Palladium-Catalyzed Ring-Forming Aminoalkenylation of Alkenes with Aldehydes Initiated by Intramolecular Aminopalladation

Photocatalyzed Azidofunctionalization of Alkenes via Radical-Polar Crossover

The azidofunctionalization of alkenes under mild conditions using commercially available starting materials and easily accessible reagents is reported based on a radical-polar crossover strategy. A broad range of alkenes, including vinyl arenes, enamides, enol ethers, vinyl sulfides, and dehydroamino esters, were regioselectively functionalized with an azide and nucleophiles such as azoles, carboxylic acids, alcohols, phosphoric acids, oximes, and phenols. The method led to a more efficient synthesis of 1,2-azidofunctionalized pharmaceutical intermediates when compared to previous approaches, resulting in both reduction of step count and increase in overall yield. The scope and limitations of these transformations were further investigated through a standard unbiased selection of 15 substrate combinations out of 1,175,658 possible using a clustering technique.

A rapid pathway to molecular complexity: a palladium-catalyzed six-fold domino process to access polycyclic frameworks

Herein, we present a hitherto unexplored efficient strategy for rapidly constructing structurally constrained and intriguing polycyclic frameworks with two adjacent quaternary centers. Remarkably, this becomes possible through palladium-catalyzed six-fold domino crossover annulations of simple 1,2-bis(2-bromoaryl)ethynes and 1,2-diarylethynes. Notably, this approach demonstrates the synthesis of both C2-symmetric and unsymmetric polycyclic products.

Mechanistic insights into the α-branched amine formation with pivalic acid assisted C-H bond activation catalysed by Cp*Rh complexes

Density functional theory computations revealed a pivalic acid assisted C-H bond activation mechanism for rhodium catalyzed formation of α-branched amines with C-C and C-N bond couplings. The reaction energies of the [Cp*RhCl₂]₂ dimer and silver cations indicate that the Cp*RhCl⁺ cation is the active catalyst. The essential role of pivalic acid is a co-catalyst for the activation of the ortho-C(sp²)-H bond in phenyl(pyrrolidin-1-yl)methanone, while the reaction of NaHCO₃ and HCl reduces the overall barrier of the catalytic cycle. In the presence of both pivalic acid and NaHCO₃ in the reaction, the C(sp²)-H bond is activated through a concerted metallation deprotonation process, and the C-C bond coupling is the rate-determining step with a total free energy barrier of 23.9 kcal mol^-1. Without pivalic acid and NaHCO₃, the C(sp²)-H bond can only be activated through a σ-bond metathesis process and the free energy barrier increases to 32.2 kcal mol^-1. We also investigated the mechanisms of a side reaction for β-branched amine formation and the reaction without styrene and found that their free energy barriers are 33.4 and 30.5 kcal mol^-1, respectively.

Divergent Syntheses of Indoles and Quinolines Involving N1-C2-C3 Bond Formation through Two Distinct Pd Catalyses

Pd-catalyzed annulative couplings of 2-alkenylanilines with aldehydes using alcohols as both the solvent and hydrogen source have been developed. These domino processes allow divergent syntheses of two significant N-heterocycles, indoles and quinolines, from the same substrate by tuning reaction parameters, which seems to invoke two distinct mechanisms. The nature of the ligand and alcoholic solvent had a profound influence on the selectivity and efficiency of these protocols. Particularly noteworthy is that indole formation was achieved by overcoming two significant challenges, regioselective hydropalladation of alkenes and subsequent reactions between the resulting Csp³-Pd species and less reactive imines.

