Showing papers on "Cyclopropane published in 2003"
1,211 citations
TL;DR: This communication discloses the first reaction of a nitrone with a cyclopropane to produce a tetrahydro-1,2oxazines and investigates their reactions with nitrones in what is naively a dipolar homo [3+ 2] cycloaddition (Scheme 1).
Abstract: Cycloadditions are among the most trusted of chemical transformations available to the synthetic chemist. The predictability of the transition state based on steric and electronic considerations allows for the strategic construction of complex molecular assemblies. While the Diels–Alder reaction has received the most attention, 1,3-dipolar cycloadditions have also maintained a place of prominence in the toolbox of the synthetic chemist. During recent studies of the synthetic reactions of cyclopropanediesters, we were struck by the fact that simple 1,1cyclopropane diesters behaved very much like a,b-unsaturated carbonyl compounds in their ability to react with nucleophiles in what could be considered a homo-Michael addition (an observation not unnoticed by others). The strained bonds in the cyclopropane ring have long been considered to have a significant p character and in 1,1cyclopropane diesters this bond can be polarized and further weakened by coordination of a Lewis acid to one or both of the ester moieties. This reactivity suggests that such compounds are one-carbon homologues of electron-deficient olefins, and led us to investigate their reactions with nitrones in what is naively a dipolar homo [3+ 2] cycloaddition (Scheme 1) resulting in the formation of tetrahydro-1,2oxazines. In this communication we disclose the first reaction of a nitrone with a cyclopropane to produce a
273 citations
272 citations
TL;DR: On the basis of DFT calculations, a cyclopropyl platinacarbene complex was found as the key intermediate in the process, and dicarbonyl compounds are obtained, which support the proposed mechanism.
Abstract: 5-(2-Furyl)-1-alkynes react, with PtCl2 as catalyst, to give phenols. On the basis of DFT calculations, a cyclopropyl platinacarbene complex was found as the key intermediate in the process. The cyclopropane and dihydrofuran rings of this intermediate open to form a carbonyl compound, which reacts with the platinum carbene to form an oxepin, which is in equilibrium with an arene oxide. When the reaction is carried out in the presence of water, dicarbonyl compounds are obtained, which support the proposed mechanism. Other cyclizations of alkynes with furans or electron-rich arenes give products of apparent Friedel−Crafts-type reactions, although these processes could also proceed by pathways involving the formation of cyclopropyl platinum carbenes.
238 citations
TL;DR: The reactions of nickel complexes bearing terminal imido, phosphinidene, and carbene ligands with ethylene are reported, and corresponding three-membered rings, aziridine, phosphirane, and cyclopropane were produced in moderate to excellent yields.
Abstract: The reactions of nickel complexes bearing terminal imido, phosphinidene, and carbene ligands with ethylene are reported. In all three cases, corresponding three-membered rings, aziridine, phosphirane, and cyclopropane, were produced in moderate to excellent yields. NMR spectra of the phosphinidene (dtbpe)Ni=P(dmp) reaction with ethylene show a [2+2] cycloaddition adduct before phosphirane formation. A labeling study with trans-ethylene-d2 shows formation of aziridine and phosphirane proceeds with net retention of relative stereochemistry.
149 citations
TL;DR: Kinetic studies revealed that the metalation of methane proceeds exclusively via a second-order pathway described by the rate law, and high selectivity toward methane activation suggested the participation of this chemistry in a catalytic hydromethylation, which was observed in the slow, Cp*(2)ScMe-catalyzed addition of methane across the double bond of propene to form isobutane.
Abstract: The scandium alkyl Cp*2ScCH2CMe3 (2) was synthesized by the addition of a pentane solution of LiCH2CMe3 to Cp*2ScCl at low temperature. Compound 2 reacts with the C−H bonds of hydrocarbons including methane, benzene, and cyclopropane to yield the corresponding hydrocarbyl complex and CMe4. Kinetic studies revealed that the metalation of methane proceeds exclusively via a second-order pathway described by the rate law: rate = k[2][CH4] (k = 4.1(3) × 10-4 M-1s-1 at 26 °C). The primary inter- and intramolecular kinetic isotope effects (kH/kD = 10.2 (CH4 vs CD4) and kH/kD = 5.2(1) (CH2D2), respectively) are consistent with a linear transfer of hydrogen from methane to the neopentyl ligand in the transition state. Activation parameters indicate that the transformation involves a highly ordered transition state (ΔS‡ = −36(1) eu) and a modest enthalpic barrier (ΔH‡ = 11.4(1) kcal/mol). High selectivity toward methane activation suggested the participation of this chemistry in a catalytic hydromethylation, which...
