Showing papers on "Cyclopropane published in 2014"
TL;DR: A review of cyclopropane ring reactions can be found in this article, with a critical comparison of preparations using chiral auxiliaries, chiral metal complexes and organocatalysts.
Abstract: Both physical and organic chemists are interested in the cyclopropane ring, the former owing to the strain inherent to the small ring structure, the latter prompted by the importance of this ring in naturally occurring compounds. In recent years, the increasing interest in enantioselective organic synthesis has led to a large number of papers on the preparation of cyclopropane compounds in enantioenriched form. The last review on asymmetric cyclopropanation reactions is dated 2008, thus an update is necessary with critical comparison of preparations using chiral auxiliaries, chiral metal complexes and organocatalysts. The aim of this review is an overview of these topics from 2008 to mid-2013. 1 Introduction 2 Simmons–Smith Cyclopropanation 2.1 Chiral Auxiliaries 2.2 Chiral Catalysts 3 Transition-Metal-Catalyzed Decomposition of Diazoalkanes 3.1 Cobalt 3.2 Copper 3.3 Rhodium 3.4 Ruthenium 3.5 Other Metals 4 Michael-Initiated Ring Closure (MIRC) 4.1 Chiral Auxiliaries 4.2 Organocatalysis 4.3 Metal Catalysis 5 Miscellaneous 5.1 C–H Insertion 5.2 Nucleophilic Ring Closure 5.3 Cycloisomerization of 1,n-Enynes 5.4 Other Methods 6 Conclusion 7 Abbreviations
130 citations
TL;DR: The mechanisms of the discovered reactions involving the formation of a comparatively stable 1,2-ylide intermediate have been studied and the strategy for selective hetero-combination of donor-acceptor cyclopropanes was also been developed.
Abstract: A new type of donor–acceptor cyclopropane reactivity has been discovered. On treatment with anhydrous GaCl3, they react as sources of even-numbered 1,2- and 1,4-dipoles instead of the classical odd-numbered 1,3-dipoles due to migration of positive charge from the benzyl center. This type of reactivity has been demonstrated for new reactions, namely, cyclodimerizations of donor–acceptor cyclopropanes that occur as [2+2]-, [3+2]-, [4+2]-, [5+2]-, [4+3]-, and [5+4]-annulations. The [4+2]-annulation of 2-arylcyclopropane-1,1-dicarboxylates to give polysubstituted 2-aryltetralins has been developed in a preparative version that provides exceedingly high regio- and diastereoselectivity and high yields. The strategy for selective hetero-combination of donor–acceptor cyclopropanes was also been developed. The mechanisms of the discovered reactions involving the formation of a comparatively stable 1,2-ylide intermediate have been studied.
97 citations
TL;DR: The hydrophobic electrophilic bowl formed by 1,1',2,2'-tetracyano cyclopropane or cyclobutane derivatives is proposed as a new and synthetically accessible supramolecular synthon.
Abstract: High-level calculations (RI-MP2/def2-TZVP) disclosed that the σ-hole in between two C atoms of cycloalkane X2 CCX2 structures (X=F, CN) is increasingly exposed with decreasing ring size. The interacting energy of complexes of F(-) , HO(-) , N≡C(-) , and H2 CO with cyclopropane and cyclobutane X2 CCX2 derivatives was calculated. For X=F, these energies are small to positive, while for X=CN they are all negative, ranging from -6.8 to -42.3 kcal mol(-1) . These finding are corroborated by a thorough statistical survey of the Cambridge Structural Database (CSD). No clear evidence could be found in support of non-covalent carbon bonding between electron-rich atoms (El.R.) and F2 CCF2 structures. In marked contrast, El.R.⋅⋅⋅(CN)2 CC(CN)2 interactions are abundant and highly directional. Based on these findings, the hydrophobic electrophilic bowl formed by 1,1',2,2'-tetracyano cyclopropane or cyclobutane derivatives is proposed as a new and synthetically accessible supramolecular synthon.
81 citations
TL;DR: A method for synthesis of 3-azabicyclo[3.1.0]hex-2-enes has been developed by intramolecular cyclopropanation of readily available N-allyl enamine carboxylates by CuBr-mediated aerobic and CuBr2-catalyzed-PhIO2-mediated systems effectively induced stepwise cycloprostanation via carbocupration of alkenes.
