Showing papers on "Cyclopropane published in 1997"
TL;DR: In this article, the authors present theoretical proof that the nature of the interactions existent in the complexes formed between hydrogen fluoride and a series of π-systems (acetylene, ethylene, cyclopropene, cyclobutadiene, and benzene) and three-memebered-ring derivatives (cyclopropane and tetrahedrane) is that of a hydrogen bond between the hydrogen atom and the π cloud.
Abstract: We present theoretical proof that the nature of the interactions existent in the complexes formed between hydrogen fluoride and a series of π-systems (acetylene, ethylene, cyclopropene, cyclobutadiene, and benzene) and three-memebered-ring derivatives (cyclopropane and tetrahedrane) is that of a hydrogen bond between the hydrogen atom and the π-cloud. Geometric and energetic data and mainly the study of the topology of the electronic density within the frame of the theory of atoms in molecules established by Bader have been used for this analysis.
172 citations
TL;DR: In this article, rotation-tunneling spectra of the van der Waals complex Ne-cyclopropane and pure rotational spectra for Ar and Kr cyclopropane were measured with a Fourier transform microwave spectrometer in the frequency range from 4 to 19 GHz.
Abstract: Rotation-tunneling spectra of the van der Waals complex Ne-cyclopropane, and pure rotational spectra of Ar-cyclopropane and Kr-cyclopropane, were measured with a Fourier transform microwave spectrometer in the frequency range from 4–19 GHz The observed transitions are all of a-type and are in accord with those of prolate symmetric top molecules where the rare gas atom is positioned on the C3 axis of the cyclopropane subunit above its symmetry plane Altogether transitions of five isotopomers of the Ne complex with J values ranging from 0 to 4 and K values from 0 to 1 were measured Three isotopomers of the Ar complex (J from 1 to 5 and K from 0 to 2) and nine isotopomers of the Kr complex (J from 1 to 8 and K from 0 to 2) were observed Effective separations between the center-of-mass of cyclopropane and the rare gas atoms were obtained from the ground state rotational constants and were found to be 3673, 3802, and 3906 A for the Ne-, Ar-, and Kr-containing complexes, respectively The derived centrif
142 citations
93 citations
TL;DR: The use of metal complexes of chiral nonracemic ligands in asymmetric cyclopropanation reactions via homogeneous catalysis is one of the recent developments in synthetic organic chemistry as mentioned in this paper.
Abstract: Use of metal complexes of chiral nonracemic ligands in asymmetric cyclopropanation reactions via homogeneous catalysis is one of the recent developments in synthetic organic chemistry. The extra carbon in the cyclopropane unit from the cyclopropanation of olefins comes from diazo esters or dihalomethanes. In this article we shall discuss the recent aspects of asymmetric intermolecular cyclopropanation reactions where decomposition of these compounds to carbenoid species takes place by organometallic complexes.
88 citations
TL;DR: The spiro-annelated methano-fullerenes bearing quinone-type addends including TCNQ and DCNQI analogues (3a−c, 6a,b, 8, 10, and 11) have been prepared, and their structural and electronic properties have been characterized by both experimental techniques and quantum-chemical calculations as discussed by the authors.
Abstract: Spiroannelated methanofullerenes bearing quinone-type addends including TCNQ and DCNQI analogues (3a−c, 6a,b, 8, 10, and 11) have been prepared, and their structural and electronic properties have been characterized by both experimental techniques and quantum-chemical calculations. The spiro[2,5-cyclohexadienone-4,61‘-methanofullerene] derivatives (3a−c), the spiro[10-anthrone-9,61‘-methanofullerene] (8), and the TCNQ- and DCNQI-type derivatives (10 and 11) were isolated as [6,6] adducts. The spiro[cyclohexanone-4,61‘-methanofullerene] (6) was however obtained as a mixture of [5,6] and [6,6] isomers. The novel methanofullerenes, with the only exception of 6, show irreversible cyclic voltammograms with additional reduction peaks. The conjugated cyclohexadienone derivatives 3 exhibit better acceptor abilities than the parent C60. Semiempirical PM3 calculations show that the addend lies perpendicular to the transanular bond in 3, while it folds down and adopts a butterfly shaped structure for compounds 8, 10...
86 citations
TL;DR: Reaction studies and spectroscopic investigations show that this remarkable influence is the result of reagent modification via a Schlenk equilibrium that produces the more reactive and selective species (iodomethyl)zinc iodide.
