Showing papers on "Intramolecular reaction published in 1993"
TL;DR: In this paper, the intrinsic processes and mechanisms of proton transfer in relation to the nature of the intramolecular hydrogen bond ring are reviewed. But the authors focus on the intrinsic process and not the mechanisms of transfer.
Abstract: Excited-state intramolecular proton transfer reactions are reviewed. Special emphasis is given to the intrinsic processes and to the mechanisms of proton transfers in relation to the nature of the intramolecular hydrogen bond ring.
647 citations
218 citations
147 citations
TL;DR: In this article, the reaction of unsaturated hydroxy esters (X=OMe, R 2 =H, Me) and amides with benzaldehyde and potassium alkoxide or amide bases is reported.
Abstract: Reaction of the illustrated unsaturated hydroxy esters (X=OMe, R 2 =H, Me) and amides (X=N(Me)OMe, R 2 =H, Me) with benzaldehyde and potassium alkoxide or amide bases is reported. The resulting benzylidene acetals are obtained in good yields (71-84%) and with hidh selectivity (>90:10). In addition to an exploration of the scope of the reaction, a mechanistic study, involving the use of deuterated benzaldehyde to ascertain the rate-determining step of the process, is described
147 citations
128 citations
TL;DR: The enantioselectivity in intramolecular C-H insertion reactions of α-diazo β-keto esters catalyzed by dirhodium(II) tetrakis[N-phthaloyl-(S)-phenylalaninate] was found to be substantially improved by evaluation of the alkoxy group of the ester moiety as mentioned in this paper.
126 citations
TL;DR: The Pauson-Khand cycloaddition has become a synthetically important reaction as discussed by the authors, and several modifications have increased the utility of the reaction, including reports that tertiary amine N-oxides greatly accelerate the rate of cycloadding in both intra- and some intermolecular reactions.
Abstract: The Pauson-Khand cobalt-mediated cycloaddition has become a synthetically important reaction. Several modifications have increased the utility of the reaction, including reports that tertiary amine N-oxides greatly accelerate the rate of cycloaddition in both intra- and some intermolecular reactions. To date, there has been no direct evidence to support the mechanistic hypothese for either the thermal or amine oxide promoted reactions beyond complete identification of the hexacarbonyl alkyne complex. While the amine oxide promoted reaction is normally greatly accelerated over the analogous thermal one, in the presence of amine oxides, the rate of cycloaddition of a 1,6-enyne may be enhanced even further by the presence of sulfur, nitrogen, or oxygen in the homopropargylic or bishomopropargylic position
126 citations
TL;DR: The one-pot intramolecular double Michael reaction of compounds having two different α, β-unsaturated carbonyl groups to form polycyclic compounds can be carried out by three different methods: in the first, the substrate is treated with lithium hexamethyldisilazide, in the second, with chlorotrimethylsilane, triethylamine, and zinc chloride at an elevated temperature, and in the third, with tert-butyldimethylsilyl trifluoromethanesulfonate, and triethy
Abstract: The one-pot intramolecular double Michael reaction of compounds having two different α, β-unsaturated carbonyl groups to form polycyclic compounds can be carried out by three different methods: in the first the substrate is treated with lithium hexamethyldisilazide, in the second with chlorotrimethylsilane, triethylamine, and zinc chloride at an elevated temperature, and in the third with tert-butyldimethylsilyl trifluoromethanesulfonate and triethylamine. The reaction proceeds with complete regioselectivity and high stereoselectivity following a stepwise mechanism. Spiro-fused bicyclo[2.2.2]octane derivatives can be constructed with high stereoselectivity by the intromolecular double Michael reaction by using the first method. Enantiomerically pure atisine and the enantiomer of atisirene were synthesized stereoselectively by application of this methodology. The syntheses of steroids and angular triquinane-type sesquiterpenoids were possible with the second method. Heterocyclic compounds with a bridgehead nitrogen atom were obtained by the reaction of α, β-unsaturated amides following the second and third methods. The asymmetric synthesis of tylophorine with diastereofacial control was achieved by the intramolecular reaction according to the third method. The sulfur-mediated intramolecular double Michael reaction utilizing the third method produced trans-hydroindane derivatives. Furthermore, the intramolecular Michael-aldol reaction can be employed in synthesizing polycyclic systems with cyclobutane units by treatment with tert-butyldimethylsilyl trifluoromethanesulfonate in the presence of triethylamine. The intermolecular double Michael reaction and related reactions will also be described.
