Showing papers in "Advanced Synthesis & Catalysis in 2012"
TL;DR: In this paper, the authors focus on two unique aspects of modern flow chemistry where substantial advantages over the corresponding batch processes have become evident, namely, the ability to carry out multistep synthesis by designing a flow set-up composed of several flow reactors.
Abstract: Laboratory scaled flow-through processes have seen an explosive development over the past decade and have become an enabling technology for improving synthetic efficiency through automation and process optimization. Practically, flow devices are a crucial link between bench chemists and process engineers. The present review focuses on two unique aspects of modern flow chemistry where substantial advantages over the corresponding batch processes have become evident. Flow chemistry being one out of several enabling technologies can ideally be combined with other enabling technologies such as energy input. This may be achieved in form of heat to create supercritical conditions. Here, indirect methods such as microwave irradiation and inductive heating have seen widespread applications. Also radiation can efficiently be used to carry out photochemical reactions in a highly practical and scalable manner. A second unique aspect of flow chemistry compared to batch chemistry is associated with the option to carry out multistep synthesis by designing a flow set-up composed of several flow reactors. Besides their role as chemical reactors these can act as elements for purification or solvent switch.
546 citations
TL;DR: The field of asymmetric organocatalytic biomolecular cascades has become one of the most fascinating and current fields in organic chemistry as discussed by the authors, and the literature has been rapidly developing.
Abstract: Since about the year 2000, the research area of asymmetric organocatalysis has grown rapidly to become one of the most fascinating and current fields in organic chemistry. In the last years, asymmetric domino reactions have widely benefited from this fast-growing field, as exemplified by the development of an explosive number of novel and powerful asymmetric organocatalytic domino processes, which allowed the easy construction of complex chiral molecular architectures from simple materials with high yields and very often remarkable enantioselectivities in a metal-free environment. Indeed, the possibility to join two or more organocatalytic reactions in one asymmetric domino process has become a challenging goal for chemists, due to several advantages from economical and environmental points of view, avoiding costly protecting groups and time-consuming purification procedures after each step, for example. This review aims to update the latest developments of this hot and fascinating field, covering the literature since the beginning of 2009.
Abbreviations: Ac: acetyl; Ar: aryl; BDHP: 1,1′-binaphth-2,2′-diyl hydrogen phosphate; BA: Bronsted acid; BINAPO: 2-diphenylphosphino-2′-diphenylphosphinyl-1,1′-binaphthalene; BINOL: 1,1′-bi-2-naphthol; Boc: tert-butoxycarbonyl; Bn: benzyl; Bu: butyl; Bz: benzoyl; CSA: camphorsulfonic acid; Cy: cyclohexyl; Cbz: benzyloxycarbonyl; DABCO: 1,4-diazabicyclo[2.2.2]octane; DBU: 1,8-diazabicyclo[5.4.0]undec-7-ene; DCE: dichloroethane; de: diastereomeric excess; DFT: density functional theory; DHQ: hydroquinine; DHQD: dihydroquinidine; DIPEA: diisopropylethylamine; DKR: dynamic kinetic resolution; DMAD: dimethyl acetylenedicarboxylate; E: electrophile; ee: enantiomeric excess; ESI: electrospray ionization; Et: ethyl; Fu: furyl; Hept: heptyl; Hex: hexyl; HOMO: highest occupied molecular orbital; IBX: o-iodoxybenzoic acid; LB: Lewis base; LUMO: lowest unoccupied molecular orbital; Me: methyl; MOM: methoxymethyl; Mes: mesyl; MS: mass spectroscopy; MTBE: methyl tert-butyl ether; NADH: nicotinamide adenine dinucleotide; Naph: naphthyl; NHC: N-heterocyclic carbene; NMM: N-methylmorpholine; NMP: N-methylpyrrolidinone; Ns: nosyl; Nu: nucleophile; Oct: octyl; PCC: pyridinium chlorochromate; Pent: pentyl; PFBA: pentafluorobenzoic acid; Ph: phenyl; PMB: para-methoxybenzyl; Pr: propyl; Py: pyridine; r.t.: room temperature; TBA: tribromoacetic acid; TBS: tert-butyldimethylsilyl; TCBA: 2,4,6-trichlorobenzoic acid; TES: triethylsilyl; TFA: trifluoroacetic acid; THF: tetrahydrofuran; Thio: thiophene; TMEDA: tetramethylethylenediamine; TMS: trimethylsilyl; Tol: tolyl; Ts: 4-toluenesulfonyl (tosyl).
