NaBH4/PhCO2H: AnEfficient system for Reductive Amination of Aldehydes (original) (raw)
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NaBH4/Ga(OH)3: An efficient reducing system for reductive amination of aldehydes
Oriental Journal of Chemistry, 2013
Amines are important functionalities in active pharmaceutical intermediates and drugs.The reduction of nitro, cyano, azide, carboxamide compounds and alkylation of amines are common routes for the synthesis of amines. These methodologies for secondary amines are often problematic because of harsh reaction conditions, overalkylation, low chemical selectivity and generally poor yields. Therefore, there is a specific interest in developing controlled synthesis of secondary amines due to its vast applications. Other approach is reductive amination reaction in a single operationi.e direct reductive amination (DRA). Reductive aminationcan be carried out by amination of carbonyl compounds with sodiumborohydride under different reducing
NaBH4/C: A Convenient System for Reductive Amination of Aldehydes
Oriental Journal of Chemistry, 2014
In this context, NaBH 4 in the presence of activated charcoal has been used for thereductive aminationofa varietyof aldehydes withanilines. The reductive amination reactions have been performed within 60-100 min in THFunder reflux conditionsin high to excellent yields of products (85-90%).
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General Methods Reagents were purchased from commercial suppliers and were used without purification unless otherwise noted. Anhydrous tetrahydrofuran was purchased from Fluka Chemika. Dibutyltin dichloride (96%) was purchased from Aldrich Chemical Company. All reactions were performed in borosilicate test tubes with magnetic stirring. Reactors were assembled open to the air, and placed under nitrogen after the addition of all reagents. Chromatography was performed using manual injection on an ISCO SQ16 chromatograph with 10 g prepacked RediSep silica cartridges, and gradients of either ethyl acetate-hexane (anilines) or 2 M methanolic ammonia-dichloromethane (alkylamines). 1 H and 13 C NMR spectra were recorded on a Bruker spectrometer. Chemical shifts are reported in parts per million downfield from an internal Me 4 Si standard. In cases where reactions were monitored by 1 H NMR, samples were prepared by dissolving an aliquot of the crude reaction mixture (approx. 0.04 mL) in CDCl 3 (approx. 1 mL). Melting points are uncorrected and were obtained on a MelTemp apparatus. Combustion analyses were performed by Desert Analytics. Representative Procedure for the Reductive Amination of 4-Methoxybenzaldehyde with Aniline A solution of 4-methoxybenzaldehyde (0.18 mL, 1.5 mmol, 1.0 eq) in THF (0.3 mL) was treated with aniline (0.14 mL, 1.5 mmol, 1.0 eq) and dibutyltin dichloride (9 mg, 3x10-2 mmol, 0.02 eq). The resulting yellow solution was allowed to stir for 2 min, and treated with phenylsilane (0.20 mL, 1.7 mmol, 1.1 eq). After 2 h, thin layer chromatography showed no remaining aniline. The colorless reaction was diluted with
Oriental Journal of Chemistry, 2014
The chemoselective reduction of aldehydes without affecting ketones is a wellknown strategy in organic synthesis. This subject is of great interest 1 and numerous reducing systems and modified hydroborates have been reported for this subject 2-4 such as by use of low temperatures 5-6 addition of thiols 7 , metal salts 8 , resins 9 and polyethylene glycol 10 or by several modified borohydrides 11-13. We decided to investigate the reducing properties of NaBH 4 in the presence of NaNO 3 as the co-reagent for the reduction of aldehydes vs. ketones to their corresponding
Selective Aldehyde Reduction in Ketoaldehydes with NaBH4-Na2CO3-H2O at Room Temperatures
Synthetic Communications, 2014
Synthesis and characterization data Instruments employed: Perkin-Elmer 410 (FTIR); Bruker AV-400 (NMR); Micromass Q-TOF AMPS MAX 10/6A (HRMS); Stuart SMP10 (melting point); Büchi Rotavapor R-200 (rotary evaporator). IR values are for neat samples and are quoted in cm-1. NMR spectra were recorded in CDCl 3 solution with tetramethylsilane as internal standard at either 400 MHz (δ H) or 100 MHz (δ C); the coupling constants (J) are in Hz. Abbreviations: Mp (melting point), s (singlet); d (doublet); t (triplet); q (quartet); br (broad); dd (doublet of doublet), etc. The nomenclatures of all the compounds were derived by ChemDraw (CambridgeSoft). The ketoaldehydes 6a-b, 1 6c-f, 2 6h, 3 6i, 4 and 6j 5 were synthesized according to literature procedures. 4-Acetylbenzaldehyde (6g) was purchased from Sigma-Aldrich and used without any further purification. (cf. Scheme 2 and Table 1 of main paper for 6a-j.) Representative procedure for the selective reduction of aldehydes and ketones To a clear solution of sodium borohydride (48 mg, 1.25 mmol) and Na 2 CO 3 (1.0 g, 10.5 mmol) in deionised water (2 ml) at room temperature was added a solution of mixed aldehyde (4.2 mmol) and ketone (4.2 mmol). After stirring for 2.5 h, the mixture was worked-up with saturated NH 4 Cl solution, extracted with diethyl ether and the solvent was evaporated in vacuo. The 1 H NMR spectrum of the crude residue provided the chemoselectivity ratio. The residue was chromatographed on silica gel (100-200 mesh, eluted with ethyl acetate-hexane 5:95-10:90), to obtain pure 1° alcohol and unreacted ketone. This procedure is followed for other aldehydes and ketones.