Showing papers on "Cyclopropane published in 2002"
TL;DR: The incorporation of CAAs into peptides or peptidomimetics induce conformational restrictions and provide importantstructural effects and the preparation of conformationallyconstrained CAAs and their derivatives is provided.
145 citations
TL;DR: The structures of the meromycolic acids, including those with three functional groups extracted from Mycobacterium tuberculosis H37Ra, MycOBacterium bovis BCG and Myc Cobacterium microti, were established and were structurally closely related to those with one cis cyclopropane ring.
Abstract: Mycobacterial α-, methoxy- and keto-mycolic acid methyl esters were separated by argentation chromatography into mycolates with no double bond, with one trans double bond or with one cis double bond. Meromycolic acids were prepared from each methyl mycolate fraction by pyrolysis, followed by silver oxide oxidation, and analysed by high-energy collision-induced dissociation/fast atom bombardment MS to reveal the exact locations of the functional groups within the meromycolate chain. The locations of cis and trans double bonds, cis and trans cyclopropane rings, methoxy and keto groups, and methyl branches within the meromycolate chain were determined from their characteristic fragment ion profiles, and the structures of the meromycolic acids, including those with three functional groups extracted from Mycobacterium tuberculosis H37Ra, Mycobacterium bovis BCG and Mycobacterium microti, were established. Meromycolic acids with one cis double bond were structurally closely related to those with one cis cyclopropane ring, whereas the meromycolic acids with one trans cyclopropane ring were closely related to the corresponding meromycolic acids with one cis cyclopropane ring. A close relationship between methoxy- and keto-meromycolic acids was also implied. The relationship between the meromycolic acids with a trans double bond and the other meromycolic acids was not clearly revealed, and they did not appear to be immediate substrates for trans cyclopropanation.
115 citations
TL;DR: The chiral cyclopropane units 7, 8, ent-7, and ent-8 should be useful as versatile intermediates for synthesizing various compounds having an asymmetric cycloprostane structure.
Abstract: The cyclopropane ring can be used effectively in restricting the conformation of biologically active compounds to improve activity and also to investigate bioactive conformations. We designed (1S,2R)- and (1R,2R)-2-aminomethyl-1-(1H-imidazol-4-yl)cyclopropanes (1 and 2, respectively) and their enantiomers (ent-1 and ent-2) as conformationally restricted analogues of histamine. The four types of chiral cyclopropanes bearing two differentially functionalized carbon substituents in a cis or trans relationship on a cyclopropane ring, (1S,2R)-2-(tert-butyldiphenylsilyloxy)methyl-1-formylcyclopropane (7) and (1R,2R)-2-(tert-butyldiphenylsilyloxy)methyl-1-formylcyclopropane (8) and their enantiomers (ent-7 and ent-8), were developed as the key intermediates for synthesizing 1, 2, ent-1, and ent-2. The reaction between (R)-epichlorohydrin [(R)-12] and phenylsulfonylacetonitrile (13a) in the presence of NaOEt in EtOH followed by treatment with acid gave the chiral cyclopropane lactone 11a with 98% ee in 82% yield....
77 citations
70 citations
TL;DR: The regioselectivity in the Pd(0)-catalyzed coupling-cyclization of 2-(2',3'-allenyl)malonates with organic halides is determined by the steric and electronic effects of both substrates and may be explained by the comparison of the relative stabilities of syn- and anti-type pi-allyl palladium intermediates.
Abstract: The regioselectivity in the Pd(0)-catalyzed coupling−cyclization of 2-(2‘,3‘-allenyl)malonates with organic halides is determined by the steric and electronic effects of both substrates. By deliberate control of the reaction conditions, the regioselectivity of this reaction can be tuned. With conditions A and B, the reaction afforded vinylic cyclopropane derivatives, while with conditions C and D, the reaction afforded cyclopentene derivatives in a highly selective manner. Under similar conditions, 1-alkenyl halides tend to form more three-membered cyclic products. The increased steric hindrance at the 2‘-positon of the allene moiety and aryl halides favors the formation of five-membered cyclic products. The regioselectivity of the reaction may be explained by the comparison of the relative stabilities of syn- and anti-type π-allyl palladium intermediates.
