Showing papers in "Synlett in 2012"
TL;DR: In this paper, the authors summarize their own experiences in developing microwave-heated palladium-catalyzed Mo(CO)6-mediated gas-free carbonylative reactions.
Abstract: This Account summarizes predominately our own experiences in developing microwave-heated palladium-catalyzed Mo(CO)6-mediated gas-free carbonylative reactions, although contributions from other gro ...
205 citations
TL;DR: N-Heteropentacenes and their derivatives have been recently discovered as a new family of organic semiconductors exhibiting high performance in organic field effect transistors (OFETs).
Abstract: N-Heteropentacenes and their derivatives have been recently discoveredas a new family of organic semiconductors exhibiting high performancein organic field effect transistors (OFETs). Introducing nitrogenatoms to the pentacene moiety leads to a large number of structurallyrelated π-backbones with tunable electronic structures,stability, solubility, and molecular packing. This gives considerablefreedom when designing organic semiconductors and provides goodopportunities for studying structure-property relationships.In this account, efforts on developing N-heteropentacenes and N-heteropentacenequinonesas organic semiconductors are reviewed, with focus on the recentwork of our own group. 1 Overview 2 Brief Introduction to Organic Semiconductors and Organic FieldEffect Transistors 3 Dihydrodiazapentacenes and Diazapentacenes 4 A Dihydrotetraazapentacene and Its Methylated Derivatives 5 N-Heteropentacenequinones 6 Silylethynylated N-Heteropentacenes 7 Conclusion and Outlook
155 citations
TL;DR: In this article, recent advances made on the reactions of several types of organic azides, such as vinyl azides and cyclic 2-azido alcohols, towards the synthesis of nitrogen-containing molecules are described.
Abstract: In this account, recent advances made on the reactions of several types of organic azides, such as vinyl azides, cyclic 2-azido alcohols, a-azido carbonyl compounds, towards the synthesis of nitrogen-containing molecules are described.
152 citations
TL;DR: In this paper, diverse nucleophilic carbon-electrophilic carbon σ-bonds were found to undergo facile cleavage and add across carbon-carbon triple bonds of arynes without the aid of transition-metal catalysts, leading to the direct introduction of different carbon functionalities into the ortho-positions of aromatic rings.
Abstract: Diverse nucleophilic carbon–electrophilic carbon σ-bonds were found to undergo facile cleavage and to add across carbon–carbon triple bonds of arynes without the aid of transition-metal catalysts, leading to the direct introduction of different carbon functionalities into the ortho-positions of aromatic rings. Active methylene compounds including β-dicarbonyl compounds, α-cyanocarbonyl compounds, sulfonylacetonitrile, and malononitrile smoothly underwent the aryne insertion reactions, and, moreover, the reaction was applicable to fluorene and trifluoromethyl ketone derivatives. The total synthesis of cytosporone B and phomopsin C, depending upon the carbon–carbon bond cleavage reaction, is also described. 1 Introduction 2 β-Dicarbonyl Compounds 3 α-Cyanocarbonyl Compounds 4 Sulfonylacetonitrile and Malononitrile 5 Fluorenes 6 Trifluoromethyl Ketones 7 Total Synthesis of Cytosporone B and Phomopsin C 8 Conclusion
119 citations
TL;DR: In this article, the acid-promoted intramolecular cycloadditions of activated cyclo-propanes were systematically described, and the potential of this strategy has been demonstrated by the synthesis of natural products.
