Bioinspired o-Naphthoquinone-Catalyzed Aerobic Oxidation of Alcohols to Aldehydes and Ketones

NHPI-Catalyzed Electro-Oxidation of Alcohols to Aldehydes and Ketones

A practical and recyclable electro-oxidation of alcohols to aldehydes and ketones by using N-hydroxyphthalimide (NHPI) as the catalyst is presented. Through an undivided pool, under constant current conditions, various alcohols can be oxidized to the corresponding aldehydes or ketones in a high yield. Compared with previous methods, this system has the following characteristics: (1) the catalyst, electrode, electrolyte, and solvent (mainly water) are recyclable; (2) it has many advantages such as mild reaction conditions, easy operation, and good tolerance of functional groups; and (3) it can be smoothly scaled up to kilogram-scale production.

Redox-Mediated Amination of Pyrogallol-Based Polyphenols

Flavonoids are known to covalently modify amyloidogenic peptides by amination reactions. The underlying coupling process between polyphenols and N-nucleophiles is assessed by several in vitro and in silico approaches. The coupling reaction involves a sequence of oxidative dearomatization, amination, and reductive amination (ODARA) reaction steps. The C6-regioselectivity of the product is confirmed by crystallographic analysis. Under aqueous conditions, the reaction of baicalein with lysine derivatives yields C-N coupling as well as hydrolysis products of transient imine intermediates. The observed C-N coupling reactions work best for flavonoids combining a pyrogallol substructure with an electron-withdrawing group attached to the C4a-position. Thermodynamic properties such as bond dissociation energies also highlight the key role of pyrogallol units for the antioxidant ability. Combining the computed electronic properties and in vitro antioxidant assays suggests that the studied pyrogallol-containing flavonoids act by various radical-scavenging mechanisms working in synergy. Multivariate analysis indicates that a small number of descriptors for transient intermediates of the ODARA process generates a model with excellent performance (r=0.93) for the prediction of cross-coupling yields. The same model has been employed to predict novel antioxidant flavonoid-based molecules as potential covalent inhibitors, opening a new avenue to the design of therapeutically relevant anti-amyloid compounds.

Facile access to 3-sulfonylquinolines via Knoevenagel condensation/aza-Wittig reaction cascade involving ortho-azidobenzaldehydes and β-ketosulfonamides and sulfones

Quinoline-based sulfonyl derivatives, and especially sulfonamides, are relevant and promising structures for drug design. We have developed a new convenient protocol for the synthesis of 3-sulfonyl-substituted quinolines (sulfonamides and sulfones). The approach is based on a Knoevenagel condensation/aza-Wittig reaction cascade involving o-azidobenzaldehydes and ketosulfonamides or ketosulfones as key building blocks. The protocol is appropriate for both ketosulfonyl reagents and α-sulfonyl-substituted alkyl acetates providing the target quinoline derivatives in good to excellent yields.

Catalytic Aerobic N-Nitrosation by Secondary Nitroalkanes in Water: A Tandem Diazotization of Aryl Amines and Azo Coupling

Secondary nitroalkanes underwent oxygen-mediated nitro-nitrite isomerization, serving as versatile N-nitrosating agents under aerobic conditions. To capitalize on the newly discovered aerobic nitro-nitrite isomerization phenomenon, a phase-transfer catalysis system employing KSeCN and TBAI was developed, in which the tandem diazotization and azo coupling with nitroalkanes as well as N-nitrosation of amines were accomplished. The current tandem diazotization and azo coupling strategy provides a facile synthesis of areneazo-2-(2-nitro)propane derivatives, a safe synthetic alternative to aryl diazonium salts.

Redox-active molecules as organocatalysts for selective oxidative transformations - an unperceived organocatalysis field

Organocatalysis is widely recognized as a key synthetic methodology in organic chemistry. It allows chemists to avoid the use of precious and (or) toxic metals by taking advantage of the catalytic activity of small and synthetically available molecules. Today, the term organocatalysis is mainly associated with redox-neutral asymmetric catalysis of C-C bond-forming processes, such as aldol reactions, Michael reactions, cycloaddition reactions, etc. Organophotoredox catalysis has emerged recently as another important catalysis type which has gained much attention and has been quite well-reviewed. At the same time, there are a significant number of other processes, especially oxidative, catalyzed by redox-active organic molecules in the ground state (without light excitation). Unfortunately, many of such processes are not associated in the literature with the organocatalysis field and thus many achievements are not fully consolidated and systematized. The present article is aimed at overviewing the current state-of-art and perspectives of oxidative organocatalysis by redox-active molecules with the emphasis on challenging chemo-, regio- and stereoselective CH-functionalization processes. The catalytic systems based on N-oxyl radicals, amines, thiols, oxaziridines, ketone/peroxide, quinones, and iodine(I/III) compounds are the most developed catalyst types which are covered here.