53636-22-9

Upstream product

• 694-59-7 pyridine N-oxide 
• 6258-60-2 p-methoxybenzylmercaptan 
• 626-55-1 3-Bromopyridine 
• 1120-90-7 3-iodopyridine 

Relevant academic research and scientific papers

Photoredox Nickel-Catalyzed C-S Cross-Coupling: Mechanism, Kinetics, and Generalization

Photoredox-mediated nickel-catalyzed cross-couplings have evolved as a new effective strategy to forge carbon-heteroatom bonds that are difficult to access with traditional methods. Experimental mechanistic studies are challenging because these reactions involve multiple highly reactive intermediates and perplexing reaction pathways, engendering competing, but unverified, proposals for substrate conversions. Here, we report a comprehensive mechanistic study of photoredox nickel-catalyzed C-S cross-coupling based on time-resolved transient absorption spectroscopy, Stern-Volmer quenching, and quantum yield measurements. We have (i) discovered a self-sustained productive Ni(I/III) cycle leading to a quantum yield φ > 1; (ii) found that pyridinium iodide, formed in situ, serves as the dominant quencher for the excited state photocatalyst and a critical redox mediator to facilitate the formation of the active Ni(I) catalyst; and (iii) observed critical intermediates and determined the rate constants associated with their reactivity. Not only do the findings reveal a complete reaction cycle for C-S cross-coupling, but the mechanistic insights have also allowed for the reaction efficiency to be optimized and the substrate scope to be expanded from aryl iodides to include aryl bromides, thus broadening the applicability of photoredox C-S cross-coupling chemistry.

Photoredox Mediated Nickel Catalyzed Cross-Coupling of Thiols with Aryl and Heteroaryl Iodides via Thiyl Radicals

Ni-catalyzed cross-couplings of aryl, benzyl, and alkyl thiols with aryl and heteroaryl iodides were accomplished in the presence of an Ir-photoredox catalyst. Highly chemoselective C-S cross-coupling was achieved versus competitive C-O and C-N cross-couplings. This C-S cross-coupling method exhibits remarkable functional group tolerance, and the reactions can be carried out in the presence of molecular oxygen. Mechanistic investigations indicated that the reaction proceeded through transient Ni(I)-species and thiyl radicals. Distinct from nickel-catalyzed cross-coupling reactions involving carbon-centered radicals, control experiments and spectroscopic studies suggest that this C-S cross-coupling reaction does not involve a Ni(0)-species.

Deoxydative Thiation of 3-Substituted Pyridine N-Oxides with 4-Methoxytoluene-α-thiol: A Divergent Route to Pyridinethiols

Synthesis of 3-substituted 2-pyridinethiols was achieved by thiation of pyridine N-oxides with 4-methoxytoluene-α-thiol in the presence of diethylcarbamoyl chloride followed by cleavage of the resulting sulfides.The case of substitution was shown to be affected by nucleophilicity of the N-oxide oxygen.Addition of zinc bromide to the reaction, a need for triethylamine, decreased most of the yield for thiation products but the formation of 3-methoxy-2-methoxybenzylthiopyridine was only improved.A plausible mechanism of the substitution, particularly β-thiation to the N-oxide function, is discussed compared with the regiochemistry observed in the reaction with diethoxyphosphoryl chloride instead of diethylcarbamoyl chloride.The debenzylation to pyridinethiol was also found to be dependent on the electron-density in the pyridine ring.