Abstract: In this account we have systematically described the acid-promoted intramolecular cycloadditions of activated cyclopropanes, which were conceptually classified into intramolecular cross-cycloadditions (IMCC) and intramolecular parallel-cycloadditions. The IMCC provided a general and efficient strategy for construction of structurally complex and diverse bridged bicyclic skeletons. The potential of this strategy has been demonstrated by the synthesis of natural products. 1 Introduction 2 [3+2]IMCC of Cyclopropane 1,1-Diester with C=O 3 [3+2]IMCC of Cyclopropane 1,1-Diester with C=N 4 [3+2]IMCC of Cyclopropane 1,1-Diester with C=C 5 [3+3]IMCC of Cyclopropane 1,1-Diester with Nitrones 6 [3+2]IMCC of Mono-donor/Mono-acceptor Cyclopropane with C=O 7 Lewis Acid Regulated Domino Cycloisomerization/[4+2]IMCC or [3+2]IMCC of Alkynylcyclopropane Ketone with C=O and C=N 8 Conclusions and Outlook
117 citations
TL;DR: This Account describes recent efforts to address some of the challenges of developing aryl trifluoromethylation reactions involving high oxidation state Pd intermediates by exploiting AgCF3 for C-H trifLUorometHylation, and achieving Cu-catalyzed triffluoromet hylation with photogenerated CF3•.
Abstract: Trifluoromethyl-substituted arenes and heteroarenes are widely prevalent in pharmaceuticals and agrochemicals. As a result, the development of practical methods for the formation of aryl–CF3 bonds has become an active field of research. Over the past five years, transition-metal-catalyzed cross-coupling between aryl–X (X = halide, organometallic, or H) and various ‘CF3’ reagents has emerged as a particularly attractive approach to generating aryl–CF3 bonds. Despite many recent advances in this area, current methods generally suffer from limitations such as poor generality, harsh reaction conditions, the requirement for stoichiometric quantities of metals, and/or the use of costly CF3 sources. This Account describes our recent efforts to address some of these challenges by: (1) developing aryltrifluoromethylation reactions involving high oxidation state Pd intermediates, (2) exploiting AgCF3 for C–H trifluoromethylation, and (3) achieving Cu-catalyzed trifluoromethylation with photogenerated CF3
•. 1 Introduction 2 Part 1. Aryltrifluoromethylation via High-Valent Palladium 3 Part 2. Aryltrifluoromethylation Using AgCF3
4 Part 3. Cu-Catalyzed Aryltrifluoromethylation with CF3• 5 Outlook
99 citations
TL;DR: A separation-friendly Mitsunobu reaction using hydrophobic-tagged acids is reported that can react with various alcohols to afford the target products in high yield with easy purification based on C-18 silica solid-phase extraction or normal silica gel filtration.
Abstract: A separation-friendly Mitsunobu reaction using hydrophobic-tagged acids is reported. Commercially available or simply prepared and recyclable hydrophobic-tagged acids can react with various alcohols to afford the target products in high yield with easy purification based on C-18 silica solid-phase extraction or normal silica gel filtration.
82 citations
78 citations
TL;DR: In this article, the authors summarized platinum-group metal on carbon (e.g., Pd/C, Pt/C and Ru/C) catalyzed efficient multi and/or site-selective H-D exchange methods of various compounds including bioactive molecules, such as amino acids, nucleic acids, pharmaceuticals, agrochemicals, and sugars, under neutral and H2-atmospheric conditions in D2O.
Abstract: Deuterium-labeled compounds are widely utilized in various scientific fields. Although the H–D exchange reaction is a straightforward method to produce the deuterated organic compounds, it requires expensive deuterium (D2) gas and/or harsh reaction conditions in conventional methods. This Account summarizes platinum-group metal on carbon (e.g., Pd/C, Pt/C, Ru/C, Rh/C)-catalyzed efficient multi and/or site-selective H–D exchange methods of various compounds including bioactive molecules, such as amino acids, nucleic acids, pharmaceuticals, agrochemicals, and sugars, under neutral and H2-atmospheric conditions in D2O. 1 Introduction and Background 1.1 H–D Exchange Reaction under Acidic or Basic Conditions 1.2 Transition-Metal-Catalyzed H–D Exchange Reaction 1.3 H–D Exchange Reaction under Supercritical State or Hydrothermal Conditions 1.4 Other H–D Exchange Methods 2 Pd/C-Catalyzed H2–D2 Exchange Reaction 3 Site-Selective Benzylic Deuteration under Normal Pressure at Room Temperature 4 Multi H–D Exchange Reaction under Heat Conditions 4.1 Multi H–D Exchange Reaction of Alkyl-Substituted Aromatics 4.2 Multi H–D Exchange Reaction of Heterocyclic Compounds 4.3 Multi H–D Exchange Reaction of Aromatic Nuclei 4.4 Multi H–D Exchange Reaction Using a Mixture of Pd/C and Pt/C or Pd–Pt Hybrid Catalyst 5 H–D Exchange Reaction of Simple Alkanes 6 H–D Exchange Reaction of Alcohols 6.1 The Regioselective H–D Exchange at the α-Position of Aliphatic Alcohols 6.2 The Regio- and Stereoselective Deuterium Labeling of Sugars 7 Conclusion
76 citations
TL;DR: Direct electrophilic arene borylation is introduced as a new synthetic approach to aryl boronate esters in this article, which covers both the key historic breakthroughs and the more recent developments in this area.