Abstract: The effect of zinc iodide on the catalytic, enantioselective cyclopropanation of allylic alcohols is examined with bis(iodomethyl)zinc as the reagent and bis-methanesulfonamide 7 as the catalyst. Significant rate enhancement was observed when 1 equiv of zinc iodide was present, but more importantly, the enantiomeric excess of the product cyclopropane increased from 80% to 89% for the substrate cinnamyl alcohol. Reaction studies and spectroscopic investigations show that this remarkable influence is the result of reagent modification via a Schlenk equilibrium that produces the more reactive and selective species (iodomethyl)zinc iodide.
81 citations
TL;DR: In this paper, the product distribution derived from the SmI2-induced reduction of the dipolar cycloadduct was found to depend on the reaction conditions, under kinetic conditions, the reduction resulted in opening of the cyclopropyl ring adjacent to the carbonyl group.
Abstract: The Rh(II)-catalyzed reaction of 1-acetyl-1-(diazoacetyl)cyclopropane with 5,5-dimethylcyclopentenone afforded the product of a 1,3-dipolar cycloaddition in high yield. The reaction involves formation of a rhodium carbenoid and subsequent transannular cyclization of the electrophilic carbon onto the adjacent keto group to generate a five-membered cyclic carbonyl ylide which undergoes a subsequent 1,3-dipolar cycloaddition reaction. The regiochemical results encountered can be rationalized on the basis of FMO considerations. Treatment of the cycloadduct with p-toluenesulfonic acid results in loss of water followed by a subsequent acid-catalyzed cyclopropyl ketone rearrangement to give dihydrobenzofuran 21. The product distribution derived from the SmI2-induced reduction of the dipolar cycloadduct was found to depend on the reaction conditions. Under kinetic conditions, the reduction resulted in opening of the cyclopropyl ring adjacent to the carbonyl group. However, under thermodynamic conditions, cleavage...
69 citations
TL;DR: In this paper, it was shown that the major source of the additional strain that results from the introduction of each trigonal center into cyclopropane is not an increase in angle strain but the loss of a very strong cycloprocessane C−H bond.
Abstract: Ab Initio calculations have been performed in order to investigate why the introduction of each trigonal center into a cyclopropane ring results in an increase in strain energy of 12−14 kcal/mol. Our calculations find that, as is commonly believed, introduction of a trigonal center into a three-membered ring does create some additional angle strain. However, our computational results show that the major source of the additional “strain” that results from the introduction of each trigonal center into cyclopropane is not an increase in angle strain but the loss of a very strong cyclopropane C−H bond.
64 citations
TL;DR: In this article, the nucleophilic substitution reactions on substituted arylcyclopropane cation radicals were studied by a combination of methods including product studies, time-resolved laser flash photolysis, kinetic isotope effects, and quantum chemical calculations.
Abstract: The nucleophilic substitution reactions on substituted arylcyclopropane cation radicals were studied by a combination of methods including product studies, time-resolved laser flash photolysis, kinetic isotope effects, and quantum chemical calculations. The reactions were found to proceed stereospecifically with inversion of configuration, with high regioselectivity for nucleophilic attack at the more substituted carbon atom, and with very small steric effects. Electronic effects on the nucleophilic substitution regiochemistry and the rate constants were found to be substantial for substituents on the cyclopropane moiety and on the aryl ring.
57 citations
TL;DR: In this paper, the potential energy surface for the reaction between ethylene and (chloromethyl)zinc chloride (ClCH2ZnCl), which represents a model system for the Simmons−Smith cyclopropanation reaction, was investigated.
Abstract: In this paper we have used a DFT (B3LYP) approach to investigate the potential energy surface for the reaction between ethylene and (chloromethyl)zinc chloride (ClCH2ZnCl), which represent a model system for the Simmons−Smith cyclopropanation reaction. Two reaction channels have been found: one leads to the cyclopropane product (addition channel) and the other to the propene product (insertion channel). The addition reaction has an activation energy of 24.7 kcal mol-1 and, as experimentally found, is favored with respect to the insertion, which is characterized by a larger activation energy (36.0 kcal mol-1). The addition transition state corresponds to a three-centered structure which explains the stereochemical features which have been experimentally observed for this reaction. A simple diabatic model is used to rationalize the reactivity pattern that characterizes the Simmons−Smith cyclopropanation and the different behavior observed for the reaction between singlet methylene 1CH2 and olefins.