140 citations
TL;DR: Introduction of a chelate-assisting substituent such as [PPh2] is effective in altering the kinetic selectivity and lowering the activation barrier for the catalytic processes.
Abstract: The selective catalytic activation and functionalization of carbon−carbon bonds in a series of substituted cyclopropane substrates has been developed using commercially available transition metal catalysts. Catalytic hydrogenation and olefination procedures, tolerant of a range of functional groups, have been discovered. Introduction of a chelate-assisting substituent such as [PPh2] is effective in altering the kinetic selectivity and lowering the activation barrier for the catalytic processes.
122 citations
TL;DR: In this article, the authors described the development of a highly enantioselective asymmetric catalysis on the intramolecular cyclopropanation of alpha-diazo-beta-keto sulfones.
Abstract: This work describes the development of a highly enantioselective asymmetric catalysis on the intramolecular cyclopropanation of alpha-diazo-beta-keto sulfones. We have found that the catalytic asymmetric intramolecular reactions of alpha-diazo-beta-keto sulfones generally proceed with high enantioselectivity when the alpha-diazo-beta-keto mesityl sulfone is used with the newly prepared ligand 2e. The absolute configuration of products has been determined by X-ray crystallographic analysis, and the outcome of the enantioselectivities is explained well by our proposed models A and B. The products possess great potential for natural product synthesis because (1) many different chemistries of cyclopropane, ketone, and sulfone are available, and (2) the products are generally highly crystalline, facilitating the supplies of enantiomerically pure synthetic intermediates.
113 citations
TL;DR: The catalytic system formed by Mn(II and Co(II) or Cu( II) nitrates has shown to be particularly effective for the oxidation of ketones and aldehydes by molecular oxygen under mild conditions.
Abstract: The catalytic system formed by Mn(II) and Co(II) or Cu(II) nitrates has shown to be particularly effective for the oxidation of ketones and aldehydes by molecular oxygen under mild conditions. The process has a general character, but it is particularly selective for the oxidation of alkyl–aryl ketones to aromatic carboxylic acids, alkyl-cyclopropyl ketones to cyclopropane carboxylic acids and cycloalkanones to dicarboxylic acids. Mn salt plays a key role in this catalysis, which catalyses the enolisation of the carbonyl compound and initiates a free-radical redox chain with oxygen by an electron-transfer process. Co and Cu salts alone are inert, but they exalt the catalytic activity of the Mn salt, being more effective in the decomposition of the hydroperoxides. The same metal salt complexes, associated with TEMPO revealed particularly effective for the aerobic oxidation of primary and secondary alcohols to the corresponding aldehydes and ketones under mild conditions (with air or oxygen at room temperature and atmospheric pressure); the mechanism of the catalysis is discussed. Thermochemical and kinetic investigations by EPR spectroscopy, concerning N-hydroxy compounds, have allowed to evaluate the Bond Dissociation Enthalpies (BDE) of several OH bonds and the absolute rate constants for the formation of the phthalimide-N-oxyl (PINO) radical from N-hydroxyphthalimide (NHPI) and for the hydrogen abstraction from several CH bonds by the PINO radical. The thermochemical and kinetic results have allowed us to explain the opposite catalytic behaviour of the two nitroxyl radicals, TEMPO and PINO, the former being an inhibitor of free radical processes, the latter a promoter of free-radical chain, and to develop new selective processes concerning the aerobic oxidation of alcohols, amines, amides, silanes and the substitution of heteroaromatic bases.
86 citations
TL;DR: It was found that thermal 1,3-dipolar cycloaddition followed by nitrogen extrusion gave the cyclopropane amino acid derivatives with good E selectivity, while reactions in the presence of meso-tetraphenylporphyrin iron chloride gave predominantly the corresponding Z isomers.
Abstract: A simple and high-yielding method for the preparation of cyclopropane amino acids is described. The novel method involves the one-pot cyclopropanation of readily available dehydroamino acids using ...
79 citations
TL;DR: The reaction of [Cu(CH3CN)4]-BF4 with racemic pyrazole-3,5-dicarboxylic acid di-sec-butyl ester (3, 5-Dicarbo-sec)-butoxypyrazole, Hdcsbpz) or with pyrazoles-3-5-di-ter-butyric (3.5-DI-terbutyl) (3
TL;DR: In this article, an alkyl cobalt(III) complex CoIII(TPP) was isolated by X-ray diffraction, and its structure has been solved by Xray diffusion.
