Highly selective oximation of aldehydes by reusable heterogeneous sandwich-type polyoxometalate catalyst

The selectivity of oximation of a variety of aliphatic aldehydes and polycyclic aromatic aldehydes as substrates has been greatly improved by applying a reusable heterogeneous sandwich-type polyoxometalate as catalyst under mild conditions.     

House bulb light-induced photochemical acetalization of carbonyl compounds catalyzed by Eosin Y

We have systematically studied the reactions of acetalization and found that high reaction efficiency can be achieved using cheap and readily available organic Eosin Y as catalyst. The reaction proceeds smoothly under house bulbs and shows excellent functional group tolerance. The substrates of the reaction system are compatible with aromatic aldehydes, aliphatic aldehydes, aromatic ketones, and cyclic ketones with high yields.     

Domino‐Hydroformylation/Aldol Condensation Catalysis: Highly Selective Synthesis of α,β‐Unsaturated Aldehydes from Olefins

A general and highly chemo‐, regio‐, and stereoselective synthesis of α,β‐unsaturated aldehydes by a domino hydroformylation/aldol condensation reaction has been developed. A variety of olefins and aromatic aldehydes were efficiently converted into various substituted α,β‐unsaturated aldehydes in good to excellent yields in the presence of a rhodium phosphine/acid–base catalyst system. In view of the easy availability of the substrates, the high atom‐efficiency, the excellent selectivity, and the mild conditions, this method is expected to complement current methodologies for the preparation of α,β‐unsaturated aldehydes.     

A convenient one-pot three component synthesis of 3-aminoalkylated indoles catalyzed by 3-chlorophenylboronic acid

An efficient protocol was developed for the synthesis of 3-aminoalkylated indoles using 3-chlorophenylboronic acid as a catalyst under ambient temperature conditions. The three-component reaction of indoles, aromatic aldehydes and N-methyl aniline offered corresponding 3-aminoalkylated indoles in excellent yields. This protocol presents some remarkable features such as mild reaction conditions, simple workup procedure and excellent yields.     

Nickel-catalyzed, carbonyl-ene-type reactions: selective for alpha olefins and more efficient with electron-rich aldehydes

Described are several classes of unusual or unprecedented carbonyl-ene-type reactions, including those between alpha olefins and aromatic aldehydes. Catalyzed by nickel, these processes complement existing Lewis acid-catalyzed methods in several respects. Not only are monosubstituted alkenes, aromatic aldehydes, and tert-alkyl aldehydes effective substrates, but monosubstituted olefins also react faster than those that are more substituted, and large or electron-rich aldehydes are more effective than small or electron-poor ones. Conceptually, in the presence of a nickel-phosphine catalyst, the combination of off-the-shelf alkenes, silyl triflates, and triethylamine functions as a replacement for an allylmetal reagent.     

KF/Al2O3 Mediated Multicomponent Reactions for the Efficient Synthesis of Highly Substituted Dihydropyridines

KF/Al₂O₃ was found to be an efficient solid supported catalyst for the facile access of highly substituted dihydropyridine derivatives from the multicomponent reaction of aromatic aldehydes, amines, malononitrile, and alkylacetylenedicarboxylates. The notable advantages of this protocol are reusable catalyst, good yields, applicable to a wide range of substrates for the synthesis of pharmacologically interesting dihydropyridine derivatives.     

Ferric sulfate [Fe2(SO4)3·xH2O]: an efficient heterogeneous catalyst for the synthesis of tetrahydroquinoline derivatives using Povarov reaction

Fe₂(SO₄)₃·xH₂O can be used as an efficient and reusable catalyst for the synthesis of pyrano- and furanotetrahydroquinolines via one-pot three-component Povarov reaction involving aromatic aldehydes, aromatic amines, and cyclic enol ethers. The catalyst is recyclable, economically viable, and environmentally benign. This protocol provides good yields and diastereoselectivity as well as applicability on a wide range of substrates.     

