Showing papers on "Intramolecular reaction published in 2000"
TL;DR: A possible mechanism involving ethynyl chelation-assisted electrophilic metalation of aromatic C-H bonds by in-situ generated cationic Pd(II) species has been discussed and the involvement of vinylcationic species have been suggested.
Abstract: A new and general method has been developed for preparation of coumarins and quinolinones by intramolecular hydroarylation of alkynes. Various aryl alkynoates and alkynanilides undergo fast intramolecular reaction at room temperature in the presence of a catalytic amount of Pd(OAc)(2) in a mixed solvent containing trifluoroacetic acid (TFA), affording coumarins and quinolinones in moderate to excellent yields with more than 1000 turnover numbers (TON) to Pd. The methodology proved to tolerate a number of functional groups such as Br and CHO. On the basis of isotope experiments, a possible mechanism involving ethynyl chelation-assisted electrophilic metalation of aromatic C-H bonds by in-situ generated cationic Pd(II) species has been discussed. Also the involvement of vinylcationic species has been suggested.
209 citations
TL;DR: Aqueous hydrogen sulfite reacts with Hg2+ to form, in the absence of excess HSO3-, the HgSO3 complex, observed here for the first time.
Abstract: Aqueous hydrogen sulfite reacts with Hg2+ to form, in the absence of excess HSO3-, the HgSO3 complex, observed here for the first time. Its UV spectrum is described by e(234 nm) = (1.57 ± 0.05) × 104 M-1 cm-1. HgSO3 decomposes in an intramolecular redox reaction which is kinetically first-order. The rate constant is independent of [Hg2+], [HSO3-], [O2(aq)], and ionic strength. An acid-assisted pathway becomes significant at pH ≤ 1, attributed to the contribution of HgSO3H+. The rate of the intramolecular reaction of HgSO3 was measured by trapping the Hg0 product as Hg22+; the value of the rate constant is k0 = (0.0106 ± 0.0009) s-1 at 25.0 °C, pH 3. The activation parameters for pH 3, ΔH‡ and ΔS‡, are (105 ± 2) kJ/mol and (68 ± 6) J/mol·K, respectively, consistent with a unimolecular bond cleavage mechanism. A pathway involving H2O-induced concerted 2e- transfer is proposed.
138 citations
80 citations
TL;DR: The acylphosphoranes formed in a sequential manner from the reaction of the silyl ester of O-acyl(aroyl)salicylic acids and (trimethylsilyl)methylenetriphenylph phosphorane undergo intramolecular Wittig cyclization on the ester carbonyl to afford the 4H-chromen-4-ones in good to excellent yields.
76 citations
TL;DR: In this paper, a ring-opening polymerization of (D,L)-lactide by using different lanthanide alkoxide initiators was examined by SEC, 13 C NMR and MALDI-TOF MS techniques.
Abstract: Polylactide samples obtained by the ring-opening polymerization of (D,L)-lactide by using different lanthanide alkoxide initiators were examined by SEC, 13 C NMR and MALDI-TOF MS techniques. The evidence of substantial transesteriffcation was observed in the case of a polymerization initiated by lanthanum alkoxide and bimetallic aluminium-yttrium alkoxide initiators. In the case of Y and Sm alkoxide initiators, the MWD remains narrow up to high conversions for reasonable polymerization times, but the prolongation of the post-polymerization time increases the amount of ester-eschange reactions, The extent of the transesterification reactions was evaluated on the basis of the intensity of the stereosequence resonances for the methine carbon signal in the 13 C NMR spectra. MALDI-TOF MS analysis revealed the presence of add-numbered oligomers in all spectra. Thus, transesterification reactions occus from the beginning of the polymerization. Linear and cyclic oligomers were detected in some cases indicating the simultaneous occurrence of inter- and intramolecular exchange reactions. The microstructure analysis of the polymers by 13 C NMR spectroscopy indicates a preference for a syndiotactic addition during the polymerization process.
73 citations
TL;DR: A highly effective method for the synthesis of the core indolo[2,3-alpha]quinolizidine skeleton found in yohimbine is described, which results in several tetrahydroisoquinoline alkaloids in good yield.