Abstract: Cobalt(II) porphyrin complexes catalyze reactions between ethyl diazoacetate (EDA) and styrenes to give the corresponding cyclopropanes with trans selectivity. The reactions of other diazoalkanes and other olefins have also been carried out, and the mechanism of the reaction has been investigated. Kinetic data and stoichiometric reactions support the formation of a diazoalkane cobalt-porphyrin complex that reacts with the olefins to generate the cyclopropane. Diethyl maleate and fumarate are not formed in the presence of an excess of olefin. On treatment of EDA with CoII(TPP) (TPP = dianion of meso-tetraphenylporphyrin) in the absence of the olefin, an alkyl cobalt(III) complex CoIII(TPP)(CH2CO2Et) was isolated, and its structure has been solved by X-ray diffraction. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
TL;DR: The carbenoid reactivity of iodopalladio-trialkylstannanylalkanes complexes validates the Busacca-Farina mechanism of the cine-substitution in the Stille coupling.
Abstract: Two complementary routes to sp3-gem-organodimetallic iodopalladio-trialkylstannanylalkanes are presented. Such intermediates have been proposed as Pd-carbenoid precursors in the Busacca−Farina cine-substitution mechanism in the Stille coupling. The decomposition of iodomethyltrialkylstannanes by Pd(0) catalysts was monitored by 1H, 2D, and 119Sn NMR. The formation of ethylene, trace formaldehyde, and iodotrialkylstannanes was detected. When the reaction was carried out in the presence of norbornene, the corresponding cyclopropane was produced in good yield. These observations are consistent with the intermediacy of a Pd-carbenoid species. sp3-gem-Organodimetallic iodopalladio-trialkylstannanylalkane complexes were also prepared under stoichiometric conditions via transmetalation from tin to Pd(II). Me3SnCH2Sn(CH2CH2CH2)3 reacted with [(D-t-BPF)PdI]+I-, yielding the (D-t-BPF)Pd(II)ICH2SnMe3 complex that dimerized to form ethylene and cyclopropanated norbornene. The carbenoid reactivity of iodopalladio-tria...
TL;DR: These studies showed that the cis-cyclopropane structure is very effective in the conformational restriction of histamine to improve the specific binding to the histamine H(3) receptor.
Abstract: A series of cyclopropane-based conformationally restricted analogues of histamine, the “folded” cis-analogues, i.e., (1S,2R)-2-(aminomethyl)-1-(1H-imidazol-4-yl)cyclopropane (11), (1S,2S)-2-(2-aminoethyl)-1-(1H-imidazol-4-yl)cyclopropane (13), and their enantiomers ent-11 and ent-13, and the “extended” trans-analogues, i.e., (1R,2R)-2-(aminomethyl)-1-(1H-imidazol-4-yl)cyclopropane (12) and its enantiomer ent-12, were designed as histamine H3 receptor agonists. These target compounds were synthesized from the versatile chiral cyclopropane units, (1S,2R)- and (1R,2R)-2-(tert-butyldiphenylsilyloxy)methyl-1-formylcyclopropane (14 and 15, respectively) or their enantiomers ent-14 and ent-15. Among the conformationally restricted analogues, the “folded” analogue 13 (AEIC) having the cis-cyclopropane structure was identified as a potent H3 receptor agonist, which showed a significant binding affinity (Ki = 1.31 ± 0.16 nM) and had an agonist effect (EC50 value of 10 ± 3 nM) on the receptor. This compound owes its...
TL;DR: In this article, the complete catalytic cycle of copper-catalyzed cyclopropanation is investigated by density functional model calculations, and the relative stabilities of the ligand-metal cores of all catalytic intermediates and transition states are obtained.
TL;DR: The measured product branching ratios verify the relative potential energy barrier heights for C-C and C-H insertion predicted by ab initio calculations.
Abstract: The competition between C−C and C−H insertion in model transition-metal reactions with cyclopropane and propene (C3H6) was studied as a function of total energy. Insertion of neutral transition metal atoms M (= Y, Zr, Nb, and Mo*) into the C−C bonds of cyclopropane led to formation of MCH2 + C2H4, whereas C−H insertion produced MC3H4 + H2. The measured product branching ratios verify the relative potential energy barrier heights for C−C and C−H insertion predicted by ab initio calculations.
TL;DR: The ingenious and unique strategies that are used to achieve the specific activity of 1-Aminocyclopropane-1-carboxylate deaminase are revealed.
TL;DR: Experiments which probe the stereochemistry of deuterium labeling in the vinyl group of the vinylcyclopropanecarboxylate products were carried out, and these results are consistent with the proposed mechanism.
