Abstract: In this study, we developed a metal-free and highly chemoselective method for the reduction of aromatic nitro compounds. This reduction was performed using tetrahydroxydiboron [B2(OH)4] as the reductant and 4,4'-bipyridine as the organocatalyst and could be completed within 5 min at room temperature. Under optimal conditions, nitroarenes with sensitive functional groups, such as vinyl, ethynyl, carbonyl, and halogen, were converted into the corresponding anilines with excellent selectivity while avoiding the undesirable reduction of the sensitive functional groups.
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With formaldehyd; hydrogen; propionic acid;aluminum nickel; In methanol; water;
EXAMPLE 6 181 parts of 4-nitrobenzoic acid methyl ester are suspended in 475 parts of methanol and are hydrogenated at 60 C under 100 atmospheres hydrogen pressure, after addition of 225 parts of aqueous formaldehyde solution (40% strength by weight), 30 parts of propionic acid and 12 parts of Raney nickel. After 112 parts by volume of hydrogen have been taken up in the course of 6 hours, the mixture is separated from the catalyst. The solvent is then distilled off at the same time the decrease in volume is made up with water. 4-dimethylaminobenzoic acid methyl ester, which is insoluble in water, separates out as crystals on cooling. The end product is filtered off, washed with water and dried. 170 parts of 4-dimethylaminobenzoic acid methyl ester of melting point 95 to 98 C are obtained, corresponding to a yield of 95% of theory.
With tert.-butylhydroperoxide; ammonium iodide; water; In dimethyl sulfoxide; at 90℃; for 4h;Sealed tube;
General procedure: Under air, 1 (0.2 mmol), NH4I (0.8 mmol), 70% TBHP in water (2.4 mmol) and DMSO (0.5 mL) were added to a 10 mL Schlenk tube sealed with a Teflon lined cap. The reaction mixture was stirred at 90 C for 4 h in an oil bath. Upon completion, the reaction mixture was left to cool to room temperature and slowly quenched with anhydrous sodium sulfite. The reaction mixture was then diluted with ethyl acetate (5 mL) and then washed with water (5 × 5 mL). The aqueous layer was extracted with EtOAc (3 × 5 mL). The combined organic layers were dried over Na2SO4. The filtrate was concentrated and the crude product was purified by column chromatography on silica gel with petroleum ether (60-90 C)/ethyl acetate eluent. Characterisation data are consistent with literature data.
With sodium carbonate; In water; dimethyl sulfoxide; at 130℃; for 15h;Schlenk technique; Sealed tube; Green chemistry;
General procedure: In a typical procedure, a sealable Schlenk reaction tubeequipped with a magnetic stir bar was charged with the catalystCu/Al2O3 (6 mg, 27 mol% of Cu), p-nitrotoluene (0.25 mmol), paraformaldehyde(3.75 mmol), and Na2CO3 (0.5 mmol). Then, DMSOwater(3 mL, 1:1 v/v) was injected into the tube and the reactionwas tested under stirring at 130 C for 15 h. After completion ofthe reaction, the reaction mixture was extracted with ethyl acetateand then filtered. The liquid was analysed by GC and GC-MS on anAgilent HP-7890 instrument with a flame ionization detector (FID)and an HP-5MS capillary column (30 m, 0.25 mm i.d., 0.25 lm filmthicknesses) using nitrogen as the carrier gas to determine the conversionand selectivity using mesitylene as an internal standard.The desired N,N-dimethylated amines were purified by columnchromatography using an appropriate eluent and structurally confirmedby 1H/13C NMR and HR-MS.
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