Reduction of aromatic and aliphatic keto esters using sodium borohydride/MeOH at room temperature: a thorough investigation

Reduction of keto esters is a valuable alternative to produce diols. Sodium borohydride/MeOH system at room temperature and short reaction time efficiently reduced α, β, γ, and δ-keto esters having α-keto esters as the most reactive. The ester functionality was reduced effectively due to the presence of oxo group that somehow facilitates the formation of ring intermediate. As expected, the chemoselective experiments showed that ester functionality was not reduced using this system. This study presents a simple, easy, and benign reduction process of various keto esters to its corresponding diols.     

Reductive removal of methoxyacetyl protective group using sodium borohydride

Herein, we have developed a mild and selective reductive deprotection method for the MAc protected alcohols using sodium borohydride. The new deprotection conditions provide a complete orthogonality between O-MAc and other protecting groups such as tert-butyl ester, N-Boc, Fmoc, Cbz, O-TBDMS, N-benzyl, O-benzyl, O-acetyl, N-acetyl, N-MAc, etc. In addition to O-MAc deprotection, this method is also applicable for S-MAc deprotection.     

Iron triflate catalyzed reductive amination of aldehydes using sodium borohydride

An efficient and convenient procedure for the reductive amination of aldehydes using NaBH₄ in the presence of catalytic amount of Fe(OTf)₃ is described.     

Borane-catalyzed hydroboration of substituted alkenes by lithium borohydride or sodium borohydride

In the presence of a catalytic amount of BH₃·Me₂S, TiCl₄ or Me₃SiCl, LiBH₄ or NaBH₄ are capable of hydroborating alkenes by following the unusual order of decreasing reactivity: tetramethylethylene > 1-methylcyclohexene > cyclohexene; the key step of the catalytic cycle is the exchange reaction between LiBH₄ and the mono- or dialkylboranes resulting from hydroboration of the more substituted alkenes with BH₃.     

Solvent-free reduction of aldehydes and ketones using solid acid-activated sodium borohydride

A simple and convenient procedure for the reduction of aldehydes and ketones with sodium borohydride activated by solid acids such as boric acid, benzoic acid, and p-toluenesulfonic acid monohydrate under solvent-free conditions is described.     

Activity of transition metal sulfides in hydrogenation of thiolene-1,1-dioxides

The activity and selectivity of sulfides of group VI–VIII metals in the liquid-phase hydrogenation of thiolene-1,1-dioxides were studied at elevated hydrogen pressure. The generation of thiolane-1,1-dioxide is accompanied by the substrate decomposition, which is especially intensive for 3-thiolene-1,1-dioxide hydrogenation. These processes follow absolutely independent routes. The catalytic activity of sulfides in the generation of thiolane-1,1-dioxide decreases in the following row: PdS>Rh₂S₃>Re₂S₇>OsS₂>PtS₂>CoOS>WS₂>RuS₂ >NiOS.     

The reductive mechanism of nitrobenzene catalyzed by nine charcoals in sulfides solution

Due to the different sources of charcoals, there are significant differences in their properties. In order to study the catalytic effect of different charcoals to nitrobenzene (NB), we selected nine charcoal-sources to prepare nine charcoals with different properties. The experiments showed that NB could be rapidly reduced by sulfides in the presence of all charcoals. The surface area normalized reduction rate constants of NB increased with H/C and (O+N)/C ratio of charcoals increasing. The difference of catalytic effect for nine charcoals was mainly due to their different species and content of surface functional groups and original organic matter. Based on the theoretical calculation and experimental results, the reaction mechanism of NB catalyzed by charcoal in sulfides solution was analyzed. Some active surface functional groups and original organic matter of charcoals were regarded as the active sites and played an important role in catalyzing the reduction of NB by accelerating the transfer of electrons from sulfides to NB.     

Thermal properties of alkaline sodium borohydride solutions

Alkaline sodium borohydride solutions are potential hydrogen sources for fuel cells. Thermal properties of the NaBH₄–NaOH–H₂O ternary system were measured by DSC and temperature-rise calorimetry. Liquidus temperatures showed that it is possible to store and use the solutions well below 0 °C if NaOH concentration is less than 20 wt%. The solubility of sodium borohydride was found to be large in these solutions, but decreased with increasing NaOH concentration. The optimum composition for alkaline borohydride solutions seems to be 15 wt% NaBH₄ in 10 wt% NaOH considering both the liquidus temperature and hydrogen storage density.     

