Showing papers on "Cyclopropane published in 2000"
TL;DR: In this paper, the absolute stereochemistry of cyclopropane 10 was proven by X-ray analysis and the origin of the stereochemical induction has been rationalised, and the use of the chiral 1,3-oxathiane derived from camphorsulfonyl chloride in 2 steps in this process furnished cyclop-ropane in good yield and very high enantiomeric excess (>97% ee).
Abstract: Phenyldiazomethane reacts with electron deficient alkenes in the presence of catalytic amounts of transition metal catalyst [Rh2(OAc)4 was better than Cu(acac)2] and catalytic amounts of sulfide to give cyclopropanes. Pentamethylene sulfide was found to be superior to tetrahydrothiophene and the optimum solvent was toluene. Under these optimised conditions a range of enones were cyclopropanated in high yields. Cyclic enones and acrylates were not successful in this process. The use of the chiral 1,3-oxathiane derived from camphorsulfonyl chloride in 2 steps in this process furnished cyclopropanes in good yield and very high enantiomeric excess (>97% ee). The absolute stereochemistry of cyclopropane 10 was proven by X-ray analysis and the origin of the stereochemical induction has been rationalised. Extension of this work to include diazoesters was partially successful. Again pentamethylene sulfide was found to be superior to tetrahydrothiophene, but this time both Rh2(OAc)4 and Cu(acac)2 were found to be equally effective. Enones, fumarates and unsaturated nitro compounds worked well but simple acrylates and unsaturated aldehydes were not effective substrates. Control experiments were conducted in which the stabilised ylide was isolated and reacted with the less successful substrates and, whilst unsaturated aldehydes still gave low yields, simple acrylates gave high yields of the corresponding cyclopropane. The use of the chiral 1,3-oxathiane was not successful with these more stable diazo compounds.
88 citations
88 citations
TL;DR: In this article, the authors used molecular dynamics techniques to simulate the diffusion of n-heptane, 2-methylhexane and cyclopropane reaction intermediates in two unidimensional medium pore zeolites, ZSM-48 and Theta-1.
81 citations
TL;DR: In this article, the rotational constants of cyclopropane were analyzed at the CCSD(T)/cc-pVQZ level using the vibrational corrections.
Abstract: A long-standing controversy regarding the re structure of cyclopropane is resolved by performing high-level quantum chemical calculations and analyzing the experimental rotational constants for C3H6 and C3H4D2 augmented by calculated vibrational corrections. For the latter, a least-squares fit yields the following set of parameters: re (CC) = 1.5030(10) A, re(CH) = 1.0786(10) A, and αe(HCH) = 114.97(10)°, which compare favorably with both the pure computational result obtained at the CCSD(T)/cc-pVQZ level as well as an earlier estimate of the re structure of cyclopropane based on analysis of gas-phase electron diffraction data. Our results are in rather poor agreement with a structure based on a previous analysis of the rotational constants that used empirically estimated vibrational corrections.
68 citations
TL;DR: In this paper, a quantum-chemical investigation showed that the reactions of carbenoids LiCH2X 1-X, X=F, Cl, Br, I and OH, with ethene 3 to cyclopropane 4+LiX profit from a weakening of the C-X bonds by the C−Li bonds in the carbenoid and in the complexes [1-X·3].
60 citations
TL;DR: In this paper, α-Diazoketones derived from pyrrolyl- and indolyl-carboxylic acids were prepared and their Rh2(OAc)4 catalyzed decomposition chemistry was studied.
59 citations
TL;DR: In this article, the influence of alkene structure and catalyst has been obtained using the 1,2-benzenedimethanol linker between the allylic double bond and diazoacetate.
Abstract: Stereoselectivity in intramolecular cyclopropanation reactions resulting in cyclopropane fusion with ten- and larger-membered rings has been examined using chiral copper(I) and dirhodium(II) catalysts. The influence of alkene structure and catalyst has been obtained using the 1,2-benzenedimethanol linker between the allylic double bond and diazoacetate. Control features in the addition reaction, especially those for diastereoselectivity and enantioselectivity, have been elucidated, and they are associated with the metal itself or its attendant ligands that influence the trajectory of the alkene to the carbene center. The influence of ring size, from five- to twenty-membered rings, on stereoselectivity has been determined with selected copper(I) and dirhodium(II) catalysts, and the changes in stereocontrol as a function of ring size can be understood as being due to a change in the olefin trajectory to the carbene center. Hydride abstraction from a benzylic position accompanies addition when dirhodium cata...
59 citations
59 citations
TL;DR: In this paper, the first isolated tertiary alkyl complexes of iridium have been obtained by a tandem C−H bond activation/decarbonylation reaction, where the iridium ion was used to give the hydrocarbyl carbonyl salts [Cp*(PMe3)Ir(R)(CO)][OTf] and aldehydes (RCHO) respectively.
