Showing papers in "Synthesis in 2004"
TL;DR: In this paper, a review of the recent advances in the asymmetric hydrosilylation of ketones and imines is presented, which leads to very effective and selective protocols for the reduction of prochiral ketones, imines and electrophilic double bonds.
Abstract: This literature review focuses on the recent advances in the asymmetric hydrosilylation of ketones and imines. New catalyst systems based on various transition metals, such as rhodium, titanium, zinc, copper and tin, combined with classical or new ligand structures, are presented. These systems lead to very effective and selective protocols for the reduction of prochiral ketones, imines and electrophilic double bonds.
234 citations
TL;DR: The Dry Column Vacuum Chromatography pre- sented here, has excellent resolving power, is easily applied to large scale chromatography (up to 100 g) and is fast, making it an excellent alternative to the commonly used Flash Column Chromatography for purification in organic synthesis.
Abstract: Chromatographic purification is an integrated part of or- ganic synthesis. The Dry Column Vacuum Chromatography pre- sented here, has excellent resolving power, is easily applied to large scale chromatography (up to 100 g) and is fast. Furthermore, the technique is economical and environmentally friendly due to signif- icant reductions in solvent and the amount of silica used. Therefore, it is an excellent alternative to the commonly used Flash Column Chromatography for purification in organic synthesis.
169 citations
TL;DR: A review with 206 references covers the literature published until March 2004 on the development and applications of new efficient catalyst systems for the Suzuki palladium-catalysed cross-coupling reaction of organoboron compounds with organic electrophiles as mentioned in this paper.
Abstract: This review with 206 references covers the literature published until March 2004 on the development and applications of new efficient catalyst systems for the Suzuki palladium-catalysed cross-coupling reaction of organoboron compounds with organic electrophiles. Where possible, the relative advantages of the new catalyst systems in this synthetically very important carbon-carbon bond forming reaction have been compared.
155 citations
TL;DR: In this article, the Na 2 S 2 O 4 reduction of o-nitroanilines in the presence of aldehydes was used for the synthesis of benzimidazoles.
Abstract: A highly efficient and versatile method for the synthesis of benzimidazoles was achieved in one step via the Na 2 S 2 O 4 reduction of o-nitroanilines in the presence of aldehydes. Heating a solution of o-nitroaniline (1c) and an aldehyde in EtOH or another appropriate solvent, in the presence of aqueous or solid Na 2 S 2 O 4 , provided facile access to a series of 2-substituted N-H benzimidazoles 5a-m containing a wide range of functional groups not always compatible with the existing synthetic methods. This methodology has also been applied to the regioselective synthesis of N-alkyl and N-aryl benzimidazoles 6a-fvia the cyclization of the corresponding N-substituted nitroanilines 13a-e, respectively. In addition, the method was applied successfully to the synthesis of other imidazole containing heterocyclic ring systems such as 1H-imidazo[4,5-b]pyridines 14a,b and 1H-imidazo[4,5-f]quinoline 15.
142 citations
TL;DR: In this paper, the reaction between lithiated allenic compounds and isothiocyanates, R'N=C=S, in most cases gives exclusively thioimidates with the allenic structure, C =C=CC(SLi)=NR 1.
Abstract: Reaction between lithiated allenic compounds and isothiocyanates, R'N=C=S, in most cases gives exclusively thioimidates with the allenic structure, C=C=CC(SLi)=NR 1 . These intermediates have been used in novel approaches to 2,3-dihydropyridines, pyrroles, quinolines, cyclobutanopyrrolines, and thiophene or dihydrothiophene derivatives. The procedures leading to the heterocycles with a nitrogen atom in the ring involve 5-alkylation followed by simple heating or by treatment with copper(I) halide. 2-Aminothiophenes and 2-imino-2,5-dihydrothiophenes are formed by intramolecular nucleophilic attack of the thiolate moiety on the allenic system and subsequent addition of methyl iodide or protonation. 1 Introduction 2 Generation of Allenic Lithium Compounds 3 Formation of 2,3-Dihydropyridines or Mixtures of 2,3-Dihydropyridines and Pyrroles 4 Directed Synthesis of Pyrroles 5 Synthesis of Quinolines 6 Synthesis of Cyclobutanopyrrolines 7 Synthesis of Thiophene and Dihydrothiophene Derivatives 8 Concluding Remarks.
