Palladium-Catalyzed Weak-Chelation-Assisted C4-Nitration of Indoles with tert-Butyl Nitrite: Formal Access to Aminated Indoles

Palladium-catalyzed weak-chelation-assisted C4-selective nitration of indoles has been accomplished employing tert-butyl nitrite in the presence of oxone under molecular oxygen at a moderate temperature. Aerobic conditions, C4-selectivity, substrate scope, conversion to valuable aminated indoles, and late-stage natural product modifications are the important practical features.

Multifunctional Regioisomeric Passivation Strategy for Fabricating Self-Driving, High Detectivity All-Inorganic Perovskite Photodetectors

The fluorination of the aromatic multifunctional Lewis base passivation strategy has been demonstrated recently as an effective approach to markedly enhance the performance of perovskite photovoltaic devices. However, the regulation mechanisms of the passivation efficiency by varying the functional group position of fluorine (F) in the regioisomers have received little attention and inadequate research. Herein, a pair of bifluorine-substituted aminobenzoic acid regioisomers [3-amino-2,6-difluorobenzoic acid (13-FABA) and 4-amino-3,5-difluorobenzoic acid (14-FABA)] were employed to investigate the passivation effects of Lewis bases dependent on behaviors of the ortho/meta-substituted position of fluorine. The density functional theory calculation on electron cloud density, interaction energy, and the basicity of Lewis bases combined with experimental evidence reveal that the ortho-effect induced by fluorine substitution weakens the passivating effect of 13-FABA Lewis base and induces its molecular propensity to form internal salts, accelerating the degradation and deterioration of the device performance. Conversely, 14-FABA with meta-connected fluorine atoms exhibit superior efficacy in suppressing defects and enhancing hydrophobicity. Eventually, the 14-FABA-modified photodetectors (PDs) achieved a high detectivity of 1.69 × 1013 Jones, the comparatively lower dark current density of 2.2 × 10-10 A/cm2 among all-inorganic perovskite PD systems. Our work has not only clarified the fundamental mechanisms of the F-substituted position effects of Lewis base on suppressing defects but also provided a promising passivation strategy for perovskite films via designing the regioisomeric atoms in a multifunctional Lewis base molecule.

Fluoroalkylations and Fluoroalkenylations with Iodonium Salts

Synthesis and applications of fluoroalkyl and fluoroalkenyliodonium salts are summarized in this account article, focusing preferably to the reagents designed in our laboratory in the last decade. Among these reagents trifluoroethyl(aryl)iodonium salts have been used most frequently to build carbon-carbon and carbon-heteroatom bonds in simple nucleophilic substitutions and through transition metal catalyzed coupling reactions. Iodonium salts equipped with unsaturated fluorinated function showed diverse reactivity due to their electron deficient character, and these molecular motifs enable cycloadditions and nucleophilic additions to prepare fluorinated carbo- and heterocyclic molecules. Beyond the overview of existing transformations, with the presented collection, we aim to inspire future developments of iodonium reagents and their application in organic synthesis.

Mechanistic Insights into Cobalt-Catalyzed Regioselective C4-Alkenylation of 3-Acetylindole: A Detailed Theoretical Study

A detailed mechanistic study of Co(III)-catalyzed C4-alkenylation of 3-acetylindole (1a) was done based on calculations at density functional theory (DFT) and correlated wave function levels. The whole catalytic cycle consists of four steps: C-H activation, olefin insertion, β-hydride elimination, and regeneration of the catalyst. The theoretical results support olefin insertion as the rate-determining step leading to the experimentally observed regioselectivity of the C4 site over the C2 site. By the analysis of three-dimensional (3D) geometries and the NCl plot, the preference for the C4 site over the C2 site could be attributed to the weaker repulsive interaction between the indole moiety and olefin in the transition states of the olefin insertion step for the former. The reliability of the theoretical mechanistic results is further confirmed through the DFT calculation of other related indole derivatives and olefin substrates.

Directed C-H Functionalization of C3-Aldehyde, Ketone, and Acid/Ester-Substituted Free (NH) Indoles with Iodoarenes via a Palladium Catalyst System

Pd(II)-catalyzed C-H arylations of free (NH) indoles including different carbonyl directing groups on C3-position with aryl iodides are demonstrated. Importantly, the reactions are carried out using the same catalyst system without any additional transient directing group (TDG). In this study, the formyl group as a directing group gave the C4-arylated indoles versus C2-arylation. Using this catalyst system, C-H functionalization of 3-acetylindoles provided domino C4-arylation/3,2-carbonyl migration products. This transformation involves the unusual migration of the acetyl group to the C2-position following C4-arylation in one pot. Meanwhile, migration of the acetyl group could be simply controlled and N-protected 3-acetylindoles afforded C4-arylation products without migration of the acetyl group. Functionalization of indole-3-carboxylic acid (or methyl ester) with aryl iodides using the present Pd(II)-catalyst system resulted in decarboxylation followed by the formation of C2-arylated indoles. Based on the control experiments and the literature, plausible mechanisms are proposed. The synthetic utilities of these acetylindole derivatives have also been demonstrated. Remarkably, C4-arylated acetylindoles have allowed the construction of functionalized pityiacitrin (a natural product).

Palladium-catalyzed C–H activation of anisole with electron-deficient auxiliary ligands: a mechanistic investigation

In this work, the experimentally observed site-selectivity and ligand choice of Yu's meta-arylation reaction were rationalized through DFT calculations.