Carbon-based solid acid: an efficient and reusable catalyst for the diastereoselective ring opening reaction of α-epoxyketones

Carbon-based solid acid efficiently catalyzes diastereoselective ring opening of α-epoxyketones in the presence of methanol to produce the corresponding α-hydroxy-β-methoxyketones in excellent yield.     

Highly diastereoselective Friedel-Crafts reaction of arenes with N-tert-butanesulfinylimino ester towards the efficient synthesis of α-arylglycines

Lewis acid-catalyzed highly diastereoselective asymmetric Friedel-Crafts alkylation of arenes with a chiral N-tert-butanesulfinylimino ester is described. The reaction can be accomplished with ease in the presence of a catalytic amount of In(OTf)(3) at room temperature, providing a series of enantiomerically enriched α-arylglycines in good yields and with excellent diastereoselectivities (up to 99% de). Highly stereoselective double Friedel-Crafts alkylation to afford dialkylation product was also investigated.     

Phosphomolybdic acid: An efficient and reusable catalyst for the synthesis of ��-phosphono malonates

Phosphomolybdic acid (H₃PMo₁₂O₄₀) is an efficient and reusable catalyst for the synthesis of the phospha-Michael addition of phosphite esters with different types of ??,??-unsaturated malonates to produce a variety of ??-phosphono malonates.     

Amberlyst-15® in ionic liquid: an efficient and recyclable reagent for the benzylation and hydroalkylation of β-dicarbonyl compounds

Benzylation and hydroalkylation of 1,3-dicarbonyl compounds using Amberlyst-15 immobilized in ionic liquid [Bmim][PF₆] as an efficient reusable reagent was studied. The reagent was compared with other solid acid reagents along with role of the ionic liquid. The effect of various reaction parameters like type of reagent, solvent, substrate molar ratio, reaction time, and temperature were studied. Present protocol is advantageous due to the ease in handling of reagent, simple work-up procedure, economical and environmentally benign process. The products were obtained in good to excellent yield and applicable to wide variety of substrates.     

Silica sulfate as an efficient recyclable catalyst for protection of α-hydroxy acids with cyclohexanone

Silica sulfate has been found to be an effective catalyst for protection of α-hydroxy acids under mild reaction conditions. Although the reaction can be carried out in diethyl ether, a remarkable rate enhancement was observed when the reaction was carried out under solvent-free condition. The catalyst could also be recovered and reused without any significant loss of reactivity. A wide range of α-hydroxy acids could be protected using cyclohexanone derivatives in high yield in presence of silica sulfate catalyst at room temperature.     

Titanium-mediated reductive cross-coupling reactions of imines with nitriles: an efficient route for the synthesis of α-aminoketones or 1,2-diketones

The reaction of imines with low-valent titanium species, generated in situ by using Ti(OⁱPr)₄/2 c-C₅H₉MgCl reagent, affords titanium–imine complex, which can couple with nitriles to provide 2,5-diazatitanacyclopentenes. α-Aminoketones are obtained in good yields by quenching the corresponding 2,5-diazatitanacyclopentenes with aqueous HCl solution. However, when the reaction is first quenched with MeOH in air followed by addition of aqueous HCl solution, 1,2-diketones are formed in good to high yields.     

Tris(pentafluorophenyl)borane [B(C6F5)3]-catalyzed Friedel-Crafts reactions of activated arenes and heteroarenes with α-amidosulfones: the synthesis of unsymmetrical triarylmethanes

Tris(pentafluorophenyl)borane [B(C₆F₅)₃] has found to be an efficient catalyst for Friedel-Crafts reactions between activated arenes or heteroarenes and α-amidosulfones. The products undergo further Friedel-Crafts reactions with activated heteroarenes leading to the synthesis of unsymmetrical triarylmethanes. The present synthetic method displayed significant advantages such as low catalyst loading, mild reaction conditions, highly regioselective, high yield, and broad applicability to various substrates.     

Practical synthesis of N-Boc- and N-Cbz-α-amido stannanes from α-amido sulfones using TMSSnBu3 and CsF

In the presence of TMSSnBu(3) and CsF, stannylation of N-Boc- and N-Cbz-α-amido sulfones proceeded very well to afford the corresponding α-amido stannanes in moderate-to-high yields. This reaction tolerated α-aryl-, alkenyl-, and alkyl-substituted α-amido sulfones as well as substrates containing either an ester or cyano moiety, which might be reactive with lithium or magnesium stannides employed in conventional stannylation.     

Amberlyst®-15: a reusable heterogeneous catalyst for the dehydration of tertiary alcohols

Tertiary alcohols react under mild conditions in the presence of Amberlyst^®-15 (dry) (solid-supported sulfonic acid) to give predominantly the most stable alkene in very good yield. The dehydration of tertiary alcohol functionality occurs without observation of rearrangement and polymerization products, and with outstanding substrate tolerance, which include the NHCBz, NHBoc, OSEM, OTBDMS, OBOM and ethylene ketal functional groups. Amberlyst^®-15 (dry) can be easily recovered from the reaction medium and reused for five cycles, maintaining the catalytic efficiency. In addition, the dehydration can occur under continuous operation.     