Abstract: The addition of stabilized carbon nucleophiles to tricarbonyl(1-methoxycarbonylpentadienyl)iron(1+) cation (1a) proceeds via attack at C2 on the face of the ligand opposite the Fe(CO)3 group to generate tricarbonyl(pentenediyl)iron complexes 2. Oxidation of complexes 2 affords vinylcyclopropanecarboxylates in good yield. In general, the relative stereochemistry about the cyclopropane ring reflects reductive elimination with retention of configuration. In cases where the C2 substituent is bulky (i.e., 2b) the major cyclopropane product 9b represents ring closure with inversion at C3. A mechanism involving π−σ−π rearrangement of the initially oxidized (pentenediyl)iron species is proposed to account for these results. Experiments which probe the stereochemistry of deuterium labeling in the vinyl group of the vinylcyclopropanecarboxylate products were carried out, and these results are consistent with the proposed mechanism. This methodology for the preparation of vinylcyclopropanecarboxylates was applied to...
TL;DR: The reaction of alkylidenecyclopropanes with HCl or with HBr proceeds very smoothly at 120°C to produce the corresponding homoallylic halides stereoselectively in good to excellent yields as discussed by the authors.
TL;DR: Asymmetric cyclopropanation of styrene was demonstrated using excess ethyl diazoacetate and catalytic Ru(ip-Pybox) selective hydrolysis as mentioned in this paper.
Abstract: Asymmetric cyclopropanation of styrene 1 (as the limiting reagent) was demonstrated using excess ethyl diazoacetate and catalytic Ru(ip-Pybox) Selective hydrolysis of the resulting 90:10 trans : cis mixture of cyclopropane 4 generated cyclopropyl acid 2 as a 96:4 trans : cis mixture with 84% ee for the trans -cyclopropane Further purification and enantiomeric enrichment was achieved by diastereoselective crystallization with (+)-dehydroabeitylamine to afford the ( R , R )-isomer with ≥999% ee in 60–65 M% yield starting from styrene 1
TL;DR: In this article, a detailed experimental and theoretical analysis of the metal-induced softening of C-H vibrational modes has been carried out for highly symmetric cyclic saturated hydrocarbons.
Abstract: A detailed experimental and theoretical analysis of the metal-induced softening of C–H vibrational modes has been carried out for highly symmetric cyclic saturated hydrocarbons and short chain linear saturated hydrocarbons. The softening of the C–H stretching modes of cyclopropane, cyclohexane, as well as propane and its deuterated analogs adsorbed on Cu(111) was examined experimentally using reflection absorption infrared spectroscopy and theoretically using ab initio Hartree–Fock and correlated calculations. The investigation showed that molecules are present in two bound orientations for both cyclopropane and propane. The data further reveal that significant mode softening is associated with only some (not all) of the bound states of these molecules. Soft modes with significant intensity were found to be present for cyclohexane and propane bound on Cu(111) in a planar orientation. A theoretical analysis of the various adsorbed forms of these three types of molecules confirms the surprising experimental...
TL;DR: In this article, a series of 2,6-bis(oxazolinyl)-pyridines bearing a hydroxyalkyl group on the oxazoline ring has been synthesized from readily available amino acid derivatives.
Abstract: As a C 2 symmetric hydrophilic chiral ligand, a series of 2,6-bis(oxazolinyl)-pyridines ( pyboxs ) bearing a hydroxyalkyl group on the oxazoline ring has been synthesized from readily available amino acid derivatives. Catalytic asymmetric intermolecular cyclopropanation of electron rich terminal alkenes with diazoesters in the presence of hydrophilic pybox ligand, pybox- hm and Ru(II) complex proceeded smoothly in protic or biphasic media to give the corresponding cyclopropanation products in 97:3 to 99:1 trans / cis ratios and 90 to 97% ee. In the case of the intramolecular cyclopropanation reaction of trans -cinnamyl diazoester using Ru(II)(pybox- he ) complex in biphasic medium gave the corresponding cyclopropane ring fused lactone in 52% ee. Steric tuning of the chiral environment of pybox ligands was simply achieved by using a weak interaction between the solvent and the hydroxyl groups of the chiral ligand. The solubility of the new hydrophilic pybox and Ru(II) complexes in protic solvents is dramatically increased; hence, the efficiency of these catalysts enhanced the rate of cyclopropanation. Furthermore, the active catalyst in the water phase can be re-used several times for the cyclopropanation reaction.
