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Showing papers on "Cyclopropane published in 1999"


Journal ArticleDOI
TL;DR: The role of the bifunctional catalyst is decisive: the magnesium ion as Lewis acid and its nucleophilic iodide counterion contribute in synergy to the successful ring expansion of the cyclopropane 1 by aldimine 2.
Abstract: The role of the bifunctional catalyst is decisive: The magnesium ion as Lewis acid and its nucleophilic iodide counterion contribute in synergy to the successful ring expansion of the cyclopropane 1 by aldimine 2 [Eq. (1)]. This reaction offers a novel route to spiro[pyrrolidin-3,3'-oxindoles] 3.

239 citations


Journal ArticleDOI
TL;DR: Partially and fully protected, and unprotected β-oligopeptides were prepared from 1-(aminomethyl)cyclopropanecarboxylic acid, which, in turn, is readily available from cyanoacetate and dibromoethane as mentioned in this paper.
Abstract: Partially and fully protected, and unprotected β-oligopeptides (3 – 9) were prepared from 1-(aminomethyl)cyclopropanecarboxylic acid, which, in turn, is readily available from cyanoacetate and dibromoethane. N-Boc and C-OMe protection were applied for the fragment-coupling (1-hydroxy-1H-benzotriazole (HOBt)/1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide hydrochloride (EDC)) solution synthesis. X-Ray crystal structures of the dimer (3), trimer (5), and tetramer (6) are described, and compared with those of the Boc-protected building blocks (2) and of the corresponding trimer (10) consisting of 1-(aminomethyl)cyclohexanecarbonyl residues (cf. Figs. 1 and 2). While the cyclohexane derivative forms ten-membered hydrogen-bonded rings, the characteristic secondary-structural motif in the cyclopropane derivatives is an eight-membered ring with H-bonding between next neighbors (Fig. 1). All cyclopropanecarbonyl moieties in the reported structures have the – generally more stable – s-cis (`bisected') conformation of the C=O groups on the three-membered rings (not preferred with the cyclohexane analog, the exocyclic CO group of which may be in an s-trans, a perpendicular, an axial, or an equatorial position). The bisecting effect and the large exocyclic bond angle (120°) in the cyclopropane units are proposed to provide the `ordering' elements – on top of the staggering effect of the C(2)−C(3) ethane bond in all β-peptides – which lead to the observed substituent-induced turn formation. A high degree of intramolecular H-bonding is evident also from IR spectroscopy (Fig. 3), and concentration- and temperature-dependent NMR measurements (Fig. 4) of CHCl3 and CD2Cl2 solutions, indicating that the boat-type arrangement of the eight-membered rings with their unusual H-bonding geometry (Fig. 1, f ) is also present in solution. A possible structure of a poly[1-(aminomethyl)cyclopropane-carboxylic acid] consisting of a flight of stairs formed by folded H-bonded eight-membered rings is modelled, using the oligomer X-ray data (Fig. 5). The type of secondary structure found in the solid state of the β2,2-peptides reported here is unprecedented in the realm of α-peptides and proteins.

91 citations


Journal ArticleDOI
TL;DR: Alpha-Cyclodextrin improved the selectivity and yields of the reactions conducted in an aqueous medium and was pictured as a sequential Favorskii type reaction.
Abstract: Zerumbone (1) was isolated from fresh rhizomes of Zingiber zerumbet Smith in yields of 0.3-0.4% by simple steam distillation and recrystallization. 1 accepted 2 equiv of hydrogen cyanide at the C6 and C9 double bonds of the cross-conjugated dienone system to give a mixture of diastereomers 3a-d. In the presence of potassium cyanide, the dominant isomer 3a was isomerized to a mixture of 3a-d. Under controlled conditions, 1 added one mole of methanol regio- and stereoselectively at the C6 double bond to give adduct 4a. With potassium cyanide, 4a was transformed to the mixture of 3a-d. 1 took up one mole of bromine at C6 double bond to give a diastereomeric mixture of adducts 5a and 5b. Treatment of 5a with potassium cyanide gave a mixture of cyclopropanecarboxylic acid 6a and 6b. This unique ring-contracting cyclopropane formation is pictured as a sequential Favorskii type reaction. alpha-Cyclodextrin improved the selectivity and yields of the reactions conducted in an aqueous medium.