505 citations
TL;DR: A historical perspective on the underlying discoveries that led to the current state of the art, a mechanistic description of these reactions, and a summary of the recent advances in this area are provided.
Abstract: N-heterocyclic carbenes are well known for their role in catalyzing benzoin and Stetter reactions: the generation of acyl anion equivalents from simple aldehydes to react with a variety of electrophiles. However, when an aldehyde bearing a leaving group or unsaturation adjacent to the acyl anion equivalent is subjected to an NHC, a new avenue of reactivity is unlocked, leading to a number of novel transformations which can generate highly complex products from simple starting materials, many of which are assembled through unconventional bond disconnections. The field of these new reactions - those utilizing α-reducible aldehydes to access previously unexplored catalytic intermediates – has expanded rapidly in the past eight years. This review aims to provide the reader with a historical perspective on the underlying discoveries that led to the current state of the art, a mechanistic description of these reactions, and a summary of the recent advances in this area.
327 citations
TL;DR: In this article, an iron(III) amine triphenolate complex, [FeTPhOA]2, is described, able to efficiently catalyze the cycloaddition of carbon dioxide to a range of terminal epoxides under mild conditions.
Abstract: An iron(III) amine triphenolate complex, [FeTPhOA]2, able to efficiently catalyze the cycloaddition of carbon dioxide to a range of terminal epoxides under mild conditions, is described. In addition, it has also been found that the complex is able to catalyze the conversion with more sterically congested oxiranes and oxetanes which are generally considered challenging substrates to activate. Variation of the co-catalyst, required for ring-opening of the substrates, has also been examined. The results show that terminal epoxide substrates are converted more efficiently with an iodide co-catalyst, whereas more bulky oxirane substrates give better product yields in the presence of a bromide co-catalyst. The combined results demonstrate the broad applicability of these iron(III) complexes in this type of carbon dioxide fixation chemistry.
239 citations
TL;DR: A series of easily accessible arene-1,2-diynes, bearing one aryl substituent on one of the alkynyl groups, is readily converted to dibenzopentalenes in good yields by gold(I) catalysts.
Abstract: A series of easily accessible arene-1,2-diynes, bearing one aryl substituent on one of the alkynyl groups, is readily converted to dibenzopentalenes in good yields by gold(I) catalysts The participation of gold acetylides could be proven by the direct conversion to the corresponding gem-diaurated dibenzopentalenes with a gold catalyst From an experiment with a gold acetylide complex and stoichiometric amounts of the gold “catalyst” the corresponding gem-diaurated complex of a dibenzopentalene could be obtained and characterized by X-ray crystal structure analysis Labelling studies with deuterated alkynes show the expected deuteration of the two remaining positions of the pentalene core All this provides evidence for a dual activation mode of the reaction and gold(I) vinylidene complexes as intermediates of the catalytic cycle
225 citations
TL;DR: In this article, a new strategy for the generation of carbon-centered radicals via oxidation of alkyl-, allyl-, benzyl- and arylborates by visible-light-driven single electron transfer (SET) photoredox catalysis has been established.
Abstract: A new strategy for the generation of carbon-centered radicals via oxidation of alkyl-, allyl-, benzyl- and arylborates by visible-light-driven single electron transfer (SET) photoredox catalysis has been established. The generated radicals smoothly react with TEMPO and electron-deficient alkenes to afford CO and CC coupling products, respectively. In this radical initiating system, cyclic organo(triol)borates turn out to be useful radical precursors.
