5-Nitroso-1,3-diphenyltetrazolium salt as a mediator for the oxidation of alcohols

Nitrosotetrazolium‐Catalyzed Aerobic Oxidation of Alcohols to the Corresponding Carbonyl Compounds

“…We have previously reported that the addition of acid is crucial for stabilizing the reversible redox cycle of 1. [14] As nitric acid acts not only as an oxidizing agent but also as a proton source, we examined these functions by supplying NO x and proton sources individually (Table 3). When TFA (10 mol-%), a nonoxidizing proton source, was used along with nitric acid (10 mol-%), the yield remained almost constant (Table 3, entry 1).…”

“…Thus, the use of nitric acid alone ( Table 2, entry 11) again proved to be optimum for the catalytic oxidation. Based on the stoichiometric oxidation reaction with nitric acid, [14] nitrogen dioxide should also function as an oxidizing agent. Therefore, we examined the role of nitrogen dioxide instead of nitric acid under neutral conditions.…”

“…5-Nitroso-1,3-diphenyltetrazolium tetrafluoroborate (1) was also synthesized according to a literature procedure. [14] General Procedure for the Catalytic Oxidation of Alcohol 3a in the Presence of 1 and a Stoichiometric Amount of Reoxidant: See Table 1 Oxidation of 3a with NO 2 under an Argon Atmosphere: See Scheme 2. Cu powder (3.1 g, 0.049 mol) was added to concentrated HNO 3 (10 mL, 0.13 mol) at room temperature.…”

“…[7][8][9][10][11][12][13] We have recently developed mesoionic nitrosotetrazolium salt 1 through oxidation of mesoionic hydroxyamide 2 (Scheme 1). [14] Although nitroso compounds generally do not function as oxidation catalysts, a positively charged tetrazolium ring can render the nitroso group capable of acting as a mediator in the oxidation of alcohols. A catalytic amount of 1 (5 mol-%) was sufficient to obtain aldehydes in high yields by oxidation of benzylic alcohols using HNO 3 as a terminal oxidant.…”

“…The metal‐free aerobic oxidation of alcohols is regarded as one of the most environmentally benign methods for the formation of aldehydes and ketones, because there is no metal contamination in the products and water is the only by‐product In recent years, organocatalyst‐mediated aerobic oxidation has been successfully achieved using nitroxyl radicals such as 2,2,6,6‐tetramethylpiperidine‐ N ‐oxyl (TEMPO), 9‐azabicyclo[3.3.1]nonane‐ N ‐oxyl (ABNO), and 2‐azaadamantane‐ N ‐oxyl (AZADO) with nitrogen oxides (H)NO x as cocatalysts . We have recently developed mesoionic nitrosotetrazolium salt 1 through oxidation of mesoionic hydroxyamide 2 (Scheme ) . Although nitroso compounds generally do not function as oxidation catalysts, a positively charged tetrazolium ring can render the nitroso group capable of acting as a mediator in the oxidation of alcohols.…”