60 citations
TL;DR: The reaction of cis vicinal acetylethynylcyclopropanes 1 with a catalytic amount of M(CO)5(THF) in the presence of Et3N at room temperature gave ortho-substituted phenols 7 in good yields as valence isomerized products.
Abstract: The reaction of cis vicinal acetylethynylcyclopropanes 1 with a catalytic amount of M(CO)5(THF) (M = Cr or W) in the presence of Et3N at room temperature gave ortho-substituted phenols 7 in good yields as valence isomerized products. In the absence of Et3N the reactions did not work at all. The reaction of a cyclopropane having an ester or an amide instead of an acetyl moiety with M(CO)5(THF) did not take place, whereas an ethynylvinylcyclopropane gave a mixture of 1- and 2-substituted 1,3,5-cycloheptatrienes. These valence isomerization reactions are assumed to proceed via the formation of vinylidene−metal intermediates 2 from terminal alkynyl moieties followed by [3,3]sigmatropy of 2 to give seven-membered carbene complexes 3.
57 citations
TL;DR: In this article, the Henry reaction was used to synthesize optically active β-amino acids and cyclopropane γ amino acids by reducing the nitro group and oxidative cleavage of the dioxolane substituent.
52 citations
TL;DR: By using the described reaction, 1-aminocyclopropanecarboxylic acids were prepared in four steps, in good overall yields, from the readily available benzyloxyacetonitrile.
Abstract: Alpha-alkoxy, amino-, and thio nitriles undergo a Ti(II)-mediated coupling with Grignard reagents to afford heterofunctionalized cyclopropylamines. A chelation effect appears to be generally responsible for the spontaneous contraction of the intermediate azatitanacycle leading to cyclopropane. By using the described reaction, 1-aminocyclopropanecarboxylic acids were prepared in four steps, in good overall yields, from the readily available benzyloxyacetonitrile.
51 citations
TL;DR: An unprecedented cyclopropanation by cyclopolymerization reaction is presented, in particular, catalytic copolymerization processes of ethene and butadiene lead with high trans selectivity to a complete cyclocopolymersization of butadienes units.
Abstract: An unprecedented cyclopropanation by cyclopolymerization reaction is presented. In particular, catalytic copolymerization processes of ethene and butadiene lead with high trans selectivity to a complete cyclocopolymerization of butadiene units. Ethene-based copolymers including cyclopropane and cyclopentane rings, which can be relevant to polyolefin applications, are obtained with high yields. Several aspects relative to the mechanism of this cyclocopolymerization reaction, including the high stereoselectivity, are discussed.
50 citations
TL;DR: Reactions of zirconacyclopentadienes with dichlorocarbene afforded cyclopropanation products in good yields and gave vinylcyclopropanes in good yield after hydrolysis, in sharp contrast to the formation of usual 1,2,3,4-tetrasubstituted benzene derivatives from zir ConACYclopents.
Abstract: Reactions of zirconacyclopentadienes with dichlorocarbene afforded cyclopropanation products in good yields. In a similar manner, reactions of zirconacyclopentadienes with a Simmons-Smith type cyclopropanation reagent also gave vinylcyclopropanes in good yields after hydrolysis. Before hydrolysis, the formation of 1-zirconabicyclo[3.1.0]hexene was observed by 13C NMR spectroscopy. The 1-zirconabicyclo[3.1.0]hexene deriatives reacted with CO to produce 1,2,3,5-tetrasubstituted benzene derivatives in good yields via the C-C bond cleavage of the cyclopropane rings. This is in sharp contrast to the formation of usual 1,2,3,4-tetrasubstituted benzene derivatives from zirconacyclopentadienes.
49 citations
TL;DR: It is found that the chemical reactivity of the carbenoid species is dependent on its electrophilic behavior, steric effects, the leaving group character and the mechanism of the cyclopropanation reactions.