Abstract: A method for synthesis of 3-azabicyclo[3.1.0]hex-2-enes has been developed by intramolecular cyclopropanation of readily available N-allyl enamine carboxylates. Two complementary reaction conditions, CuBr-mediated aerobic and CuBr2-catalyzed-PhIO2-mediated systems effectively induced stepwise cyclopropanation via carbocupration of alkenes. Oxidative cyclopropane ring-opening of 5-substituted 3-azabicyclo[3.1.0]hex-2-enes was also developed for synthesis of highly substituted pyridines. In addition, diastereoselective reduction of 3-azabicyclo[3.1.0]hex-2-enes to 3-azabicyclo[3.1.0]hexanes was achieved using NaBH3CN in the presence of acetic acid.
75 citations
TL;DR: An efficient one-pot two-step procedure for asymmetric synthesis of piperidine-fused trans-cycloalkenes and a concerted mechanism is proposed for the latter thermal rearrangement reaction together with a closed transition state model.
Abstract: An efficient one-pot two-step procedure for asymmetric synthesis of piperidine-fused trans-cycloalkenes is reported. The method comprises the initial enantioselective installation of another cyclopropane ring onto methylenecyclopropanes and the subsequent thermal skeletal rearrangement in which the installed and inherent cyclopropane rings are both opened. A concerted mechanism is proposed for the latter thermal rearrangement reaction together with a closed transition state model.
74 citations
TL;DR: A bioinsipred gold-catalyzed tandem Diels-Alder/Friedel-Crafts tandem reaction of an enynal and a 1,3-diene, forming the highly-strained benzotricyclo[3.2.1.0(2,7) ]octane skeleton, was reported.
Abstract: A bioinsipred gold-catalyzed tandem Diels-Alder/Diels-Alder reaction of an enynal and a 1,3-diene, forming the highly-strained benzotricyclo[3.2.1.0(2,7) ]octane skeleton, was reported. In contrast, a Diels-Alder/Friedel-Crafts tandem reaction occurred instead when silver salts were used as the catalyst. Although both reactions experienced the similar Diels-Alder reaction of a pyrylium intermediate with a 1,3-diene, they have different reaction mechanisms. The former proceeded with a stepwise Diels-Alder reaction, while the latter one with a concerted one.
65 citations
TL;DR: A TiCl4 promoted formal [3 + 3] cycloaddition of cyclopropane 1,1-diesters with azides has been developed for the synthesis of highly functionalized triazinines and could be easily converted to biologically important azetidines by simple thermolysis.
63 citations
TL;DR: Heteroatom-directed C-H borylation of cyclopropanes and cyclobutanes was achieved with silica-supported monophosphane-Ir catalysts with exceptional cis stereoselectivity relative to the directing groups.
Abstract: Heteroatom-directed CH borylation of cyclopropanes and cyclobutanes was achieved with silica-supported monophosphane–Ir catalysts. Borylation occurred at the CH bonds located γ to the directing N or O atoms with exceptional cis stereoselectivity relative to the directing groups. This protocol was applied to the borylation of a tertiary CH bond of a ring-fused cyclopropane.
58 citations
TL;DR: A triflic acid-catalyzed formal [3 + 2] cycloaddition of cyclopropane 1,1-diesters with nitriles was developed, which supplies an efficient and practical method for the synthesis of 1-pyrrolines.
Abstract: A triflic acid-catalyzed formal [3 + 2] cycloaddition of cyclopropane 1,1-diesters with nitriles was developed. This reaction was expeditious, and the scope of the substituents in both cyclopropanes and nitriles was broad. This supplies an efficient and practical method for the synthesis of 1-pyrrolines.
58 citations
TL;DR: After the first step a cyclopropane intermediate is obtained which is directly converted to indole derivatives (III), (VI), (VII), and (IX) after silica gel column chromatography as discussed by the authors.
Abstract: After the first step a cyclopropane intermediate is obtained which is directly converted to indole derivatives (III), (VI), (VII), and (IX) after silica gel column chromatography.
58 citations
TL;DR: Copper(I)-catalyzed enantioselective hydroboration of 3-aryl substitutedcyclopropene-3-carboxylate is described, providing chiral cyclopropylboronates with excellent enantiOSElectivities and the chiral boronates could be conveniently converted into chiral 1,2-diaryl substituted Cyclopropane derivatives.
