Showing papers on "Cyclopropane published in 2017"
TL;DR: The regioselective Heck arylation of terminal olefins as a distant trigger for the ring-opening of cyclopropanes is reported, demonstrating its efficiency and versatility as the reaction proceeded regardless of the molecular distance between the initiation (double bond) and termination (alcohol) sites.
Abstract: Combining functionalization at a distant position from a reactive site with the creation of several consecutive stereogenic centres, including the formation of a quaternary carbon stereocentre, in acyclic system represents a pinnacle in organic synthesis. Here we report the regioselective Heck arylation of terminal olefins as a distant trigger for the ring-opening of cyclopropanes. This Pd-catalysed unfolding of the strained cycle, driving force of the chain-walking process, remarkably proved its efficiency and versatility, as the reaction proceeded regardless of the molecular distance between the initiation (double bond) and termination (alcohol) sites. Moreover, employing stereodefined polysubstituted cyclopropane vaults allowed to access sophisticated stereoenriched acyclic scaffolds in good yields. Conceptually, we demonstrated that merging catalytically a chain walking process with a selective C-C bond cleavage represents a powerful approach to construct linear skeleton possessing two stereogenic centres.
104 citations
TL;DR: The focus of this research is a direct transformation of 2-(aryl)cyclopropane 1,1-diester derivatives into 1-benzazepines using a cyclopropane moiety as the hydride acceptor in internal redox reactions.
92 citations
TL;DR: A general strategy for the 1,3-oxidation of cyclopropanes using aryl iodine(I-III) catalysis, with emphasis on 1, 3-difluorination reactions, is described and the generality of this strategy is demonstrated through the catalytic oxidative ring-opening of cyclipropanes for the synthesis of 1,1-fluoroacetoxylated products.
Abstract: Electronegative substituents arrayed in 1,3-relationships along saturated carbon frameworks can exert strong influence over molecular conformation due to dipole minimization effects. Simple and general methods for incorporation of such functional group relationships could thus provide a valuable tool for modulating molecular shape. Here, we describe a general strategy for the 1,3-oxidation of cyclopropanes using aryl iodine(I–III) catalysis, with emphasis on 1,3-difluorination reactions. These reactions make use of practical, commercially available reagents and can engage a variety of substituted cyclopropane substrates. Analysis of crystal and solution structures of several of the products reveal the consistent effect of 1,3-difluorides in dictating molecular conformation. The generality of the 1,3-oxidation strategy is demonstrated through the catalytic oxidative ring-opening of cyclopropanes for the synthesis of 1,3-fluoroacetoxylated products, 1,3-diols, 1,3-amino alcohols, and 1,3-diamines.
90 citations
TL;DR: Highly substituted tetrahydrothiophenes with two adjacent quaternary carbon atoms were obtained in a stereospecific manner under mild conditions and in high yield when using AlCl3 as Lewis acid.
Abstract: Lewis-acid-catalyzed reactions of 2-substituted cyclopropane 1,1-dicarboxylates with thioketones are described. Highly substituted tetrahydrothiophenes with two adjacent quaternary carbon atoms were obtained in a stereospecific manner under mild conditions and in high yield when using AlCl3 as Lewis acid. Moreover, an intramolecular approach was successfully implemented to gain access to sulfur-bridged [n.2.1] bicyclic ring systems. Conversion of selenoketones, the heavier analogues, under similar conditions resulted in the formation of various tetrahydroselenophenes.
90 citations
TL;DR: This work reports the enantioselective yttrium-catalyzed C(sp3 )-H bond addition of 2-methyl azaarenes, such as 2- methyl pyridines, to various substituted cyclopropenes and norbornenes, which afforded a new family of chiral pyrIDylmethyl-functionalizedcyclopropane andnorbornane derivatives in high yields and high enantiOSElectivities.
