Showing papers in "Tetrahedron Letters in 2005"

Abstract: A simple, inexpensive and efficient one-pot synthesis of 1,4-dihydropyridine derivatives at room temperature using catalytic amount of iodine were reported with excellent product yields. An easy access to various substituted 1,4-dihydropyridine derivatives quantitatively using commercially available iodine as a catalyst.

Abstract: The use of molecular iodine as the catalyst for a one-pot synthesis of quinoxaline derivatives at room temperature is reported.

Abstract: A simple and convenient procedure for the synthesis of aryl-14 H -dibenzo[ a . j ]xanthenes is described through a one-pot condensation of β-naphthol with aryl aldehydes in the presence of sulfamic acid as the catalyst in a solvent-free media using both conventional heating and microwave irradiation.

Abstract: Knoevenagel condensation of various aromatic and heteroaromatic aldehydes with active methylene compounds like malononitrile, ethyl cyanoacetamide, ethyl cyanoacetate, barbituric acids, Meldrum’s acid, dimedone and pyrazolone proceeds smoothly with stirring in an aqueous medium. The reactions occur at room temperature giving excellent yields of the products. The work-up procedure is very simple and the products do not require further purification.

Abstract: Direct one-step synthesis of various benzimidazoles from phenylenediamines and aldehydes is described using air as the oxidant. The salient features of this method include a simple procedure, mild conditions, no coupling agents or commercial oxidants/additives used, no waste produced (only by-product being water), easy purification, and high generality.

Abstract: Various biologically important quinoxaline derivatives were efficiently synthesized in excellent yields using inexpensive, nontoxic, and readily available bench top chemical, iodine in catalytic amount (10 mol %). Besides this, a systematic study was carried out to evaluate parameters such as solvent and catalyst loading. Several aromatic as well as aliphatic 1,2-diketones and aromatic 1,2-diamines, such as substituted phenylene diamines, tetra amines were further subjected to condensation using catalytic amounts of iodine to afford the products in excellent yield.

Abstract: KAl(SO4)2·12H2O was found to catalyze efficiently a one-pot three-component cyclocondensation of isatoic anhydride and primary amines or ammonia sources such as (NH4)2CO3, NH4OAc and NH4Cl with aromatic aldehydes under mild conditions to afford the corresponding mono- and disubstituted 2,3-dihydroquinazolin-4(1H)-ones in good yields.

Abstract: A water-soluble ruthenium-based olefin metathesis catalyst supported by a poly(ethylene glycol) conjugated N-heterocyclic carbene ligand is reported. The catalyst displays greater activity in aqueous ring-opening metathesis polymerization (ROMP) reactions than previously reported water-soluble metathesis catalysts.

Abstract: A new fluorescent chemosensor for Hg 2+ based on a dansyl amide-armed calix[4]-aza-crown was reported. It exhibits high sensitivity and selectivity toward Hg 2+ over a wide range of metal ions in MeCN–H 2 O (4:1, v/v). The association constant of the 1:1 complex formation for 2 -Hg 2+ was calculated to be 1.31 × 10 5 M −1 , and the detection limit for Hg 2+ was found to be 4.1 × 10 −6 mol L −1 .

Abstract: The electrophilic α-alkylation of ketones with alcohols was accomplished by a [Ru(DMSO) 4 ]Cl 2 catalyzed process, water being the only wasted material. The reaction can be successfully governed to produce either the expected ketones or their related alcohols only by changing the reaction conditions. When 2-aminobenzyl alcohol was used, a cyclization process took place to yield 2,3-disubstituted quinolines.

Abstract: Highly efficient one-pot synthesis of 1,2,3-triazole-linked glycoconjugates was presented involving a Cu(I) catalyzed 1,3-dipolar cycloaddition as the key step. It offers a convenient route to prepare neoglycoconjugates derived from unprotected saccharides or peracetylated saccharides.

Abstract: Michael reaction of indoles with unsaturated ketones has been accomplished in the presence of catalytic amount of iodine under solvent-free condition.

Abstract: An efficient two-step procedure for the deprotection of pinacolyl organoboronate esters is described. Reaction with excess potassium hydrogen fluoride produces the corresponding stable, crystalline potassium organotrifluoroborate salts. Treatment of the trifluoroborates with either inorganic base or trimethylsilyl chloride and water affords the corresponding organoboronic acid in high yield.

Abstract: A simple, efficient and practical procedure for the Biginelli reaction using strontium(II) triflate [Sr(OTf) 2 ] as a novel catalyst is described under solvent-free conditions in high yields. The catalyst exhibited remarkable reactivity and it is reusable. Some of dihydropyrimidiones showed strong pesticidal activity.

Abstract: We report the simple and efficient synthesis of 2-arylbenzothiazoles (‘BTA’) and 2-arylbenzoxazoles by direct coupling of benzothiazoles or benzoxazoles with aryl bromides. This method permits direct one-step access to precursors of radiolabeled BTA-1 and BTA-2 and their 6-methoxy analogues, used for in vivo imaging of β-amyloid plaques with positron emission tomography (PET).