Abstract: A highly effective method for the synthesis of the core indolo[2,3-a]quinolizidine skeleton found in yohimbine is described. The reaction of N-monosubstituted thioamides with bromoalkenoyl chlorides furnishes thioisomunchnones as transient 1,3-dipoles that undergo ready intramolecular cycloaddition across the tethered π-bond to give thio-bicycloannulated products in a one-pot operation. The stereochemical outcome of the intramolecular reaction is the consequence of an endo cycloaddition of the neighboring π-bond across the transient thioisomunchnone dipole. A major limitation of the method is that when a hydrogen is present in the α-position of the thioamide the initially formed thio-N-acyliminium ion undergoes proton loss to produce a S,N-ketene acetal at a faster rate than dipole formation. Treatment of tetrahydro-β-carboline-1-thione with 2-bromooct-7-enoyl chloride followed by reductive removal of sulfur from the cycloadduct resulted in the formation of (±)-alloyohimbanone. Attempts to cycloadd the th...
69 citations
TL;DR: The first total synthesis of the oxindole alkaloid gelsedine starting from (S)-malic acid is described, which leads to the unnatural (+)-enantiomer of gelsingine in 21 steps and 0.10% overall yield.
Abstract: The first total synthesis of the oxindole alkaloid gelsedine (1) starting from (S)-malic acid is described. The key step is a novel iodide-promoted intramolecular reaction of an allene with an N-acyliminium ion intermediate which provided in a single step the bicyclic vinyl iodide 11. Other important steps are the highly stereoselective Pd-catalyzed Heck cyclization of N-methylanilide 23a which led to the desired spiro-oxindole 24a, the fully regioselective intramolecular oxymercuration of 25a to the desired cyclic ether, and the remarkable oxindole N-demethylation of 29 via a radical mechanism by using dibenzoyl peroxide. The total synthesis was concluded by the stereoselective introduction of the ethyl group from the bis-Boc compound 41 followed by methoxylation of the oxindole nitrogen. This total synthesis leads to the unnatural (+)-enantiomer of gelsedine in 21 steps and 0.10% overall yield.
67 citations
TL;DR: In this article, C-H activation of benzylic methyl groups has been realized catalytically under mild conditions through intramolecular reaction on a palladium complex with mild conditions.
60 citations
TL;DR: Highly stereocontrolled, intramolecular [2 + 2] cycloadditions between ketenimines and imines leading to 1,2-dihydroazeto[2, 1-b]quinazolines have been achieved and models can be extended to other related systems for predicting the stereochemical outcome in this intramolescular reaction.
Abstract: Highly stereocontrolled, intramolecular [2 + 2] cycloadditions between ketenimines and imines leading to 1,2-dihydroazeto[2, 1-b]quinazolines have been achieved. The source of stereocontrol is a chiral carbon atom adjacent either to the iminic carbon or nitrogen atom. In the first case, the stereocontrol stems from the preference for the axial conformer in the first transition structure. In the second case, the origin of the stereocontrol lies on the two-electron stabilizing interaction between the C-C bond being formed and the sigma orbital corresponding to the polar C-X bond, X being an electronegative atom. These models can be extended to other related systems for predicting the stereochemical outcome in this intramolecular reaction.
33 citations
TL;DR: In this paper, the reactivity of model systems for the proposed [4+2] cycloaddition in the biosynthesis of the brevianamides, paraherquamides and marcfortines is explored.
33 citations
TL;DR: In this article, the synthesis of heterotelechelic poly(methyl methacrylate) (PMMA) containing α-maleimide-ω-dienyl end-groups and its subsequent intramolecular cyclization are described.
Abstract: The synthesis of heterotelechelic poly(methyl methacrylate) (PMMA) containing α-maleimide-ω-dienyl end-groups and its subsequent intramolecular cyclization are described. The anionic polymerization of methyl methacrylate was carried out with 3-tert-butyldimethylsilyloxypropyl-1-lithium and 5-bromo-1,3-pentadiene as the initiator and terminator, respectively, to synthesize α-hydroxy-ω-dienyl-PMMA. The introduction of the maleimide group to the a chain end by the reaction of the sodium salt of the polymer with N-(3-chloromethylphenyl)-maleimide or N-(3-bromomethylphenyl)-maleimide was not successful because of the nucleophilic addition of alkoxide to the carbon-carbon double bond of the maleimide group. When 4,4'-bismaleimidediphenylether was allowed to react with the alkoxide, the aimed α-maleimide-ω-dienyl-PMMA was obtained in a good yield. Ring closure by the intramolecular Diels-Alder reaction was carried out by the heating of the dilute polymer solution in tetrahydrofuran.