Abstract: The insertion reaction of zinc into the C-I bond of CH(2)I(2) and subsequent cyclopropanation reactions with CH(2)CH(2) have been investigated using B3LYP level density functional theory calculations. The Simmons-Smith cyclopropanation reaction of olefins does not proceed easily due to the relatively large barriers on the insertion and cyclopropanation pathways. The computed results indicate that the IZnCH(2)I molecule is the active reagent in the Simmons-Smith reaction. This is consistent with the IZnCH(2)I reactive species being generated from diiodomethane and a Zn-Cu couple as proposed by several other research groups. The Simmons-Smith IZnCH(2)I carbenoid and CH(2)I-I carbenoid cyclopropanation reactions with olefins are compared. The reactions of olefins with the radicals from the decomposition of the IZnCH(2)I and CH(2)I-I species were also compared. We found that the chemical reactivity of the carbenoid species is dependent on its electrophilic behavior, steric effects, the leaving group character and the mechanism of the cyclopropanation reactions.
TL;DR: A new azetidine-ligated dirhodium(II) catalyst that possesses a l-menthyl ester attachment provides significant diastereocontrol and high enantiocont control for the formation of cis-cyclopropane products from reactions of substituted styrenes with diazo esters.
TL;DR: Significant amounts of novel gem-dizinc carbenoids (RZnCHIZnR) are formed when diethylzinc is mixed with iodoform in CH2Cl2 at 0 degrees C.
Abstract: Significant amounts of novel gem-dizinc carbenoids (RZnCHIZnR) are formed when diethylzinc is mixed with iodoform in CH2Cl2 at 0 °C. This reagent was shown to be effective in the cyclopropanation of butenediol derivatives to generate a cyclopropylzinc intermediate that could be trapped with a variety of electrophiles. 1,2,3-Substituted cyclopropane derivatives are formed with excellent diastereoselectivities by using this simple procedure.
TL;DR: The reaction of α-unsubstituted nitroacetates with Mn(OAc)3 gives mixtures of isoxazolines, formed by dehydration to a nitrile oxide that undergoes cycloaddition, and isoxoxoline oxides or cyclopropane, forming by oxidative cyclization as discussed by the authors.
TL;DR: In this paper, quantum mechanics methods have been applied to investigate the effects of the selective orientation of the side chains on the conformational features of cyclopropane analogues of phenylalanine.
Abstract: Quantum mechanics methods have been applied to investigate the effects of the selective orientation of the side chains on the conformational features of cyclopropane analogues of phenylalanine. For...
Journal Article•
TL;DR: In this paper, the absolute total cross sections (TCSs) for the electron scattering from two structured isomers of C3H6 (propene and cyclopropane) have been determined over the energy range from 0.5 up to 370 eV in a linear electron-beam transmission experiment.
Abstract: Absolute total cross sections (TCSs) for the electron scattering from two structured isomers of C3H6 (propene and cyclopropane) have been determined over the energy range from 0.5 up to 370 eV in a linear electron-beam transmission experiment. The TCS for propene is generally higher than that for cyclopropane, especially around the main maximum which in both TCSs is centred near 9.5 eV. Besides this broad enhancement, already observed in earlier measurements, some additional new TCS features - specific for each target - have been noticed in the present experiment. The TCS for propene has a distinct resonant narrow peak visible at around 2.2 eV. For cyclopropane, a very weak hump at around 2.6 eV and a shoulder near 6 eV on the low-energy slope of the cross section function are distinguishable. On the descending side of the cross section energy dependence the change of the slope is located at around 40 eV. These weak cyclopropane features seem to be common for cyclic molecules. The present results are compared with earlier C3H6 TCS measurements available above 4 eV and with calculations above 10 eV. A distinct difference in magnitudes is visible, especially around the main maximum. On the basis of the present propene and previous hexafluoropropene data a fluorination effect is indicated and discussed.
TL;DR: The use of (-)-sparteine as a chiral ligand instead of TMEDA allows the synthesis of cyclopropane derivatives with up 81% ee.
TL;DR: The diastereoselective synthesis of azabicyclo[3.1.0]hexanes bearing different substituents on all positions of the cyclopropane ring has been achieved in moderate to good yields.
TL;DR: E-(S)-(1-Dimethoxyphosphoryl-2-phenyl)vinyl ptolyl sulfoxide 3 was found to undergo cyclopropanation with sulfur ylides [dimethyl(oxo)sulfonium methylide, diphenyl sulfonium isopropylide and ethyl (dimethylsulfuranylidene)acetate (EDSA)] in a highly diastereoselective manner.