Abstract: Direct electrophilic arene borylation is introduced as a new synthetic approach to aryl boronate esters. This perspective covers both the key historic breakthroughs and the more recent developments in this area.
69 citations
TL;DR: The need to use a static directing group represents a major limitation for the emerging field of ortho-selective C-H activation and functionalization as discussed by the authors, and this limitation has been addressed by allowing partial removal or minor transformations for certain directing groups.
Abstract: The need to use a static directing group represents a major limitation for the emerging field of ortho-selective C–H activation and functionalization. Chemistry was recently developed that allowed partial removal or minor transformations for certain directing groups. Our recent work demonstrated that triazenes were a class of excellent directing groups for C–H activation/functionalization, and subsequent chemical manipulations generated key compounds with synthetic versatility.
TL;DR: Recent developments on nitrogen radical cation chemistry under visible-light photocatalysis are highlighted.
Abstract: Amines have been used as sacrificial electron donors to reduce photoexcited Ru(II) or Ir(III) complexes, during which they are oxidized to nitrogen radical cations. Recently, the synthetic potential of these nitrogen radical cations have caught synthetic organic chemists’ attention. They have been exploited in various transformations yielding a number of elegant methods for amine synthesis. This article highlights recent developments on nitrogen radical cation chemistry under visible-light photocatalysis.
TL;DR: In this paper, the authors highlight some of the achievements and important challenges that remain in the area of C-H bond functionalization and highlight the challenges that need to be solved.
Abstract: Among the frontier challenges facing synthetic chemistry in the 21st century are the interconnected goals of increasing control of chemical reactivity and synthesizing complex molecules with higher levels of efficiency. Catalytic C–H bond functionalization reactions are increasingly being discovered that meet the criterion for useful reactivity (i.e. preparative, predictably selective, and general). Consequently, such reactions are enabling chemists to exploit strategies for complex molecule synthesis and derivatization previously accessible only in nature. This preface highlights some of the achievements and important challenges that remain in the area of C–H bond functionalization.�
TL;DR: In this paper, the authors describe some recent breakthroughs in the development of new transformations of nitrones, including formal [3+3] cycloaddition of n-drone and vinyl carbenes to give 3,6-dihydro-1,2-oxazines, tandem cyclization, and reaction of 2-azido acrylates to form 1,2,4,5-tetra-substituted imidazoles.
Abstract: Despite the long history of nitrone chemistry, novel transformations of nitrones continue to be discovered. This article describes some recent breakthroughs in the development of new transformations of nitrones. These new reactions include formal [3+3] cycloaddition of nitrones and vinylcarbenes to give 3,6-dihydro-1,2-oxazines, tandem cyclization–[3+3] cycloaddition of nitrones and enynones to give furo[3,4-d][1,2]oxazines, [2+2+3] cycloaddition of nitrones and 1,6-enynes to give tricyclic 1,2-oxazepanes, reaction of nitrones and 2-azido acrylates to form 1,2,4,5-tetrasubstituted imidazoles, and reactions of α,β-unsaturated N-aryl ketonitrones and activated alkynes to generate C3-quaternary indolenines.
