Chemoselective deoxygenation of 4,5-dinitroacenaphthenequinone with hexaethyltriamidophosphite

Deoxygenation under the action of the P(III) derivatives is widely used in organic chemistry [1, 2]. Among the variety of reactions a separate group includes the deoxygenation of nitro compounds with the P(III) derivatives resulting in the nitrogencontaining heterocycles of different structures [3]. The tertiary phosphines and phosphites are most commonly used as the P(III) derivatives. One of the most studied reactions of this type is the cyclization of nitroarenes to form the corresponding nitrogen-containing heterocycles (indoles, pyrrolopyrimidines, carbazoles, quinolines) under the action of the phosphorous acid esters. Presumably, the reaction proceeds through the intermediate formation of nitrenes. If 2-nitrobiaryls were used, the nitrene inserts on the C–H bond adjacent to the aryl moiety, to give the corresponding carbazoles [4, 5] or δ-carbolines [6]. The reaction of 2nitrophenylsulfide with an excess of triethyl phosphite, resulting in phenothiazine, can be attributed to the same type of the reactions [7, 8]. If the aryl contains a double bond ortho-positioned relative to the nitro group (o-nitrostyrene), the nitrene inserts on the β-C– H bond of the vinyl moiety to give the substituted indoles [9–11]. The reactions of o-dinitrobenzene with the P(III) derivatives should be specially noted. For example, under the action of triethyl phosphite, diphenylethylphosphinite, or methyldiethylphosphonite one of the nitro groups is substituted by the phosphorus moiety and ethyl nitrite is eliminated [12]. At the same time, the reduction of 2,2'-dinitrobiphenyl with the gaseous PH3 stops when benzocinnoline-2,2'dioxide forms [13].