A carrier-free and recyclable protocol for the cross-coupling of terminal alkynes with arylboronic acids in H2O/TBAB

A new and recyclable protocol was developed for Pd(OAc)₂-catalyzed the cross-coupling reaction of terminal alkynes with arylboronic acids using environmentally friendly H₂O/TBAB as reaction medium. A series of cross-coupling products containing internal acetylenic bond can be obtained with good selectivity and yield. The Pd(OAc)₂/H₂O/TBAB system was stable in the Sonogashira-type cross-coupling reaction and could be used at least three cycles without considerable decrease in catalytic performance. The results suggest that the unsupported and recyclable systems can be extended to the other realm of CC bond formation in synthetic organic chemistry.     

Silica chloride: An efficient promoter for oxidation of arylboronic acids to phenols

This work reports simple, highly efficient protocol for the oxidation of arylboronic acids. Various arylboronic acids were selectively and completely converted into their corresponding oxidized phenols using H₂O₂ as an oxidant in presence of catalytic amount of silica chloride. The results show that silica chloride is a suitable and efficient promoter for the oxidation of arylboronic acids. Heterogeneous catalyst, mild reaction conditions, easy availability of the reagent, easy work-up, excellent yield of corresponding phenols, short reaction time and broad substrate scope makes this protocol attractive and a practical alternative to the existing methods.     

Synthesis of chiral quaternary fluorinated cyclic sulfamidates via palladium-catalyzed arylation with arylboronic acids

An enantioselective palladium-catalyzed arylation of fluorinated cyclic N-sulfonyl ketimines with arylboronic acids is described. This methodology provides an efficient and convenient route to chiral quaternary fluorinated cyclic sulfamidates in high yields with up to 99% ee.     

Catalysis by Amberlite IR-120 resin: a rapid and green method for the synthesis of phenols from arylboronic acids under metal, ligand, and base-free conditions

A clean process has been developed for the ipso-hydroxylation of aryl and heteroaryl boronic acids to the corresponding phenols using commercially available and recyclable Amberlite IR-120 resin and aqueous hydrogen peroxide as an oxidizing agent. The ion-exchange sulfonic acid resin catalyst could be readily recycled by filtration and directly reused at least four times without any significant loss of activity.     

Biogenic synthesis of Fe2O3@SiO2 nanoparticles for ipso-hydroxylation of boronic acid in water

Here, biogenic synthesis of Fe₂O₃@SiO₂ nanoparticles using fruit extract of Zanthoxylum rhetsa is reported. The SiO₂ nanoparticles was synthesized using paddy straw which is a byproduct obtained in cultivation of rice. The composite was characterised by spectroscopic method like XRD, SEM, TEM and EDX analysis. The ipso-hydroxylation reactions were carried out with excellent yield within a moderate time period with mild reaction condition in all cases. Therefore, this approach may be considered as simple, easy, cheap and greener, environment friendly protocol for ipso-hydroxylation of arylboronic acids at 50 °C temperature.     

Cooperation of biopolymer chitosan with hydrogen peroxide for ipso-hydroxylation of arylboronic acids under green conditions

Oxidative hydroxylation of arylboronic acids to the corresponding phenolic compounds under metal- and base-free aerobic conditions is successfully demonstrated on a biopolymer support (chitosan or chitosan immobilized onto carbon nanotubes ([email protected])). Hydrogen peroxide, as an eco-friendly oxidant, is compatible with the biopolymer supports and provides hydroxylation products in an efficient manner. The [email protected] biopolymer support is particularly interesting for its potential recyclability.     

A facile green synthesis of silver nanoparticles: An investigation on catalytic hydroxylation studies for efficient conversion of aryl boronic acids to phenol

Ag nanoparticles (AgNPs) catalyst material is bio-synthesized and fully examined using various spectroscopy and microscopy techniques. Further this synthesized material is used for hydroxylation reaction, for this purpose we developed a simple and versatile bio-based method from aryl boronic acids to phenol. The reaction was studied in the presence of low cost ligand in a hydrated reaction medium without any hazardous organic solvents, as a result a finite amount of yield was achieved in short time (<15 min). The hydroxylation reaction is further carried out in a series of different arenes substituted samples with good amount of yields.     

Water-acetic acid mediated an efficient one-pot eco-friendly synthesis of novel bis-isoxazolopyrroloquinoline derivatives

An efficient, cost-effective and environmentally benign synthesis of novel tetracyclic bis-isoxazolopyrroloquinoline derivatives has been developed via one-pot four-component reaction of 4-amino-3-methyl-5-styrylisoxazoles, dimedone, aryl glyoxal monohydrates and 5-amino-3-methylisoxazole by employing water as a reaction medium and acetic acid (AcOH) as a green promoter. The advantages of this protocol are environmentally friendly, metal-free, less reaction time, operational simplicity, high yields, broad substrate scope and easy purification. Most significant of all, this method is green.     

Ferrocenophane-based bifunctional organocatalyst for highly enantioselective Michael reactions

Highly enantioselective Michael reactions between acetylacetone and trans-β-nitroolefins are achieved by a novel ferrocenophane-based tertiary amine-thiourea organocatalyst to provide the corresponding products in good to excellent yields (up to 95%) and enantioselectivities (up to 99% ee).     