Abstract: Copper(I)-catalyzed enantioselective hydroboration of 3-aryl substituted cyclopropene-3-carboxylate is described, providing chiral cyclopropylboronates with excellent enantioselectivities (89–95% ee) in moderate to high yields (55–86%). The non-directing effect of the ester group was observed, and the reaction proceeded with solely trans-selectivity. The chiral boronates could be conveniently converted into chiral 1,2-diaryl substituted cyclopropane derivatives.
TL;DR: Trans-2-Aryl-3-nitro-cyclopropane-1,1-dicarboxylates and aroylmethylidene malonates are found to be potential precursors for heterocycles, such as imidazoles, quinoxalines, and benzo[1,4]thiazines.
Abstract: trans-2-Aryl-3-nitro-cyclopropane-1,1-dicarboxylates, upon treatment with BF3·OEt2, undergo ring-opening rearrangement and the Nef reaction to give aroylmethylidene malonates. The products are found to be potential precursors for heterocycles, such as imidazoles, quinoxalines, and benzo[1,4]thiazines.
TL;DR: A concise synthesis of spiro-cyclopropane compounds from indole derivatives and sulfur ylides has been developed via a dearomatization strategy and could be conveniently transformed to rearomatized indoles derivatives in the presence of acids.
TL;DR: Enantiospecific first total syntheses of (+)-hydroxyancepsenolide and its acetate are achieved confirming their absolute stereochemistry.
TL;DR: Continuous flow heterogeneous asymmetric cyclopropanations catalysed by supported hydrogen-bonded chiral copper(I) complexes of pyridine containing tetraazamacrocyclic ligands Pc-L* using CO2 as a transport vector are described in this paper.
TL;DR: A novel and highly efficient Pd(0)-catalyzed domino reaction to prepare cyclopropane derivatives has been established and preliminary DFT calculations suggest that a four-membered palladacycle intermediate is involved.
TL;DR: In this article, the stereoselective construction of spirooxindolic cyclopropane derivatives is achieved by means of a vinylogous cascade reaction that successfully integrates a Vinylogous iminium ion/dienamine tandem sequence.
TL;DR: The results suggest that even gas-phase leaving-group bond-dissociation energy differences of 2-3 kcal mol(-1) enormously affect the rate of gold carbene formation in solution, especially when there are competing reactions.
Abstract: The gas-phase bond-dissociation energies of a SO2 -imidazolylidene leaving group of three gold(I) benzyl imidazolium sulfone complexes are reported (E0 =46.6±1.7, 49.6±1.7, and 48.9±2.1 kcal mol(-1) ). Although these energies are similar to each other, they are reproducibly distinguishable. The energy-resolved collision-induced dissociation experiments of the three [L]-gold(I) (L=ligand) carbene precursor complexes were performed by using a modified tandem mass spectrometer. The measurements quantitatively describe the structural and electronic effects a p-methoxy substituent on the benzyl fragment, and trans [NHC] and [P] gold ligands, have towards gold carbene formation. Evidence for the formation of the electrophilic gold carbene in solution was obtained through the stoichiometric and catalytic cyclopropanation of olefins under thermal conditions. The observed cyclopropane yields are dependent on the rate of gold carbene formation, which in turn is influenced by the ligand and substituent. The donation of electron density to the carbene carbon by the p-methoxy benzyl substituent and [NHC] ligand stabilizes the gold carbene intermediate and lowers the dissociation barrier. Through the careful comparison of gas-phase and solution chemistry, the results suggest that even gas-phase leaving-group bond-dissociation energy differences of 2-3 kcal mol(-1) enormously affect the rate of gold carbene formation in solution, especially when there are competing reactions. The thermal decay of the gold carbene precursor complex was observed to follow first-order kinetics, whereas cyclopropanation was found to follow pseudo-first-order kinetics. Density-functional-theory calculations at the M06-L and BP86-D3 levels of theory were used to confirm the observed gas-phase reactivity and model the measured bond-dissociation energies.
TL;DR: Trans-2-Aryl-3-nitro-cyclopropane-1,1-dicarboxylates when reacted with nitriles in the presence of tin(IV) chloride afford 2,4,5-trisubstituted oxazoles in good to excellent yields.
