaction

Reported is a novel palladium(II)-initiated Catellani-type reaction that utilizes widely accessible aryl boronic acids as the substrates instead of aryl halides, thereby greatly expanding the existing scope of this powerful transformation. This borono-Catellani reaction was promoted by cooperative catalysis between Pd(OAc)₂ and the inexpensive 5-norbornene-2-carbonitrile. Practicality is the striking feature of the reaction: it is run open to air at ambient temperature and no phosphine ligand is needed. This mild, chemoselective, and scalable protocol is compatible with a large range of readily available functionalized aryl boronic acids and bromides, as well as terminating olefins (50 examples, 39-97 % yields). Moreover, the orthogonal reactivity between the borono-Catellani and classical Catellani reaction was demonstrated. This work is expected to open new avenues for developing novel Catellani-type reactions.

Palladium/Norbornene-Catalyzed C-H Alkylation/Alkyne Insertion/Indole Dearomatization Domino Reaction: Assembly of Spiroindolenine-Containing Pentacyclic Frameworks

Reported is a highly chemoselective intermolecular annulation of indole-based biaryls with bromoalkyl alkynes by using palladium/norbornene (Pd/NBE) cooperative catalysis. This reaction is realized through a sequence of Catellani-type C-H alkylation, alkyne insertion, and indole dearomatization, by forming two C(sp² )-C(sp³ ) and one C(sp² )-C(sp² ) bonds in a single chemical operation, thus providing a diverse range of pentacyclic molecules, containing a spiroindolenine fragment, in good yields with excellent functional-group tolerance. Preliminary mechanistic studies reveal that C-H bond cleavage is likely involved in the rate-determining step, and the indole dearomatization might take place through an olefin coordination/insertion and β-hydride elimination Heck-type pathway.

Intermolecular domino reaction of two aryl iodides involving two C-H functionalizations

A palladium-catalyzed intermolecular cross-coupling of two aryl iodides is reported, giving polycyclic ring systems with a high level of convergence and efficiency.

Palladium/norbornene-mediated tandem C-H amination/C-I alkenylation reaction of aryl iodides with secondary cyclic O-benzoyl hydroxylamines and activated terminal olefins

A novel palladium-catalyzed norbornene-mediated three-component reaction for the construction of ortho-alkenyl aromatic tertiary amines has been achieved, which represents a useful extension of the Catellani-type tandem ortho-selective CH amination transformations.