181 citations
TL;DR: A photoredox palladium/iridium-catalyzed C-H arylation with diaryliodonium reagents that is believed to proceed via an 'ionic' 2e- pathway and requires a much higher reaction temperature (100 ºC).
Abstract: This paper describes a photoredox palladium/iridium-catalyzed C-H arylation with diaryliodonium reagents. Details of the reaction optimization, substrate scope, and mechanism are presented along with a comparison to a related method in which aryldiazonium salts are used in place of diaryliodonium reagents. The unprecedentedly mild reaction conditions (25 oC in methanol), the requirement for light and a photocatalyst, the inhibitory effect of radical scavengers, and the observed chemoselectivity trends are all consistent with a radical-thermal reaction with diaryliodonium reagents that is believed to proceed via an 'ionic' 2e- pathway and requires a much higher reaction temperature (100 oC).
180 citations
TL;DR: In this article, the major progress in the field of enantioselective one-, two-, and multi-component domino reactions promoted by chiral metal catalysts, covering the literature since the beginning of 2012, is discussed.
Abstract: This review updates the major progress in the field of enantioselective one-, two-, and multi-component domino reactions promoted by chiral metal catalysts, covering the literature since the beginning of 2012. It illustrates how enantioselective metal-catalyzed processes have emerged as outstanding tools for the development of a wide variety of fascinating one-pot asymmetric domino reactions, allowing complex and diverse structures to be easily generated from simple materials in a single step. During the last 4 years, a myriad of already existing as well as completely novel and powerful asymmetric domino processes have been developed on the basis of asymmetric metal catalysis, taking economical advantages, such as avoiding costly protecting groups and time-consuming purification procedures after each step. Abbreviations: acac: acetylacetonate; Ad: 1-adamantyl; Ar: aryl; BArF: tetrakis[3,5-bis(trifluoromethyl)phenyl]borate; BBN: 9-borabicyclo[3.3.1]nonane; BINAP: 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl; BINAP(O): 2-diphenylphosphino-2′-diphenylphosphinyl-1,1′-binaphthalene; BINOL: 1,1′-bi-2-naphthol; BIPHEP: 2,2′-bis(diphenylphosphino)-1,1′-biphenyl; Bipy: bipyridine; Bn: benzyl; Boc: tert-butoxycarbonyl; bod: bicyclo[2.2.2]octane-2,5-diene; Box: bisoxazoline; bpe: 1,2-bis(2-pyridyl)ethane; Bs: p-bromobenzenesulfonyl (brosyl); Bz: benzoyl; Cat: catalyst; Cbz: benzyloxycarbonyl; CMOF: chiral mixed metal-organic framework; cod: cyclooctadiene; coe: cyclooctene; Cp: cyclopentadienyl; CPME: cyclopentyl methyl ether; Cy: cyclohexyl; DABCO: 1,4-diazabicyclo[2.2.2]octane; dba: (E,E)-dibenzylideneacetone; DBDMH: 1,3-dibromo-5,5-dimethylhydantoin; DCE: dichloroethane; de: diastereomeric excess; Dec: decyl; DET: diethyl tartrate; DIPEA: diisopropylethylamine; DME: 1,2-dimethoxyethane; DMF: N,N-dimethylformamide; DTBM: di-tert-butylmethoxy; ee: enantiomeric excess; EWG: electron-withdrawing group; Fesulphos: 1-phosphino-2-sulfenylferrocene; Hept: heptyl; Hex: hexyl; HFIPA: hexafluoroisopropyl alcohol; HMPA: hexamethylphosphoramide; JohnPhos: (2-biphenyl)di-tert-butylphosphine; Josiphos: 1-[2-(diphenylphosphino)ferrocenyl]ethyldicyclohexylphosphine ethanol