86 citations


Journal ArticleDOI
TL;DR: Relative rate experiements were used to measure rate constants and temperature denpendencies of the reactions of OH with propane, n-butane and n-pentane as mentioned in this paper.
Abstract: Relative rate experiements were used to measure rate constants and temperature denpendencies of the reactions of OH with propane, n-butane, n-pentane, n-hexane, cyclopropane, cyclobutane, cyclopentane, and dimethyl ether.

82 citations


Journal ArticleDOI
TL;DR: Studies on the stereo- and regioselectivity of rhodium(I)-catalyzed [5 + 2] cycloadditions of 2-substituted-1-vinylcyclopropanes are described, finding the relative stereochemistry of vicinal cyclopropane substituents is found to be conserved in these reactions.

61 citations


Journal ArticleDOI
TL;DR: By using [RhCl(CO)2]2 as a catalyst, bicyclo[4.3.0]-nonenones are prepared from 4-pentynyl cyclopropanes under CO atmosphere via cleavage of cyclopricane ring.
Abstract: By using [RhCl(CO)2]2 as a catalyst, bicyclo[4.3.0]-nonenones are prepared from 4-pentynyl cyclopropanes under CO atmosphere via cleavage of cyclopropane ring.

53 citations


Journal ArticleDOI
TL;DR: The first asymmetric cyclopropanation of ketene silyl acetal with allylic acetate was achieved in this paper, where chiral oxazolidinylpyrazole ligands and their η 3 -allylpalladium complexes were synthesized.

35 citations


Journal ArticleDOI
TL;DR: In this paper, a cycloaddition of diazomethane and ethyl diazoacetate to α-(diethoxyphosphoryl)vinyl p-tolyl sulfoxide 1a and its β-substituted analogues (Me, Ph) results in the formation of 3-phosphoricl-pyrazoles in high yield.

32 citations


Journal ArticleDOI
TL;DR: This article showed that β-unsaturated esters with various substituents at the β- and γ-positions readily cyclise to cyclopropane compounds in the presence of samarium diiodide and a proton source.

25 citations



Journal ArticleDOI
TL;DR: Fullerene derivatives consisting of a phosphorus ylide group and a cyclopropane ring on the fullerene moiety in good to excellent yields are determined on the basis of their spectral data and single-crystal X-ray diffraction measurements.
Abstract: A unique method to introduce phosphorus substituents onto C60 is based on the reaction of phosphines with acetylenes and C60. Treatment of C60 with phosphines (PR3) and electron-deficient acetylenes (A) in toluene at ambient temperature gave fullerene derivatives (1, R = C6H5 and A = MeO2CC⋮CCO2Me; 2, R = C6D5 and A = MeO2CC⋮CCO2Me; 3, R = C6H5 and A = EtO2CC⋮CCO2Et; 4, R = p-CH3C6H5 and A = MeO2CC⋮CCO2Me; 6, R = C6H5 and A = trans-MeO2CC⋮CCHCHCO2Me) consisting of a phosphorus ylide group and a cyclopropane ring on the fullerene moiety in good to excellent yields. The structures of these ylide derivatives are determined on the basis of their spectral data and single-crystal X-ray diffraction measurements. All these ylides show temperature-dependent NMR spectra that can be rationalized on the basis of interchange between two Z,E isomers and restricted rotation of the substituents on the fullerene moiety. Based on the known chemistry of phosphines and acetylenes, we propose a mechanism to account for the fo...

Journal ArticleDOI
TL;DR: Conformationally restricted analogs of baclofen, i.e., 5, 6, and their enantiomers ent-5, and ent-6, the conformations of which were restricted by introducing a cyclopropane ring, were designed as potential GABAB receptor ligands.
Abstract: Conformationally restricted analogs of baclofen (2), i.e., 5, 6, and their enantiomers ent-5, and ent-6 , the conformations of which were restricted by introducing a cyclopropane ring, were designed as potential GABAB receptor ligands. Reaction of (R)-epichlorohydrin [(R)-7] and (4-chlorophenyl)acetonitrile in the presence of NaNH2 in benzene/tetrahydrofuran gave chiral cyclopropane derivatives 11 and 12, which were then converted into the target compounds 5 and 6, respectively. Their corresponding enantiomers, ent-5 and ent-6, were also synthesized starting from (S )-epichlorohydrin [(S )-7].