59 citations
TL;DR: In this article, an enantiomerically pure cyclopropane trans-β-amino acid, bearing a quaternary center, has been synthesized from a homochiral precursor easily available from d -glyceraldehyde.
Abstract: Synthetic approaches to carbocyclic compounds, namely cyclopropane and cyclobutane β-amino acids, are presented. One of them is based on enzymatic desymmetrization of meso diesters, leading to the enantioselective production of cis-hemiesters, which afforded β-amino acids through Curtius rearrangements. The enantiomeric excess for the cyclobutane derivatives was 91% whereas the cyclopropanes were obtained in 63% ee. According to another strategy, an enantiomerically pure cyclopropane trans-β-amino acid, bearing a quaternary center, has been synthesized from a homochiral precursor easily available from d -glyceraldehyde. The preparation and structural investigation of the first synthesized cyclobutane containing dipeptide is also described. A hairpin-like conformation of this molecule in the solid state has been demonstrated by X-ray structural analysis, showing crystal packing induced by the presence of the rigid cyclobutane moiety and the formation of intermolecular hydrogen bonds. NMR experiments confirmed that these molecules also tend to produce aggregates in solution. On the contrary, theoretical calculations suggest that intramolecular interactions are important in the gas phase, as expected.
58 citations
TL;DR: In this article, a new reaction was described catalyzed by Zeise's dimer that allowed for ring opening of 1,2-cyclopropanated sugars with O-nucleophiles to give 2-C-branched carbohydrates.
Abstract: A new reaction is described catalyzed by Zeise's dimer that allows for ring opening of 1,2-cyclopropanated sugars with O-nucleophiles to give 2-C-branched carbohydrates. A number of O-nucleophiles can participate in the ring opening including alcohols, phenols, and water. A wide range of alcohols has been employed giving 2-C-branched glycosides ranging from simple methyl glycosides to more complex disaccharides. A very high diastereoselectivity is obtained at the newly formed C-1 stereocenter. The α-glycoside, favored by the anomeric effect, is always the major product in the ring opening with alcohols regardless of the stereochemistry of the starting cyclopropane. When electron-rich phenols are employed as O-nucleophiles, rearrangement to the glycosyl arene has been observed. In general, the ring opening occurs readily with unsubstituted sugar cyclopropanes to give 2-C-methyl carbohydrates. However, cyclopropanes with ester or alkyl substituents are significantly less reactive and some even completely in...
TL;DR: The catalytic reaction of styrene with ethyl diazoacetate and Cu-11b yields ethyl trans-phenylcyclopropane carboxylate in >99% yield and 87% e.g. at 0°C as discussed by the authors.
Abstract: Substituted mono- and bis-pinene-[5,6]-bipyridines are useful ligands in asymmetric copper-catalyzed cyclopropanation by styrenes. Copper complexes were prepared either in situ or prior to the reaction. The catalytic reaction of styrene with ethyl diazoacetate and Cu – 11b yields ethyl trans -phenylcyclopropane carboxylate in >99% yield and 87% e.e. at 0°C. The corresponding cis -configured cyclopropane was produced with an e.e. of 90%. The cis / trans ratio is 22:78. Other ligands of this series are less effective. Various olefins were tested as substrates but exo -methylene olefins show the best results.
TL;DR: Both the selective cleavage of thecyclopropyl group from the aromatic amine nitrogen and nature of the products derived from the cyclopropane ring support a mechanism involving the formation of an amine radical cation.
Abstract: A group of N-cyclopropyl-N-alkylanilines has been synthesized, and their reaction with nitrous acid in aqueous acetic acid at 0 degrees C was examined. All compounds reacted rapidly to produce the corresponding N-alkyl-N-nitrosoaniline by specific cleavage of the cyclopropyl group from the nitrogen. The transformations were unaffected by the nature of the alkyl substituent (Me, Et, (i)()Pr, Bn). The reaction of 4-chloro-N-2-phenylcyclopropyl-N-methylaniline with nitrous acid gave 4-chloro-N-methyl-N-nitrosoaniline (76%), cinnamaldehyde (55%), 3-phenyl-5-hydroxyisoxazoline (26%), and 5-(N-4-chlorophenylmethylamino)-3-phenylisoxazoline (8%). Both the selective cleavage of the cyclopropyl group from the aromatic amine nitrogen and nature of the products derived from the cyclopropane ring support a mechanism involving the formation of an amine radical cation. This step is followed by rapid cyclopropyl ring opening to produce an iminium ion with a C-centered radical which either combines with NO or is oxidized.
TL;DR: In this paper, an anti-selective biotransformation of racemic trans -2-arylcyclopropanecarbonitriles catalyzed by Rhodococcus sp. AJ270 cells is described.