TL;DR: The oxa-di-pi-methane (ODPM) photochemical rearrangement, a triplet-sensitized sigmatropic 1,2-acyl shift of beta,gamma-enones, was successful utilizing methyl and heptyl 1-aza-3-carboalkoxybicyclo-oct-2-en-5-ones (quinuclidinones) as the photoprecursors.
TL;DR: Comparison with literature reports describing similar oxidations by dimethyldioxirane demonstrate that methyl(trifluoromethyl)dioxiranes (1b) presents similar selectivity and remarkably superior reactivity.
Abstract: The powerful methyl(trifluoromethyl)dioxirane (1b) was employed to achieve the direct oxyfunctionalization of 2,4-didehydroadamantane (5), spiro[cyclopropane-1,2'-adamantane] (9), spiro[2.5]octane (17), and bicyclo[6.1.0]nonane (19). The results are compared with those attained in the analogous oxidation of two alkylcyclopropanes, i.e., n-butylcyclopropane (11) and (3-methyl-butyl)-cyclopropane (14). The product distributions observed for 11 and 14 show that cyclopropyl activation of alpha-C-H bonds largely prevails when no tertiary C-H are present in the open chain in the tether; however, in the oxyfunctionalixation of 14 cyclopropyl activation competes only mildly with hydroxylation at the tertiary C-H. The application of dioxirane 1b to polycyclic alkanes possessing a sufficiently rigid framework (such as 5 and 9) demonstrates the relevance of relative orientation of the cyclopropane moiety with respect to the proximal C-H undergoing oxidation. At one extreme, as observed in the oxidation of rigid spiro compound 9, even bridgehead tertiary C-H's become deactivated by the proximal cyclopropyl moiety laying in the unfavorable "eclipsed" (perpendicular) orientation; at the other end, a cyclopropane moiety constrained in a favorable "bisected" orientation (as for didehydroadamantane 5) can activate an "alpha" methylene CH2 to compete effectively with dioxirane O-insertion into tertiary C-H bonds. Comparison with literature reports describing similar oxidations by dimethyldioxirane (1a) demonstrate that methyl(trifluoromethyl)dioxirane (1b) presents similar selectivity and remarkably superior reactivity.
TL;DR: The intrinsic conformational preferences of (2S,3S)-1-amino-2,3-diphenylcyclopropanecarboxylic acid, a phenylalanine cyclopropane analogue bearing two phenyl substituents, have been examined theoretically and its N-acetyl-N'-methylamide derivative has been investigated by using ab initio HF and DFT methods.
Abstract: The intrinsic conformational preferences of (2S,3S)-1-amino-2,3-diphenylcyclopropanecarboxylic acid, a phenylalanine cyclopropane analogue bearing two phenyl substituents, have been examined theoretically. For this purpose, its N-acetyl-N'-methylamide derivative, Ac-(2S,3S)-c 3 diPhe-NHMe, has been investigated by using ab initio HF and DFT methods. Results have been compared with those previously reported for other cyclopropane analogues of phenylalanine, and with experimental data available for c 3 diPhe-containing peptides.
TL;DR: Trifluoromethylated polyfunctionalized cyclopropanes were obtained in high stereoselectivity by reacting 2-bromo-3, 3,3,3-trifLUoropropene (BrTFP) with active methylenes by a novel method.
TL;DR: The electrochemical properties of F-Cu-F suggest the existence of ground-state electronic interactions in this multicomponent array based on the mutual effects exerted by the fullerene units to the bis(2,9-diphenyl-1,10-phenanthroline)Cu(I) complex and vice versa.
Abstract: A new fullerene-substituted phenanthroline ligand has been obtained by reaction of a phenanthroline derivative bearing a 1,3-phenylenebis(methylene)-tethered bis-malonate with C60 in a double Bingel cyclopropanation. The relative position of the two cyclopropane rings in the resulting bis-methanofullerene derivatives has been determined on the basis of the molecular symmetry (Cs) deduced from the 1H and 13C NMR spectra. The corresponding Cu(I) complex F−Cu−F has been prepared in good yields by treatment of the ligand with Cu(CH3CN)4BF4. In the resulting multicomponent system, both C60 moieties are in a tangential orientation relative to their bridging phenyl ring, and the central bis(phenanthroline)Cu(I) core is sandwiched between the two carbon spheres. The electrochemical properties of F−Cu−F suggest the existence of ground-state electronic interactions in this multicomponent array based on the mutual effects exerted by the fullerene units to the bis(2,9-diphenyl-1,10-phenanthroline)Cu(I) complex and vi...