adduct; L: ligand; Mandyphos: 1,1′-bis[(dimethylamino)benzyl]-2,2′-bis(diphenylphosphino)ferrocene; Me-DuPhos: 1,2-bis(2,5-dimethylphospholano)benzene; MOM: methoxymethyl; Ms: mesyl; MS: molecular sieves; MTBE: methyl tert-butyl ether; Naph: naphthyl; NBS: N-bromosuccinimide; Ns: nosyl (4-nitrobenzenesulfonyl); Oct: octyl; Pent: pentyl; Phos: phosphinyl; Phox: phosphinooxazoline; Pin: pinacolato; PG: protecting group; Phth: phthalimido; Piv: pivaloyl; PMB: p-methoxybenzyl; PMP: 1,2,2,6,6-pentamethylpiperidine; PTAD: 4-phenyl-1,2,4-triazoline-3,5-dione; Py: pyridyl; Pybox: 2,6-bis(2-oxazolyl)pyridine; QUINOX: (quinolin-2-yl)-oxazoline; rs: regioselectivity ratio; r.t.: room temperature; SDS: sodium dodecyl sulfate; Segphos: 5,5′-bis(diphenylphosphino)-4,4′-bi-1,3-benzodioxole; SES: β-trimethylsilylethanesulfonyl; Taniaphos: [2-diphenylphosphinoferrocenyl](N,N-dimethylamino)(2-diphenylphosphinophenyl)methane; TBS: tert-butyldimethylsilyl; TEA: trimethylamine; Tf: trifluoromethanesulfonyl; TFA: trifluoroacetic acid; THF: tetrahydrofuran; TIPS: triisopropylsilyl; TMG: 1,1,3,3-tetramethylguanidine; TMS: trimethylsilyl; Tol: tolyl; Ts: 4-toluenesulfonyl (tosyl); VANOL: 3,3′-diphenyl-2,2′-bi-1-naphthol; Walphos: 1-{2-[2′-(diphenylphosphino)phenyl]ferrocenyl}ethyldi[3,5-bis(trifluoromethyl)phenyl]phosphine; Xyl: 3,5-dimethylphenyl.
175 citations
TL;DR: An N-heterocyclic carbene (NHC) polymer supported silver nanoparticle catalyst system was developed in this paper, which demonstrated high activity and excellent stability and reusability in the carboxylation of terminal alkynes with carbon dioxide at ambient conditions.
Abstract: An N-heterocyclic carbene (NHC) polymer supported silver nanoparticle catalyst system was developed. The novel nano-composite catalyst demonstrated very high activity and excellent stability and reusability in the carboxylation of terminal alkynes with carbon dioxide at ambient conditions. The unique N-heterocyclic carbene polymer and silver nanoparticle composite structure provided a synergistic effect on activation of terminal alkynes and carbon dioxide that contributed to the high catalytic activity. The poly-NHC-silver catalyst exhibited excellent substrate generality and tolerance to various functionalities. In addition, the catalyst is stable to air and moisture and can be easily recovered and reused.
170 citations
TL;DR: In this article, a magnetic nanoparticle-supported palladium catalyst has been developed for the Suzuki, Sonogashira and Heck reactions, and the performance of the magnetic separation of the catalyst was very efficient, and it was possible to recover and reuse it at least eight times without significant loss of its catalytic activity.
Abstract: A highly efficient, air- and moisture-stable and easily recoverable magnetic nanoparticle-supported palladium catalyst has been developed for the Suzuki, Sonogashira and Heck reactions. A wide range of substrates was coupled successfully under aerobic conditions. In particular, the performance of the magnetic separation of the catalyst was very efficient, and it is possible to recover and reuse it at least eight times without significant loss of its catalytic activity.
169 citations
TL;DR: In this paper, the gold-and palladium-catalysed cross-coupling reactions were investigated on two substrates containing an aryl iodide and an allenoate ester.