Abstract: An enantioselective C-H addition to a C=C bond represents the most atom-efficient route for the construction of chiral carbon-carbon skeletons, a central research topic in organic synthesis. We herein report the enantioselective yttrium-catalyzed C(sp3 )-H bond addition of 2-methyl azaarenes, such as 2-methyl pyridines, to various substituted cyclopropenes and norbornenes. This process efficiently afforded a new family of chiral pyridylmethyl-functionalized cyclopropane and norbornane derivatives in high yields and high enantioselectivities (up to 97 % ee).
90 citations
TL;DR: Donor–acceptor cyclopropanes with two geminal carboxylic esters are reacted with chalcogenyl chlorides and bromides to afford ring-opened products bearing the halogen atoms in the 1-position, adjacent to the donor, and the chalCogenyl residue in the 3-position next to the two acceptor groups.
83 citations
TL;DR: The study demonstrates the unique activity of open-shell iron alkylidene species beyond its closed-shell analogues, thus pointing out their potential synthetic usage in catalysis.
Abstract: Transition-metal alkylidenes are important reactive organometallic intermediates, and our current knowledge on them has been mainly restricted to those with closed-shell electronic configurations. In this study, we present an exploration on open-shell iron alkylidenes with a weak-field tripodal amido-phosphine-amido ligand. We found that a high-spin (amido-phosphine-amido)iron(II) complex can react with (p-tolyl)2CN2 to afford a high-spin (amido-ylide-amido)iron(II) complex, 2, which could transfer its alkylidene moiety to a variety of alkenes, either the electron-rich or electron-deficient ones, to form cyclopropane derivatives. The reaction of 2 with cis-β-deuterio-styrene gave deuterated cyclopropane derivatives with partial loss of the stereochemical integrity with respect to the cis-styrene. Kinetic study on the cyclopropanation reaction of 2 with 4-fluoro-styrene disclosed the activation parameters of ΔH⧧ = 23 ± 1 kcal/mol and ΔS⧧ = −20 ± 3 cal/mol/K, which are comparable to those of the cyclopropan...
57 citations
TL;DR: An enantioselective three-step synthesis of the GABA uptake inhibitor (S)-(+)-homo-β-proline was developed using a CuI-catalyzed cyclopropanation of N-Boc-pyrrole, a substrate that persistently has proved to be challenging in transformations.
42 citations
TL;DR: Mechanistic studies and DFT calculations are used to elucidate the key factors in this new ring expansion reaction, and the need for the nitro group on the cyclopropane.
Abstract: Described herein is a new visible-light photocatalytic strategy for the synthesis of enantioenriched dihydrofurans and cyclopentenes by an intramolecular nitro cyclopropane ring expansion reaction. Mechanistic studies and DFT calculations are used to elucidate the key factors in this new ring expansion reaction, and the need for the nitro group on the cyclopropane.
38 citations
TL;DR: The cyclopropanation of bench-stable enaminones with in situ generated diazo reagents from N-tosylhydrazones, followed by selective C-C bond cleavage of thecyclopropane ring, affords 1,4-ketoaldehyde derivatives in good to excellent yields.
37 citations
TL;DR: In this paper, the authors discuss the recent progress in catalytic insertion and cyclopropane-forming reactions of α-diazocarbonyl compounds with a focus on regio-, diastereo-, and enanti-lective reactions.
Abstract: Metal–carbenoids from α-diazocarbonyl compounds are well-known reactive intermediates with a long history of useful applications in synthetic organic chemistry. The carbenoids, generated in situ from the catalytic decomposition of α-diazocarbonyls, react by different pathways such as insertions, cyclopropane formation, and cycloadditions of ylides, etc. in inter- and intramolecular versions of the reactions. These reactions have been employed in the architecture of several complex molecules of natural origin. The present review paper discusses the recent progress in catalytic insertion (X–H: X = C, N, O, S, Si, and B), and cyclopropane-forming reactions of α-diazocarbonyl compounds with a focus on regio-, diastereo-, and enantioselective reactions.
