H_6P_2W_（18）O_（62）á18H_2O： A green and reusable catalyst for one-pot synthesis of pyrano[4,3-b]pyrans in water

A convenient,effcient and environmentally benign procedure has been developed for the synthesis of pyrano[4,3-b]pyran derivatives via a one-pot,three-component reaction of 4-hydroxy-6-methylpyran-2-one,aldehydes and malononitrile in water using H6P2W18O62á18H2O as catalyst.Reusability of the catalyst and reaction media,short reaction times and easy isolation of products are some added advantages of the present methodology.     

重金属铊在环境介质中的分布及其迁移行为

铊是剧毒重金属元素,它在自然界中是典型的稀有分散金属。环境介质中铊的自然本底值较低,但随着铊矿床的开发和铊资源的广泛应用,岩矿石中的铊在自然力或人为作用下向环境介质中迁移。综述了铊在岩（矿）石、土壤、水体、动植物和人体中的分布,以及在上述环境介质及大气中的迁移行为。研究表明,人类活动是导致环境介质中铊含量增加的主要原因。铊在环境介质中的迁移是反复循环的复杂过程,通过风化、溶解、淋滤、吸收、沉降、固结等方式在环境介质中循环往复,从而危害环境生态和人体健康。铊污染应引起人们的普遍重视。     

Synthesis of Schiff's bases in aqueous medium: a green alternative approach with effective mass yield and high reaction rates

Abstract

Schiff's bases constitute a class of pharmaceutical and medicinally important molecules. The conventional methods for the synthesis of Schiff's bases require long reaction times and use of organic solvents. We report a novel and eco-friendly condensation reaction method permitting the “green synthesis” of various Schiff's bases by stirring 1,2-diaminobenzene with various aromatic aldehydes in water as solvent. This method is experimentally simple, clean, high yielding, green, and with reduced reaction times. The product is purified by simple filtration followed by washing with water and drying processes.     

One-Pot Oxidation of Alanine and Its Ethyl Ester with a Mild Oxidant 4′-Methylazobenzene-2-sulfenyl Bromide

One-pot oxidation of alanine and its ethyl ester with a mild oxidant 4′-methylazobenzene-2-sulfenyl bromide is described. Using a nonreactively water-soluble electrophilic species, 4′-methylazobenzene-2-sulfenyl bromide, with L-alanine and its ethyl ester (in 3:1 molar proportions) in aqueous solution at room temperature, the corresponding sulfenimines are prepared. On hydrolysis in acidic medium at room temperature, these sulfenimines give ethanal and pyruvic acid respectively.

A simple catalytic system based on PdCl2(CH3CN)2 in water for cross-coupling reactions using diazonium salts

Aryl–heteroaryl and heteroaryl–heteroaryl compounds are obtained through the Suzuki–Miyaura cross-coupling reactions between diazonium salts and potassium trifluoroborates using PdCl₂(CH₃CN)₂ as the catalyst in water and in the absence of any additive, ligand or base. In addition, the same mild catalytic system is effective for the Matsuda–Heck reaction between several monoolefins with aryldiazonium salts.     

Thiamine hydrochloride as a promoter for the efficient and green synthesis of 12-aryl-8,9,10,12 tetrahydrobenzoxanthene-11-one derivatives in aqueous micellar medium

An environmentally benign, three-component, one-pot integrated chemical process has been developed for the synthesis of 12-aryl-8,9,10,12-tetrahydrobenzoxanthene-11-one by nucleophilic addition reaction between aldehyde and β-naphthol followed by Michael addition of dimedone, catalyzed by thiamine hydrochloride in aqueous micellar medium with excellent yield. Simple reaction conditions, no requirement of chromatographic separation, short reaction time, ease of isolation, use of inexpensive, easily recoverable and reusable catalyst makes this protocol very interesting from an economic and environmental perspective.     

Ni‐Catalyzed [4+3+2] Cycloaddition of Ethyl Cyclopropylideneacetate and Dienynes: Scope and Mechanistic Insights

A detailed study of the Ni‐catalyzed [4+3+2] cycloaddition reaction between ethyl cyclopropylideneacetate and dienynes has been conducted, resulting in the development of a new method for the synthesis of compounds containing nine‐membered rings. We studied the reactivity of various dienynes, together with their substituent and conformational effects. The mechanism of the reaction was probed by examining the stoichiometric reactions of the Ni complexes and dienynes.     

Mild method for the synthesis of 1H-indazoles through oxime-phosphonium ion intermediate

The synthesis of 1H-indazoles from o-aminobenzoximes is achieved via N–N bond formation using triphenylphosphine, I₂, and imidazole. Selective formation of oxime-phosphonium ion intermediate in the presence of the amino group is the driving force for this reaction. The nucleophilicity of the arylamino group and electrophilicity toward the N–O bond of oxime also control the reaction. The reaction proceeds at a faster rate with good to excellent yield under this mild reaction condition and is amenable to scale-up.     

An organocatalytic synthesis of N-sulfonyl imines using chloramine-T in aqueous medium

N-Sulfonyl imines have been synthesized in good to excellent yields from aldehydes and chloramine-T using proline as an organocatalyst in aqueous medium at ambient temperature. The protocol is applicable to a wide range of aldehydes, especially enals exhibit remarkable efficiency in the reaction. The reaction presumably occurs via iminium activation and opens new avenues for the synthesis of N-sulfonyl imines under environmentally benign and mild conditions.