Substrate-Controlled Regio- and Stereoselective Synthesis of ( Z)- and ( E)- N-Styrylated Carbazoles, Aza-carbazoles, and γ-Carbolines via Hydroamination of Alkynes

Substrate-Dependent Stereoselective Synthesis of Pyrrolo[3,4-b]Pyridin-5-Ones and Pyridyl Isoindoline-1-Ones Using Bis(benzotriazol-1-yl) Ligand

The documented work highlighted the synthesis of bis(benzotriazol-1-yl) methane derivatives using silicomolybdic acid (SMA) and successfully implemented in the stereoselective synthesis of diverse pyrrolo[3,4-b]pyridin-5-one and pyridyl isoindolinones derivatives in one-pot. The pyridinamide precursor with diverse alkynes furnished Z-selectivity of pyrrolo[3,4-b]pyridin-5-one across exocyclic C=C bond while the various benzamides on treating with 2-ethynyl pyridine afforded (E)-pyridylisoindoline-1-ones as a major isomer. The single-crystal X-ray diffraction provides strong evidence in favor of the existence and orientation of developed compounds. The broad substrate scope, easy accessibility of substrates, high stereoselectivity, scale-up synthesis, and crystal evidence demonstrate the merits of the current decorum.

Exploring the Impact of Elements on the Reactivity of a Straightforward Procedure for Generating Vinyl-Carbazole Derivatives via a Frustrated Lewis Pair Mechanism

The effect of chemical element on the reactivity for carbazolation reaction of phenylacetylene utilizing G13(C6F5)3 (Lewis acid) and G15-carbazole (Lewis base) was theoretically investigated using density functional theory (M06-2X-D3/def2-TZVP), where G13 represents Group 13 elements and G15 represents Group 15 elements. Through activation strain model (ASM) analysis, it is apparent that the reactivity of the entire carbazolation reaction is chiefly governed by the structural strain energy of the alkyne fragment. In other words, if G13(C6F5)3 or G15-carbazole features an atomic radius that is either too small (e.g., B atom) or too large (e.g., Tl or Bi atom), it results in inadequate orbital overlap between the reactants due to the impact of steric effects. This, in turn, results in an elevation of the activation energy for such reactions, thereby impeding the alkyne from undergoing the carbazole catalytic reaction. In light of the above analyses, our theoretical findings suggest that, except for Tl(C6F5)3, the other four Lewis acid catalysts (B(C6F5)3, Al(C6F5)3, Ga((C6F5)3, and In((C6F5)3) demonstrate effectiveness in catalyzing the carbazolation reaction of alkyne alongside with N-carbazole. Additionally, it is anticipated that, among the five categories of G15-carbazole molecules studied, only N-carbazole can participate in the carbazolation reaction with alkyne catalyzed by B(C6F5)3, considering both kinetic and thermodynamic factors at room temperature. Our theoretical investigations, as outlined in this study, indicate that the carbazolation reaction of the alkyne, catalyzed by G13(C6F5)3 and G15-carbazole, follows Hammond's postulate. To put it more plainly, when the transition state of the chemical reaction occurs earlier, it results in a decrease in activation energy.

Selective Hydrofunctionalization of N-Allenyl Derivatives with Heteronucleophiles Catalyzed by Brønsted Acids

In this study, we present a novel and environmentally sustainable protocol for the γ-hydrofunctionalization of N-allenyl compounds using various heteronucleophiles catalyzed solely by simple Brønsted acids. The method displays remarkable attributes, highlighting its sustainability, efficiency, regio- and stereoselectivity, as well as its versatile applicability to diverse heteroatom-containing enamides. Notably, our approach eliminates the need for metal catalysts and toxic solvents, representing a significant advancement in greener chemistry practices. We demonstrate the broad scope of our protocol by successfully scaling up reactions to gram-scale syntheses, underscoring its robustness for potential industrial implementation. The resulting γ-heterosubstituted enamides offer new possibilities for further synthetic transformations, yielding highly functionalized compounds with diverse applications. Mechanistic investigations reveal the pivotal role of CSA as a catalyst, enabling alcohol addition via a covalent activation mode.