Cyclometalated Ir(III) complexes-catalyzed aerobic hydroxylation of arylboronic acids induced by visible-light

The cyclometalated Ir(III) complexes-catalyzed aerobic hydroxylation of arylboronic acids under visible-light has been successfully developed. This catalytic system has a broad substrate scope, affording a series of phenols smoothly with the highest isolated yield up to 95%. Moreover, this protocol is capable to synthesize several useful phenols containing bulky moieties, which are potential candidates or intermediates used as pharmaceuticals and functional materials. The Ir(III)-catalyzed hydroxylation of arylboronic acids could be applied in a one-pot synthesis of several important phenol derivatives, including 1,1′-methylene-bis(2-naphthol), 2,3-dihydro-1H-naphtho[2,1-e][1,3]oxazine and a bioactive compound LUF5771.     

1,1′-Carbonyldiimidazole as a cyclodehydrating agent for the Castagnoli–Cushman reaction of dicarboxylic acids and imines

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An efficient protocol for synthesis of novel polyheterocyclic chromeno pyrimido[1,2-b]indazolone derivatives using [Et3NH][HSO4] as a reusable catalyst under solvent-free conditions

A convenient and highly efficient method for the synthesis of novel polyheterocyclic chromeno pyrimido[1,2-b]indazolone derivatives via a three-component condensation of 1H-indazol-3-amine, aldehydes and 4-hydroxycoumarin catalyzed by Bronsted acid ionic liquid [Et₃NH][HSO₄] under solvent-free reaction conditions is presented. This ionic liquid is air and water stable and easy to prepare from amine and acid. The main advantages of this protocol includes short reaction time, excellent yield, easy work-up, operational simplicity, a wide range of functional group tolerance and column chromatography-free method. The catalyst can be recovered and reused for at least four runs without any significant impact on the product yields.     

Multicomponent synthesis of substituted 3-styryl-1H-quinoxalin-2-ones in an aqueous medium

A multicomponent synthesis of substituted 3-styryl-1H-quinoxalin-2-ones is described. Sequential reactions of o-phenylenediamine with sodium pyruvate and aldehydes in 20% aqueous acetic acid containing sodium acetate provided the target products in good to high yields. The reaction is proposed to proceed via initial condensation of the diamine and pyruvate partners followed by an aldol condensation-type mechanism.     

ipso-Bromination/iodination of arylboronic acids: Poly(4-vinylpyridine)-Br2/I2 complexes as safe and efficient reagents

Poly(4-vinyl pyridine) supported bromine/iodine complexes were prepared and probed for ipso-bromination/iodination of arylboronic acids. These solid complexes with catalytic amount of additive are found to be safe and efficient reagent system for the ipso-bromination/iodination. The reaction occurs under mild conditions and tolerates various functional groups resulting in products with high selectivity and yields.     

Polymeric tertiaryphosphine as a green and recyclable organocatalyst for stereoselective isomerization reaction

A green, simple and effective polymeric organocatalytic system, polymer-supported triphenylphosphine (PS-TPP), for the stereoselective isomerization of α,β-ynones to (E,E)-α,β-γ,δ-dienones is reported here. The catalyst, PS-TPP could be recovered by simple filtration and reused several times with high activity.     

Cellulose conformation responsible for resolution of DL-amino acids

Summary For the purpose of biochemical study, the resolution of non-derivatized DL-amino acids was carried out by using native-cellulose thin-layer and column chromatography. Its resolution capability was known to be in proportion to the increase of environmental hydrophobicity. It is suggested that the resolutions of DL-amino acids might be resulted from the cellulose conformation change under hydrophobic conditions. The model structures of cellulose are proposed in order to understand the mechanism of chiral selection of amino acids on its molecular surface. LEB/OU contribution No. 70     

Efficient synthetic approach to copolymers of glycolic and lactic acids for biomedical applications

An efficient approach to copolymers of glycolic and lactic acids applied in biomedical materials was developed using ring-opening polymerization catalysts based on alkoxy complexes of ‘biometals’ (Mg, Al, and Zn) and 3-methyl- 1,4-dioxane-2,5-dione and glycolide as comonomers.     

Efficient synthesis of N- and O-linked glycopeptides using acid-labile Boc groups for the protection of carbohydrate moieties

Development of a synthetic method for the preparation of homogeneous glycopeptides and glycoproteins is important for the elucidation of their structures and functions. Here, we report on the concise and facile synthesis of glycopeptides using Boc groups for the protection of carbohydrate hydroxyl groups. This method enables us to remove the protecting groups from peptide and carbohydrate moieties in a single-step process without undesirable any side reaction.     

Banana pulp extract mediated synthesis of Cu2O nanoparticles: An efficient heterogeneous catalyst for the ipso-hydroxylation of arylboronic acids

A green and facile novel procedure has been developed for the synthesis of Cu₂O nanoparticles within a very short reaction time using banana pulp extract as a reducing agent. The synthesized nanoparticles are well characterized by SEM (Scanning Electron Microscope), TEM (Transmission Electron Microscope) and powder XRD (X-ray Diffraction) methods. An environmental benign and highly efficient protocol for the ipso-hydroxylation of aryl and hetero arylboronic acids using bio-fabricated Cu₂O nanoparticles as a catalyst and aqueous H₂O₂ as an oxidant has also been developed. The main advantages of this protocol are the base free reaction condition, reusable and heterogeneous catalytic system, and short reaction time with excellent yields.     

Total synthesis of 4-epi-atpenin A5 as a potent nematode complex II inhibitor

It is clear that atpenins and their analogs are useful chemical tools for elucidation of complex II functionality and that they could act as lead compounds for the development of novel helminth complex II-specific inhibitors. Recently, we discovered 4-epi-atpenin A5 as a potent nematode complex II inhibitor during our SAR studies of atpenin A5. This result led us to embark on a concise total synthesis of 4-epi-atpenin A5. In this study, we describe the total synthesis of 4-epi-atpenin A5. Importantly, this was more concise and practical synthesis than our previous total synthesis of atpenin A5.