PAA-supported Hantzsch 1,4-dihydropyridine ester: an efficient catalyst for the hydrogenation of α,β-epoxy ketones

A new type of water-soluble polymer-supported NADH co-enzyme model-PAA (polyacrylic acid)-supported Hantzsch 1,4-dihydropyridine ester (PAA–HEH) was designed and synthesized. Catalytic amount of the supported reagent was used in the hydrogenation of α,β-epoxy ketones to the corresponding β-hydroxy ketones and showed great catalytic efficiency in the reduction reaction. This PAA–HEH was an optimal potential for recycling use.     

Superparamagnetic iron oxide as an efficient catalyst for the one-pot, solvent-free synthesis of α-aminonitriles

Superparamagnetic Fe₃O₄ is shown to act as a very efficient catalyst for the one-pot, three-component synthesis of α-aminonitriles from aldehydes, amines, and TMSCN. The catalyst is easily recovered by the use of an external magnet and reused in several reactions without any noticeable loss of activity. The products are obtained rapidly at room temperature in good purity upon separation of the catalyst and evaporation of the volatiles of the reaction mixture.     

Silica-bonded S-sulfonic acid: an efficient and recyclable solid acid catalyst for the three-component synthesis of α-amino nitriles

Silica-bonded S-sulfonic acid (SBSSA) is employed as a recyclable catalyst for the synthesis of α-amino nitriles. These syntheses were performed via a one-pot three-component condensation of aldehydes, amines, and trimethylsilyl cyanide under mild reaction conditions at room temperature.     

Pd–S-methylisothiourea supported on magnetic nanoparticles as an efficient and reusable nanocatalyst for Heck and Suzuki reactions

Supported Pd–S-methylisothiourea on magnetic nanoparticles (Pd–SMU-MNPs) as an efficient and magnetically reusable nanocatalyst was prepared and applied for the Heck and Suzuki cross-coupling reactions. All coupling reactions proceeded in short reaction times with good to excellent yields. After completion of reactions, the catalyst was easily separated from the reaction mixture using an external magnetic field and reused for several consecutive runs without significant loss of its catalytic efficiency and activity. This nanomagnetic catalyst was characterized by FT-IR spectroscopy, XRD, VSM, ICP-OES, TEM and SEM techniques. The leaching of the catalyst has been examined by a hot filtration test and ICP-OES analysis.     

Choline chloride·2ZnCl2 ionic liquid: an efficient and reusable catalyst for the solvent free Kabachnik–Fields reaction

The choline based Zn containing deep eutectic mixture was applied as an efficient and eco-friendly ionic liquid catalyst for the one pot three-component synthesis of α-aminophosphonates under solvent-free condition at room temperature. The reactions were completed in short times and products were obtained in good to excellent yields.     

Solventless DBU-promoted Mannich-type reactions of α-amido p-tolylsulfones with diethyl fluoromalonates and diethyl malonates

Mannich-type reactions of α-amido p-tolylsulfones with diethyl fluoromalonates and diethyl malonates, respectively in presence of catalytic amount of DBU have been developed. A variety of α-amido p-tolylsulfones prepared from aromatic and aliphatic aldehydes reacts with diethyl fluoromalonates and diethyl malonates, respectively under mild reaction conditions to afford α-fluoro β-amino esters and β-amino esters in moderate to good yield.     

One-pot highly enantioselective catalytic Mannich-type reactions between aldehydes and stable α-amido sulfones: asymmetric synthesis of β-amino aldehydes and β-amino acids

A highly enantioselective catalytic route to carbamate- and benzoate-protected β-amino aldehydes and β-amino acids is presented. The amino acid-catalyzed one-pot asymmetric reaction between unmodified aldehydes and α-amido sulfones gives the corresponding β-amino compounds with up to 95:5 dr and 97->99% ee.     

Acidic-functionalized ionic liquid as an efficient, green and reusable catalyst for hetero-Michael addition of nitrogen, sulfur and oxygen nucleophiles to α,β-unsaturated ketones

A series of acidic-functionalized ionic liquids were synthesized and applied to the hetero-Michael addition of nitrogen, sulfur and oxygen nucleophiles to α,β-unsaturated ketones under solvent-free conditions. Notably, 1-methylimidazolium p-toluenesulfonic ([Hmim]OTs) was found to be the most efficient catalyst and could realize "homogeneous catalysis, two-phase separation". Additionally, the catalytic system has wide substrate scope and good to excellent yields (up to 99%) could be obtained at room temperature.