Density Functional Theory Study on the Mechanism of Iridium-Catalyzed Benzylamine ortho C-H Alkenylation with Ethyl Acrylate

Iridium-catalyzed oxidative o-alkenylation of benzylamines with acrylates was enabled by the directing group pentafluorobenzoyl (PFB). Density functional theory calculations were performed to explore the detailed reaction mechanism. The calculated results reveal that N-deprotonation prior to C-H activation is favored over direct C-H activation. Moreover, C-H activation is reversible and not the rate-determining step, which has been supported by the experimental observation. The regio- and stereoselectivity of ethyl acrylate insertion are controlled by the steric effect and the carbon atom with a larger orbital coefficient of the π* antibonding orbital in the nucleophilic attack, respectively. The migratory insertion of ethyl acrylate is computationally found to be rate-determining for the whole catalytic cycle. Finally, the seven-membered ring intermediate IM11 undergoes a sequential N-protonation and β-H elimination with the assistance of AcOH, rather than β-H elimination and reductive elimination proposed experimentally, to afford the o-alkenylated product. IM11 is unable to directly cyclize through C-N reductive elimination because both sp³-hybridized N and C atoms are unfavorable for N-C reductive elimination. The origin of the directing group PFB preventing the product and intermediates undergoing aza-Michael addition has been explained.

Substrate controlled, regioselective carbopalladation for the one-pot synthesis of C4-substituted tetrahydroisoquinoline analogues

6-Exo-trig cyclization reaction through regioselective carbopalladation was demonstrated with N-(2-halobenzyl)-N-allylamines to furnish the corresponding C4-substituted tetrahydroisoquinoline derivatives.

Cobalt(iii)-catalyzed ketone-directed C–H vinylation using vinyl acetate

Weakly coordinating, ketone-directed C–H vinylation using vinyl acetate is reported here for a wide range of aromatic ketones such as acetophenones, diaryl ketones, chromones and chalcones under cost-effective and air-stable cobalt(iii)-catalysis.

Palladium-Catalyzed Regioselective Syn-Chloropalladation-Olefin Insertion-Oxidative Chlorination Cascade: Synthesis of Dichlorinated Tetrahydroquinolines

A palladium catalyzed cascade process involving syn-chloropalladation, intramolecular olefin insertion, and oxidative C-Cl bond formation reactions was demonstrated for the synthesis of dichlorinated tetrahydroquinolines in high yields (up to 93%). The N-propargyl arylamines having a tethered α,β-unsaturated carbonyl moiety underwent a regioselective syn-chloropalladation followed by a Heck-type reaction to deliver the tetrahydroquinoline scaffold. The rare insertion of the second chlorine atom was rationalized comprising a Pd^II/IV catalytic cycle and oxidative cleavage of the C-Pd^II bond.

Iridium-Catalyzed Benzylamine C-H Alkenylation Enabled by Pentafluorobenzoyl as the Directing Group

The first iridium-catalyzed oxidative alkeynylation of benzylamines with acrylates enabled by a new directing group pentafluorobenzoyl has been developed. The reaction proceeded efficiently in the presence of silver acetate as oxidant and chlorobenzene as solvent. A good range of benzylamines could be selectively monoalkenylated without interfering with further aza-Michael addition. The kinetic isotope effect experiments showed that C-H activation is not the rate-limiting step. In addition, a five-membered iridacycle species was isolated and established as the possible key intermediate.

Multicomponent Synthesis of Tetrahydroisoquinolines

A multicomponent synthesis of tetrahydroisoquinolines from carboxylic acids, alkynyl ethers, and dihydroisoquinolines is described. This process features readily available starting materials, simple experimental procedures for achievement of molecule complexity, and structural diversity. The preliminary control experiment and crossover reaction provide important insight into the reaction mechanism. The formed tetrahydroisoquinolines could be transformed to an array of compounds.

Palladium-catalysed stereoselective synthesis of 4-(diarylmethylidene)-3,4-dihydroisoquinolin-1(2H)-ones: expedient access to 4-substituted isoquinolin-1(2H)-ones and isoquinolines

Palladium-catalysed stereoselective synthesis of 4-(diarylmethylidene)-3,4-dihydroisoquinolin-1(2H)-ones and their straightforward transformations to 4-substituted isoquinolin-1(2H)-ones and isoquinolines are described.

A practical approach for the synthesis of oxindole and isatin derivatives by Pd-catalyzed intramolecular amination

A highly efficient approach for the selective synthesis of bioactive oxindole/isatin-N-acetamide derivatives via Pd-catalyzed intramolecular amination has been developed.