54 citations
TL;DR: In this paper, the synthesis of 1,2,3,4,11,11ahexahydrocyclopropa[c]naphtho[2,1−b]azepin-6-one (CNA), a seven-membered C-ring analog of the alkylation subunits of CC-1065 and the duocarmycins, is detailed.
Abstract: The synthesis of 1,2,3,4,11,11a-hexahydrocyclopropa[c]naphtho[2,1−b]azepin-6-one (CNA), a seven-membered C-ring analog of the alkylation subunits of CC-1065 and the duocarmycins, is detailed. The core structure of CNA was prepared through the implementation of an intramolecular Heck reaction for assemblage of the key tricyclic tetrahydronaphtho[2,1−b]azepine skeleton and a final Winstein Ar-3' spirocyclization for introduction of the reactive cyclopropane. A study of the solvolysis reactivity of N-BOC-CNA revealed that incorporation of the seven-membered fused C-ring system increased the reactivity 4750× compared to the corresponding five-membered C-ring analog. Solvolysis occurs with SN2 nucleophilic attack at the more substituted carbon of the activated cyclopropane to afford exclusively the abnormal ring expansion product in a reaction that was shown to proceed with complete inversion of configuration at the reaction center. Single crystal X-ray structure analyses of N-CO2Me-CNA (29) and CNA (11) and t...
TL;DR: In this article, a cyclopropane diastereoisomer is observed, but increasing ring size allows stereochemistries in macrocyclization reactions that resemble those of their intermolecular cyclOPropanation counterparts.
Abstract: Catalytic intramolecular cyclopropanation by diazoacetates onto a remote carbon−carbon double bond resulting in the formation of 9- to 20-membered ring lactones is reported. When competition exists between proximal allylic and remote olefinic cyclopropanation, macrocyclization is favored by catalysts of increasing electrophilicity: Rh2(pfb)4 > Rh2(OAc)4, Cu(MeCN)4PF6 > Rh(cap)4, and Cu(acac)2. Terpene systems, cis-nerolidyl diazoacetate and related structures, malonic ester derivatives, and those with 1,2-benzenedimethanol, pentaerythritol, and cis-2-buten-1,4-diol linkers all undergo cyclopropanation onto the most remote carbon−carbon double bond in good yield. Generally, only one cyclopropane diastereoisomer is observed, but increasing ring size allows stereochemistries in macrocyclization reactions that resemble those of their intermolecular cyclopropanation counterparts. In one system (25) macrocyclic addition is accompanied by ylide formation/[2,3]-sigmatropic rearrangement resulting in the formatio...
TL;DR: The stereocontrolled conjugate addition of anions derived from chiral α-chlorophosphonamides to α,β-unsaturated esters leads to the corresponding 3-chloro ester adducts which undergo intramolecular expulsion of the chlorine atom to give the corresponding cyclopropanes as discussed by the authors.
TL;DR: In this paper, the treatment of β,γ-unsaturated thioacetals with Cp2Ti(π-CH2CR3R4) 5 in the presence of PPh3 or P(OEt)3 gave vinylcyclopropanes 6 in good yields.
Abstract: Preparation of vinylcyclopropanes 6 utilizing 2-(alk-1-enyl)-1,3-dithianes 1 or 1,3-bis(phenylthio)alk-1-enes 2 was studied. The treatment of β,γ-unsaturated thioacetals 1 or their analogues 2 with Cp2Ti(π-CH2CR3R4) 5 in the presence of PPh3 or P(OEt)3 gave vinylcyclopropanes 6 in good yields. A part of the cyclopropane 6 originates from the alkene formed by the thermal degradation of dialkyltitanocene 4, an intermediate formed during the reduction of Cp2TiCl2 with alkyllithium to 5. By using the titanocene reagent Cp2Ti(P(OEt)3)2 7 as a reducing agent, cyclopropanes 6 were obtained by the reaction of unsaturated organosulfur compounds 1 or 2 with various alk-1-enes. 1,2-Dibromoalkanes could be successfully employed as substitutes for volatile alkenes in this reaction. The intermediate of this reaction is presumed to be a vinylcarbene complex of titanium 8.
TL;DR: In this paper, B3LYP/6-31G* calculations were carried out on the mechanism of the zeolite-catalyzed hydrocarbon skeletal isomerization via cyclopropane ring intermediates.
