Metal-Free Visible-Light Induced Oxidative Cleavage of C(sp3 )-C, and C(sp3 )-N Bonds of Nitriles, Alcohols, and Amines.

Selective cleavage of unstrained (sp3 ) C-C/ C-N bonds under mild conditions is highly challenging due to the higher bond dissociation energy. A visible light mediated metal-free oxidative dehomologation of aryl acetonitriles, primary alcohols and diols to carboxylic acids via organophotocatalyzed C(sp3 )-CN, C(sp3 )-C(OH) bond cleavage is reported. Notably, this methodology was further extended towards selective synthesis of aldehydes via deamination of both primary as well as secondary amines. This mild protocol features wide array of substrate variation with excellent functional group tolerance, preparative-scale synthesis, and operational simplicity. Possible mechanisms for these transformations were demonstrated through a series of control experiments.

Activation of Ethanol via Conjunction of a Photocatalyst and a HAT Reagent for the Synthesis of Benzimidazoles.

The transformation of ethanol to value-added chemicals has tremendous potential. However, generally, harsh reaction conditions are needed for the functionalization of ethanol due to its high dehydrogenation energy. Herein, a metal-free photo-mediated activation of challenging ethanol and higher aliphatic alcohols for the synthesis of differently functionalized benzimidazoles under mild conditions is disclosed. The interplay of a photocatalyst and a HAT reagent facilitated the activation of aliphatic alcohols. A wide array of diamines with different functional groups were well tolerated, and the protocol was also extended to N-substituted diamines for the synthesis of industrially important benzimidazoles. A probable catalytic cycle was proposed based on various mechanistic studies.

Reductive Alkylation of Azides and Nitroarenes with Alcohols: A Selective Route to Mono- and Dialkylated Amines.

Herein, we demonstrated an efficient protocol for reductive alkylation of azides/nitro compounds via a borrowing hydrogen (BH) method. By following this protocol, selective mono- and dialkylated amines were obtained under mild and solvent-free conditions. A series of control experiments and deuterium-labeling experiments were performed to understand this catalytic process. Mechanistic studies suggested that the Ir(III)-H was the active intermediate in this reaction. KIE study revealed that the breaking of the C-H bond of alcohol might be the rate-limiting step. Notably, this solvent-free strategy disclosed a high TON of around 5600. Based on kinetic studies and control experiments, a metal-ligand cooperative mechanism was proposed.

Pd-Catalyzed regioselective synthesis of 2,6-disubstituted pyridines through denitrogenation of pyridotriazoles and 3,8-diarylation of imidazo[1,2-a]pyridines.

Synthesis of 2,6-disubstituted pyridines from pyridotriazoles through palladium-catalyzed aerobic oxidative denitrogenative reactions has been described. Denitrogenation of arylated pyridotriazoles generates metal-carbene intermediates in situ and provides selectively 6-aryl-2-benzoylpyridines. The same conditions have been extended to regioselective C-3 and C-8 diarylation of several imidazo[1,2-a]pyridines.

Indium-Catalyzed Denitrogenative Transannulation of Pyridotriazoles: Synthesis of Pyrido[1,2- a]indoles.

Pyrido[1,2- a]indoles are known for medicinally and pharmaceutically important compounds; however, the efficient synthetic routes are scarce in the literature. We report herein a convenient and efficient route to synthesize these molecules through indium-catalyzed transannulation of pyridotriazoles with arenes. A library of compounds have been synthesized employing the method developed with various substituted pyrido[1,2- a]indole derivatives in moderate to good yields. The density functional theory study using SMDDCB-M06/6-31++G(d,p)/LANL2DZ//B3LYP/6-31G(d)/LANL2DZ method suggests that the reactions proceed via indium-carbenoid complex.

Visible-light-promoted selective C-H amination of heteroarenes with heteroaromatic amines under metal-free conditions.

The regioselective C-H amination of quinoline amides (C5) and imidazopyridines (C3) under transition-metal-free conditions at room temperature with a high degree of functional group tolerance is reported. The C-H amination promoted by visible light in the presence of a photocatalyst with a wide range of heteroamines makes the present protocol more sustainable.

Lewis Acid-Catalyzed Denitrogenative Transannulation of Pyridotriazoles with Nitriles: Synthesis of Imidazopyridines.

The synthesis of imidazo[1,5-a]pyridines through denitrogenative transannulation of pyridotriazoles with nitriles using BF3·Et2O as catalyst has been described. The combination of solvents (dichlorobenzene-dichloroethane) plays a crucial role in achieving quantitative yields of desired products under metal-free conditions.

Copper-Catalyzed Denitrogenative Transannulation Reaction of Pyridotriazoles: Synthesis of Imidazo[1,5-a]pyridines with Amines and Amino Acids.

The copper-catalyzed aerobic oxidative synthesis of imidazo[1,5-a]pyridines via cascade denitrogenative transannulation reaction of pyridotriazoles with benzylamines with good functional group tolerance is developed. The present methodology is also applicable to amino acids to obtain imidazo[1,5-a]pyridines via decarboxylative oxidative cyclization.