Showing papers on "Intramolecular force published in 2005"
TL;DR: This review aims to describe the background and mechanisms of azomethine ylide formation and intramolecular cycloaddition, giving a critical account including the very first example and covering to early 2005.
Abstract: It was in 1963 that Huisgen laid out the classification of 1,3-dipoles and the concepts for 1,3-dipolar cycloaddition reactions, although it was not until 1976 that the first intramolecular 1,3-dipolar cycloaddition reaction of an azomethine ylide was reported. Since then, impressive developments have been described in this area, with the establishment of various useful methods for the formation of azomethine ylides and the determination of the requirements for a successful intramolecular cycloaddition reaction. Use of this methodology for the synthesis of pyrrolidineand pyrrole-containing natural products has been expanding rapidly. This review aims to describe the background and mechanisms of azomethine ylide formation and intramolecular cycloaddition, giving a critical account including the very first example and covering to early 2005. It is hoped that this review will be a useful resource for chemists interested in cycloaddition reactions and will inspire further exciting developments in this area. Cycloaddition reactions are one of the most important class of reactions in synthetic chemistry. Within * Corresponding author. Tel: +44 (0)114 222 9428. Fax: +44 (0)114 222 9346. E-mail: i.coldham@sheffield.ac.uk. † University of Sheffield. ‡ Tripos Discovery Research Ltd. Iain Coldham (b. 1965) is a Reader in Organic Chemistry at the University of Sheffield. He obtained his undergraduate degree and Ph.D. from the University of Cambridge, completing his Ph.D. in 1989 under the supervision of Stuart Warren. After postdoctoral studies at the University of Texas with Philip Magnus, he joined the staff in 1991 at the University of Exeter, U.K. In 2003, he moved to the University of Sheffield where he is involved in research on chiral organolithium compounds and on dipolar cycloaddition reactions in synthetic organic chemistry.
863 citations
TL;DR: The rate-limiting step is the electrophilic attack of the palladium on an ortho arene C-H bond to form an agostic complex rather than a Wheland intermediate, and the cyclometalated product is formed by intramolecular deprotonation by acetate via a six-membered transition state.
Abstract: Various mechanisms for the cyclometalation of dimethylbenzylamine by palladium acetate have been studied by DFT calculations. Contrary to previous suggestions, the rate-limiting step is the electrophilic attack of the palladium on an ortho arene C−H bond to form an agostic complex rather than a Wheland intermediate. The cyclometalated product is then formed by intramolecular deprotonation by acetate via a six-membered transition state; this step has almost no activation barrier.
622 citations
TL;DR: New heptamethine cyanine dyes with an alkylamino group at the central position were found to exhibit a large Stokes shift and strong fluorescence and were suggested to be a new paradigm for excited-state intramolecular charge transfer (ICT).
Abstract: New heptamethine cyanine dyes with an alkylamino group at the central position were found to exhibit a large Stokes shift (>140 nm) and strong fluorescence. They were suggested to be a new paradigm for excited-state intramolecular charge transfer (ICT). The configuration change of the bridgehead amine accompanying ICT was investigated in different viscosity and pH media.
482 citations
TL;DR: The calcium-catalyzed intramolecular hydroamination of alkenes and alkynes is reported and affects catalytic cyclization of a range of aminoalkenes and aminoalkynes with activities that are broadly commensurate to those of established rare earth catalysts.
Abstract: The calcium-catalyzed intramolecular hydroamination of alkenes and alkynes is reported. The β-diketiminato complex [{HC(C(Me)2N-2,6-iPr2C6H3)2}-Ca{N(SiMe3)2}(THF)] affects catalytic cyclization of a range of aminoalkenes and aminoalkynes with activities that are broadly commensurate to those of established rare earth catalysts.
345 citations
TL;DR: The reaction is truly catalytic in metal catalyst and represents the proof of principle for this elusive type of alkene oxidation.