TL;DR: Copper(I) oxide has been found to effectively catalyse the multicomponent click synthesis of fully substituted 5-alkynyl 1,2,3-triazoles from organic halides, sodium azide, and terminal alkynes in methanol under ambient conditions.
Abstract: Copper(I) oxide has been found to effectively catalyse the multicomponent click synthesis of fully substituted 5-alkynyl 1,2,3-triazoles from organic halides, sodium azide, and terminal alkynes in methanol under ambient conditions.
TL;DR: This account summarizes the results of recent studies conducted in this group on the development of chiral thiourea/cinchona and Bronsted acid derived bifunctional organocatalysts to delineate the underlying mechanism of various asymmetric transformations by BINOL-phosphoric acid-induced activation of imines.
Abstract: This account summarizes the results of recent studies conducted in our group on the development of chiral thiourea/cinchona and Bronsted acid derived bifunctional organocatalysts. Selected asymmetric organocatalytic transformations were targeted to obtain enantioenriched bioactive products. Special emphasis was placed on the preparation of environmentally friendly anti-plant viral agents such as enantiomerically enriched α-aminophosphonates and methods to assess the enantiomeric purity of these products on selected chiral stationary phases. The review also tries to delineate the underlying mechanism of various asymmetric transformations by BINOL-phosphoric acid-induced activation of imines and to make unambiguous assignments of the absolute configuration of α-aminophosphonates obtained from organocatalytic hydrophosphonylation of pregenerated and in situ generated imines. 1 Introduction 2 BINOL-Derived Bronsted Acid Organocatalysts and Their Applications 2.1 Two-Component Reaction 2.2 Three-Component Reaction 2.3 Analytical Aspects 2.4 Absolute Configuration and Proposed Mechanism 3 Chiral Thiourea/Cinchona Derived Bifunctional Organocatalysts and Their Applications 4 Ongoing Activities 5 Concluding Remarks
TL;DR: In this article, an easy and efficient one-pot, three-component method for the synthesis of 5-substituted 1H-tetrazole derivatives, via the reaction of aldehydes, hydroxylamine, and [bmim]N3, is reported.
Abstract: An easy and efficient one-pot, three-component method for the synthesis of 5-substituted 1H-tetrazole derivatives, via the reaction of aldehydes, hydroxylamine, and [bmim]N3, is reported.
TL;DR: In this article, an iron-catalyzed synthesis of 3methyl-2-arylimidazo [1,2-a] pyridine derivatives from aminopyridines and 2-methyl-nitroolefins was reported.
Abstract: A variety of ways to synthesize imidazo[1,2-a]pyridines have been reported and many approaches are devoted to the functionalization of imidazo[1,2-a]pyridines. However, the use of a denitration reaction in the synthesis of imidazo[1,2-a]pyridines has not been reported. We report here the iron-catalyzed synthesis of 3-methyl-2-arylimidazo [1,2-a] pyridine derivatives from aminopyridines and 2-methyl-nitroolefins. The procedure, using FeCl2 as catalyst, is simple and inexpensive. Various functional groups are tolerated and provide the products in good yields.
TL;DR: In this paper, a tetracarbene iron catalyst was used to catalyze the formation of aziridines from electron-withdrawing aryl azides and a limited selection of conjugated alkenes.
Abstract: The direct synthesis of aziridines from alkenes and a nitrene source with the correct functionality on the nitrogen atom has remained an elusive goal in synthetic chemistry. Ruthenium, cobalt, and iron porphyrin complexes have been demonstrated to catalyze the formation of aziridines from electron-withdrawing aryl azides and a limited selection of conjugated alkenes. Our group is expanding the scope of catalytic aziridination to include electron-donating aryl azides and aliphatic alkenes through the use of a novel tetracarbene iron catalyst.
