Showing papers in "Advanced Synthesis & Catalysis in 2015"
TL;DR: This review highlights the advances in the rapidly growing field of amine-squaramide-catalyzed domino/cascade reactions and their mode of action.
Abstract: Organocatalytic domino/cascade reactions provide a convenient method for the construction of complex molecular structures bearing multiple stereocenters in a highly stereoselective fashion. Among various organocatalysts, bifunctional squaramides have emerged as powerful hydrogen-bonding catalysts for promoting a wide array of useful asymmetric organocascade sequences. Higher activity and ease of preparation make these catalysts excellent alternatives for thiourea-based organocatalysts. This review highlights the advances in the rapidly growing field of amine-squaramide-catalyzed domino/cascade reactions and their mode of action.
428 citations
TL;DR: Recent advances and strategies for transition metal-catalyzed CH activation of indoles and a versatile tool box for the preparation of structurally diverse indoles are discussed.
Abstract: The last decades have seen a tremendous expanse in the application of CH activation of many different substrate classes, including the invaluable indole scaffold. Following the exciting emergence of CH activation as a multi-faceted platform for functionalization, a versatile tool box has been developed for the preparation of structurally diverse indoles. This review article discusses recent advances and strategies for transition metal-catalyzed CH activation of indoles.
335 citations
TL;DR: In this paper, a review of the recent developments to perform heterogeneous catalysis in continuous-flow microreactors is presented, where three different types of catalysts, namely, packed-bed, monolithic, and wall-coated, are discussed.
Abstract: This review surveys the recent developments to perform heterogeneous catalysis in continuous-flow microreactors. Three different types, namely, (i) packed-bed, (ii) monolithic, and (iii) wall-coated approaches are discussed to implement various kinds of catalysts in a microreactor. In addition, the applications of these supported catalysts to perform a variety of organic reactions are described. Furthermore, advantages of catalytic microreactors over classical batch reactors on one or more aspects of the reaction, such as rate, conversion, selectivity, and enantioselectivity are presented
258 citations
TL;DR: Isoxazoles are important five-membered aromatic heterocycles in organic chemistry and many exciting advances in the synthesis and functionalization of isoxazoles have been reported as mentioned in this paper.
Abstract: Isoxazoles are important five-membered aromatic heterocycles in organic chemistry. Recently, many exciting advances in the synthesis and functionalization of isoxazoles have been reported. New transition metal-catalyzed reactions have resulted in the development of attractive and highly efficient synthetic approaches to densely functionalized isoxazoles. Complete control of regioselectivity can be achieved on the basis of a judicious choice of metal catalyst and reaction partners using dipolar cycloaddition and cycloisomerization reactions, while more recent studies have focused on the site-selective functionalization of isoxazoles via CH functionalization. New strategies for the use of isoxazoles as scaffolding templates in asymmetric synthesis have emerged, thus opening new prospects for the synthesis of enantioenriched motifs under the conditions that are orthogonal to other transformations. In this review, recent advances involving the synthesis and reactivity of isoxazoles are summarized. The review covers the period from January 2005 to June 2015.
234 citations
TL;DR: This review provides a comprehensive overview of biocatalytic imine reduction and reductive amination of ketones, highlighting the natural roles, substrate scopes, structural features, and potential application fields of the involved enzymes.
Abstract: Chiral amines represent a prominent functional group in pharmaceuticals and agrochemicals and are hence attractive targets for asymmetric synthesis. Since the pharmaceutical industry has identified biocatalysis as a valuable tool for synthesising chiral molecules with high enantiomeric excess and under mild reaction conditions, enzymatic methods for chiral amine synthesis are increasing in importance. Among the strategies available in this context, the asymmetric reduction of imines by NAD(P)H-dependent enzymes and the related reductive amination of ketones have long remained underrepresented. However, recent years have witnessed an impressive progress in the application of natural or engineered imine-reducing enzymes, such as imine reductases, opine dehydrogenases, amine dehydrogenases, and artificial metalloenzymes. This review provides a comprehensive overview of biocatalytic imine reduction and reductive amination of ketones, highlighting the natural roles, substrate scopes, structural features, and potential application fields of the involved enzymes.
175 citations
TL;DR: In this article, the synthesis of vinyl sulfones from aryl sulfinates and alkenes by a photoredox process was described, and a broad reaction scope was defined in a wide range of materials.
Abstract: Visible light and eosin Y catalyze the synthesis of vinyl sulfones from aryl sulfinates and alkenes by a photoredox process. The reaction scope is broad in aryl sulfinates and alkenes and the general and simple procedure provides a metal-free alternative for the synthesis of synthetically valuable vinyl sulfones.
163 citations
TL;DR: A mild metal-free photocatalytic aerobic oxidation of thiols to disulfides using Eosin Y and visible-light irradiation is described, enabling the preparation of disulfide with high purity in a time-frame of minutes.