Abstract: Intramolecular diamination reactions are described which yield cyclic ureas as direct products of an oxidative alkene transformation in the presence of palladium acetate and iodosobenzene diacetate as terminal oxidant. The reaction is truly catalytic in metal catalyst and represents the proof of principle for this elusive type of alkene oxidation.
345 citations
TL;DR: It is revealed that 1(3,4) was a sensitive chemosensor capable of optically discriminating nitroaromatic regioisomers of p-, o-, and m-nitroanilines.
Abstract: We synthesized a group of silole regioisomers 1x,y, whose photoluminescence varied dramatically with its regiostructure. By internally hindering the intramolecular rotation, we succeeded in creating a novel silole (13,4) that is strongly luminescent in solutions and whose fluorescence quantum yield in acetone is as high as 83%. We revealed that 13,4 was a sensitive chemosensor capable of optically discriminating nitroaromatic regioisomers of p-, o-, and m-nitroanilines. Against general belief, crystal formation of 12,4 blue-shifted its emission color and boosted its emission efficiency. The light-emitting diode based on the crystal of 12,4 emitted a strong blue light (464 nm) in a high current efficiency (5.86 cd/A).
342 citations
TL;DR: A mechanistic rationale is proposed, implying activation of the alkyne by the carbophilic Pt(2+) template as the primary step of the catalytic cycle.
Abstract: PtCl2 constitutes a convenient catalyst for intramolecular hydroalkoxylation, carboalkoxylation, hydroamination, and carboamination reactions of alkynes, effecting the formation of substituted benzo[b]furan, indole-, and isochromene-1-one derivatives, respectively. This procedure allows for the transfer of (substituted) allyl, methoxymethyl (MOM), benzyloxymethyl (BOM), and (trimethylsilyl)ethoxymethyl (SEM) groups from oxygen to carbon and is compatible with functional groups that are susceptible to oxidative insertion of low valent metal species previously used for similar purposes. Although some of the reactions can even be carried out in air, the rates are significantly increased when conducted under an atmosphere of CO. A mechanistic rationale is proposed, implying activation of the alkyne by the carbophilic Pt(2+) template as the primary step of the catalytic cycle.
337 citations
TL;DR: A new mechanism is proposed for ECD of multiply charged peptide and protein cations in which the electron enters a charge-stabilized electronic state delocalized over the amide group, which is a superbase that abstracts a proton from a sterically proximate amino acid residue to form a labile aminoketyl radical that dissociates by N—Cα bond cleavage.
322 citations
TL;DR: It was deduced that the four phenyl groups substituted into the imidazole ring of HPI and HPI-Ac allowed the crystals free from concentration quenching of fluorescence by limiting the excessive tight-stacking responsible for intermolecular vibrational coupling and relevant nonradiative relaxation.
Abstract: We have synthesized a novel class of imidazole-based excited-state intramolecular proton-transfer (ESIPT) materials, i.e., hydroxy-substituted tetraphenylimidazole (HPI) and its derivative HPI-Ac, which formed large single crystals exhibiting intense blue fluorescence and amplified spontaneous emission (ASE). Transparent, clear, and well-defined fluorescent single crystals of HPI-Ac as large as 20 mm x 25 mm x 5 mm were easily grown from its dilute solution. From the X-ray crystallographic analysis and semiempirical molecular orbital calculation, it was deduced that the four phenyl groups substituted into the imidazole ring of HPI and HPI-Ac allowed the crystals free from concentration quenching of fluorescence by limiting the excessive tight-stacking responsible for intermolecular vibrational coupling and relevant nonradiative relaxation. Fluorescence spectral narrowing and efficient ASE were observed in the HPI-Ac single crystal even at low excitation levels attributed to the intrinsic four-level ESIPT photocycle.
299 citations
TL;DR: A new structure reported here of the bovine mitochondrial bc1 complex at 2.28 A resolution allows for the first time to reliably describe the binding of antimycin and shows that the intramolecular hydrogen bond described in solution and in the small-molecule structure is replaced by one involving the NH rather than carbonyl O of the amide linkage.