126 citations
TL;DR: In this paper, Aminoaryl ketones undergo smooth condensation with α-methylene ketones on the surface of silver heteropoly acid (Ag 3 PW 1 2 O 4 0 ) under mild reaction conditions to afford the corresponding polysubstituted quinolines in excellent yields with high selectivity.
Abstract: o-Aminoaryl ketones undergo smooth condensation with α-methylene ketones on the surface of silver heteropoly acid (Ag 3 PW 1 2 O 4 0 ) under mild reaction conditions to afford the corresponding polysubstituted quinolines in excellent yields with high selectivity. The catalyst can be recovered by simple filtration and can be recycled in subsequent reactions.
106 citations
TL;DR: In this paper, the reaction of aromatic aldehyde, 5,5-dimethyl-1,3-cyclohexanedione and p-toluidine in water was successfully carried out in the presence of p-dodecylbenezenesulfonic acid (DBSA) as a BrΦnsted acid-surfactant-combined catalyst.
Abstract: Reaction of aromatic aldehyde, 5,5-dimethyl-1,3-cyclohexanedione and p-toluidine in water were successfully carried out in the presence of p-dodecylbenezenesulfonic acid (DBSA) as a BrΦnsted acid-surfactant-combined catalyst. This method provides several advantages such as environment friendliness, high yields and simple work-up procedure. In addition, water was chosen as a green solvent.
100 citations
TL;DR: This work reviews one class of synthetic methods, direct condensation of a pre-formed aglycon unit with an appropriate sugar component, and its application in glycosylation of C-nucleosides.
Abstract: The study and synthesis of C-nucleosides has been extensive owing to their biological activity and potential as drug candidates for antiviral and anticancer therapy. Numerous synthetic strategies have also been investigated in order to optimize yields and stereoselectivity in the glycosylation reaction. Here we review one class of synthetic methods, direct condensation of a pre-formed aglycon unit with an appropriate sugar component.
TL;DR: In this article, a simple and general method for one-pot three-component synthesis of α-aminophosphonates catalyzed by several metal triflates was developed.
Abstract: A simple and general method has been developed for one-pot three-component synthesis of α-aminophosphonates catalyzed by several metal triflates [M(OTf) n , M = Li, Mg, Al, Cu, Ce] in the absence of solvent in good to highyields.
TL;DR: In this article, a review summarizes the recent developments in the rhodium-catalyzed intermolecular C-H insertion chemistry of diazo compounds and its application in total synthesis.
Abstract: The development of practical methods to achieve catalytic enantioselective methods for the transformation of C-H bonds is a research area of considerable current interest. This review summarizes the recent developments in the rhodium-catalyzed intermolecular C-H insertion chemistry of diazo compounds. The resulting rhodium carbenoid intermediates are capable of spectacular chemoselectivity in the C-H transformations, as long as the carbenoid is functionalized with both electron donor and acceptor groups. Examples will be given to illustrate the synthetic scope of this chemistry and its application in total synthesis. The reaction can be considered as a new strategic process for synthesis. This will be illustrated by examples of reactions which compliment some of the classic reactions of synthesis, such as the aldol reaction, the Mannich reaction, the Claisen rearrangement and the Michael addition.
TL;DR: In this paper, the deoxygenation of sulfoxides to sulfides was carried out by P(OPh 3 in mild conditions catalyzed by dichlorodioxomolybdenum(Vl).
Abstract: Chemoselective deoxygenation of sulfoxides to sulfides was carried out by P(OPh) 3 in mild conditions catalyzed by dichlorodioxomolybdenum(Vl).
TL;DR: The use of mo- lecular halogens for direct halogenation has drawbacks in the difficult and dangerous handling of chlorine and bro- mine, while iodine is less reactive.
Abstract: Oxidative iodination of arenes was carried out with one equivalent of KI and two equivalents of 30% hydrogen peroxide in MeOH in the presence of strong acid. Reactions of various substi- tuted anisoles, phenols and anilines, as well as mesitylene and uracil, were selective and effective with very good yields of isolated halogenated aromatic molecules. Halogenated organic molecules are important compounds in pharmaceutical and agricultural chemistry, 1 and they are important synthetic intermediates in chemical synthe- sis, especially for C-C coupling reactions. 2 The use of mo- lecular halogens for direct halogenation has drawbacks in the difficult and dangerous handling of chlorine and bro- mine, while iodine is less reactive. Nature has solved this problem by evolving haloperoxidases, enzymes that oxi- dize halide salts into reactive hypohalous derivatives. 3 Its counterpart in chemistry, named oxidative halogenation, has been utilized for iodination with a plethora of catalysts and oxidants in combination with molecular iodine or less
TL;DR: In this article, an array of aromatic aldehydes undergoes crossed aldol condensation with ketones in the presence of a catalytic amount of Yb(OTf) 3 under solvent-free conditions to afford the corresponding α,α'-bis(substituted benzylidene)cycloalkanones in excellent yields without occurrence of any side reactions.