Reduction of pentafluorophenyl esters to the corresponding primary alcohols using sodium borohydride

Primary alcohols and chiral N-protected 2-amino alcohols can be obtained in high yields from the reaction of pentafluorophenyl esters of the corresponding carboxylic acids with sodium borohydride in THF under mild conditions. This reductive method is rapid and compatible with various functional groups as well as with the most common N-protective groups Z, Boc and Fmoc.     

Ultrafast room-temperature reduction of graphene oxide by sodium borohydride,sodium molybdate and hydrochloric acid

Since graphene-based materials have shown great potential in many fields,it is important to explore ultrafast and high-efficient methods to synthesize reduced graphene oxide(rGO) using inexpensive reducing agents under mild conditions.Here,we reported a novel method for the ultrafast chemical reduction of graphene oxide(GO) at room temperature using sodium borohydride(NaBH₄),sodium molybdate(Na₂MoO₄) and hydrochloric acid(HCl).The reduction was carried out within 2 min.A series of characterization results revealed that the obtained reduced graphene oxide has higher reduction degree than that synthesized by NaBH₄ alone at high temperature.Moreover,rGO electrode based on the present reducing method exhibited a superior specific capacitance of 139.8 F/g at a current density of1 A/g,indicating that it can be used as electrode materials for supercapacitors.     

Reductive amination of aldehydes and ketones using sodium borohydride in the presence of silica chloride under solvent free conditions

<正>A simple and convenient procedure for the preparation of amines from aldehydes and ketones with sodium borohydride activated by silica chloride as a catalyst under solvent-free conditions is described.A variety of aliphatic and aromatic aldehydes,ketones and amines when mixed with NaBH_4/silica chloride at room temperature,afforded excellent yield of the corresponding amines.     

NaBH4/DOWEX(R)50WX4: A Convenient Reducing System for Fast and Efficient Reduction of Carbonyl Compounds to Their Corresponding Alcohols

The reduction of a variety of carbonyl compounds was efficiently carried out with NaBH₄/DOWEX(R)50WX4 system. The reactions were performed to give the corresponding alcohols derivatives in perfect yields in THF at room temperature. Reduction of acyloins and a‐diketones by this reducing system produced efficiently the corresponding vicinal diols. Also, the reduction of aldehydes over ketones has been accomplished successfully by this system. Regioselectivity of this system was also investigated with exclusive 1,2‐reduction of conjugated carbonyl compounds to their corresponding allylic alcohols in high to excellent yields.     

Testing catalytic activity of ruthenium(III) acetylacetonate in the presence of trialkylphosphite or trialkylphosphine in hydrogen generation from the hydrolysis of sodium borohydride

Catalytic activity of Ru(acac)₃ in the presence of different phosphorus compounds (P(OMe)₃, P(OPh)₃, PPh₃ and dppe) was investigated for the first time in the hydrolysis of NaBH₄. Phosphorus compound, usually known as poison in catalysis, is involved in the formation of a species which has higher catalytic activity in comparison with Ru(acac)₃ alone. Varying the phosphorus compound affects the catalytic activity and lifetime of the catalyst as well as the kinetics and the activation parameters of the hydrolysis of NaBH₄. For all of the phosphorus compounds, the hydrogen generation was found to be zero-order with respect to the substrate concentration and first-order regarding the catalyst concentration. The catalyst system with P(OMe)₃ shows the highest catalytic activity and provides the largest total turnover number (TTON = 20,700 over 72 h) in the hydrolysis of NaBH₄. The highest activation energy and enthalpy values were obtained for the catalyst with dppe (E_a = 59 ± 2, ΔH^# = 60 ± 2 kJ/mol) while the lowest values were found for the catalyst system with PPh₃ (E_a = 46 ± 2, ΔH^# = 43 ± 1 kJ/mol).     