((3-(3-硅胶丙基)硫基)丙基)硫酸酯作为可回收催化剂用于合成4,4'-芳亚甲基-双(1H-吡唑-5-醇)(英文)

Sulfuric acid ([3-(3-silicapropyl)sulfanyl]propyl)ester is employed as a recyclable catalyst for the condensation reaction between aromatic aldehydes and 3-methyl-l-phenyl-5-pyrazolone. This condensation reaction was performed in ethanol under refluxing conditions giving 4,4'-alkylmethylene-bis(3-methyl-5-pyrazolones) in 74-90% yields. The heterogeneous catalyst was recycled and used in eleven runs for the reaction between benzaldehyde and 3-methyl-l-phenyl-5-pyrazolone without losing catalytic activity.     

Highly Enantioselective Henry Reactions of Aromatic Aldehydes Catalyzed by an Amino Alcohol-Copper(II) Complex

Amino alcohol-Cu(II) catalyst: Highly enantioselective Henry reactions between aromatic aldehydes and nitromethane have been developed. The reactions were catalyzed by an easily available and operationally simple amino alcohol-copper(II) catalyst. In total, 38 substrates were tested and the R-configured products were obtained in good yields with excellent enantioselectivities.     

Mesoporous nickel hydroxyapatite nanocomposite for microwave-assisted Henry reaction

The utility of nickel hydroxyapatite nanocomposite (Ni-HAp) as a green catalyst for solvent free, microwave-assisted Henry reaction using nitromethane and a series of aromatic aldehydes as substrates is presented. The selected catalyst performed well to afford the respective nitrostyrenes which were quantified by gas chromatography equipped with a mass spectral detector (GC–MS). A few of the products were identified from the respective nuclear magnetic resonance (NMR) spectral data.     

A simple method for knoevenagel condensation of α,β‐conjugated and aromatic aldehydes with barbituric acid

Several aromatic and α,β‐conjugated aromatic aldehydes were condensed with barbituric acid in methanol solution in the absence of acid or base as a catalyst, affording 5‐ylidenebarbituric acid derivatives in almost quantitative yields.     

Silica Phosphoric Acid: An Efficient and Recyclable Catalyst for the Solvent-Free Synthesis of Acylals and Their Deprotection in MeOH

Silica phosphoric acid was used as an efficient, mild, and recyclable solid catalyst for the synthesis of acylals from various structurally diverse aldehydes and acetic anhydride under solvent-free conditions. The acylation of aldehydes was highly chemoselective, and no ketone was acylated, which provided a method for the synthesis of acylals from aldehydes in the presence of ketones. Silica phosphoric acid–catalyzed deprotection of acylals to the corresponding aldehydes in MeOH has also been developed with excellent yield. The deprotection of the acylals of aromatic aldehydes took priority over those of aliphatic aldehydes.     

Selective Activation of Aromatic Aldehydes Promoted by Dispersion Interactions: Steric and Electronic Factors of a π-Pocket within Cage-Shaped Borates for Molecular Recognition

Selective bond formations are one of the most important reactions in organic synthesis. In the Lewis acid mediated electrophile reactions of carbonyls, the selective formation of a carbonyl–acid complex plays a critical role in determining selectivity, which is based on the difference in the coordinative interaction between the carbonyl and Lewis acid center. Although this strategy has attained progress in selective bond formations, the discrimination between similarly sized aromatic and aliphatic carbonyls that have no functional anchors to strongly interact with the metal center still remains a challenging issue. Herein, this work focuses on molecular recognition driven by dispersion interactions within some aromatic moieties. A Lewis acid catalyst with a π-space cavity, which is referred to as a π-pocket, as the recognition site for aromatic carbonyls is designed. Cage-shaped borates 1 B with various π-pockets demonstrated significant chemoselectivity for aromatic aldehydes 3 b – f over that of aliphatic 3 a in competitive hetero-Diels–Alder reactions. The effectiveness of our catalysts was also evidenced by intramolecular recognition of the aromatic carbonyl within a dicarbonyl substrate. Mechanistic and theoretical studies demonstrated that the selective activation of aromatic substrates was driven by the preorganization step with a larger dispersion interaction, rather than the rate-determining step of the C−C bond formation, and this was likely to contribute to the preferred activation of aromatic substrates over that of aliphatic ones.     