TL;DR: In this paper, a chiral NHC catalyst was used to enable the direct enantio-and diastereoselective synthesis of tetrahydropyrano[2,3-b]indoles.
Abstract: Formylcyclopropanes undergo activation in the presence of an N-heterocyclic carbene catalyst generating a donor-acceptor cyclopropane intermediate with the ability to undergo ring-opening followed by formal [4+2] cycloaddition with alkylideneoxindoles. This enables the direct enantio- and diastereoselective synthesis of tetrahydropyrano[2,3-b]indoles through the use of a chiral NHC catalyst.
TL;DR: In this article, a gold-catalyzed tandem cyclization-oxidation of alkylidenecyclopropane-containing 1,5-enynes with 3,5dibromo-pyridine Noxide via a noncarbene model was developed, providing a range of synthetically valuable and useful arylacetaldehyde derivatives in moderate to good yields without oxidation of alkynes.
Abstract: A gold-catalyzed tandem cyclization–oxidation of alkylidenecyclopropane-containing 1,5-enynes with 3,5-dibromo-pyridine N-oxide via a noncarbene model was developed, providing a range of synthetically valuable and useful arylacetaldehyde derivatives in moderate to good yields without oxidation of alkynes. Moreover, the corresponding aldehydes can be further transformed into polycyclic aromatic hydrocarbons in the presence of a catalytic amount of Lewis acid In(OTf)3. The reaction represents an example of gold-catalyzed halide-free Kornblum-type oxidation through the oxidation of the cyclopropane moiety.
TL;DR: A strategy and extensive synthetic studies for the preparation of a diverse collection of cyclopropane‐containing lead‐like compounds, fragments and building blocks exploiting a single precursor are described.
TL;DR: Rhodium-catalyzed formal aza-[4 + 3] cycloaddition reaction of 3-diazoindolin-2-imines with 1,3-dienes was demonstrated for the synthesis of azepinoindoles in good to excellent yields in one-pot.
Abstract: Rhodium-catalyzed formal aza-[4 + 3] cycloaddition reaction of 3-diazoindolin-2-imines with 1,3-dienes was demonstrated for the synthesis of azepinoindoles in good to excellent yields in one-pot. First, rhodium-catalyzed [2 + 1] cycloaddition reaction smoothly took place to produce iminyl vinyl cyclopropane intermediate at room temperature in chlorobenzene for 1 h, which was thermally converted to azepinoindoles via aza-Cope rearrangement.
TL;DR: Avenaol is a potent germination stimulant that can be extracted from black oat by developing a strategy to access all-cis-substituted cyclopropanes and this study confirms the proposed structure of avenaol, including its unique all- cis- SubStitutedcyclopropane moiety.
Abstract: Avenaol, isolated from the allelopathic plant black oat, was the first C20 germination stimulant related to strigolactones. Structurally, it consisted of a bicyclo[4.1.0]heptanone skeleton containing a cyclopropane ring bearing three main chains projecting in the same direction (i.e. all-cis-substituted cyclopropane). Herein, we report the total synthesis of avenaol using a robust strategy involving the formation of an all-cis-substituted cyclopropane via an alkylidenecyclopropane. The key factors in the success of this total synthesis include the Rh-catalysed intramolecular cyclopropanation of an allene, an Ir-catalysed stereoselective double-bond isomerisation, and the differentiation of two hydroxymethyl groups via the regioselective formation and oxidation of a tetrahydropyran based on the reactivity of a cyclopropyl group. This strategy effectively avoids the undesired ring opening of the cyclopropane ring and the formation of a caged structure. Furthermore, this study confirms the proposed structure of avenaol, including its unique all-cis-substituted cyclopropane moiety.Avenaol is a potent germination stimulant that can be extracted from black oat. Here, the authors report the total synthesis of avenaol by developing a strategy to access all-cis-substituted cyclopropanes.