273 citations
TL;DR: The rhodium-catalyzed decomposition of N-tosyloxycarbamates to generate metal nitrenes which undergo intramolecular C-H insertion or aziridination reaction is described, as both reactions are stereospecific.
Abstract: The rhodium-catalyzed decomposition of N-tosyloxycarbamates to generate metal nitrenes which undergo intramolecular C−H insertion or aziridination reaction is described. Aliphatic N-tosyloxycarbamates produce oxazolidinones with high yields and stereospecificity through insertion in benzylic, tertiary, and secondary C−H bonds. Intramolecular aziridination occurs with allylic N-tosyloxycarbamates to produce aziridines as single diastereomers. The reaction proceeds at room temperature using a rhodium catalyst and an excess of potassium carbonate and does not require the use of strong oxidant, such as hypervalent iodine reagents. A rhodium nitrene species is presumably involved, as both reactions are stereospecific.
TL;DR: Reactivity and structural studies of unusual rhodium and iridium systems bearing two N-heterocyclic carbene (NHC) ligands are presented and DFT calculations show that these electrophilic metal centers are stabilized by pi-donation of the NHC ligands.
Abstract: Reactivity and structural studies of unusual rhodium and iridium systems bearing two N-heterocyclic carbene (NHC) ligands are presented. These systems are capable of intramolecular C−H bond activation and lead to coordinatively unsaturated 16-electron complexes. The resulting complexes can be further unsaturated by simple halide abstraction, leading to 14-electron species bearing an all-carbon environment. Saturation of the vacant sites in the 16- and 14-electron complexes with carbon monoxide permits a structural comparison. DFT calculations show that these electrophilic metal centers are stabilized by π-donation of the NHC ligands.
TL;DR: A number of gamma- and delta-amino olefins underwent intramolecular hydroamination to form the corresponding pyrrolidine derivatives in moderate to good yield and displayed excellent functional group compatibility and low moisture sensitivity.
Abstract: Reaction of benzyl-2,2-diphenyl-4-pentenylamine with a catalytic 1:2 mixture of [PtCl2(H2CCH2)]2 (2.5 mol %) and PPh3 in dioxane at 120 °C for 16 h led to isolation of 1-benzyl-2-methyl-4,4-diphenylpyrrolidine in 75% yield. A number of γ- and δ-amino olefins underwent intramolecular hydroamination to form the corresponding pyrrolidine derivatives in moderate to good yield. The reaction displayed excellent functional group compatibility and low moisture sensitivity.
TL;DR: In this paper, a helical 3,3,butylsalen−zinc(II) complex has a red-shifted fluorescence as compared to that of a half-structured mononuclear complex of [Zn2L12], which exhibits a fluorescence color change from green to light blue under external stimulations.
Abstract: When a fluorescent compound shows unique optical properties, an elucidation of the mechanism may lead to an important development of novel sensing strategies. A helical 3,3‘-di-tert-butylsalen−zinc(II) complex, [Zn2L12], has a red-shifted fluorescence as compared to that of [ZnL22], a half-structured mononuclear complex of [Zn2L12]; in addition, [Zn2L12] exhibits a fluorescence color change from green to light blue under external stimulations. We investigated the origins of these phenomena by spectroscopy, fluorescence lifetime measurement, fluorescence microscopy, X-ray powder diffraction, and X-ray single-crystal analysis. From the experimental data, we concluded that intramolecular and intermolecular π−π interactions are critical elements that determine the shifts of the fluorescence to a longer wavelength.
TL;DR: The field of radical conjugate additions, including both intramolecular and intermolecular examples, is reviewed in this paper, where the authors highlight the applications in total synthesis.
TL;DR: Available evidence suggests the diastereoselective protonation occurs via intramolecular delivery to the sterically more hindered face of the enolate, while the scope of the trisubstituted Michael acceptors is found to be broad with respect to the size of the alpha-substituent and nature of the Michael acceptor.