TL;DR: This tunable metal cation activation of CPyI constitutes the first example of a new approach to in situ activation of a DNA binding agent complementary to the well-recognized methods of reductive, oxidative, or photochemical activation.
Abstract: The synthesis of methyl 1,2,9,9a-tetrahydrocyclopropa[c]pyrido[3,2-e]indol-4-one-7-carboxylate (CPyI) containing a one carbon expansion of the C ring pyrrole found in the duocarmycin SA alkylation subunit and its incorporation into analogues of the natural product are detailed. The unique 8-ketoquinoline structure of CPyI was expected to provide a tunable means to effect activation via selective metal cation complexation. The synthesis of CPyI was based on a modified Skraup quinoline synthesis followed by a 5-exo-trig aryl radical cyclization onto an unactivated alkene with subsequent TEMPO trap or 5-exo-trig aryl radical cyclization onto a vinyl chloride for synthesis of the immediate precursor. Closure of the activated cyclopropane, accomplished by an Ar-3‘ spirocyclization, provided the CPyI nucleus in 10 steps and excellent overall conversion (29%). The evaluation of the CPyI-based agents revealed an intrinsic stability comparable to that of CC-1065 and duocarmycin A but that it is more reactive than ...
TL;DR: In this article, the reaction of various mono-substituted methylidenemalononitriles with (−)-8-phenylmenthyl α-pyridiniumacetate in the presence of base afforded the corresponding dicyanocyclopropane compounds with exclusive trans-selectivity and good diastereoselectivity (up to 86:14).
TL;DR: In this paper, the authors synthesize the model dipeptides tBuCO- l -Pro-c3diPhe-NHiPr, where c3DiPhe represents (2S, 3S)- and (2R, 3R)-1-amino-2,3-diphenylcyclopropanecarboxylic acid, two cyclopropane analogues of phenylalanine.
TL;DR: The results indicate that the gamma-elimination of tin is faster than the beta-elIMination of silicon, but slower than the Beta-elinination of germanium and tin.
Abstract: To evaluate β-effects and γ-effects of group 14 elements, we have devised a system in which the intramolecular competition between γ-elimination of tin and β-elimination of silicon, germanium, and tin can be examined. Thus, the reactions of α-acetoxy(arylmethyl)stannanes with allylmetals (metal = Si, Ge, Sn) in the presence of BF3·OEt2 were carried out. The reactions seem to proceed by the initial formation of an α-stannyl-substituted carbocation, which adds to an allylmetal to give the carbocation that is β to the metal and γ to tin. The β-elimination of the metal gives the corresponding allylated product, and the γ-elimination of tin gives the cyclopropane derivative. In the case of allylsilane, the cyclopropane derivative was formed as a major product, whereas in the case of allylgermane the allylated product was formed predominantly. In the case of the allystannane the allylated product was formed exclusively. These results indicate that the γ-elimination of tin is faster than the β-elimination of sil...
TL;DR: The structure of a cyclopropane sorption complex of dehydrated fully Mn2+-exchanged zeolite X, Mn46Si100Al92O384·30C3H6 (a=24.690(4) A), has been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd 3 at 21(1)°C.
TL;DR: The sequential addition of functionalised chains onto a 1,2-diformylcyclopropane synthon provides rapid access to cyclopropyl oxylipins, as demonstrated by the total synthesis of Constanolactones A and B as discussed by the authors.
TL;DR: The two diastereomers of a 3-oxabicyclo[3.1.0]hexan-2-ol with the cyclopropane ring substituted by a hydroxymethyl group were synthesized from both products.
TL;DR: In this paper, the transition metal promoted ring expansion of alkynyl- and propadienylcyclopropanes is surveyed with emphasis on the Co2(CO)8-mediated reactions developed by the author's group.
Abstract: Transition metal promoted ring expansion of alkynyl- and propadienylcyclopropanes is surveyed with emphasis on the Co2(CO)8-mediated reactions developed by the author’s group. A novel rearrangement of 1-(1-alkynyl)cyclopropanols to 2-cyclopenten-1-ones proceeds on complexation of their alkynyl part with Co2(CO)8. In the case of the reactions of 1-alkynylcyclopropanols with an alkyl substituent on the cyclopropane, either 4-substituted or 5-substituted 2-cyclopenten-1-ones can be selectively obtained by appropriate choice of stereochemistry and protective group of the substrates. This rearrangement is successfully applied to cyclopentenone annelation reactions onto cycloalkenes. The rearrangement proceeds catalytically on addition of triaryl phosphite as ligand. The same type of rearrangement proceeds when 1-[o-(1-alkynyl)phenyl]cyclopropanols are employed as substrates; these are converted to 2,3-dihydro-1-naphthalenone derivatives on heating their hexacarbonyldicobalt complexes in 2-propanol. Furthermore, a new type of isomerization-cyclization reaction proceeds to give 3a,4-dihydro-3H-cyclopenta[a]inden-2-one derivatives when the same reaction is carried out in the presence of 1,4-diazabicyclo[2.2.2]octane (DABCO). A novel transformation of 1-propadienylcyclopropanols into substituted 1,4-hydroquinones is developed utilizing the interaction of the 1,2-propadienyl group and Co2(CO)8. This reaction is applied to the synthesis of vitamin E and K analogs.