Abstract: An array of aromatic aldehydes undergoes crossed aldol condensation with ketones in the presence of a catalytic amount of Yb(OTf) 3 under solvent-free conditions to afford the corresponding α,α'-bis(substituted benzylidene)cycloalkanones in excellent yields without occurrence of any side reactions. This method is very general, simple and environmental friendly in contrast with the existing methods, which use many classical Lewis acids. Furthermore, the catalyst can be recovered conveniently and reused efficiently without the loss of activity.
TL;DR: In this article, a useful method for oxidation of various thiols to their corresponding disulfides with 1,3-dibromo-5,5-dimethylhydantoin (DBDMH) in very short reaction times and mild conditions under both solution and solvent-free conditions is described.
Abstract: A useful method for oxidation of various thiols to their corresponding disulfides with 1,3-dibromo-5,5-dimethylhydantoin (DBDMH) in very short reaction times and mild conditions under both solution and solvent-free conditions is described.
TL;DR: In this paper, the biological relevance of C-substituted morpholines, their synthesis and important applications in other syntheses are discussed, and a review of morpholine synthesis is presented.
Abstract: C-Functionalized morpholines are found in a variety of natural products and biologically active compounds, but have also for other reasons been applied in organic synthesis. This review deals with the biological relevance of C-substituted morpholines, their synthesis and important applications in other syntheses. 1 Introduction 2 Biological Relevance of Morpholines 2.1 Naturally Occurring Morpholines 2.2 Bioactive Morpholines 2.2.1 Antidepressants 2.2.2 Appetite Suppressants 2.2.3 Antitumor Activity 2.2.4 Antioxidants 2.2.5 Miscellaneous 3 Morpholine Synthesis 3.1 Synthesis from Amino Alcohols 3.2 Synthesis from Epoxides 3.3 Synthesis via Organometallic Reactions 3.4 Synthesis from Olefins 3.5 Synthesis from Carboxylic Acid Derivatives 3.6 Miscellaneous 4 Morpholines as Synthetic Tools 4.1 The Williams Chiral Auxiliary 4.2 Chiral Auxiliaries 5 Conclusions.
TL;DR: In this paper, a mixture of α,β-unsaturated carbonyl compounds and OXONE® in CH 2 Cl 2 followed by treatment of Et 3 N in moderate to good yields.
Abstract: Mixtures of OXONE® and hydrobromic acid or hydro-chloric acid afford solutions of bromine or chlorine, respectively. α-Bromo- or a-chloro-α,β-unsaturated carbonyl compounds were prepared by addition of hydrobromic acid or hydrochloric acid to the mixture of α,β-unsaturated carbonyl compounds and OXONE® in CH 2 Cl 2 followed by treatment of Et 3 N in moderate to good yields.
TL;DR: These results demonstrate the utility of N-acylbenzotriazoles as mild S-ACYlating agents, especially when the corresponding acid chlorides are not readily available.
Abstract: Diverse thiol esters were synthesized in good to excellent yields (76-99%) by reactions of thiophenol, benzyl mercaptan, ethyl mercaptoacetate, and mercaptoacetic acid with N-acylbenzotriazoles under mild conditions. These results demonstrate the utility of N-acylbenzotriazoles as mild S-acylating agents, especially when the corresponding acid chlorides are not readily available.
TL;DR: The photochemical cycloaddition of benzene derivatives with alkenes yield polycyclic compounds, which are of great interest in organic synthesis as discussed by the authors, which are often followed by photochemical or thermal rearrangements.