TL;DR: It is demonstrated here that other sulfinate salts, such as sodium 1,1-difluoroethanesulfinate, sodium 2-(4-bromophenyl)-1,1 -difloroethaneulfinate and sodium 1-(trifluoromethyl)cyclopropanesulfinates, can be used as fluoroalkylation reagents, resulting in the corresponding fluorinated ketones.
Abstract: Tertiary cyclopropanols easily available from carboxylic esters have been used in the synthesis of distally fluorinated ketones. Cyclopropane ring cleavage reactions in methanol with aqueous tert-butyl hydroperoxide in the presence of a copper(II) acetate catalyst and sodium triflinate (Langlois reagent) afford β-trifluoromethyl ketones in 16–74% isolated yields. Sodium triflinate serves as a precursor of reactive trifluoromethyl copper species, enabling ring-opening trifluoromethylation, as evidenced by mechanistic studies. We also demonstrate here that other sulfinate salts, such as sodium 1,1-difluoroethanesulfinate, sodium 2-(4-bromophenyl)-1,1-difluoroethanesulfinate and sodium 1-(trifluoromethyl)cyclopropanesulfinate, can be used as fluoroalkylation reagents, resulting in the corresponding fluorinated ketones.
TL;DR: In this article, a cyclopropane fused pyrrolidines can be readily converted to other N-heterocycles with potential synthetic and biological interests, with high chemo-and regio-selectivity.
Abstract: Cobalt(II)-porphyrin catalyzed intramolecular Buchner reaction and arene cyclopropanation of alkyl diazomethanes in situ generated from N-tosylhydrazones to give a range of bicyclic cycloheptatriene fused pyrrolidines and tetracyclic cyclopropane fused pyrrolidines in good to high yields and with high chemo- and regio-selectivity. The obtained cyclopropane fused pyrrolidines can be readily converted to other N-heterocycles with potential synthetic and biological interests.
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03 Nov 2017
TL;DR: In this paper, the shape of Molecules Structure and Bonding Clasification of Stereoisomers is described as a three dimensional VSEPR drawing of three dimensional Chemical Stuctures.
Abstract: MOLECULAR STRUCTURE AND BONDING Isomerism Drawing Three Dimensional Chemical Stuctures VSEPR and the Shape of Molecules Structure and Bonding Clasification of Stereoisomers CIS-TRANS ISOMERISM Cis-Trans Isomerism in Alkenes Cis-Trans Isomerism in Other Systems Which Contain a double Bond Cis-Trans Isomerism in Cyclic Systems Cis-Trans Isomerism in Square Planar and Octohedral Metal Complexes Cis-Trans Isomerism about Single Bonds (Conformational Diastereomers) Methods for Distinguishing Cis-Trans Isomers ENANTIOMERS Structure of Enantiomers Nomenclature for Enantiomers (Speciation of Absolute Configuration) Chemical Properties of Enantiomers Physical Properties of Enantiomers Enantiomeric Excess Biological Properties of Enantiomers Chirality Due to Stereocentres at Atoms Other than Carbon Other Stereogenic Elements Which Can Produce Molecular Chirality COMPOUNDS WITH TWO OR MORE STEREOCENTRES Compounds with Two Stereocentres Compounds with More Than Two Stereocentres Polymer Stereochemistry Relative Stereochemistry Nomenclature Diastereomeric Excess INTERCONVERSION AND ANALYSIS OF STEREOISOMERS Racemization Epimerization Resolution Methods for Determining Enantiomeric Excess Determination of Absolute Configuration Determination of Relative Configuration MOLECULAR SYMMETRY Introduction Symmetry Elements and Symmetry Operations Symmetry of Molecules with Multiple Conformations Point Groups Symmetry and Chirality TOPISM AND PROSTEREOGENICITY Homotopic, Enantiopic and Diastereotopic Groups Homotopic, Enantiopic and Diastereotopic Faces Nomenclature for Heterotopic Groups and Faces CONFORMATION OF ACYLIC AND CYCLIC MOLECULES Introduction Conformations of Acyclic Molecules Conformations of Cyclic Alkanes and their Derivatives Cyclopropane Cyclobutane Cyclohexane Medium and Large Rings Conformation of Inorganic and Organometallic Compounds Conformation of Biopolymers Methods for Determining Molecular Conformation STEREOCHEMISTRY OF CHEMICAL REACTIONS Introduction Substitution Reactions Elimination Reactions Addition Reactions to Alkenes Addition of Nucleophiles to Aldehydes and Ketones Pericyclic Reactions ASYMMETRIC SYNTHESIS Introduction Use of Chiral Auxiliaries Use of Enantiomerically Pure Reagents Index
TL;DR: In this article, a nickel-catalyzed hydrocyanation triggered by hydronickelation of the carbon-carbon double bonds of allenes followed by cyclopropane cleavage is described.