Journal ArticleDOI
TL;DR: In this article, coupled cluster methods indicate that the isomerization of cyclopropane to propene might involve two differentmechanisms: the barrier for the newly proposed pathway through propylidene is only slightly higher (ΔE‡ = 66.6kcal mol−1) than that of the traditional trimethylene route.

Journal ArticleDOI
TL;DR: In this article, the potential energy surfaces corresponding to the reaction of the 16-electron [CpM(PH3)] (M = Rh, Ir) with propane and cyclopropane have been investigated at the B3LYP/LANL2DZ level of theory.
Abstract: The potential energy surfaces corresponding to the reaction of the 16-electron [CpM(PH3)] (M = Rh, Ir) with propane and cyclopropane have been investigated at the B3LYP/LANL2DZ level of theory. It was experimentally found that highly reactive [CpIr(PH3)] tends to be less discriminating and reacts randomly, while less reactive [CpRh(PH3)] is highly selective. Moreover, for both [CpRh(PH3)] and [CpIr(PH3)], the ease of oxidative addition is in the order: secondary cyclopropane>primary propane>secondary propane. The computational results are in good agreement with the experimental findings.

Journal ArticleDOI
TL;DR: In this paper, a cyclopropane substituent was used as a proton donor for the first time in argon matrices at 16 K. Ab initio calculations yield an essentially linear BrC−H−NH3 hydrogen bond with a C−H···N distance of 2.301 A and a hydrogen bond energy of 2,35 kcal/mol.
Abstract: Hydrogen-bonded complexes of bromocyclopropane with the strong bases ammonia and trimethylamine have been isolated and characterized for the first time in argon matrices at 16 K. Coordination of the proton adjacent to the Br substituent on the cyclopropane ring to the nitrogen of the base was evidenced by distinct blue shifts of the C−H(Br) bending modes in the infrared spectrum. These shifts (∼12 cm-1 for the in-plane bend and ∼6 cm-1 for the out-of-plane bend) are much smaller than those observed for alkenes and alkynes, suggesting a distinct but extremely weak interaction. Ab initio calculations yield an essentially linear BrC−H···NH3 hydrogen bond with a C−H···N distance of 2.301 A and a hydrogen bond energy of 2.35 kcal/mol, thus supporting that this hydrogen bond is one of the weakest observed thus far in a matrix. This study represents the first example of a (substituted) cyclopropane acting as a proton donor and only the second example of an alkane taking part in a C−H···N hydrogen bond.

Journal ArticleDOI
TL;DR: Two possible types of competing [1, 3]-sigmatropic rearrangements of divinylcyclopropane derivatives and of the hetero-analogous compounds vinylcyclopropanecarbaldehyde and vinylcyclopropane(thio)aldehyde to five-membered ring compounds have been investigated theoretically by (U)DFT (Becke3LYP/6-31G*) methodology as discussed by the authors.

Journal ArticleDOI
TL;DR: In this article, a new synthesis of (+)-(Z)-methanohomoserine, one of the key intermediates employed, is described, where an amino group is attached to a quaternary carbon of the cyclopropane ring.
Abstract: Some title compounds have been synthesized in enantiomerically pure form starting from d - or l -glyceraldehyde as chiral precursors. A new synthesis of (+)-(Z)-methanohomoserine, one of the key intermediates employed, is also described. The target molecules are densely functionalized. Thus, in addition to one or two hydroxyl groups on a side-chain, an amino group is attached to a quaternary carbon of the cyclopropane ring, and the fourth substituent of such a stereogenic center contains a halogen atom, an alkyl group, or an alcohol, thioether or ester function. Some of these compounds are useful precursors in the synthesis of new cyclopropane nucleosides.

Journal ArticleDOI
TL;DR: In this paper, the kinetic resolution of trans-substituted cyclopropane car with a solid support by lipase is described, and the same authors also describe the stability of the car.