Abstract: The photochemical cycloaddition of benzene derivatives with alkenes yield polycyclic compounds, which are of great interest in organic synthesis. Three modes are observed: [2+2] (ortho), [3+2] (meta) and, less frequently,[4+2] (para) photocycloaddition. The [3+2] cycloaddition has preferentially been studied and its intramolecular version was frequently applied to the synthesis of natural products. The [2+2] photocycloaddition is observed when electron active subsituents are present on the reaction partners. This mode is often followed by photochemical or thermal rearrangements. Furthermore, the [2+2] mode occurs concomitantly with the [3+2] photocycloaddition and leads frequently to complex reaction mixtures. More recent investigations deal with this item and show how the reaction may be directed to the [2+2] mode.
TL;DR: In this article, the synthesis of membrane-bound ion channels is reviewed and important results from several groups are highlighted and contributions from the authors' group are summarized, including synthetic approaches towards oligo-THF amino acids, oligopyrrolidines and gramicidin hybrid channels.
Abstract: Progress in the synthesis of membrane-bound ion channels is reviewed. Important results from several groups are highlighted and contributions from the authors' group are summarized. Topics covered include synthetic approaches towards oligo-THF amino acids, oligopyrrolidines and gramicidin hybrid channels. Points of interest are the importance of self-assembly systems, the functional analysis (ion selectivity, gating, asymmetric insertion and asymmetric function) and the structural characterization of the channel.
TL;DR: In this article, a 53-80% yield from anilines la-k by oxidation with H 2 O 2 catalysed with MoO 3 /KOH, ammonium molybdate or other molydenum salts is described.
Abstract: Nitroso arenes 2a-k are prepared in 53-80% yield from anilines la-k by oxidation with H 2 O 2 catalysed with MoO 3 /KOH, ammonium molybdate or other molybdenum salts. Further oxidation to nitro arenes 3a,d,j in 66-90% is also described.
TL;DR: In this article, the authors show that phenylenediamines undergo smooth condensation with ketones having hydrogens at α position on the surface of heteropoly acid (Ag 3 PW 1 2 O 4 0 ) under extremely mild conditions to afford the corresponding 1,5-benzodiazepines in excellent yields with high selectivity.
Abstract: o-Phenylenediamines undergo smooth condensation with ketones having hydrogens at α-position on the surface of heteropoly acid (Ag 3 PW 1 2 O 4 0 ) under extremely mild conditions to afford the corresponding 1,5-benzodiazepines in excellent yields with high selectivity. The catalyst can be recovered by simple filteration and can be reused in subsequent reactions.
TL;DR: In this article β-Keto esters react with a variety of amines in the presence of 0.1 equivalents of acetic acid without any solvents under ultrasound to give good yields of the corresponding p-enamino esters.
Abstract: β-Keto esters react with a variety of amines in the presence of 0.1 equivalents of acetic acid without any solvents under ultrasound to give good yields of the corresponding p-enamino esters.
TL;DR: Coupling an unprotected amino acid or dipeptide in partially aqueous solution with a readily available N-(Z-α-aminoacyl)benzotriazole or N-a-aminopetidoyl affords N-terminal-protected di-, tri-, and tetrapeptides in yields of 85-98% with minimal epimerization.
Abstract: Coupling an unprotected amino acid or dipeptide in partially aqueous solution with a readily available N-(Z-α-aminoacyl)benzotriazole or N-(Z-a-aminopetidoyl)benzotriazole affords N-terminal-protected di-, tri-, and tetrapeptides in yields of 85-98% (average 95% for 2a-i, 93% for 4a-f and 4a', 86% for 5a-b) with minimal epimerization.
TL;DR: A facile and efficient method for the preparation of α,α'-bis(substituted benzylidene)cycloalkanones is described for the first time using iodotrimethylsilane generated in situ from chlorotrim methylsilane and sodium iodidein acetonitrile.
Abstract: A facile and efficient method for the preparation of α,α'-bis(substituted benzylidene)cycloalkanones is described for the first time using iodotrimethylsilane generated in situ from chlorotrimethylsilane and sodium iodidein acetonitrile. The reaction proceeds rapidly at room temperature, giving high yields of products.
TL;DR: In this paper, a simple and chemoselective procedure for oxidizing sulfides to sulfoxides with 30% aqueous H 2 O 2 in phenol at room temperature is described.
Abstract: A novel, convenient and chemoselective procedure for oxidizing sulfides to sulfoxides with 30% aqueous H 2 O 2 in phenol at room temperature is described. The procedure is very simple and no strict conditions were requiredfor the selective conversion without affecting the functional groups even including the highly reactive aldehyde group. The reactions proceeded very quickly in excellent yields. Some experimental evidences are presented describing the role of the solvent.