Abstract: A nickel-catalyzed hydrocyanation triggered by hydronickelation of the carbon-carbon double bonds of allenes followed by cyclopropane cleavage is described. The observed regio- and stereochemistries in the products are strongly influenced by the initial hydronickelation step, and allenyl- and methylenecyclopropanes reacted smoothly to promote the cleavage of cyclopropane. In contrast, this cleavage was not observed with vinylidenecyclopropanes, because the initial hydronickelation does not give a suitable intermediate for cleavage of the cyclopropanes.
TL;DR: Visible-light-promoted addition of α-bromoacetophenones onto the cyclopropene π-system in the presence of the fac-Ir(ppy)3 catalyst was shown to afford the corresponding 1(4H)-naphthalenones bearing an all-carbon benzylic quaternary stereocenter.
TL;DR: An asymmetric synthesis of wickerol A is presented that is based on a Jung Diels-Alder reaction, an intramolecular alkylation to complete the 6-5-6-6 ring system, and a conjugate addition, all of which overcome considerable steric strain.
Abstract: Wickerol A (1) is an unusual diterpene with remarkable activity against the H1N1 influenza virus. Its tetracyclic skeleton contains three quaternary carbons and is marked by several syn-pentane interactions which force a six-membered ring into a twist-boat conformation. We present an asymmetric synthesis of wickerol A (1) that is based on a Jung Diels–Alder reaction, an intramolecular alkylation to complete the 6–5–6–6 ring system, and a conjugate addition, all of which overcome considerable steric strain. During the synthesis, we isolated an unexpected cyclopropane that presumably stems from a carbonium ion intermediate.
TL;DR: The collective data corroborate a mechanism involving nickel(0)-mediated benzylic oxidative addition with inversion of stereochemistry followed by reversible olefin insertion to form a (cyclopropylcarbinyl)nickel complex, which upon reductive elimination releases the cyclopropane.
Abstract: Under the conditions of nickel(0) catalysis, enantiomerically enriched vinyl dioxanones engage boroxines or B2(pin)2 in stereospecific cross-coupling to form diverse tetrasubstituted cyclopropanes bearing all-carbon quaternary stereocenters. The collective data corroborate a mechanism involving nickel(0)-mediated benzylic oxidative addition with inversion of stereochemistry followed by reversible olefin insertion to form a (cyclopropylcarbinyl)nickel complex, which upon reductive elimination releases the cyclopropane.
TL;DR: A new stereoselective arylative cyclopropanation process involving treatment of halogenated dienone systems in the presence of a Michael donor containing a nitro-aryl-sulfone has been developed, reflecting the concepts of green chemistry and atom economy.
TL;DR: It is shown that upon electrophile activation phosphorus homocycles exhibit analogous reactivity, which is modulated by the amount of ring strain and extent of bond polarization, which deconvolute the influence ofRing strain and bond polarization on the chemistry of inorganic Homocycles and unlock new synthetic possibilities.