Abstract: A highly enantio- and diastereoselective intramolecular Stetter reaction has been developed. Subjection of α,α-disubstituted Michael acceptors to an asymmetric intramolecular Stetter reaction results in a highly enantioselective conjugate addition and a diastereoselective proton transfer. Available evidence suggests the diastereoselective protonation occurs via intramolecular delivery to the sterically more hindered face of the enolate. The scope of the trisubstituted Michael acceptors has been examined and found to be broad with respect to the size of the α-substituent and nature of the Michael acceptor. Aliphatic and aromatic aldehydes were examined and found to afford the desired product in good overall yield with high enantio- and diastereoselectivity.
TL;DR: A rhenium complex, [ReBr(CO)3(thf)]2, catalyzes the reaction of an aromatic aldimine with an acetylene to give an indene derivative in a quantitative yield via C-H bond activation, insertion of the acetylene, intramolecular nucleophilic cyclization, and reductive elimination.
Abstract: A rhenium complex, [ReBr(CO)3(thf)]2, catalyzes the reaction of an aromatic aldimine with an acetylene to give an indene derivative in a quantitative yield. The reaction proceeds via C-H bond activation, insertion of the acetylene, intramolecular nucleophilic cyclization, and reductive elimination. In contrast to ruthenium and rhodium catalysts, which are usually employed in this type of reaction, the rhenium catalyst promotes the intramolecular nucleophilic cyclization of the alkenylmetal species generated by insertion of the acetylene.
TL;DR: A practical method for the intramolecular hydroalkylation of electron-deficient olefins has been developed and the mechanism of these transformations is proposed to involve a tandem hydride transfer/cyclization sequence.
Abstract: A practical method for the intramolecular hydroalkylation of electron-deficient olefins has been developed. The direct transformation of benzylic, tertiary, and sterically hindered secondary sp3 C-H bonds into C-C bonds under the action of a catalytic amount of a variety of Lewis acids is described. The mechanism of these transformations is proposed to involve a tandem hydride transfer/cyclization sequence.
TL;DR: Application of the two-step carbohydrate synthesis technology has enabled to access a selectively substituted glucose derivative for use as an intramolecular cycloaddition tether and serves to support the proposed biosynthetic origins of 1 from 2.
Abstract: The first total syntheses of littoralisone (1) and brasoside (2) have been achieved in 13 overall steps. Both natural products are forged from a common intermediate which is rapidly assembled using organocatalytic technology, including a proline-catalyzed α-aminoxylation and a contra-thermodynamic intramolecular Michael addition. Application of the two-step carbohydrate synthesis technology has enabled to access a selectively substituted glucose derivative for use as an intramolecular cycloaddition tether. This synthesis culminates with an intramolecular [2+2] photocycloaddition that serves to support the proposed biosynthetic origins of 1 from 2.
TL;DR: Ti(NMe(2))(4) has been used effectively as a precatalyst in a facile protocol for the intramolecular hydroamination of aminoalkenes to yield pyrrolidine and piperidine heterocyclic products with isolated yields up to 92%.
TL;DR: Asymmetric intramolecular Michael reaction catalyzed by an organocatalyst derived from cysteine has been developed for the synthesis of chiral bicyclo and cis-disubstituted cyclopentane skeletons with a creation of three or two contiguous chiral centers in good yield with high diastereo- and excellent enantioselectivities.
Abstract: Asymmetric intramolecular Michael reaction catalyzed by an organocatalyst derived from cysteine has been developed for the synthesis of chiral bicyclo[4.3.0]nonene and cis-disubstituted cyclopentane skeletons with a creation of three or two contiguous chiral centers in good yield with high diastereo- and excellent enantioselectivities.
TL;DR: This is the first reported example of intramolecular diamination of olefins, enabled by Cu(OAc)2 and demonstrates a new transformation for this metal.
Abstract: A concise method for the synthesis of cyclic sulfamides and vicinal diamines is presented. This method is enabled by Cu(OAc)2 and demonstrates a new transformation for this metal. Both five- and six-membered vicinal diamine-containing heterocycles have been synthesized in good to excellent yields, and substrate-based asymmetric induction has been achieved. This is the first reported example of intramolecular diamination of olefins.