A series of 1,8-dioxooctahydroxanthenes are prepared using trichloroisocyanuric acid

A series of aromatic aldehydes are turned in to 3,3,6,6-tetramethyl-9-aryl-1,8-dioxooctahydroxanthene derivatives using trichloroisocyanuric acid(TCCA) as the catalyst.     

A simple synthesis of 2-methylidene-3-aminopropanoates

Coupling of ethyl acrylate to N-(para-toluenesulphonyl)imines of aromatic aldehydes is readily achieved using 1,4-diazabicyclo[2.2.2]octane as catalyst.     

Direct catalytic asymmetric aminoallylation of aldehydes: synergism of chiral and nonchiral Brønsted acids

The development of a catalytic asymmetric method for the direct aminoallylation of aldehydes is described that gives high asymmetric inductions for a broad range of substrates including both aromatic and aliphatic aldehydes. This method allows for direct isolation of unprotected analytically pure homoallylic amines without chromatography. The unique catalyst system developed for this process involves the synergistic interaction between a chiral and a nonchiral Br?nsted acid.     

Synthesis of aromatic aldehydes by organocatalytic [4+2] and [3+3] cycloaddition of α,β-unsaturated aldehydes

Organocatalytic inter- and intramolecular [4+2] and [3+3] cycloadditions of α,β-unsaturated aldehydes to give polysubstituted aromatic aldehydes are described. High periselectivity for the cycloadditions, with catalyst effects exerted by l-proline and pyrrolidine-HOAc, as well as cocatalyst, additive effects, has been observed.     

Titanium tetrachloride incorporated crosslinked polystyrene copolymer as an efficient and recyclable polymeric Lewis acid catalyst for the synthesis of Β-amino carbonyl compounds at room temperature

An efficient and eco-friendly procedure for one-pot synthesis of β-amino carbonyl compounds by three-component reaction of aromatic aldehydes, acetophenone, and aromatic amines via a Mannich type reaction using a stable tightly bound complex, titanium tetrachloride incorporated crosslinked polystyrene copolymer (PS/TiCl₄), as a water tolerant, recoverable, and reusable polymeric Lewis acid catalyst in ethanol at room temperature is reported. The complex of the polystyrene and TiCl₄ provides a shelf-stable acidic, water tolerant material, and it is not easily hydrolyzed by water. Our findings thus show a novel and improved modification of the Mannich type reaction in terms of mild reaction conditions, clean reaction profiles, applicability to various substrates using a simple workup procedure which makes this reaction an interesting alternative to previously applied procedures. The recyclability of the catalyst makes this protocol environmentally benign.     

Fe3+‐Montmorillonite: An Efficient Solid Catalyst for One‐Pot Synthesis of Decahydroacridine Derivatives

Fe³⁺‐montmorillonite was used as a solid acidic catalyst for the synthesis of decahydroacridine derivatives through the condensation of aromatic aldehydes, dimedone and aniline in ethanol. The influence of reaction time, reaction temperature, and the amount of catalyst were studied. All the compounds were characterized by IR, Mp, ¹H NMR and ¹³C NMR analysis.     

A simple and efficient large-scale synthesis of 3-hydroxyphthalans via oxa-Pictet-Spengler reaction catalyzed by nanosilica sulfuric acid

Nanosilica sulfuric acid is found to be a new, powerful and reusable heterogeneous catalyst for the rapid synthesis of 3-hydroxyphthalans via condensation of aromatic aldehydes and 3-hydroxybenzyl alcohols under conventional heating and microwave irradiation. Scale-up preparation of these heterocycles is also carried out.