TL;DR: The binding behaviour as well as the time-dependent reaction of five platinum(II) complexes with 5′-GMP have been investigated by capillary electrophoresis under simulated physiological conditions referred to chloride concentration, pH and temperature.
Abstract: The binding behaviour as well as the time-dependent reaction of five platinum(II) complexes with 5'-GMP have been investigated by capillary electrophoresis under simulated physiological conditions referred to chloride concentration, pH and temperature. Different amine ligands influenced the binding properties towards 5'-GMP and resulted in different half-times of the overall reaction. Complexes with bidentate ligands reacted faster with the monophosphate compared to complexes with monodentate ligands. Complexes consisting of two monodentate hydroxyethylamine ligands reacted very slowly owing to a competitive intramolecular reaction of the hydroxyethyl residues, which was proven by NMR investigations. Reducing the number of hydroxyethyl residues increased the half-times of the reactions. Moreover, the major adducts formed with 5'-GMP were identified by MALDI-MS analysis.
TL;DR: 2,3]-2′,2″-Biindolyl-3,3′-dithiete, dibromomaleimide and n -Bu 3 P, undergoes an intramolecular reaction to provide arcyriaflavin-A as discussed by the authors.
TL;DR: The results support that the intramolecular cyclization process in APM proceeded in three steps: the methoxyl group of ester was first thermolyzed to release methanol, then an acyl cation was attacked by the lone pair of electrons available on nitrogen by an S(N)1 pathway, and finally ring-closure occurred.
Abstract: A novel Fourier transform infrared (FT-IR) microspectrophotometer equipped with differential scanning calorimetry (DSC) was used to investigate the kinetics of intramolecular cyclization of aspartame (APM) sweetener in the solid state under isothermal conditions. The thermal-dependent changes in the peak intensity of IR spectra at 1543, 1283, and 1259 cm-1 were examined to explore the reaction. The results support that the intramolecular cyclization process in APM proceeded in three steps: the methoxyl group of ester was first thermolyzed to release methanol, then an acyl cation was attacked by the lone pair of electrons available on nitrogen by an SN1 pathway, and finally ring-closure occurred. The intramolecular cyclization of APM determined by this microscopic FT-IR/DSC system was found to follow zero-order kinetics after a brief induction period. The bond cleavage energy (259.38 kJ/mol) of thermolysis for the leaving group of −OCH3, the bond conversion energy (328.88 kJ/mol) for the amide II NH band ...
TL;DR: Pyridones, well-known for their ability to photodimerize, have been found to undergo [4 + 4] photocycloaddition with furan and naphthalene but not with benzene.
Abstract: Pyridones, well-known for their ability to photodimerize, have been found to undergo [4 + 4] photocycloaddition with furan and naphthalene but not with benzene. In some cases these reactions can be highly regio- and stereospecific. Intramolecular reaction with furan produces both cis and trans [4 + 4] products. The cycloaddition with naphthalene can occur both inter- and intramolecularly. The intermolecular reaction yields primarily the cis isomer, whereas the trans isomer is the major product from the intramolecular reaction. A mixture of 4-methoxy-2-pyridone and 2-methoxynaphthalene that could form up to eight regio- and stereoisomers forms largely one [4 + 4] product.
TL;DR: The anthryl groups of the fullerene derivatives 3, 7, and 10 react readily with singlet oxygen to form the 9,10-epidioxides 4, 8, and 12 under photooxidation as discussed by the authors.
TL;DR: Varying the Mitsunobu reaction conditions led to the expected epimerization product of the glucose derivative, which was determined as (3R,4R, 5R,6S)-4,5,6,7-tetrabenzyloxy-3-hydroxy-1-heptene.