Abstract: Heterolytic cleavage of homoatomic bonds is a challenge, as it requires separation of opposite charges. Even highly strained homoatomic rings (e.g., cyclopropane and cyclobutane) are kinetically stable and do not react with nucleophiles or electrophiles. In contrast, cycloalkanes bearing electron-donating/withdrawing substituents on adjacent carbons have polarized C–C bonds and undergo numerous heterolytic ring-opening and expansion reactions. Here we show that upon electrophile activation phosphorus homocycles exhibit analogous reactivity, which is modulated by the amount of ring strain and extent of bond polarization. Neutral rings (tBuP)3, 1, or (tBuP)4, 2, show no reactivity toward nitriles, but the cyclo-phosphinophosphonium derivative [(tBuP)3Me]+, [3Me]+, undergoes addition to nitriles giving five-membered P3CN heterocycles. Because of its lower ring strain, the analogous four-membered ring, [(tBuP)4Me]+, [4Me]+, is thermodynamically stable with respect to cycloaddition with nitriles, despite simil...
TL;DR: The behaviour of several aldehydes and ketones under reductive amination conditions with deprotected halogenated secondary cyclopropylamines was investigated, showing that this transformation typically triggers cyclopropane ring cleavage to give access to interesting nitrogen-containing ring-expanded products.
Abstract: A series of 6,6-dihalo-2-azabicyclo[3.1.0]hexane and 7,7-dihalo-2-azabicyclo[4.1.0]heptane compounds were prepared by the reaction of dihalocarbene species with N-Boc-2,3-dihydro-1H-pyrroles or -1,2,3,4-tetrahydropyridines. Monochloro substrates were synthesised as well, using a chlorine-to-lithium exchange reaction. The behaviour of several aldehydes and ketones under reductive amination conditions with deprotected halogenated secondary cyclopropylamines was investigated, showing that this transformation typically triggers cyclopropane ring cleavage to give access to interesting nitrogen-containing ring-expanded products.
TL;DR: The stabilization of a phosphirane ring by complexation to tungsten pentacarbonyl allows the emergence of the Cloke-Wilson rearrangement in 1-acylphosphirane complexes around 130 °C.
Abstract: The stabilization of the phosphirane ring by complexation to tungsten pentacarbonyl allows the emergence of the Cloke-Wilson rearrangement in the 1-acylphosphirane complexes around 130oC. Contrary to the cyclopropane case, this transformation of the 1-acylphosphirane to the 1,3-oxaphosphol-3-ene complexes is reversible. It is favored by a 2-phenyl and, even more, a 2-vinyl substitution. The 1,3-oxaphosphol-3-ene complexes are trapped by conjugated dienes.
TL;DR: In this paper, the carbon-carbon bonding in cubane is shown not to be along the C-C vectors between carbon atoms at the corners of a cube, but instead, the bonding is "bent" as seen in a new single-crystal X-ray structure of cubane at 93 K.
TL;DR: Lanthanide amide-catalyzed one-pot reaction of isatins, dialkyl phosphite, and activated alkenes was developed and a series of spiro[cyclopropan-1,3'-oxindoles] were obtained in moderate to excellent yields.
Abstract: Lanthanide amide-catalyzed one-pot reaction of isatins, dialkyl phosphite, and activated alkenes was developed and a series of spiro[cyclopropan-1,3'-oxindoles] were obtained in moderate to excellent yields. The reaction is stereoselective and the two substituents at the 2 and 3-positions of the cyclopropane in the major product are in the trans configuration. A four-step mechanism involving the Pudovik reaction, Brook rearrangement, Michael addition, and intramolecular nucleophilic substitution is proposed, and an umpolung strategy was used in the process.
TL;DR: A remarkably mild, catalyst-freecyclopropanation reaction is confirmed by low-temperature isolation of a fused bicyclic cyclopropane intermediate.
Abstract: A remarkably mild, catalyst-free cyclopropanation reaction is confirmed by low-temperature isolation of a fused bicyclic cyclopropane intermediate. This intermediate is one of two that were isolated and fully characterised in a three-step temperature-controllable reaction cascade.