Triethyl phosphite reducing agent

Common reducing agents are hydrogen in the presence of metallic or complex catalysts (e.g. Ni, Pd, Pt, Ru, Rh), hydrides (e.g. alanes, boranes, LIAIH, NaBHJ, reducing metals (e.g. Li, Na, Mg, Ca, Zn), and low-valent compounds of nitrogen (e.g. NjHj, NjHJ, phosphorus (e.g. triethyl phosphite, triphenyiphosphine), and sulfur (e.g. HO-CHj-SOjNa = SFS, sodium dithionite = Na S O. ... 

More recently, a double reductive ring closure of the dinitrodiphenylbenzene 139 with triethyl phosphite as the reducing agent has been reported to produce 3 in 59% yield (Scheme 18). The precursor 139 was prepared in excellent yield by Pd(0)-catalyzed coupHng of phenylboronic acid and 1,3-dibromo-4,6-dinitro-benzene (92JHC1237). 

Azoxy compounds can be obtained from nitro compounds with certain reducing agents, notably sodium arsenite, sodium ethoxide, NaTeH, NaBH4—PhTeTePh, and glucose. The most probable mechanism with most reagents is that one molecule of nitro compound is reduced to a nitroso compound and another to a hydroxylamine 119-42), and these combine (12-51). The combination step is rapid compared to the reduction process. Nitroso compounds can be reduced to azoxy compounds with triethyl phosphite or triphenylphosphine or with an alkaline aqueous solution of an alcohol. ... 

An interesting method of reducing nitroso compounds involves the use of triethyl phosphite as reducing agent [29, 38]. The generality of this procedure requires further exploration. 

As shown in equation 2, the lithium enolate oxidation with O2, followed by sodium sulphite reduction, has been applied with success to oxidation of the enolate derived from 1 the nature of the reducing agent has been decisive for the direct preparation of the hepatoprotective agent Clausenamide (2). As a matter of fact, 2 forms when the treatment with O2 is done in the presence of triethyl phosphite as reducing agent, whereas sodium sulphite reduction affords compound 3. It has been postulated that the transformation 1 —3 occurs through the intermediacy of the peroxide 4. 

When the required 1,2-diaminoarencs are not readily available it is often possible to utilize o-nitroanilines as substitutes. They can be successively reduced or hydrogenated and then cyclized [82, 91, 133], or the cyclization and reduction processes can be combined. Suitable reducing agents are triethyl phosphite, iron pentacarbonyl, titanium(III) chloride, Raney nickel-hydrazine, palladium-carbon, bisulfite or dithionitc, and metal-acid [54, 134,135]. Thus, 4,5-dimethyl 2-nitroaniline heated at 90"C (1 h) with formic acid and sodium dithionitc gives 5,6-dimethyIbenzimidazolc in 92% yield [136]. 

A nitro group can yield7V-heterocycles (see Vol. I,p. 195) through the action of various reducing agents such as metal oxalates [165, 166), triethyl phosphite [167-169] or iron pentacarbonyl [170] (35) ... 

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