Abstract: Two substrates containing an aryl iodide and an allenoate ester were prepared and the gold-induced cycloisomerisation to vinylgold(I) species and their proto-deauration as well as the intramolecular palladium-catalysed cross-coupling reactions were investigated. Switching to catalytic amounts of gold and palladium and stoichiometric amounts of silver did indeed furnish the product of a cycloisomerisation/intramolecular cross-coupling. Control experiments revealed that silver cannot substitute for gold or palladium in these reactions, but a different palladium catalyst in a different oxidation state also afforded the cycloisomerisation/intramolecular cross-coupling products in only slightly reduced yields. By ICP analysis the palladium was shown to contain gold only at the sub-ppm level. This shows how carefully results obtained with such systems have to be interpreted. Then a series of allylic and benzylic o-alkynylbenzoates were investigated in gold- and palladium-catalysed reactions. For esters of benzyl alcohol and cinnamyl alcohol no palladium co-catalyst was needed for the conversion. All reagents were thoroughly checked for palladium traces by ICP analysis in order to thoroughly exclude a gold/palladium co-catalysis. Optimisation of the gold complex, counter ion and solvent showed that gold(I) isonitrile pre-catalysts and silver triflate as activator in dioxane are suitable to convert a number of substrates with aryl, alkyl and even cyclopropyl substituents. Crossover experiments proved an intermolecular allyl transfer.
TL;DR: In this article, an efficient metal-free oxidative esterification of benzyl CH bonds was developed using tetrabutylammonium iodide as catalyst and tert-butyl hydroperoxide as co-oxidant.
Abstract: An efficient metal-free oxidative esterification of benzyl CH bonds was developed. Using tetrabutylammonium iodide as catalyst and tert-butyl hydroperoxide as co-oxidant, benzylic substrates could react smoothly with various carboxylic acids to give the esters with good to excellent yields. The method was also suitable for the O-protection of N-Boc amino acids. The reaction mechanism was primarily investigated and a radical process was proposed.
TL;DR: In this paper, simple copper(I) chloride (CuCl) salt, in the absence of Pd and ligands, can catalyze the Sonogashira reaction with high yields (80-99%) under blue LED light irradiation at room temperature.
Abstract: The conventional thermal Sonogashira CC coupling reaction requires the use of a palladium catalyst and a large amount of ligands Although there were a few reports describing the use of inexpensive metal catalysts, such as, copper (Cu), iron (Fe), and nickel (Ni), for replacement of palladium (Pd) in the Sonogashira reactions, it was later questioned that the observed effects were due to ppb levels contamination of Pd present in the reagents used in the reactions Herein, we report that simple copper(I) chloride (CuCl) salt, in the absence of Pd and ligands, can catalyze the Sonogashira reaction with high yields (80–99%) under blue LED light irradiation at room temperature Control experiments show that no cross-coupling product was formed, when palladium(II) chloride (PdCl2) was used to replace CuCl as a catalyst A series of electron-rich and electron-poor substituted aryl halides (bromides and iodides) as well as aryl- and alkylacetylenes are examined and the reaction mechanism is discussed
TL;DR: The application of this novel amide formation reaction to the synthesis of pharmaceuti- cal compounds has been successfully demonstrated and a wide range of amides have been obtained under mild conditions.
Abstract: A practical and efficient method for the synthesis of amides has been developed by iron-cat- alysed oxidative amidation of aldehydes with amine hydrochloride salts. A wide range of amides have been obtained in good to excellent yields under mild conditions. The application of this novel amide formation reaction to the synthesis of pharmaceuti- cal compounds has been successfully demonstrated.
TL;DR: In this article, the inorganic, magnetic, solid acid catalyst was characterized via Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), XPS, transmission electron microscopy (TEM), dynamic light scattering (DLS), vibrating sample magnetometer (VSM), and titration.
Abstract: Surface functionalization of magnetic particles is an elegant way to bridge the gap between heterogeneous and homogeneous catalysis. The introduction of magnetic particles (MPs) in a variety of solid matrices allows the combination of well-known procedures for catalyst heterogenization with techniques for magnetic separation. We have conveniently loaded sulfonic acid groups on magnetic particles supports in which chlorosulfonic acid is used as sulfonating agent. The main targets are room temperature, solvent-free conditions, rapid (immediately) and easy immobilization technique, and low cost precursors for the preparation of highly active and stable MPs with high densities of functional groups. The inorganic, magnetic, solid acid catalyst was characterized via Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), dynamic light scattering (DLS), vibrating sample magnetometer (VSM) and titration. The catalyst is active for the Hantzsch reaction and the products are isolated in high to excellent yields (90–98%). Supporting this acid catalyst on magnetic particles offers a simple and non-energy-intensive method for recovery and reuse of the catalyst by applying an external magnet. Isolated catalysts were reused for new rounds of reactions without significant loss of their catalytic activity.
