Lithium compound catalyzed deoxygenative hydroboration of primary, secondary and tertiary amides

A selective and efficient route for the deoxygenative reduction of primary to tertiary amides to corresponding amines has been achieved with pinacolborane (HBpin) using simple and readily accessible 2,6-di-tert-butyl phenolate lithium·THF (1a) as a catalyst. Both experimental and DFT studies provide mechanistic insight.

Chemoselective hydroborative reduction of nitro motifs using a transition-metal-free catalyst

The first transition-metal-free catalysts for deoxygenative reduction of nitroarenes, nitro heteroarenes and even notoriously challenging nitroalkanes using pinacolborane have been reported.

Mechanistic insights into the dearomative diborylation of pyrazines: a radical or non-radical process?

The mechanisms of the dearomative diborylation of pyrazines were investigated via a combination of density functional theory calculations and experimental studies.

Combined KOH/BEt3 Catalyst for Selective Deaminative Hydroboration of Aromatic Carboxamides for Construction of Luminophores

The selective catalytic C-N bond cleavage of amides into value-added amine products is a desirable but challenging transformation. Molecules containing iminodibenzyl motifs are prevalent in pharmaceutical molecules and functional materials. Here we established a combined KOH/BEt₃ catalyst for deaminative hydroboration of acyl-iminodibenzyl derivatives, including nonheterocyclic carboxamides, to the corresponding amines. This novel transition-metal-free methodology was also applied to the construction of Clomipramine and luminophores.

General and Efficient Copper-Catalyzed Oxazaborolidine Complex in Transfer Hydrogenation of Isoquinolines under Mild Conditions

A general and efficient method for copper-catalyzed transfer hydrogenation of isoquinolines with an oxazaborolidine-BH₃ complex, under mild reaction conditions, is successfully developed. A broad range of isoquinolines has been reduced to the corresponding products with 61-85% yields. The method is applied to the synthesis of biologically active tetrahydrosioquinoline alkaloid (±)-norlaudanosine in 62% yield, which is the key precursor for the preparation of (±)-laudanosine, (±)-N-methyl-laudanosine, and (±)-xylopinine in one or two steps.

Arsenic adsorption mechanism on palm oil fuel ash (POFA) powder suspension

The contribution of palm oil fuel ash (POFA), an agricultural waste as a low cost adsorbent for the removal of arsenite (As(III)) and arsenate (As(V)) was explored. Investigation on the adsorbency characteristics of POFA suspension revealed that the surface area, particle size, composition, and crystallinity of the SiO₂ rich mullite structure were the crucial factors in ensuring a high adsorption capacity of the ions. Maximum adsorption capacities of As(III) and As(V) at 91.2 and 99.4 mg g^-1, respectively, were obtained when POFA of 30 μm particle size was employed at pH 3 with the highest calcination temperature at 1150 °C. An optimum dosage of 1.0 g of dried POFA powder successfully removed 48.7% and 50.2% of As(III) and As(V), respectively. Molecular modeling using the density functional theory consequently identified the energy for the proposed reaction routes between the SiO^- and As⁺ species. The high stability of the POFA suspension in water in conjunction with good adsorption capacity of As(III) and As(V) seen in this study, thus envisages its feasibility as a potential alternative absorbent for the remediation of water polluted with heavy metals.

The Hydrosilylation and Cyanosilylation of Ketones Catalyzed using Metal Borohydrides

AIM AND OBJECTIVE

The hydrosilylation reaction of carbonyl compounds has emerged as a powerful method in organic synthesis. The catalytic hydrosilylation of ketones is a valuable transformation because it generates protected cyanosilylation reaction of carbonyl compounds is an efficient procedure for the synthesis of silylated cyanohydrins, which are readily converted into useful functionalized compounds, such as cyanohydrins, α-hydroxy acids, β-amino alcohols and other biologically active compounds.

MATERIALS AND METHODS

A facile, economic and efficient method has been developed for the hydrosilylation and cyanosilylation of ketones using metal borohydrides. A series of silylated ethers and silylated cyanohydrins can be isolated via direct distillation.