TL;DR: In this paper, a base-promoted ring-opening of siloxydifluorocyclopropanes is presented for a convenient access to cyclic fluoroketones.
Abstract: A convenient access to cyclic fluoroketones that involves base-promoted ring-opening of siloxydifluorocyclopropanes is presented. Selective formation of gem-difluorinated cycloalkanones and monofluorinated enones has been achieved.
TL;DR: An unprecedented AlCl3-promoted formal [2 + 3]-cycloaddition of 1,1-cyclopropanes with readily available N-benzylic sulfonamides has been developed and experimental evidence supports an unusual mechanism wherein the donor-acceptor cyclopropane serves as a source of 2-styrylmalonate rather than the "classical" 1,3-dipole.
TL;DR: In this article, a new synthetic procedure for polysubstituted 2-aminothiophenes was developed via Gewald type ring-opening reaction of 1,1-dicyano-2,3-diarylcyclopropanes with elemental sulfur in N,N-dimethylformamide in the presence of morpholine as base.
TL;DR: In this paper, a hybrid quantum mechanics/molecular mechanics (QM/MM) model and the quasiclassical trajectory (QCT) method were combined to study the reaction of alkene methylation by methanol catalyzed by the zeolite H-MFI.
Abstract: A hybrid quantum mechanics/molecular mechanics (QM/MM) model and the quasiclassical trajectory (QCT) method have been combined to study the reaction of alkene methylation by methanol catalyzed by the zeolite H-MFI. The rate-limiting step of this reaction is the methylation of the alkene, and the apparent activation energy calculated at the ωB97X-D/6-31G(d,p)//ωB97X-D/6-311++G(3df,3pd) level of theory for this step agrees well with experiment and previous full QM studies. Following the ethene methylation transition state toward the products along the intrinsic reaction coordinate reveals the existence of a protonated cyclopropane (PCP+) carbocation intermediate. A similar protonated methylcyclopropane (mPCP+) carbocation intermediate is found for propene methylation. The intermediates produced during the alkene methylation reaction are metastable with a lifetime of O(1 ps) obtained from QCTs. Because of the short lifetime of these intermediates, the available energy in the carbocation is not in thermal equ...
TL;DR: Trans-2-Aroyl-3-arylcyclopropane-1,1-di-carboxylates upon treatment with aluminiumA chloride (AlCl3) underwent ring-opening, fragmen-tation, recombination and lactonization to give highly substituted 2-pyrones as discussed by the authors.
Abstract: trans-2-Aroyl-3-arylcyclopropane-1,1-di- carboxylates upon treatment with aluminiumA chloride (AlCl3) underwent ring-opening, fragmen- tation, recombination and lactonization to give highly substituted 2-pyrones. Alternatively, when treated with titanium(IV) chloride (TiCl4), the cy- clopropane diesters underwent a Nazarov cycliza- tion to afford 1-indanones with high diastereoselec- tivity.
TL;DR: The potential application of hypervalent iodine(III) reagent was successfully extended to the dialkylation and cyclopropa(e)nation of unsaturated alkenes and alkynes, and a plausible mechanism of iodo( III)cyclopropanation, ring opening attack by the carbon-nucleophile, and recyclization was proposed for the cycloprostanation of trans-alkene substrates.
Abstract: Hypervalent iodine(III)-mediated dioxygenation and diamination of alkenes have been previously developed. In this study, the potential application of hypervalent iodine(III) reagent was successfully extended to the dialkylation and cyclopropa(e)nation of unsaturated alkenes and alkynes. The reactions of alkenes with malononitrile and other active methylene compounds as the carbon nucleophiles give access to multisubstituted cyclopropane derivatives in moderate to excellent yields. Both electron-rich and electron-deficient alkenes are suitable substrates. Alkynes, no matter terminal or internal alkynes, work well, affording the corresponding highly functionalized cyclopropenes efficiently. A plausible mechanism of iodo(III)cyclopropanation, ring opening attack by the carbon-nucleophile, and recyclization was proposed for the cyclopropanation of trans-alkene substrates. The cyclopropenation was thought to proceed via iodo(III)cyclopropanation, ring-opening attack by the carbon-nucleophile, recyclization into a four-membered iodo(III)cyclobutene and final reductive elimination. The protocol might provide a complementary route to cyclopropanation/cyclopropenation.