TL;DR: Zinc is the 24th most abundant element in the Earth's crust and has been widely used as a catalysts in the last three decades as mentioned in this paper ; however, the main application of zinc metal is as materials.
Abstract: Zinc is the 24th most abundant element in the Earth’s crust. Since the discovery of pure zinc metal in the 18th century, the main application of zinc metal is as materials. Because zinc salts are abundant, cheap, non-toxic, and exhibit environmentally benign properties, organic chemists have been interested in using zinc salts as catalysts in organic synthesis during the last three decades. Within this review, we have summarized the progress on applications of zinc salts in organic reactions. Our the target is to emphasize the special properties of zinc catalysts, and further promote the interest of organic chemists.
TL;DR: In this article, a copper catalyst bearing a suitable Xantphos derivative or NHC ligand was found to be highly efficient for the selective semihydrogenation of non-polar unsaturated compounds using a mixture of a silane and an alcohol as reducing agent.
Abstract: A copper catalyst bearing a suitable Xantphos derivative or NHC ligand was found to be highly efficient for the selective semihydrogenation of non-polar unsaturated compounds using a mixture of a silane and an alcohol as reducing agent. The catalytic system was useful for the selective semihydrogenation of internal alkynes to (Z)-alkenes with suppression of overreduction to the corresponding alkanes. Furthermore, semihydrogenations of terminal alkyne, 1,2-diene, 1,3-diene, 1,3-enyne and 1,3-diyne systems were also achieved selectively.
TL;DR: The eosin Y-catalyzed borylation of aryldiazonium salts under irradiation with visible light has been developed and provides an attractive route for the prepared arylboronates due to its operational simplicity and practicability as well as the mild reaction conditions.
Abstract: The eosin Y-catalyzed borylation of aryldiazonium salts under irradiation with visible light has been developed. This novel protocol provides an attractive route for the preparation of arylboronates, due to its operational simplicity and practicability as well as the mild reaction conditions.
TL;DR: A metal-free, visible light-induced [4+2]-benzannulation of biaryldiazonium salts with alkynes was developed in this paper, where eosin Y was used as photoredox catalyst.
Abstract: A metal-free, visible light-induced [4+2] benzannulation of biaryldiazonium salts with alkynes was developed. With eosin Y as photoredox catalyst, a variety of 9-substituted or 9,10-disubstituted phenanthrenes were obtained via a cascade radical addition and cyclization sequence.
TL;DR: This critical review with 341 references covers developments on the chemo- and site-selective Suzuki–Miyaura monocoupling reactions of polyhalogenated heteroarenes with different or identical halogen atoms.
Abstract: The palladium-catalyzed Suzuki–Miyaura reaction of multiply halogenated, electron-rich and electron-deficient heteroarenes is one of the most reliable and environmentally friendly tools for installing a wide range of non-functionalized and functionalized carbon substituents onto heteroaromatic systems with exquisite chemo- and site-selectivity. For substrates with different halogen groups the chemoselectivity of the Suzuki–Miyaura reactions has been found to be dependent on the reactivity difference between the halogens. However, the hardest achievement of selectivity in Suzuki–Miyaura monocouplings involving polyhalogenated heteroarenes with identical halogen atoms has been shown to be dominated by steric and electronic effects and the presence of directing groups at positions neighbouring the reaction sites. Moreover, in the case of symmetrically substituted dihaloheteroarenes with identical halogen atoms, highly selective monocoupling reactions have often been achieved only after a careful optimization of reaction parameters including the catalyst precursor, base, solvent, and the molar ratio between electrophile and organoboron reagent. This critical review with 341 references covers developments on the chemo- and site-selective Suzuki–Miyaura monocoupling reactions of polyhalogenated heteroarenes with different or identical halogen atoms. It also includes the synthesis of polysubstituted heteroarenes, not easily accessible by other means, via consecutive monocoupling reactions and/or a more synthetically valuable approach involving one-pot polycoupling reactions.