Abstract: Mitsunobu reaction on the glucose derivative (3S,4R,5R,6R)-3,4,5,7-tetrabenzyloxy-6-hydroxy-1-heptene yielded an unexpected rearrangement major product. Its structure was determined as (3R,4R,5R,6S)-4,5,6,7-tetrabenzyloxy-3-hydroxy-1-heptene. The suggested rearrangement mechanism involves an initial intramolecular cyclization, followed by ring opening by the nucleophile p-nitrobenzoate. Product distribution of the Mitsunobu reaction was substrate-dependent, with the corresponding mannose derivative (the 3R epimer) giving less of the initial intramolecular reaction products and the corresponding galactose derivative (the 5S epimer) yielding almost exclusively the expected epimerization product. Varying the Mitsunobu reaction conditions (addition of base and using nonpolar solvent) led to the expected epimerization product of the glucose derivative.
TL;DR: In this article, an intermediate in the Hamaguchi−Ibata reaction involving the RhII-catalyzed intramolecular reaction of a diazo group with the carbonyl of an adjacent amido group, has been isolated and characterized.
Abstract: Methyl 4,6-dichloro-3-(diethylamino)furo[3,4-c]pyridine-1-carboxylate (6), an intermediate in the Hamaguchi−Ibata reaction involving the RhII-catalyzed intramolecular reaction of a diazo group with the carbonyl of an adjacent amido group, has been isolated and characterized. PM3 calculations reveal the heat of formation (ΔHf) of this remarkably stable molecule to be −77.7 kcal/mol. Compound 6 undergoes a facile Diels−Alder cycloaddition with a variety of dienophiles to give polysubstituted isoquinoline derivatives via ring opening of initially formed cycloadducts. In each case the cycloaddition proceeds with high regioselectivity, with the electron-withdrawing group located ortho to the amino group. The most favorable FMO interaction is between the HOMO of the azaisobenzofuran 6 and the LUMO of the dienophile. The atomic coefficient at the ester carbon of the azaisobenzofuran 6 is larger than the amino center, and this nicely accommodates the observed regioselectivity.
TL;DR: In this paper, different deactivation pathways are available to the excited state, depending on the conformers present in the starting material, and it is shown that these pathways compete with the observed cycloaddition.
TL;DR: The non-activated Mg-Al 3:1 hydrotalcite is a suitable basic catalyst both in the intramolecular cyclization reaction of malonic acid allylic esters into bicyclic cyclopropane carboxylic acid lactones and in the intermolecular cycle reaction of dibromoethane and diethyl malonate into cycloprocessor diesters as mentioned in this paper.
Abstract: The non-activated Mg-Al 3:1 hydrotalcite is a suitable basic catalyst both in the intramolecular cyclization reaction of malonic acid allylic esters into bicyclic cyclopropane carboxylic acid lactones and the intermolecular cyclization reaction of dibromoethane and diethyl malonate into cyclopropane dicarboxylic acid diester. The optimal reaction conditions of the intramolecular cyclization were determined using a 2 4 factorial design. An interesting effect on the diastereoselectivity of the intramolecular cyclization was observed compared with the diastereoselectivity of this cyclization using solid potassium carbonate as base.
TL;DR: The photolysis of 1-(o-hydroxymethyl, acetoxymethyl-, or allyloxymmethylphenyl)-2-pentamethyldisilanyl ethynes 2a, 2b, or 2c in benzene provides novel stereoselective intramolecular cycloaddition products 6, 8, or 12 via silacyclopropene intermediates.
Abstract: Photolysis of 1-(o-hydroxymethyl-, acetoxymethyl-, or allyloxymethylphenyl)-2-pentamethyldisilanyl ethynes 2a, 2b, or 2c in benzene provides novel stereoselective intramolecular cycloaddition products 6, 8, or 12 via silacyclopropene intermediates.
TL;DR: In this article, the copper(II) coordination chemistry of an acyclic diamide ligand, H 2 L1, has been investigated and two ligand types, (L1+H ) − and (L 1′ ) −, can be distinguished by cyclic voltammetry.
TL;DR: The intramolecular reaction of a triyne promoted by palladium results in the formation of an enyne and coupling of the third alkyne with the phosphine as mentioned in this paper.