TL;DR: A new intramolecular cyclopropanation reaction of unsaturated β-keto esters is reported with moderate to good yields in the presence of I2, Et3N, and Lewis acids.
TL;DR: In this paper, the photodissociation dynamics of cyclopropane at 157 nm was investigated using a new molecular beam apparatus based on vacuum ultraviolet ionization by synchrotron radiation.
Abstract: Photodissociation dynamics of cyclopropane at 157 nm has been investigated using a new molecular beam apparatus based on vacuum ultraviolet ionization by synchrotron radiation. Four distinct dissociation pathways have been observed. The observed channels are the H formation process, the H2 formation process, the CH2+C2H4 formation process, and the CH3+C2H3 formation process. Experimental results indicate that the H atom products are possibly produced via a synchronous, concerted 2H elimination process, while other channels are all binary dissociation processes. Product kinetic energy distribution of each dissociation channel has been determined from simulating the experimental time of flight spectra. Relative branching ratios for all observed dissociation channels were also estimated based on all detected products.
TL;DR: In this article, the branching point of cyclization to thiolanes and fragmentation to cyclopropanes is discussed, where intramolecular nucleophilic substitution in anti-zwitterions or unassisted heterolysis leading to a tert-carbenium zwitterion as further intermediate are discussed.
TL;DR: In this paper, the authors investigated the alkylation reaction of propene with the 2-propyl cation by ab initio density functional methods at the B3LYP/6-31G** level and found a distorted trimethyl-1-protonated cyclopropane as an energy minimum along the reaction coordinate.
Abstract: An investigation of the alkylation reaction of propene with the 2-propyl cation by ab initio density functional methods at the B3LYP/6-31G** level found a distorted trimethyl-1-protonated cyclopropane as an energy minimum along the reaction coordinate (intermediate) and an open ion, the 4-methyl-2-pentyl cation (1), as another energy minimum (product). In contrast, the open ion 1 was not an energy minimum in MP2/6-31G** calculations. Attempts at geometry optimizations of 1 at that level led invariably to the protonated cyclopropane structure (more symmetrical than in the previous case). The ion 1 was in fact a transition structure in the MP2/6-31G** optimizations. A coupled cluster (CCSD/6-31G**) geometry optimization showed, however, the open ion 1 as a true energy minimum. This result brings a note of caution concerning MP2 geometry optimizations of carbocations. In particular, when these calculations find small energy differences between bridged and open structures, but find only the bridged structures...
TL;DR: In this paper, the synthesis of phosphonates of methylenecyclopropane nucleoside analogues by alkylation-elimination approach is described.
TL;DR: This work presents the first example for a heme enzyme that catalyzes the enantioselective oxidation of cyclopropylmethanols, and enables a novel route to the synthesis of optically activecyclopropane derivatives.
Abstract: Chloroperoxidase (CPO) catalyzes the enantioselective oxidation of cyclopropylmethanols, such as 2-methylcyclopropylmethanol, to cyclopropyl aldehydes using tert-butyl hydroperoxide as the terminal oxidant. In all cases, CPO oxidation of cis-cyclopropanes shows much higher enantioselectivity than with the trans isomers, although CPO gives similar catalytic activity on both isomers. This presents the first example for a heme enzyme that catalyzes the enantioselective oxidation of cyclopropylmethanols. This finding enables a novel route to the synthesis of optically active cyclopropane derivatives, which occur widely in natural products and compounds of pharmaceutical interest. In addition, chiral cyclopropane molecules may be useful model substrates to investigate reaction mechanisms of CPO and the related cytochromes P450.
TL;DR: The diastereoselectivity of the reaction allows the preparation of cis-divinyl cyclopropanes, which evolve via Cope sigmatropic reaction toward cycloheptadiene derivatives, and the aromatic Cope rearrangement of a series of cis,aryl vinylcyclopropane prepared by means of this methodology has been studied.
TL;DR: PtI 2 (PPh 3 ) 2 -catalyzed hydrosilylation of 2,2-diphenyl-1-methylenecyclopropane with HSiEt 3 forms (2,2diphensylcyclopropyl)methyl(triethyl)silane in 87% yield as a sole product as mentioned in this paper.