Rh(III)-Catalyzed [3 + 2] Annulation of Aniline Derivatives with Vinylsilanes via C–H Activation/Alkene Cyclization: Access to Highly Regioselective Indoline Derivatives

Synthesis of indolines via palladium-catalyzed [4 + 1] annulation of (2-aminophenyl)methanols with sulfoxonium ylides

A facile strategy for the synthesis of valuable indolines has been developed, involving a palladium(II)/Brønsted acid co-catalyzed annulation of readily available (2-aminophenyl)methanols and sulfoxonium ylides. This protocol allows for the direct utilization of the OH group as a leaving group, tolerates alkyl and aryl groups on the N atom of the aniline moiety, operates under mild reaction conditions, and exhibits good efficiency.

Reverse Regioselective Cp*Co(III)-Catalyzed [4 + 2] C-H Annulation of N-Chloroamides with Vinylsilanes: Synthesis of 4-Silylated Isoquinolones and Their Synthetic Utilities

We have developed a Cp*Co(III)-catalyzed reverse regioselective [4 + 2] annulation of N-chlorobenzamides/acrylamides with vinylsilanes for the synthesis of 4-silylated isoquinolones. The reaction was performed at ambient temperature under redox-neutral conditions. The reaction utilized the N-Cl bond as an internal oxidant, furnished the required products with excellent regioselectivities, and demonstrated high functional group tolerance. The synthetic utility of 4-silylated isoquinolones has been demonstrated for the preparation of 4-heteroarylated and 4-alkylated isoquinolones via metal-free C-C couplings. Additionally, 3,4-dihydroisoquinolones were synthesized via protodesilylation of 4-silylated isoquinolones, thus making vinylsilane an ethylene surrogate.

The crucial role of silver(I)-salts as additives in C-H activation reactions: overall analysis of their versatility and applicability

Transition-metal catalyzed C-H activation reactions have been proven to be useful methodologies for the assembly of synthetically meaningful molecules. This approach bears intrinsic peculiarities that are important to be studied and comprehended in order to achieve its best performance. One example is the use of additives for the in situ generation of catalytically active species. This strategy varies according to the type of additive and the nature of the pre-catalyst that is being used. Thus, silver(I)-salts have proven to play an important role, due to the resulting high reactivity derived from the pre-catalysts of the main transition metals used so far. While being powerful and versatile, the use of silver-based additives can raise concerns, since superstoichiometric amounts of silver(I)-salts are typically required. Therefore, it is crucial to first understand the role of silver(I) salts as additives, in order to wisely overcome this barrier and shift towards silver-free systems.

Mechanistic Study on CpRh(III)-Catalyzed [3 + 2] Annulation of Aniline Derivatives with Vinylsilanes: A DFT Study

The rhodium(III)-catalyzed reaction of aniline derivatives that contain a pyrimidine-directing group with vinylsilanes results in the formation of C3-substituted indoline derivatives. The reaction path and formation of the indoline product with density functional theory calculations were analyzed. This study reveals that the whole catalysis can be characterized in the following stages: (I) C-H activation via concerted metalation deprotonation, (II) 2,1-vinylsilane insertion, (III) deprotonation of the NH amide proton, (IV) the oxidation of Ag⁺, and (V) reductive elimination. These steps are kinetically and thermodynamically feasible for experimental realization under mild conditions, and the insertion step with a barrier of 22.0 kcal/mol should not only be the critical step of regioselectivity but also the rate-determining step during the whole catalysis. Computations reveal that the Ag⁺ oxidation can accelerate the reductive elimination step after the formation of natural intermediate, thus highlighting the role of Ag⁺ as a catalytic promoter for the oxidatively induced reactivity of the Rh catalyst in C3-substituted indoline synthesis.

Ligand-assisted olefin-switched divergent oxidative Heck cascade with molecular oxygen enabled by self-assembled imines

Divergent oxidative Heck reaction has proven to be reliable for the rapid construction of molecular complexity, while olefins switched the outcome that remained underexplored.

Synthesis of Diverse γ-Lactams via Rh-Catalyzed C(sp2)-H Addition to Aliphatic Nitriles

We herein report an unprecedented pathway to access γ-lactams using acetonitrile analogues as coupling partners without oxidants, ligands, and Lewis acids. The reaction undergoes Rh-catalyzed C(sp²)-H addition to carbon-bound nitriles with the aid of an amide traceless auxiliary followed by an annulation sequence, featuring a broad substrate scope, good functional group tolerance, and excellent chemo/stereoselectivity. Scale-up reactions and late-stage derivatizations highlight the potential synthetic utility of this methodology. A plausible mechanism is proposed based on mechanistic investigations.