TL;DR: The Lewis acid-mediated reactions of allene-ene compounds, derived from 3-methylcitronellal or dimethyl malonate, were carried out using various Lewis acids, affording unexpectedly intramolecular [2+2]cycloaddition products under some particular reaction conditions without any formation of intramolescular ene reaction products.
Abstract: The Lewis acid-mediated reactions of allene-ene compounds, derived from 3-methylcitronellal or dimethyl malonate, were carried out using various Lewis acids such as ethylaluminum dichloride, diethylaluminum chloride, titanium chloride, zinc chloride etherate, or boron trifluoride etherate, affording unexpectedly intramolecular [2+2]cycloaddition products under some particular reaction conditions without any formation of intramolecular ene reaction products.
TL;DR: The results suggest several factors that influence 6-membered ring formation, including two types of intramolecular aldol reaction and intramolescular 1,4-addition, due to the C3-substituent, Lewis acid, and the presence of diol.
Abstract: The reactivity of 3-substituted 4-methyl-4-(3-oxobutyl)-2-cyclohexen-1-ones (1) in the presence of a combination of a Lewis acid and a 1,2-diol was studied. The results suggest several factors that influence 6-membered ring formation, including two types of intramolecular aldol reaction and intramolecular 1,4-addition, due to the C3-substituent, Lewis acid, and the presence of diol. In this study, novel methodology to prepare two types of decalin skeleton could be developed.
TL;DR: The palladium(0)-catalyzed alkylation of 2,3-bis(acetoxymethyl)bicyclo[2.2.1]hepta-2,5-diene 1 with malonate-type enolates as nucleophiles is investigated in this paper.
TL;DR: In this article, cycloaddition-fragmentation-recombination and cycload-dition rearrangement-mediated processes for synthesis of the title compounds are described.
Abstract: Methods are described for sequential cycloaddition–fragmentation–recombination and cycloaddition–rearrangement-mediated processes for synthesis of the title compounds. Reaction of methyl vinyl ketone with 3-methoxyestra-1,3,5(10),14,16-pentaen-17-yl acetate 1 gives a cycloadduct 2, which undergoes retroaldol cleavage followed by intramolecular Michael reaction, to generate 3-methoxy-5′,6′-dihydro-15αH-benzo[14,15]-14β-estra-1,3,5(10)-triene-4′(3′H),17-dione 4. Similarly, it is shown that various 16α-alkenyl-14α,17α-ethenoestradiols undergo ready [3,3]-sigmatropic rearrangement to give functional variants of this pentacyclic system. Synthetic routes to novel (perhydrobenzo)[14,15]-14β-analogues of estradiol are described, and aspects of the chemistry of 14β,16β-propano-19-norsteroids derived from alternative intramolecular reaction pathways are outlined.
TL;DR: This reaction was found to be both thermodynamically and kinetically controlled under restricted conditions.
Abstract: Asymmetric spirocyclization based on intramolecular conjugate addition using a combination of a Lewis acid and an optically active cyclohexane-1,2-diol has been studied in connection with 1) the effect of substituents on the cyclohexane-1,2-diol and 2) the effect of substituents on the substrate. This reaction was found to be both thermodynamically and kinetically controlled under restricted conditions.
TL;DR: In this article, the high-temperature condensation of 4-benzoyl-1,8-naphthalene anhydride with 2,6-dimethylaniline and o-phenylenediamine was investigated.
TL;DR: In this paper, the stereocontrol of intramolecular [2 + 2] cycloadditions between ketenimines and imines leading to 1,2-dihydroazeto[2, 1-b]quinazolines has been achieved.
Abstract: Highly stereocontrolled, intramolecular [2 + 2] cycloadditions between ketenimines and imines leading to 1,2-dihydroazeto[2, 1-b]quinazolines have been achieved. The source of stereocontrol is a chiral carbon atom adjacent either to the iminic carbon or nitrogen atom. In the first case, the stereocontrol stems from the preference for the axial conformer in the first transition structure. In the second case, the origin of the stereocontrol lies on the two-electron stabilizing interaction between the C-C bond being formed and the sigma orbital corresponding to the polar C-X bond, X being an electronegative atom. These models can be extended to other related systems for predicting the stereochemical outcome in this intramolecular reaction.