TL;DR: A challenging deprotection of a late-stage permethylated lithospermic acid was achieved and represents the first application of this chiral imine-directed C-H bond functionalization method to natural product synthesis.
Abstract: The total synthesis of (+)-lithospermic acid is described The efficient synthesis features an asymmetric alkylation via C−H bond activation to assemble the dihydrobenzofuran core of the natural product This was accomplished via a chiral imine-directed C−H bond functionalization and represents the first application of this C−H activation method to natural product synthesis Furthermore, a challenging deprotection of a late-stage permethylated lithospermic acid was achieved
TL;DR: A wide variety of 3-halospiro[4.5]trienones are readily prepared in good to excellent yields by the intramolecular ipso-halocyclization of 4-(p-methoxyaryl)-1-alkynes under mild reaction conditions.
Abstract: A wide variety of 3-halospiro[4.5]trienones are readily prepared in good to excellent yields by the intramolecular ipso-halocyclization of 4-(p-methoxyaryl)-1-alkynes under mild reaction conditions. ICl, I2, and Br2 are all effective electrophiles for this process under carefully optimized reaction conditions.
TL;DR: The present formal [4 + 2] intramolecular cycloaddition proceeds most probably through the coordination of the triple bond at the ortho position of substrates to Lewis acids, the formation of benzopyrylium ate complex 16 via the nucleophilic addition of the carbonyl oxygen atom, the reverse electron demand type Diels-Alder added of the tethered alkynes or alkenes to the ate complex, and subsequent bond rearrangement.
Abstract: Treatment of tethered alkynyl enynones 8, in which a carbon chain is attached to the carbonyl group, with a catalytic amount of AuBr3 in (ClCH2)2 gave the naphthyl ketones 9 in good to high yields (top-down approach). Analogously, the AuBr3-catalyzed benzannulations of 10, in which a carbon tether is extended from the alkynyl terminus, also proceeded smoothly, and the cyclized naphthyl ketones 11 were obtained in high yields (bottom-up approach). Similarly, when two kinds of tethered alkenyl enynones 12 and 14 were treated with Cu(OTf)2 catalyst, the corresponding dihydronaphthyl ketone products 13 and 15 were obtained in high yields, respectively. The present formal [4 + 2] intramolecular cycloaddition proceeds most probably through the coordination of the triple bond at the ortho position of substrates to Lewis acids, the formation of benzopyrylium ate complex 16 via the nucleophilic addition of the carbonyl oxygen atom, the reverse electron demand type Diels−Alder addition of the tethered alkynes or al...
TL;DR: A yttrium(III) complex derived from proligand 7c has been shown to be a superior catalyst for enantioselective intramolecular alkene hydroaminations that provide cyclic amines with ee's ranging from 69% to 89%.
TL;DR: Good to excellent yields can be obtained for a range of substrates under relatively mild conditions in this reaction, which represents one of the simplest methods to construct cyclic ethers or lactones.
TL;DR: In this paper, the effect of spin-orbit perturbations on the photophysics of organic molecules introduced by heavy atoms (the intramolecular, or "internal", heavy-atom effect) was studied.
Abstract: This review systematizes the data on the effect of intramolecular spin–orbit perturbations on the photophysics of organic molecules introduced by heavy atoms (the intramolecular, or 'internal', heavy-atom effect). The focus is on two classes of compounds: (1) halogenated derivatives of aromatic and heteroaromatic compounds and (2) porphin derivatives (halogenated porphyrins and metalloporphyrins). The enhancement of radiative and nonradiative intercombination transitions under the heavy-atom effect is responsible for fluorescence quenching and the shortening of phosphorescence duration. Photophysical investigations show that the transition probabilities in different channels of deactivation of excited electronic states exhibit specific dependence on the structure of heavy-atom bearing molecules. This allows one to acquire information on the spin–orbit interaction in molecules and their electronic structure, and to control the parameters of chromophores and luminophors in optical systems.