TL;DR: 2-Aryl-4-quinazolinones undergo smooth acetoxylation in the presence of 5 mol% Pd(OAc)2 and a stoichiometric amount of PhI(O Ac2)2 via C–H activation to produce the corresponding acetoxy-substituted 4(3H)-quinazolone derivatives in good yields with high regioselectivity.
Abstract: 2-Aryl-4-quinazolinones undergo smooth acetoxylation in the presence of 5 mol% Pd(OAc)2 and a stoichiometric amount of PhI(OAc)2 via C–H activation to produce the corresponding acetoxy-substituted 4(3H)-quinazolinone derivatives in good yields with high regioselectivity.
TL;DR: Copper-catalyzed hydrosulfonylations of alkynes can be carried out using sodium sulfinates in air as mentioned in this paper, which affords syn-selectively (E)-alkenyl sulfones in good yields.
Abstract: Copper-catalyzed hydrosulfonylations of alkynes can be carried out using sodium sulfinates in air. The procedure affords syn-selectively (E)-alkenyl sulfones in good yields. Then, both terminal and internal alkynes are available.
TL;DR: Secondary and tertiary amides are formed in high yields, in an efficient and environmentally benign titanium(IV) isopropoxide catalyzed direct amidation of carboxylic acids with primary and secondary amines.
Abstract: Secondary and tertiary amides are formed in high yields, in an efficient and environmentally benign titanium(IV) isopropoxide catalyzed direct amidation of carboxylic acids with primary and secondary amines.
TL;DR: An overview of the chemistry of conjugate addition to N-heterocyclic compounds can be found in this paper, where a wide variety of heterocycles and nucleophiles undergo this chemistry.
Abstract: Conjugate or Michael addition to vinyl-substituted aromatic N-heterocycles has been a useful synthetic method for the synthesis of functionalized heterocyclic compounds. A wide variety of heterocycles and nucleophiles undergo this chemistry. Recent work in this area has utilized transition-metal catalysts and some asymmetric synthesis has been accomplished. An overview of this chemistry is presented in this account. 1 Introduction 2 General Aspects 3 Carbon-Centered Nucleophiles 4 Nitrogen-Centered Nucleophile 5 Oxygen and Sulfur Nucleophiles 6 Transition-Metal-Catalyzed Reactions 7 Asymmetric Conjugate Addition 8 Summary and Outlook
TL;DR: In this paper, a direct arylation of pyridine N-oxides with arylboronic acids through C-H functionalization has been developed, which is performed at room temperature using catalytic silver(l) nitrate in the presence of potassium persulfate.
Abstract: A novel direct arylation of pyridine N-oxides with arylboronic acids through C-H functionalization has been developed. This new reaction is performed at room temperature using catalytic silver(l) nitrate in the presence of potassium persulfate and give 2-pyridyl arylation derivatives of pyridine N-oxides.
TL;DR: A copper-catalyzed aerobic oxidative method for the synthesis of primary aryl amides has been developed, and the direct oxygenation of (aryl)methanamines to primary aries by molecular oxygen showed convenient, practical, and environment-friendly advantages.
Abstract: A copper-catalyzed aerobic oxidative method for the synthesis of primary aryl amides has been developed, and the direct oxygenation of (aryl)methanamines to primary aryl amides by molecular oxygen showed convenient, practical, and environment-friendly advantages. This method will find wide application in chemistry and biology.
TL;DR: Using this approach, a variety of hetero-Diels-Alder cycloadducts are obtained in yields of up to 96% at 0.1 mol% catalyst loading.
Abstract: An effective protocol is described for the generation and in situ Diels-Alder trapping of acylnitroso derivatives. In this procedure, the oxidation of hydroxamic acid is efficiently catalyzed by dirhodium(II) caprolactamate with tert-butyl hydroperoxide (TBHP) in the presence of dienes at room temperature. Using this approach we obtained a variety of hetero-Diels-Alder cycloadducts in yields of up to 96% at 0.1 mol% catalyst loading.