Abstract: Disulfides represent significant molecular and structural features in various biologically active compounds and fine chemicals. Therefore, the development of mild, efficient and sustainable methods to access disulfides is of great importance. Here, we describe the development of a mild metal-free photocatalytic aerobic oxidation of thiols to disulfides using Eosin Y and visible-light irradiation. A continuous flow procedure was developed to accelerate the photocatalytic process, enabling the preparation of disulfides with high purity in a time-frame of minutes. The mildness and applicability of our method was exemplified by the flow synthesis of the cyclic peptide hormone, oxytocin, requiring only a 200 s reaction time and an efficient one-pot batch protocol for the preparation of the therapeutic thiuram disulfide, disulfiram.
151 citations
TL;DR: In this paper, the transition metal catalysts are the most crucial factor that controls the selectivity in the nitrile hydrogenation reaction and the effect of reaction parameters, selectivity to different substrate structures and reaction mechanisms.
Abstract: Amines are important building blocks possessing various applications in agrochemicals, the fine chemical industry, pharmaceuticals, materials science and biotechnology. The catalytic hydrogenation of nitriles is an important reaction for the one-step synthesis of diverse amines. However, significant amounts of side product formation during the course of the reaction is a major issue. In recent years, an enormous amount of work has been reported using both homogeneous and heterogeneous transition metal complex catalysts for the selective reduction of nitriles. Transition metal catalysts are the most crucial factor that controls the selectivity in this reaction. Therefore, transition metal catalysts are the central point of this review. We have also briefly discussed the effect of reaction parameters, selectivity to different substrate structures and reaction mechanisms. This review provides an overview of recent developments in transition metal-catalyzed nitrile reduction along with examples which highlight its vast potential in organic transformations.
140 citations
136 citations
TL;DR: Ruthenium pincer complexes (RPCs) exhibit a versatile chemistry, serve as excellent precursors and find potential applications in many organic transformations as discussed by the authors, and a large number of novel and valuable reactions has been developed using both stoichiometric and catalytic amounts of RPCs.
Abstract: Pincer-based catalysts possess an exceptional balance of stability versus reactivity, aspects of fundamental interest in catalyst design. This balance has been well-controlled by systematic ligand modifications along with the variation of the metal center. Ruthenium pincer complexes (RPCs), exhibit a versatile chemistry, serve as excellent precursors and find potential applications in many organic transformations. A large number of novel and valuable reactions has been developed using both stoichiometric and catalytic amounts of RPCs. Compared to the traditional ruthenium catalysts, pincer complexes often present high efficiency, selectivity and functional group tolerance. This review highlights different methodologies for the synthesis of RPCs and their catalytic applications for different reactions reported in the last decade. Additionally, the factors affecting the catalytic reactivity of the RPCs and the reaction mechanisms are discussed.
124 citations
TL;DR: A review of recent advances in this area can be found in this article, mainly including C-methylation, N-methylations, and O-methylization, and the respective reaction mechanisms are also discussed.
Abstract: Methylation is one of the most fundamental synthetic transformations in organic chemistry, but usually employs hazardous and toxic reagents, such as methyl iodide, dimethyl sulfate, diazomethane and dimethyl carbonate. In order to address sustainable development and green strategies, synthetic chemists have devoted much effort to the discovery and development of new methylating reagents, which are successfully being applied in transition metal-catalyzed cross-coupling reactions. In this review, recent advances in this area are summarized, mainly including C-methylation, N-methylation and O-methylation. The respective reaction mechanisms are also discussed.
TL;DR: In this article, a review article reports new procedures and practical application of the nitro to carbonyl conversion that appeared in the literature after our comprehensive report published in 2004, and new procedures including the utilization of molecular oxygen and photoredox catalysis have been introduced for the Nef reaction.
Abstract: This review article reports new procedures and practical application of the nitro to carbonyl conversion that appeared in the literature after our comprehensive report published in 2004. Beside traditional and well explored reactant systems, new procedures including the utilization of molecular oxygen and photoredox catalysis have been introduced for the Nef reaction. Of notable interest is the utilization of the nitro to carbonyl conversion in tandem and cascade processes aimed at the preparation of hetero and carbocyclic derivatives.
TL;DR: In this article, an electrophilic trifluoromethylthiolating reagent for a broad scope of hetero-arenes, electron-donating group (EDG)-activated benzenes, and several electron-rich olefins was applied.
Abstract: (N-Trifluoromethylthio) saccharin has been applied as an electrophilic trifluoromethylthiolating reagent for a broad scope of heteroarenes, electron-donating group (EDG)-activated benzenes, and several electron-rich olefins. Iron(III) and gold(III) catalysts showed complementary activity for different substrates.
TL;DR: In this paper, a protocol for C-7 cyanated indolines and C-2c yanated indole with high site selectivity and excellent functional group tolerance is described.
Abstract: Th er hodium-catalyzed selective cyana- tion of C¢ Hb onds of indolines an di ndole sw ith N- cyano-N-phenyl-para-methylbenzenesulfonamide is described. This protocol offer sa facile access to C-7 cyanated indolines and C- 2c yanated indole sw ith high site selectivity and excellent functional group tolerance.