Abstract: o-Aminoaryl ketones undergo smooth condensation with α-methylene ketones in the presence of sulfamic acid (NH2SO3H) (SA) under mild reaction conditions to afford the corresponding polysubstituted quinolines in excellent yields. The catalyst can be recovered by simple filtration and can be recycled in subsequent reactions. The method is simple, cost-effective and environmentally benign.

Abstract: 2-Aminoaryl ketones undergo condensation with α-methylene ketones in the presence of a catalytic amount of Y(OTf)3 at room temperature under mild conditions to afford the corresponding polysubstituted quinolines in excellent yields.

Abstract: The oxidation of alcohols has been achieved using Grubbs’ catalyst or a ruthenium p-cymene complex without the presence of an added oxidant.

Abstract: Boric acid efficiently catalyzes the conjugate addition of aliphatic amines to α,β-unsaturated compounds to produce β-amino compounds, with great alacrity and excellent yields, in water under mild conditions. Aromatic amines do not participate effectively in the reaction.

Abstract: The reactions of alkyl nitriles, acetyl chloride, aldehydes and β-ketoesters or simple ketones was studied for the one-pot synthesis of β-acetamido carbonyl compounds. It was observed that the reaction proceeds in the absence of Lewis acids. However, a Lewis acid catalyzes the reaction and several were tested. It was found that whereas Cu(OTf) 2 is suitable for the coupling of β-ketoesters with aldehydes, Sc(OTf) 3 is the best for ketones. A possible mechanism is proposed based on the isolation and characterization of an intermediate.

Abstract: A practical synthesis of 2,3-disubstituted 3 H -quinazolin-4-ones 1 with broad chemistry scope is described. The key step is the microwave promoted one-pot, two-step reaction sequence combining anthranilic acids, carboxylic acids, and amines providing efficient access to this important class of heterocycles.

Abstract: 2-Aminobenzyl alcohol reacted with 2 equiv amount of ketones under the influence of [IrCl(cod)] 2 or IrCl 3 and KOH without any solvent, giving the corresponding quinoline derivatives in good yields.

Abstract: A straightforward and efficient method for the regioselective synthesis of functionalized 1,4-disubstituted [1,2,3]-triazoles, from terminal alkynes and azides, has been established utilizing Cu(0) as the source of the catalytic species. The presumed catalytic Cu(I) species is generated by the combination of 10 mol % copper nanosize activated powder and 1 equiv of an amine hydrochloride salt. The addition of an amine hydrochloride salt into the reaction mixture enhanced the dissolution of copper metal, and subsequently facilitated the formation of the Cu(I)-acetylide intermediate required for the regioselective cycloaddition.

Abstract: The solvent-free acylation of alcohols and phenols with acyl chlorides using ZnO as a catalyst is described. The remarkable selectivity under mild and neutral conditions, and recyclability of the catalyst, are advantages.

Abstract: The development of a general Cu-catalyzed synthesis of (hetero)aromatic nitriles from the corresponding aryl bromides and potassium hexacyanoferrate(II) is described. This novel protocol avoids the use of highly toxic alkali cyanides and precious palladium catalysts. Best results were achieved applying Cu(BF 4 ) 2 ·6H 2 O (0.1 equiv) and N , N ′-dimethyl ethylenediamine (DMEDA; 1.0 equiv) in N , N -dimethyl acetamide (DMAc).

Abstract: A straightforward and general method has been developed for the synthesis of α-aminonitriles by simply combining aldehydes or ketones, amines, and trimethylsilyl cyanides in the presence of a catalytic amount of molecular iodine at room temperature.

Abstract: Pd-catalyzed homo- and cross-couplings of boronic acids and aryl halides were successfully carried out both in aqueous media under high-intensity ultrasound (US) and in DME under microwave (MW). Heterogeneous catalysis with Pd/C was employed, avoiding phosphine ligands and phase-transfer catalysts. In a trial series involving 15 different iodo- and bromoaryls and 7 boronic acids, both energy sources drastically reduced reaction times affording biaryls in acceptable to good yields. With palladium(II) acetate as catalyst, electron-deficient aryl chlorides also reacted, affording a few biaryls in acceptable yields. Ullmann-type zinc-mediated homocoupling of iodo- and bromoaryls in the presence of Pd/C under CO2 atmosphere was achieved in aqueous media under US, though not under MW. Suzuki homo- and cross-couplings were also carried out in a new reactor developed in our laboratory, featuring combined US and MW irradiation, further improving a green synthetic method.

Abstract: Hetero-biaryl compounds were prepared via the Suzuki–Miyaura coupling reaction of hetero-aryl moieties containing an unprotected NH2 group and arylboronic acids. D-t-BPF was found to be an efficient ligand for the cross-coupling of NH2-unprotected hetero-aryl chlorides with phenylboronic acid.

Abstract: PEG-PS resin-supported tripeptide/zinc chloride catalyst system has been developed for use in the direct asymmetric aldol reaction of acetone with aldehydes in aqueous media. The peptide catalyst could be separated from the reaction mixture by filtration, and was reusable at least five times without significant change in its activity and selectivity.

Abstract: The 2- or 2,6-position(s) of aromatic aldehydes were directly and selectively arylated with aryl chlorides or bromides in the presence of a catalytic system prepared in situ from Pd(OAc)2, imidazolinium chlorides ( 1–5 ) and Cs2CO3.