TL;DR: In this article, triflic acid-functionalized silica-coated magnetic nanoparticles [γ-Fe2O3@SiO2-TfOH] were readily prepared and identified as an effictive catalyst for the transformation of aldehydes or ketones into their corresponding gem-dihydroperoxides with 30% aqueous hydrogen peroxide.
Abstract: Triflic acid-functionalized silica-coated magnetic nanoparticles [γ-Fe2O3@SiO2-TfOH] were readily prepared and identified as an effictive catalyst for the transformation of aldehydes or ketones into their corresponding gem-dihydroperoxides with 30% aqueous hydrogen peroxide. The catalyst was easily separated by magnetic decantation and the recovered catalyst was reused for seven cycles without significant loss of catalytic activity.
TL;DR: In this paper, an efficient, operatively simple, acceptorless, and base-free dehydrogenation of secondary alcohols and nitrogen-containing heterocyclic compounds was achieved by using readily available ruthenium hydride complexes as precatalysts.
Abstract: An efficient, operatively simple, acceptorless, and base-free dehydrogenation of secondary alcohols and nitrogen-containing heterocyclic compounds was achieved by using readily available ruthenium hydride complexes as precatalysts. The complex RuH2(CO)(PPh3)(3) (1) and Shvos complex (2) showed excellent activities for the dehydrogenation of secondary alcohols and nitrogen containing heterocycles. In addition to complexes 1 and 2, the complex RuH2(PPh3)(4) (3) also showed moderate to excellent activity for the acceptorless dehydrogenation of nitrogen-containing heterocyclic compounds. Kinetic studies on the oxidation reaction of 1-phenylethanol using complex 1 were carried out in the presence and the absence of external triphenylphosphine (PPh3). External addition of PPh3 had a negative influence on the rate of the reaction, which suggested that dissociation of PPh3 occurred during the course of the reaction. Hydrogen was evolved from the oxidation reaction of 1-phenylethanol by using 1 mol% of 1 (88%) and 2 (92%), which demonstrated the possible usage of the catalytic systems in hydrogen generation.
TL;DR: In this paper, a bipyridyl-based PNN ruthenium(II) pincer catalyst was used for cross-dehydrogenative coupling of primary alcohols with secondary alcohols to obtain mixed esters.
Abstract: Cross-dehydrogenative coupling of primary alcohols with secondary alcohols to obtain mixed esters with the liberation of molecular hydrogen is achieved in high yield and good selectivity under neutral conditions, using a bipyridyl-based PNN ruthenium(II) pincer catalyst.
TL;DR: In this paper, an efficient method was developed for the desulfitative arylation of indoles with sodium sulfinates using palladium as catalyst and copper chloride dihydrate as oxidant.
Abstract: An efficient method was developed for the desulfitative arylation of indoles with sodium sulfinates using palladium as catalyst and copper chloride dihydrate as oxidant. The direct arylation occurred exclusively in the C-2 position of indoles and proceeded well for a range of different substrates.
TL;DR: Tertiary anilines can react with N-aryl and N-benzylmaleimides to form tetrahydroquinoline products under photocatalysis using visible light irradiation, the ruthenium or iridium complexes Ru(bpy)3Cl2 or Ir(ppy)2(dtbbpy)PF6 as catalyst, and air as terminal oxidant as mentioned in this paper.
Abstract: Tertiary anilines can be prompted to react with N-aryl- and N-benzylmaleimides to form tetrahydroquinoline products under photocatalysis using visible light irradiation, the ruthenium or iridium complexes Ru(bpy)3Cl2 or Ir(ppy)2(dtbbpy)PF6 as catalyst, and air as terminal oxidant.
