The Hydrazine–O₂ Redox Couple as a Platform for Organocatalytic Oxidation: Benzo[c]cinnoline‐Catalyzed Oxidation of Alkyl Halides to Aldehydes

Abstract

An organocatalytic oxidation platform that capitalizes on the capacity of hydrazines to undergo rapid autoxidation to diazenes is described. Commercially available benzo[c]cinnoline is shown to catalyze the oxidation of alkyl halides to aldehydes in a novel mechanistic paradigm involving nucleophilic attack, prototropic shift, and hydrolysis. The hydrolysis and reoxidation events occur readily with only adventitious oxygen and water. A survey of the scope of viable substrates is shown along with mechanistic and computational studies that give insight into this mode of catalysis.

In Situ Coupling of Single Molecules Driven by Gold‐Catalyzed Electrooxidation

“…Proton loss leads to the formation of ah ydrazine (-NH-NH-) which is known to oxidize readily to form the diazenyl (-N=N-) bridge. [15] This mechanism is analogous to that previously proposed for the oxidative coupling of anilines to give azobenzenes under aerobic conditions using Au nanoparticles supported on TiO 2 as catalyst. [10] We note that the necessary voltage to trigger the electrooxidation at the tip ( % 0mVv ersus the ferrocene/ferrocenium redox couple) is lower than the oxidation potential of aniline and its derivatives, [16] suggesting that the redox transformation in the junction is facilitated by the attachment of the anilines to undercoordinated Au atoms (active sites).…”

Nitrosoarene-Catalyzed HFIP-Assisted Transformation of Arylmethyl Halides to Aromatic Carbonyls under Aerobic Conditions

“…On the basis of the control experiments and literature evidence, ,, a plausible O 2 -coupled nitroso-organocatalyzed reaction mechanism is proposed in Scheme . It is evident that the use of HFIP, one of the most potent HBD solvents (α = 1.96), has an imperative role in our reaction.…”

“…On the basis of the control experiments and literature evidence, 21,22,25 a plausible O 2 -coupled nitroso-organocatalyzed reaction mechanism is proposed in Scheme 4. It is evident that the use of HFIP, one of the most potent HBD The proposal of arylhydroxylamine as an intermediate in our suggested catalytic cycle was verified by running the reaction with catalytic amount of 4-methylphenylhydroxylamine (see SI, section 9b for details).…”

“…In pursuit of a suitable, alternative, and metal-free organocatalytic expedient decorum, transition-metal-free stoichiometric oxidative approaches have been reported right through . Alongside, few environmentally benign organocatalytic methodologies for oxidative transformation of arylmethyl halides to carbonyl compounds have also been documented in the past few decades (Scheme a) − Recently, in 2018, Lambert and co-workers have come up with a newly modeled benzo­[ c ]­cinnoline (BCC) catalyst for synthesizing aldehydes from alkyl halides (Scheme b) . This unique invention organocatalytically oxidizes primary alkyl halides involving nucleophilic attack, prototropic shift and hydrolysis as key steps.…”

Efficient Catalysts In situ Generated from Zinc, Amide and Benzyl Bromide for Epoxide/CO2 Coupling Reaction at Atmospheric Pressure

“…The resulting iminium salts A was then reduced through umpolung conversion reaction by way of two‐electron transfer in the presence of Zn powder to generate complex B . The complex B was highly reactive, and could be rapidly hydrolysed to generate benzyloxy zinc bromide, formaldehyde and dimethylamine, and immediately convert to ZnBr 2 and [DBDMA]Br in the presence of BnBr , . Subsequently, the generated binary ZnBr 2 /[DBDMA]Br catalyzed the coupling reaction, which initiated with the interaction of oxygen atom in epoxide with Lewis acidic Zn 2+ center in ZnBr 2 ( C ), facilitating the ring‐opening by nucleophilic attack of Br anion of [DBDMA]Br to generate an alkoxide D .…”