TL;DR: Ru-TsDPEN B is found to be a good catalyst for the formation of enantioenriched γ-lactones through a four-step sequence of azide reduction/cyclopropane ring cleavage/ketone transfer hydrogenation/lactonization, and the enantiomeric excess of the lactones was up to 94%.
TL;DR: An acid-catalyzed domino Meinwald rearrangement of epoxides/intramolecular [3+2] cross-cycloaddition of cyclopropane 1,1-diesters was developed in this paper.
TL;DR: This LIT MS(n) mass spectrometric approach led to unambiguous identification of PE molecules including many isomers in complex mixture that would otherwise be very difficult to define using other analytical approaches.
Abstract: The structures of phosphatidylethanolamine (PE) in Leishmania infantum are unique in that they consist of a rare cyclopropane fatty acid (CFA) containing PE subfamily, including CFA-containing plasmalogen PE species. In this contribution, we applied multiple-stage linear ion-trap combined with high-resolution mass spectrometry to define the structures of PEs that were desorbed as [M – H]− and [M – H + 2Li]+ ions by ESI, respectively. The structural information arising from MSn on both the molecular species are complimentary, permitting complete determination of PE structures, including the identities of the fatty acid substituents and their location on the glycerol backbone, more importantly, the positions of the double bond(s) and of the cyclopropane chain of the fatty acid chain, directing to the realization of the CFA biosynthesis pathways that were reported previously. We also uncovered the presence of a minor dimethyl-PE subclass that has not been previously reported in L. infantum. This LIT MSn mass spectrometric approach led to unambiguous identification of PE molecules including many isomers in complex mixture that would otherwise be very difficult to define using other analytical approaches. Copyright © 2014 John Wiley & Sons, Ltd.
TL;DR: The reaction stereospecificity was explored by using electronic structure calculations, and UB3LYP/6-31G* methodology allowed the energy barriers for cyclopropane stereoisomerisation, diastereoisomeric VCPR and [3,3]-rearrangement to be ranked in agreement with experiment.
Abstract: Vinyl cyclopropane rearrangement (VCPR) has been utilised to synthesise a difluorinated cyclopentene stereospecifically and under mild thermal conditions Difluorocyclopropanation chemistry afforded ethyl 3-(1'(2'2'-difluoro-3'-phenyl)cyclopropyl) propenoate as all four stereoisomers (18a, 18b, 22a, 22b) (all racemic) Trans-E isomer (18a), prepared in 70% yield over three steps, underwent near quantitative VCPR to difluorocyclopentene 23 (99%) Rearrangements were followed by 19F NMR (100-180 °C) While cis/trans cyclopropane stereoisomerisation was facile, favouring trans-isomers by a modest margin, no E/Z alkene isomerisation was observed even at higher temperatures Neither cis nor trans Z-alkenoates underwent VCPR, even up to much higher temperatures (180 oC) Cis-cyclopropanes underwent [3,3]-rearrangement to afford benzocycloheptadiene species The reaction stereospecificity was explored using electronic structure calculations and UB3LYP/6-31G* methodology allowed the energy barriers for cyclopropane stereoisomerisation, diastereoisomeric VCPR and [3,3]-rearrangement to be ranked in agreement with experiment
TL;DR: This work has shown that ultrasound irradiation can promote the 1,3-dipolar cycloaddition reaction of 2-chloropyridinium ylides with 2-benzylidenemalononitrile or 2,2'-(1,4-phenylenebis(methanylylidene))dimalon onitrile, to afford the indolizine and bis-indolIZine derivatives respectively.
Abstract: Ultrasound irradiation can promote the 1,3-dipolar cycloaddition reaction of 2-chloropyridinium ylides with 2-benzylidenemalononitrile or 2,2′-(1,4-phenylenebis(methanylylidene))dimalononitrile, to afford the indolizine and bis-indolizine derivatives respectively. While the reaction of pyridinium ylides with 2-benzylidenemalononitrile or 2,2′-(1,4-phenylenebis(methanylylidene))dimalononitrile under ultrasound irradiation provided, in an unusual manner, cyclopropane and bis-cyclopropane derivatives, respectively. These cycloaddition and cyclopropanation reactions were carried out in the presence of triethylamine, in acetonitrile, at room temperature.