TL;DR: An efficient metal-free sulfenylation of indoles with disulfides has been developed, leading to 3-arylthioindoles in moderate to excellent yields and a new family of 2-bromo-3-arylThioindole deriv- atives in good yield by the one-pot construction of C Sa nd CBr bonds.
Abstract: An efficient metal-free sulfenylation of indoles with disulfides has been developed, leading to 3-arylthioindoles in moderate to excellent yields. Furthermore, bromosulfenylation of indoles with di- sulfides has been realized for the first time provid- ing a new family of 2-bromo-3-arylthioindole deriv- atives in good yield by the one-pot construction of C Sa nd CBr bonds. It is noteworthy that the system enables the use of both the RS moieties in RSSR and shows a broad functional group toler- ance.
TL;DR: Phosphine-catalyzed [3+2] and [4+3]annulation reactions of C,N-cyclic azomethine imines with allenoates have been developed to give a variety of pharmaceutically attractive tetrahydroisoquinoline derivatives in moderate to excellent yields.
Abstract: Phosphine-catalyzed [3+2] and [4+3]annulation reactions of C,N-cyclic azomethine imines with allenoates have been developed to give a variety of pharmaceutically attractive tetrahydroisoquinoline derivatives in moderate to excellent yields. The two distinct reaction pathways, [3+2] and [4+3]cyclization, depend on the nature of the nucleophilic phosphine and the allenoate. Generally, for α-alkylallenoates, the reactions always proceed with [3 +2]cyclization as the major pathway no matter what phosphine was used; for α-ArCH2-substituted allenoates, the reaction pathway was controlled by the phosphine catalyst used.
TL;DR: In this article, the authors describe the oxidative CC bond formation of tertiary amines with various nucleophiles under very mild and environmental friendly conditions by using mesoporous graphitic carbon nitride (mpg-C3N4) semiconductor as a heterogeneous, metal-free photosensitizer in combination with visible light and oxygen as the terminal oxidation agent.
Abstract: In this communication we describe the oxidative CC bond formation of tertiary amines with various nucleophiles under very mild and environmental friendly conditions by using mesoporous graphitic carbon nitride (mpg-C3N4) semiconductor as a heterogeneous, metal-free photosensitizer in combination with visible light and oxygen as the terminal oxidation agent. This system can be further combined with proline-organocatalysis to achieve oxidative tandem photocatalysis, demonstrating a rich cascade of chemical possibilities of the current photosynthesis system.
TL;DR: In this paper, an iridium catalyst was used for the symmetrical and unsymmetrical monoalkylation of para-, meta-, and ortho-benzenediamines.
Abstract: An iridium catalyst – stabilized by an anionic P,N ligand – was used for the symmetrical and unsymmetrical monoalkylation of para-, meta-, and ortho-benzenediamines. Benzyl and aliphatic alcohols were used as alkylating reagents. 28 derivatives were synthesized. 14 of them are new compounds. Furthermore, the alkylation of the pharmacological important diamine Dapson® (dapsone) is described. 14 dapsone derivatives were synthesized among them 9 new compounds.
TL;DR: It is found that this new type of spiro alkaloid could inhibit the proliferation of various cancer cells in a preliminary biological evaluation and suggested that spirooxindole-type pyranopyrimidines, developed by an asymmetric Michael/cyclization strategy, can potentially serve as a new kind of anticancer candidate.
Abstract: Due to the lack of tumor-specific anticancer agents, the discovery and development of new types of highly selective anticancer agents is still a very urgent topic. Herein, we present our contribution to concise construction of novel chiral spirooxindole-type pyranopyrimidines exhibiting a unique profile of biological activities. We have found that this new type of spiro alkaloid could inhibit the proliferation of various cancer cells in a preliminary biological evaluation. These findings suggested that spirooxindole-type pyranopyrimidines, developed by an asymmetric Michael/cyclization strategy, can potentially serve as a new kind of anticancer candidate.