Vinylation of N-Heteroarenes through Addition/Elimination Reactions of Vinyl Selenones

A new protocol for the synthesis of N-vinyl azoles using vinyl selenones and azoles in the presence of potassium hydroxide was developed. This reaction proceeded under mild and transition metal-free conditions through an addition/elimination cascade process. Both aromatic and aliphatic vinyl selenones and various mono-, bi- and tri-cyclic azoles can be tolerated and give terminal N-vinyl azoles in moderate to high yields. A plausible mechanism is also proposed.

Catalytic hydroaminations of alkynes: A facile protocol to vinyl- carbazole derivatives via a frustrated Lewis pair mechanism

N-vinylcarbazoles are important skeletons for photoluminescent materials. Herein, a metal-free, B(C6F5)3 mediated carbazolation reaction of alkynes is reported. This provides 24 variants of N-vinylcarbazole derivatives. These N-vinylcarbazole products were obtained...

Stereoselective Direct N-Trifluoropropenylation of Heterocycles with a Hypervalent Iodonium Reagent

The availability and synthesis of fluorinated enamine derivatives such as N-(3,3,3-trifluoropropenyl)heterocycles are challenging, especially through direct functionalization of the heterocyclic scaffold. Herein, a stereoselective N-trifluoropropenylation method based on the use of a bench-stable trifluoropropenyl iodonium salt is described. This reagent enables the straightforward trifluoropropenylation of various N-heterocycles under mild reaction conditions, providing trifluoromethyl enamine type moieties with high stereoselectivity and efficiency.

Nonmetal-catalyzed hydroamination of ynamides with amines

A TfOH-catalyzed hydroamination of ynamides with primary and secondary amines under mild reaction conditions is described for the efficient synthesis of N-arylimines and ethene-1,1-diamines.

γ-Carboline synthesis enabled by Rh(iii)-catalysed regioselective C-H annulation

A redox-neutral Rh(iii)-catalyzed C-H annulation of indolyl oximes was developed. Relying on the use of various alkynyl silanes as the terminal alkyne surrogates, the reaction exhibited a reverse regioselectivity, thus giving an exclusive and easy way for the synthesis of a wide range of substituent free γ-carbolines at C3 position with high efficiency. Deuterium-labelling experiments and kinetic analysis have preliminarily shed light on the working mode of this catalytic system.

Aza-Henry Reaction: Synthesis of Nitronaphthylamines from 2-(Alkynyl)benzonitriles

A transition-metal-free approach for construction of nitronaphthylamines has been developed for the first time through aza-henry, chemoselective, and regioselective annulation of 2-alkynylbenzonitriles with nitromethane. In addition, the strategy provides an elegant, operationally simple and atom-economical route for the synthesis of nitroamino substituted heterocyclic scaffolds, featuring a range of sensitive functional groups. The reaction could also devise acetonitrile and acetophenone as nucleophile. The protocol has been successfully implemented for late-stage modification of bioactive molecules.

Novel base-initiated cascade reactions of hemiindigos to produce dipolar γ-carbolines and indole-fused pentacycles

Novel continuous-flow cascade reactions are developed for producing 1,4-diaryl-disubstituted dipolar γ-carbolines 2 that contain a carboxylate group and their two pentacyclic precursors 6, 7 from hemiindigos 1. The nucleophilic and pro-electrophilic chemistry described is new to the hemiindigos 1, and it led to the discovery of antimycobacterial scaffold characteristic of rimino-type pentacycles 6, 7 and potent drug clofazimine. The new scaffold like clofazimine appears to be useful in developing lead agents active against drug-resistant/dormant TB.

Based on hemiindigos we developed novel reactions for producing γ-carbolines and their precursors that appeared to be active against MTB.