TL;DR: The reactivity of propellane C−C bonds towards ammonium(IV) ammonium nitrate (CAN) was studied utilizing photochemical initiation in acetonitrile as mentioned in this paper.
TL;DR: In this article, the Fp anion with enantiomerically pure S-(+) or R-(−)-o-anisaldehyde(tricarbonyl)chromium complexes was used to synthesize carbene precursors.
TL;DR: The total synthesis of (+)-pinguisenol, a sesquiterpene containing a cis-1,2,6,7-tetramethylbicyclo[4.0]nonane carbon framework incorporating two vicinal quaternary carbon atoms and four cis-oriented methyl groups on four contiguous carbon atoms, isolated from a liverwort, is described in this article.
Abstract: Enantiospecific total synthesis of (+)-pinguisenol 1, a sesquiterpene containing a cis-1,2,6,7-tetramethylbicyclo[4.3.0]nonane carbon framework incorporating two vicinal quaternary carbon atoms and four cis-oriented methyl groups on four contiguous carbon atoms, isolated from a liverwort, is described. The orthoester Claisen rearrangement of the allyl alcohol 9, obtained from (R)-carvone, generates the ester 12. Intramolecular cyclopropanation of the diazo ketone 13, derived from the ester 12, furnishes the tricyclic ketone 7. Degradation of the isopropenyl group followed by regioselective reductive cyclopropane ring cleavage transforms compound 7 into the hydroxy ketone 21. Wolff–Kishner reduction of the hydroxy ketone 21 followed by oxidation and Grignard reaction furnishes pinguisenol (+)-1.
TL;DR: In this paper, the cyclic sulfate of (+)-(S)-1,2-propanediol and dimethyl t-butoxy carbonylmethylphosphonate was synthesized in an enantiomerically pure form.
TL;DR: In this article, the catalytic activities of 4-methyl-1-pentene and of 2-methylpentane were compared on two series of reduced MoO3 catalysts supported on α-type-Al2O3.
TL;DR: In this paper, the Deutsch-Mark formalism was used to calculate absolute total electron impact ionization cross sections for the two C3H6 isomers cyclopropane and propene.
Abstract: The Deutsch-Mark (DM) formalism was used to calculate absolute total electron impact ionization cross sections for the two C3H6 isomers cyclopropane (-H2C-CH2-CH2-) and propene (H2C=CH-CH3). The agreement between the calculated cross sections and the experimentally determined cross sections (Nishimura H and Tawara H 1994 J. Phys. B: At. Mol. Opt. Phys. 27 2063) is excellent in terms of the absolute magnitude for impact energies below 100 eV and satisfactory for higher impact energies. However, the DM calculation does not reproduce the slight isomer effect that was found in the experimental data: i.e. the measured ionization cross section for propene was found to be larger by a few per cent than the cross section for cyclopropane.
TL;DR: Analyses of isodesmic reactions for singlet 7-carbenanorbornene, 8-carbena-endo-tricyclo, and 2- carbenabicyclooctadiene suggest very modest bridging at the 6-31G level, and the stability of 6S with 2-carBenanor Bornane and the geometry of 6s with that of 6T and also with the singlet and triplet 2-CarbenAnorborn
Abstract: Analyses of isodesmic reactions for singlet 7-carbenanorbornene (4S), 8-carbena-endo-tricyclo[3.2.1.02,4]octane (5S), 3-carbenabicyclo[3.1.0]hexane (3S), 2-carbenanorbornene 6S, and 2-carbenabicyclooctadiene 7S at the B3LYP/6-311+G(3df,2p)//B3LYP/6-31G* level provide stabilization energies of 13.83, 13.50, 3.00, −2.22, and −3.01 kcal/mol, respectively. The C7 carbene in 4S and the C8 carbene center in 5S are strongly bent toward the double bond and cyclopropane ring, respectively, in contrast to their related triplets, 4T and 5T and parent hydrocarbons. The geometric change for 3S compared to 3T or to parent bicyclo[3.1.0]hexane is minimal. Comparison of the stability of 6S with 2-carbenanorbornane and the geometry of 6S with that of 6T and also with the singlet and triplet 2-carbenanorbornane suggests very modest bridging. The stabilization energy and geometry of 2-carbenabicyclooctadiene 7 resemble antihomoaromatic bicyclooctadienyl cation 9 rather than the related homoaromatic bicyclooctadienyl anion 8...