TL;DR: In this article, a review of the transition metal-free direct (hetero)arylation reactions of hetero-arenes is presented, which provides a thorough insight into the synthetic and mechanistic aspects of these atom economic and environmentally benign reactions also highlighting their advantages and possible disadvantages compared to conventional methods for the synthesis of arylheteroarenes.
Abstract: In recent years, environmental and economic reasons have motivated the development of transition metal-free carbon-carbon bond forming reactions and some excellent reviews have covered this research area of particular interest for the pharmaceutical industry. However, none of these reviews has been specifically dedicated to summarize and discuss the results achieved in the rapidly growing field of the transition metal-free direct (hetero)arylation reactions of heteroarenes. This review, which covers the literature from 2008 to 2014, aims to provide a thorough insight into the synthetic and mechanistic aspects of these atom economic and environmentally benign reactions also highlighting their advantages and possible disadvantages compared to conventional methods for the synthesis of arylheteroarenes and biheteroaryls via transition metal-catalyzed reactions.
TL;DR: A Cinchona alkaloid-derived squaramide-catalyzed asymmetric cycloaddition of trfluoromethyl-containing azomethine ylides with beta-nitroalkenes was realized under mild conditions as discussed by the authors.
Abstract: A Cinchona alkaloid-derived squaramide-catalyzed asymmetric cycloaddition of trfluoromethyl-containing azomethine ylides with beta-nitroalkenes was realized under mild conditions. A series of biologically important 5'-trifluoromethyl-spiro[pyrrolidin-3,2'-oxindoles] was synthesized efficiently by this process in excellent yields, enantioseletivities and diastereoselectivities.
TL;DR: In this article, a simple, practical, and metal-free protocol was developed for the synthesis of sulfonamides from sodium sulfinates and various amines through an iodine-mediated S¢N bond formation reaction at room temperature.
Abstract: A simple, practical, and metal-free protocol has been developed for the synthesis of sulfonamides from sodium sulfinates and various amines through an iodine-mediated S¢N bond formation reaction at room temperature. This green reaction is cost-effective, operationally straightforward, and especially proceeds under very mild conditions to afford the target products in good to excellent yields (up to 98%).
TL;DR: Mechanistic insights suggest the formation of a Co(III)-aryl key species via a rate-determining arene C[BOND]H activation during the annulation reaction.
Abstract: The use of cobalt as catalyst in direct C[BOND]H activation protocols as a replacement for more expensive second row transition metals is currently attracting significant attention. Herein we disclose a facile cobalt-catalyzed C[BOND]H functionalization route towards sultam motifs through annulation of easily prepared aryl sulfonamides and alkynes using 8-aminoquinoline as a directing group. The reaction shows broad substrate scope with products obtained in a highly regioselective manner in good to excellent isolated yields. Mechanistic insights suggest the formation of a Co(III)-aryl key species via a rate-determining arene C[BOND]H activation during the annulation reaction.
TL;DR: In this paper, a practical and functional group-tolerant chemoselective preparation of various (E)-vinyl esters from readily available (α,β-unsaturated ketones is described.
Abstract: A practical and functional group-tolerant chemoselective preparation of various (E)-vinyl esters from readily available (E)-α,β-unsaturated ketones is described.
TL;DR: In this paper, an efficient SN1-type reaction of 3-indolylmethanols with miscellaneous nucleophiles is described, featuring a catalyst-free procedure, low cost, wide substrate scope and mild reaction conditions.
Abstract: This paper describes an efficient SN1-type reaction of 3-indolylmethanols with miscellaneous nucleophiles, featuring a catalyst-free procedure, low cost, wide substrate scope and mild reaction conditions. This approach provides green and efficient methods for the synthesis of diverse 3-substituted indolyl derivatives as well as unsymmetrical bisindolylmethanes and triarylmethanes.
TL;DR: Under zinc Lewis acid catalysis, terminal alkynes coupled dehydrogenatively with 1,8-naphthalenediaminatoborane [HB(dan] as mentioned in this paper, and the resulting alkynylboranes with an C(sp)B(dan) bond are isolable by column chromatography on silica gel (SiO2) and are usable as coupling partners for palladium and copper-catalyzed cross-coupling reactions with (hetero)aryl halides.
Abstract: Under zinc Lewis acid catalysis, terminal alkynes coupled dehydrogenatively with 1,8-naphthalenediaminatoborane [HB(dan)]. It is important to note that the resulting alkynylboranes with an C(sp)B(dan) bond are isolable by column chromatography on silica gel (SiO2) and are usable as coupling partners for palladium- and copper-catalyzed cross-coupling reactions with (hetero)aryl halides.
TL;DR: In this paper, a 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) was used as a catalysts for the hydrogenation of carbon dioxide to formate.
Abstract: Hydrogenation of carbon dioxide to formate was achieved using copper (Cu) catalysts in the presence of strong organic bases including amidines and guanidines. Specifically, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) proved to be effective for the transformation of a 1:1 mixture of hydrogen and carbon dioxide into its formate salt under increased pressure in the presence of various Cu(I) and Cu(II) salts at 100 °C. A novel complex derived from copper iodide and DBU equally promoted the same reaction, indicating that DBU–Cu species are involved as real catalysts in this hydrogenation.