Abstract: Quantum-chemical calculations were carried out on the mechanism of the zeolite-catalyzed hydrocarbon skeletal isomerization via the cyclopropane ring intermediates. According to the B3LYP/6-31G* calculations, formation of cyclopropane from surface alkoxy species in zeolites occurs via a transition state whose hydrocarbon part resembles a corner-protonated cyclopropane (corner-PCP) ring. Two conformations of the transition state found differ in the orientation of the PCP portion with respect to the acid site. The activation energy for the cyclopropane ring closure reaction is found to be rather sensitive to the use of planar symmetry constraints and to the level of calculations and less sensitive to the level of the geometry optimization. Calculations on the mechanism of the carbon isotope scrambling in the free 2-propyl cation were also performed, at several theory levels up to the Gaussian-2 model. The relatively stable intermediates of this superacid-catalyzed reaction are carbocations, in contrast to t...
TL;DR: In this paper, homochiral bis(oxazolinyl)biferrocene ligands are synthesized from oxazolinylferrocenes through a diastereoselective directed lithiation followed by an oxidative dimerization.
Abstract: Homochiral bis(oxazolinyl)biferrocene ligands, which have both planar and central chirality, are synthesized from oxazolinylferrocenes through a diastereoselective directed lithiation followed by an oxidative dimerization. Asymmetric cyclopropanation of styrene with diazoacetates in the presence of 5 mol% CuOTf-bis(oxazolinyl)biferrocene complexes gives 2-(phenyl)cyclopropane carboxylates in up to 99% ee.
TL;DR: An examination of both radical-stabilizing substituents and stereoelectronic factors was initiated to understand what factors bias bond cleavage in a configurationally restricted alpha-ketocyclopropane via O-stannyl ketyls.
Abstract: Several investigations of rigid alpha-keto cyclopropane cleavage by O-stannyl ketyls are summarized herein. Tricyclo[3.3.0.0(2,8)]octan-3-one ring systems were treated with nBu(3)SnH, which produced different ring-cleavage products depending on the location and type of substituent present. An examination of both radical-stabilizing substituents and stereoelectronic factors was initiated to understand what factors bias bond cleavage in a configurationally restricted alpha-ketocyclopropane via O-stannyl ketyls. A preference for cleavage of the cyclopropane bond with the best orbital overlap with the ketyl radical sp(2)-orbital even in the presence of radical stabilizing groups is indicated by these results. An O-stannyl ketyl ring scission-cyclization resulted in the novel synthesis of either a linear or an angular triquinane skeleton depending on the length and location an alkene tether on the tricyclo[3.3.0.0(2,8)]octan-3-one precursor.
TL;DR: The thermal chemistry of 1,3-diiodopropane, 1,chloro-3-IOPPANE, 3-chloropropene, propene, and cyclopropANE on Ni(100) surfaces has been studied under ultrahigh vacuum conditions by using temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS).
Abstract: The thermal chemistry of 1,3-diiodopropane, 1-chloro-3-iodopropane, 1-iodopropane, 1-chloropropane, 3-chloropropene, propene, and cyclopropane on Ni(100) surfaces has been studied under ultrahigh vacuum conditions by using temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). Cyclopropane, propene, propane, and hydrogen are all produced by thermal activation of the diiodopropane at low coverages, and iodopropane and molecular desorption are also seen at higher coverages. In contrast with this, only cyclopropane, propene, and chloropropanebut no propanewere observed after thermal activation of 1-chloro-3-iodopropane. Both I 3d and Cl 2p XPS spectra suggest that the adsorption of the dihaloalkanes is molecular below 100 K and that at low coverages both halogen atoms interact directly with the surface. They also point to the fact that the C−I (C−Cl) bonds break between 140 and 180 K in steps that most likely lead to the generation of a three-carbon metallacycle on the surface. T...
TL;DR: In this article, the semistabilized telluronium ylides 2a−e, generated in situ from the corresponding fireworks, reacted with α,β-unsaturated ketones 6a−d to afford cis-2-vinyl-trans-3-substituted cyclopropyl ketones with high stereoselectivity and in high to excellent yields.