Journal ArticleDOI
TL;DR: In this paper, a cyclopropane lactone was synthesized from optically active cycloprocessane methyl guanine (A-5021, 1 ) by employing: (1) selective reduction of the ester; (2) alkylation of 2-amino-6chloropurine; and (3) reductive opening of the lactone ring.

Journal ArticleDOI
TL;DR: The total synthesis of the cytotoxic agent (-)-anthoplalone and the determination of its absolute stereochemistry are reported and several pathways were studied to secure the E-trisubstituted olefin of the left part of the molecule.
Abstract: We report the total synthesis of the cytotoxic agent (−)-anthoplalone and the determination of its absolute stereochemistry. The cyclopropane moiety was prepared using a nonracemic bicyclic chloroallyl phosphonamide anion addition to tert-butyl 3,3-dimethyl acrylate. Several pathways were studied to secure the E-trisubstituted olefin of the left part of the molecule.

Journal ArticleDOI
TL;DR: NMR data indicate that all phosphite ylides 1-3 exist as mixtures of E and Z isomers, and a mechanism is proposed to account for the formation of these phosphonate derivatives.
Abstract: Treatment of phosphites (P(OR)3) and MeO2CCCCO2Me with C60 affords the corresponding fullerene derivatives (1, R = Me; 2, R = Et; 3, R = n-Bu) consisting of a phosphite ylide group and a cyclopropane ring on the fullerene moiety in high yields. NMR data indicate that all phosphite ylides 1−3 exist as mixtures of E and Z isomers. Under similar reaction conditions, the reaction of phosphinite PPh2(OMe) and MeO2CCCCO2Me with C60 gives ylide 4. Ylides 1−3 readily undergo hydrolysis with HBr to give corresponding phosphonates 5−7 in excellent yields, while ylide 4 reacts with hydrobromic acid to afford phosphine oxide 8. A mechanism is proposed to account for the formation of these phosphonate derivatives. Further treatment of phosphonate derivative 5 with trimethylsilyl iodide followed by water gave phosphonic acid derivative 9 in 83% yield.

Journal ArticleDOI
TL;DR: Several alkylidenecyclopropanes have been synthesized in high yields and optical purity by palladium(0)-catalyzed substitution of 1-tosyloxy-1-vinyl cyclopropane using N-to-sylamino esters or glycolic ester as nucleophiles as mentioned in this paper.

Journal ArticleDOI
TL;DR: In this article, the relative stereochemistry of the cyclopropane ring carbon and selenosilylmethyl group was determined as R,R and S,S, which is consistent with previous mechanical considerations and the NOE determination.
Abstract: Reaction of 1-(phenylseleno)-2-(trimethylsilyl)ethene 1 and methyl or ethyl 2-p-toluene- or benzenesulfonylacrylates 3 in the presence of SnCl4 at −78 °C gave sulfone-substituted cyclopropanes 4 as single stereoisomers. The structure of one of these crystalline cyclopropane products was elucidated by X-ray crystallographic analysis. The relative stereochemistry of the cyclopropane ring carbon (C2) and selenosilylmethyl group was determined as R,R and S,S, which is consistent with previous mechanical considerations and the NOE determination. 2-Sulfinyl acrylate 2 did not undergo this cycloaddition. The difference in reactivity of the sulfoxide 2 and sulfones 3 toward 1 was explained by comparison of LUMO levels of 2−SnCl4 and 3−SnCl4 complexes and activation energies in the synclinal addition of 1 to the complexes.

Journal ArticleDOI
TL;DR: The addition of iodine (or related species) to β-acyl-N-alkyl-1,4-dihydropyridines 1, which possess an N-substituent with an appropriate nucleophile moiety leads to the iodobi(poly)heterocyclic ring systems 2a–f in good yields.