Metal-complex catalysis during the reduction of functional groups by sodium borohydride in the synthesis of pyrrolidine derivatives

A selective method was developed for the reduction of functional groups with sodium borohydride using complexes of CoCl₂ and CuCl₂ with triethylbenzylammonium chloride and cobalt and copper mesotetra[4-(2-hydroxyethyl)pyridyl]porphyrinates as catalysts. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 205–208, February, 2006.     

Hydrodehalogenation of halogenated pyridines and quinolines by sodium borohydride/N,N,N′,N′-tetramethylethylenediamine under palladium catalysis

A protocol for the hydrodehalogenation of halogenated pyridines and quinolines by the sodium borohydride/N,N,N′,N′-tetramethylethylenediamine (NaBH₄-TMEDA) system under palladium catalysts is reported. Catalytic amounts of [1,1′-bis(diphenylphosphino)ferrocene] dichloropalladium(II) in combination with NaBH₄-TMEDA rapidly hydrodehalogenate chloro(bromo)-pyridines and -quinolines at room temperature in quantitative yields. Chemoselective reduction of 4,7-dichloroquinoline affords 7-chloroquinoline as the sole product in almost quantitative yield. Moreover, palladium(II) acetate-triphenylphosphine and NaBH₄-TMEDA are able to reduce efficiently reactive bromo-pyridines and -quinolines.     

Ruthenium(III) acetylacetonate: A homogeneous catalyst in the hydrolysis of sodium borohydride

Ruthenium(III) acetylacetonate was employed for the first time as homogeneous catalyst in the hydrolysis of sodium borohydride. Ruthenium(III) acetylacetonate was not reduced by sodium borohydride under the experimental conditions and remains unchanged after the catalysis. Poisoning experiments with mercury and trimethylphosphite provide compelling evidence for the fact that ruthenium(III) acetylacetonate is indeed a homogenous catalyst in the hydrolysis of sodium borohydride. Kinetics of the ruthenium(III) acetylacetonate catalyzed hydrolysis of sodium borohydride was studied depending on the catalyst concentration, substrate concentration, and temperature. The hydrogen generation was found to be first order with respect to both the substrate concentration and catalyst concentration. The activation parameters of this reaction were also determined from the evaluation of the kinetic data: activation energy; E_a = 58.2 ± 2.6 kJ mol⁻¹, the enthalpy of activation; ΔH^# = 55.7 ± 2.5 kJ mol⁻¹ and the entropy of activation ΔS^# = 118 ± 5 J mol⁻¹ K⁻¹. Ruthenium(III) acetylacetonate was found to be highly active catalyst providing 1200 turnovers over 180 min in hydrogen generation from the hydrolysis of sodium borohydride before deactivation.     

Unexpected effect of alkoxides on the reactivity of sodium borohydrid in the reduction of perfluoropolyether carboxylic esters

The reduction of perfluoropolyether carboxylic esters to the corresponding alcohols with sodium borohydride in ethanol has been investigated. This reaction does not follow the expected stoichiometry but a large excess (>60% molar) of reducing agent is required for a complete conversion of the ester; this excess parallels the massive built up of hydrogen observed during the reaction.Interestingly, the addition of catalytic amount of sodium ethoxide strongly influences the course of the reaction, so that both the excess of reducing agent and the evolution of hydrogen during the reaction are strongly reduced. These experimental evidences suggest that different mechanisms are active depending on the selected experimental conditions, so indicating that the considered reduction can follow different pathways.     

AgOTf-catalyzed one-pot reaction of 2-alkynylbenzaldehyde, amine, and sodium borohydride

One-pot reactions of 2-alkynylbenzaldehydes, amines, and sodium borohydride catalyzed by AgOTf under mild conditions provide a facile protocol for the concise synthesis of 1,2-dihydroisoquinoline derivatives.     

Reduction of Aromatic Aldehydes and Ketones with Acyloxy Substituent at the Orthoposition by NaBH4 in the Presence of Waters*

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Direct and indirect reductive amination of aldehydes and ketones with solid acid-activated sodium borohydride under solvent-free conditions

A simple and convenient procedure for reductive amination of aldehydes and ketones using sodium borohydride activated by boric acid, p-toluenesulfonic acid monohydrate or benzoic acid as reducing agent under solvent-free conditions is described.