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This study proposes two different methods of photocatalytic-controlled and visible light-induced selective oxidation of pyridiniums with air as the terminal oxidant. The key to these transformations is to choose the appropriate light source and photocatal

A strategy for visible-light-induced site-selective C-H acylation of pyridinium salts was developed by employing N-methoxy-or N-aminopyridinium salts, offering a powerful synthetic tool for accessing highly valuable C2- A nd C4-acylated pyridines. The met

The use of transition-metal catalysis to enable the coupling of readily available organic molecules has greatly enhanced the ability of chemists to access complex chemical structures. In this work, an intermolecular coupling reaction that unites organotriflates and aldehydes is presented. A unique catalyst system is identified to enable this reaction, featuring a Ni0 precatalyst, a tridentate Triphos ligand, and a bulky amine base. This transformation provides access to a variety of ketone-containing products without the selectivity- and reactivity-related challenges associated with more traditional Friedel–Crafts reactions. A Heck-type mechanism is postulated, wherein the π bond of the aldehyde takes the role of the olefin in the insertion/elimination steps.

The methylene group of various substituted 2- and 4-benzylpyridines, benzyldiazines and benzyl(iso)quinolines was successfully oxidized to the corresponding benzylic ketones using a copper or iron catalyst and molecular oxygen as the stoichiometric oxidant. Application of the protocol in API synthesis is exemplified by the alternative synthesis of a precursor to the antimalarial drug Mefloquine. The oxidation method can also be used to prepare metabolites of APIs which is illustrated for the natural product papaverine. ICP-MS analysis of the purified reaction products revealed that the base metal impurity was well below the regulatory limit.

An efficient 2,3-dichloro-5,6-dicyano-1,4-benzoquinone/tert-butyl nitrite-catalyzed aerobic oxidation of diarylmethane sp3 C-H bonds in the presence of acetic acid has been developed. Under the optimal reaction conditions, a number of diarylmethanes can be directly converted to their corresponding diarylketones in good to excellent yields. In addition, a plausible reaction mechanism has been investigated.

In anhydrous CH3CN a series of nine 4-(4-substituted-benzoyl)-N-methylpyridinium cations (substituent: -OCH3, -CH3, -H, -SCH3, -Br, -C≡CH, -CHO, -NO2, and -+S(CH3)2) demonstrate two chemically reversible, well-separated one-electron (1-e) reductions in the same potential range as other main stream redox catalysts such as quinones and viologens. Hammett linear free energy plots yield excellent correlation between the E1/2 values of both waves and the substituent constants σp-X. The reaction constants for the two 1-e reductions are ρ1 = 2.60 and ρ2 = 3.31. The lower ρ1 value is associated with neutralization of the pyridinium ring, and the higher ρ2 value with the negative charge developing during the 2nd-e reduction. Structure-function correlations point to a purely inductive role for substitution in both 1-e reductions. The case of the 4-(4-nitrobenzoyl)-N-methylpyridinium cation is particularly noteworthy, because the 4-nitrobenzoyl moiety undergoes reduction before the 2nd reduction of the 4-benzoyl-N-methylpyridinium system. Correlation of the third wave of this compound with the 2nd-e reduction of the others yields σp-NO2- = -0.97 ± 0.02, thus placing the -NO2- group among the strongest electron donors. Solvent deuterium isotope effects and maps of the electrostatic potential (via PM3 calculations) as a function of substitution support that 2-e reduced forms develop H-bonding with proton donors (e.g., CH3-OH) via the O-atom. The average number of CH3OH molecules entering the H-bonding association increases with e-donating substituents. H-bonding shifts the 2nd reduction wave closer to the first one. This has important practical implications, because it increases the equilibrium concentration of the 2-e reduced form from disproportionation of the 1-e reduced form.

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