Abstract: The semistabilized telluronium ylides 2a−e, generated in situ from the corresponding telluronium salts 1a−e, reacted with α,β-unsaturated ketones 6a−d to afford cis-2-vinyl-trans-3-substituted cyclopropyl ketones with high stereoselectivity and in high to excellent yields. Conversely, these enones gave trans-2-vinyl-trans-3-substituted cyclopropyl ketones, when the corresponding arsonium ylides 10a−e were employed. Other factors such as solvent and amount of base also influenced the stereochemistry of this reaction. A mechanistic rationale is discussed briefly.
TL;DR: In this article, a highly regioselective reductive ring opening of vinylcyclopropanes induced by palladium on activated carbon has been investigated, showing that the substituent on the cyclopropane is capable of coordinating to Pd or not.
Abstract: A highly regioselective reductive ring opening of vinylcyclopropanes induced by palladium on activated carbon has been investigated. High yields and excellent regioselectivities were observed in cleaving either the less hindered bond or the more hindered bond of the cyclopropane depending on whether the substituent on the vinylcyclopropane is capable of coordinating to Pd or not.
TL;DR: In this article, a simple potential model was proposed to determine the carbon 1s electron binding energies determined by X-ray photoelectron spectroscopy and mean dipole moment derivatives obtained from experimental infrared intensities.
Abstract: Carbon 1s electron binding energies determined by X-ray photoelectron spectroscopy and mean dipole moment derivatives obtained from experimental infrared intensities are shown to be related through the simple potential model proposed by Siegbahn and collaborators. The sp3 carbon atoms in 13 halomethanes, 2 ethanes, 3 methylacetylenes, cyclopropane, and ethylene oxide have 1s energies, which, after correction for electrostatic potentials from neighboring atoms, are linearly related to the carbon mean dipole moment derivatives, presenting a slope of 15.50 ± 0.29 eV/e. The sp2 carbons of ethylene, three haloethylenes, and three carbonyl compounds also exhibit a linear relationship having a significantly different slope of 17.37 ± 0.87 eV/e. The sp carbon atoms in acetylenes, cyanides, CO, CS2, CO2, and OCS show a third linear relationship, with a slope of 18.90 ± 0.75 eV/e. These slopes are proportional to the inverse atomic radii of sp3, sp2, and sp carbon atoms and according to the simple potential equatio...
TL;DR: Hybrid HF-DFT calculations have been carried out on pairs of neutral molecules and their conjugated bases in order to determine their gas-phase acidities (ΔH values) as mentioned in this paper.
TL;DR: Application of the highly functionalized selenium- and silicon-substituted cyclopropane products to the preparation of a useful synthetic intermediate 20 for the pyrethroid class of insecticides is also demonstrated.
Abstract: The reactions of 1-seleno-2-silylethenes 1 with highly electrophilic tricarbonyl-substitued olefins in the presence of Lewis acids have been investigated. The reaction of 1-(phenylseleno)-2-(trimethylsilyl)ethene (1a) with tris(alkoxycarbonyl) olefins 2 or 1,1-bis(alkoxycarbonyl)-2-acyl olefins 3 in the presence of ZnBr(2) at -30 degrees C gave cis-substituted cyclopropanes exclusively. The origin of the cis stereochemistry is ascribed to the synclinal addition path of the ZnBr(2)-coordinated electrophilic olefin to 1. Application of the highly functionalized selenium- and silicon-substituted cyclopropane products to the preparation of a useful synthetic intermediate 20 for the pyrethroid class of insecticides is also demonstrated.
TL;DR: In this article, the synthesis and application of the cyclopropane incorporated sugar intermediate in the stereoselective synthesis of C7-C16 segment of lasonolide A is described.
TL;DR: In this paper, the first examples of the mercury-II-mediated ring opening of bicyclopropane and tercyclopropane arrays have been investigated, showing that the presence of an adjacent cyclopropyl group dramatically increased the rate of the first cyclopricane in a cycloprapane array, leading to the formation of enantiomerically pure, highly substituted tetrahydrofurans.
Abstract: The first examples of the mercury(II)-mediated ring opening of bicyclopropane and tercyclopropane arrays have been investigated. The presence of an adjacent cyclopropyl group dramatically increased the rate of the mercury-mediated opening of the first cyclopropane in a cyclopropane array. In contrast to the mercury-mediated ring opening of monocyclopropanes which usually undergo a concerted ring-opening mechanism, electrophilic openings of cyclopropane arrays occurred through a stabilized, free carbocation. Excellent regio- and stereoselectivities were observed in the mercury-mediated intramolecular openings of the second cyclopropanes in the cyclopropane arrays, giving rise to the formation of enantiomerically pure, highly substituted tetrahydrofurans.