Journal ArticleDOI
TL;DR: In this paper, the lifetime of 1-methylcyclopropylcarbene was determined to be 12 ns in 1,1,2-trichlorotrifluoroethane.
Abstract: 1-Methylcyclopropylcarbene, generated by photolysis of two isomeric hydrocarbon precursors, undergoes ring-expansion readily to give 1-methylcyclobutene. Experimentally, intramolecular carbon−hydrogen insertions are not observed. Trapping studies with TME demonstrates the formation of the expected cyclopropane adduct, and via a double-reciprocal analysis, the lifetime of 1-methylcyclopropylcarbene was determined to be 12 ns in 1,1,2-trichlorotrifluoroethane. Computational studies show that the barrier to ring-expansion is significantly smaller in 1-methylcyclopropylcarbene than in cyclopropylcarbene. The origin of the increased rate of ring-expansion is due to stabilization of the positive charge that occurs at the incipient tertiary carbon that is attached to the migrating carbon center.

Journal ArticleDOI
TL;DR: In this paper, the reaction of 1-seleno-2-silylethenes with the chiral electrophiles derived from (−)-menthol, in the presence of zinc halides, gave the cyclopropane products 5, 6, and 7, respectively, w...
Abstract: Reaction of 1-seleno-2-silylethenes 1 with the chiral electrophiles 2, 3, and 4 derived from (−)-menthol, in the presence of zinc halides gave the cyclopropane products 5, 6, and 7, respectively, w...

Journal ArticleDOI
TL;DR: In this paper, the 1-propyl cation in the ion pair with the model anion trihydrofluoroborate, proven in earlier work to be appropriate for such studies, was investigated by ab initio calculations at the level previously reported to give the definitive structure of carbocations.
Abstract: The structure of the 1-propyl cation in the ion pair with the model anion trihydrofluoroborate, proven in earlier work to be appropriate for such studies, was investigated by ab initio calculations at the level previously reported to give the definitive structure of carbocations. In previous work, it was shown that the carbocation structure does not change with the nature of the anion. The cation structure is determined, however, by the distance between the cation and anion, d, and their relative orientation. At infinite interionic distance the only stable chemical species (energy minimum) is the protonated cyclopropane, 1. As the ions move toward each other, the cyclopropane bond opposite to the anion becomes progressively longer and eventually it breaks up in the contact ion pair. Three domains of cation stability are identified as a function of d: at long distances, ion 1 is the only energy minimum; at intermediate distances 1 and the 1-propyl cation 2 are both energy minima; at short distances, ion 2...

Journal ArticleDOI
TL;DR: The structure of phenylcyclopropane radical cation (1•+, R = H) was derived from CIDNP effects observed during the electron transfer reaction of 1 with chloranil.
Abstract: The structure of phenylcyclopropane radical cation (1•+, R = H) is derived from CIDNP effects observed during the electron transfer reaction of 1 with chloranil. This species is an example of an elusive structure type. The secondary cyclopropane protons show significantly divergent hyperfine coupling constants due to an unprecedented stereoelectronic effect. Incorporation into a redox-active pentasil zeolite (Na−ZSM-5) converts 1 or its p-methoxy derivative (1, R = OCH3) to trans-propenylarene radical cations (2•+, R = H, OCH3).


Journal ArticleDOI
TL;DR: In this paper, the thermal, electron, and photon-induced chemistry of cyclopropane, c-C3H6, adsorbed on Pt(111) at 100 K has been studied.
Abstract: The thermal, electron, and photon-induced chemistry of cyclopropane, c-C3H6, adsorbed on Pt(111) at 100 K has been studied. The thermal chemistry is simple. Adsorption is saturable, no multilayer accumulates, and thermal desorption exhibits only c-C3H6 with one peak at 144 K. High-resolution electron energy loss spectra results indicate that c-C3H6 adsorbs with the plane of the ring tilted away from the surface normal. The electron-induced chemistry is more complex. Irradiation with 50 eV electrons activates dissociation of adsorbed c-C3H6 at 100 K, and there are thermally activated reactions during subsequent temperature-programmed desorption. The total cross-section for destruction of c-C3H6 is 8.2 (±0.2) × 10-17 cm2. For low electron fluences, <1016 cm-2, the chemistry involved is describable in terms of C−C bond breaking to open the ring and form metallacyclic species, some of which promptly lose H to form allylic (C3H5) moieties. In subsequent thermally activated reaction-limited processes, propylene...