RESULTS

The catalytic properties of a range of metal borohydrides in the hydrosilylation reaction of acetophenone with diphenylsilane were investigated. The relative catalytic activity of the borohydride catalyst studied was as follows: (CH3)4NBH4> (PhCH2)(CH3)3NBH4> (CH2CH3)4NBH4> (CH3CH2CH2CH3)4NBH4> NaBH4> KBH4> LiBH4. The cyanosilylation of acetophenone using trimethylsilyl cyanide (TMSCN) in the presence of NaBH4 occurred under similar reaction conditions. An excellent reaction rate and high conversion were obtained.

CONCLUSION

The metal borohydride-catalyzed hydrosilylation alcohols in one step. The and cyanosilylation of ketones could be carried out smoothly under mild reaction conditions. Among the metal borohydrides studied, an excellent reaction rate and high conversion were obtained using NaBH4, NaBH (CH2CH3)3 or (alkyl)4 NBH4 as the reaction catalyst.

DFT study of trialkylborohydride-catalysed hydrosilylation of alkenes – the mechanism and its implications

A detailed DFT study reveals the mechanism of trialkylborohydride-catalysed Markovnikov hydrosilylation of aromatic alkenes.

Transition-metal-free catalytic hydroboration reduction of amides to amines

The selective catalytic reduction of amides to value-added amine products is a desirable but challenging transformation.

NHC-Copper-Catalyzed Asymmetric Dearomative Silylation of Indoles

We report an asymmetric dearomative silylation reaction of 3-acylindoles using a chiral NHC-copper(I) complex as catalyst to afford a range of cyclic α-aminosilanes with high regio- and enantioselectivity. Initial mechanistic studies revealed that the observed high diastereoselectivity was attributed to the facile epimerization of the 3-acyl group. We also demonstrated that the product could be used as a versatile precursor for the synthesis of functionalized indolines in high enantiomeric purity.

Iridium-Catalyzed Sequential Silylation and Borylation of Heteroarenes Based on Regioselective C-H Bond Activation

An iridium-catalyzed regioselective sequential silylation and borylation of heteroarenes was developed, which represents a rare example of unsymmetrical intermolecular C-H bond difunctionalization through the introduction of two different functionalities during a one-pot transformation. Although the substrate scope for the dehydrogenative silylation of heteroarenes has been limited mainly to electron-rich five-membered rings, the current reaction proceeds with both electron-rich and electron-deficient heteroarenes with the aid of heteroatom-directing C-H bond activation. The regioselectivity of the second borylation was controlled by both steric factors and the electronic effect of the silyl group installed in the first step. In combination with the classic cross-coupling reaction, this method provides rapid access to multisubstituted heteroarenes.

Selective ligand-free cobalt-catalysed reduction of esters to aldehydes or alcohols

Activated cobalt metal salts are effective and versatile catalysts for the chemoselective reduction of esters to aldehydes or alcohols through hydrosilylation reaction.

Sodium triethylborohydride as a catalyst for the dehydrogenative silylation of terminal alkynes with hydrosilanes

Sodium triethylborohydride has been found to be a highly selective catalyst for the dehydrogenative silylation of aromatic and aliphatic alkynes with hydrosilanes.

Unexpected catalytic activity of simple triethylborohydrides in the hydrosilylation of alkenes

Highly regioselective hydrosilylation of olefins with aryl- and alkoxysilanes has been developed using a simple sodium triethylborohydride.

Phosphazenes: efficient organocatalysts for the catalytic hydrosilylation of carbon dioxide

Phosphazene superbases are efficient organocatalysts for the metal-free catalytic hydrosilylation of carbon dioxide. They react with CO2 to form the respective phosphine oxides, but in the presence of hydrosilanes, CO2 can be selectively reduced to silyl formates, which can in turn be reduced to methoxysilanes by addition of an extra loading of silanes. Activities reach a TOF of 32 h(-1) with a TON of 759. It is also shown that unexpectedly, N,N-dimethylformamide can reduce CO2 to a mixture of silyl formates, acetals and methoxides in the absence of any catalyst.

Main group catalysed reduction of unsaturated bonds

This Perspective article reviews the recent developments in reduction reactions catalysed by main-group element compounds.

Efficient metal-free hydrosilylation of tertiary, secondary and primary amides to amines

Hydrosilylation of secondary and tertiary amides to amines is described using catalytic amounts of B(C₆F₅)₃. The organic catalyst enables the reduction of amides with cost-efficient, non-toxic and air stable PMHS and TMDS hydrosilanes. The methodology was successfully extended to the more challenging reduction of primary amides.