TL;DR: In this article, the initial probability of direct dissociative chemisorption of perhydrido-and perdeuteromethane, ethane, propane, and cyclopropane was investigated as a function of beam translational energy from 1.5 to 59 kcal/mol.
Abstract: We have employed molecular beam techniques to investigate the initial probability of direct dissociative chemisorption of perhydrido- and perdeuteromethane, ethane, propane, and cyclopropane on Ir(110) as a function of beam translational energy from 1.5 to 59 kcal/mol. For each of the saturated perhydridoisotopomers, a measurable (>0.02) initial probability of direct dissociative chemisorption is observed above a beam energy of approximately 7 kcal/mol. In the case of the saturated perdeuteroisotopomers, this “threshold” energy is approximately 10 kcal/mol. For cyclopropane, the relevant energy is approximately 5 kcal/mol for both c-C3H6 and c-C3D6. Above these energies, the initial probability of direct chemisorption of each of these hydrocarbons increases approximately linearly with beam translational energy and is independent of surface temperature, indicative of direct dissociative chemisorption. However, the energy required to achieve a measurable (>0.02 in this experiment) initial probability of dir...
TL;DR: Configurationally stable analogs of the potent, A 2A -selective adenosine receptor (AR) antagonist 3, 7-dimethyl-1-propargyl-8-styrylxanthine (8- Styryl-DMPX, 3) were synthesized and investigated in radioligand binding assays for affinity to the high-affinity A 1 - and A2A -AR subtypes of rat brain.
TL;DR: In this article, the prototypical 1,2-cis-vinylcyclopropanecarbaldehyde-to-2,5-dihydrooxepin hetero-Cope-type rearrangement was studied by first-principle methods.
Abstract: The prototypical 1,2-cis-vinylcyclopropanecarbaldehyde-to-2,5-dihydrooxepin hetero-Cope-type rearrangement was studied by “exact” first-principle methods. The reaction pathway was examined. The reaction, as well activation energies, was calculated for the unimolecular transformation of vinylcyclopropanecarbaldehyde and various derivatives. The derivatives differ from vinylcyclopropanecarbaldehyde by replacement of the formyl (CHO) by the thioformyl (CHS) or formiminyl (CHNH) group and, in part, by replacement of hydrogen atoms at the substituted carbon atoms of the cyclopropane ring by hydroxyl or formyl substituents. The experimental reaction parameters of vinylcyclopropanecarbaldehyde are surprisingly well reproduced by B3LYP/6-31G* density functional and MP2/6-31G* ab initio quantum theoretical calculations. Reactant and product are nearly isoenergetic, while the activation energy amounts to about 25 kcal/mol. In the case of the nitrogen and sulfur containing compounds the isomeric seven-membered ring structures are considerably favoured over the cyclopropanes. Due to a low calculated activation energy a rapid formation of the 2,5-dihydrothiepin is expected. Substitution of the hydrogen at the substituted ring carbon atoms in vinylcyclopropanecarbaldehyde by OH and CHO also lowers the barrier and increases, in general, the exothermicity of the reaction. As shown by the reaction energies of isodesmic reactions both reactants and products are stabilized by substitution. However, the seven-memberd ring compounds are more strongly stabilized than the cyclopropanes. The OH group exerts a different effect depending on whether the linkage is geminal or vicinal to the CX group. The difference is caused by hydrogen bond formation in geminal arrangements. The substituent effects in the cyclopropane series parallel those for the prototypical Cope-type and Claisen-type series. The particular feature of the cyclopropane series is the lower stability of the cyclopropanes relative to the corresponding open chain congeners. This is obviously due to the ring strain which over-compensates for attractive interactions between cyclopropane and the substituents. In consequence, the formation of seven-membered ring compounds proceeds more easily than the formation of the corresponding compounds in related Cope-type rearrangements.
TL;DR: In this article, the synthesis of pseudo-tripeptide 9 and a pseudo-pentapeptide 1 incorporating the conformationally constrained β-amino acid (2S, 3R)-2amino cyclopropane carboxylic acid is reported.
TL;DR: Adeeva et al. as discussed by the authors showed that the surface of a sulfated zirconia catalyst contains a small number of Bronsted sites; the number ratio of sulfate ions to bronsted sites is 12.5/1.