113 citations
TL;DR: Stereoselective Intramolecular Bis-Silylation of Alkenes Promoted by a Palladium-Isocyanide Catalyst Leading to Polyol Synthesis.
Abstract: Stereoselective Intramolecular Bis-Silylation of Alkenes Promoted by a Palladium-Isocyanide Catalyst Leading to Polyol Synthesis
110 citations
TL;DR: An intramolecular triflate-arene coupling reaction mediated by bis(triphenylphosphine)palladium(II) chloride has been developed for the synthesis of each of the isomeric benzofluoranthenes as discussed by the authors.
Abstract: An intramolecular triflate-arene coupling reaction mediated by bis(triphenylphosphine)palladium(II) chloride has been developed for the synthesis of each of the isomeric benzofluoranthenes. This reaction, which results in formation of a new five-membered ring, proceeds in highest yield when performed using 0.1 equiv of the palladium catalyst, 3 equiv of lithium chloride, and 1.2 equiv of 1,8-diazabicyclo[5.4.0]undec-7-ene in N,N-dimethylformamide at 140 o C. The biaryl precursors needed for the coupling reaction can be prepared by [1,2-bis(diphenylphosphino)ethane]nickel (II) choride catalyzed coupling of an aryl bromide with an [o-(methoxymethoxy)aryl]magnesium bromide (prepared by ortho-lithiation of an aryl methoxymethyl ether followed by transmetalation with magnesium bromide). Using this procedure benzo[a]fluoranthene, benzo[b]fluoranthene, benzo[j]fluoranthene, and benzo[k]fluoranthene were prepared in yields of 84%, 85%, 93%, and 64%, respectively.
93 citations
TL;DR: A convergent synthesis of a protected version of (+)-lycoricidine has been accomplished in 13 steps from L-arabinose as mentioned in this paper, using a novel N-sulfonyliminium ion cyclization of vinylsilane aldehyde.
Abstract: A convergent synthesis of a protected version of (+)-lycoricidine has been accomplished in 13 steps from L-arabinose. Preparation of the aminocyclitol moiety 50 employed a novel vinylsilane-terminated N-sulfonyliminium ion cyclization of vinylsilane aldehyde 42. Closure of the B-ring using an intramolecular Heck reaction afforded lycoricidine derivative 58. An unexpected cyclization of vinylsilane aldehyde 42 allowed for the stereodivergent preparation of semiprotected conduritols 43 and 45
TL;DR: In this paper, the Schmidt reaction was used to generate bridged-or fused-bicyclic a-amino carbocations or iminium ions, depending on the geometry about the C(+)-N bond.
Abstract: Aliphatic azides were captured intramolecularlyby carbocations, producing aminodiazonium ion intermediates. Carbon-to-nitrogen rearrangement then occurred, generating bridged- or fused-bicyclic a-amino carbocations or iminium ions, depending on the geometry about the C(+)-N bond. In the bridged systems, rapid elimination of the α-amino carbocations produced twisted enamines with 1-azabicyclo[3.2.2]nonene, 1-azabicyclo[2.2.2]octene, and 1-azabicyclo[3.2.1]octeneskeletons. In the fused systems, the iminium ions were reduced with sodium borohydridetogive 1-azabicyclo [n.3.0]alkanes, where n=4 or 5. The carbocations for these intramolecular Schmidt reactions were generated by treatment of alkenes or alcohols with trifluoromethanesulfonic acid
TL;DR: In this article, β-Alkoxyacrylates were found to be exceptionally efficient radical acceptors in radical-mediated intramolecular cyclizations, and they were used to obtain (±) ( cis -6-methyltetrahydropyran-2-yl)acetic acid, a known component of civet.
TL;DR: In this article, a shish kebab oligomer was obtained by first inserting a ruthenium chloro carbonyl complex in tetrakis(3,5-di-tert-butyl-4-hydroxyphenyl)porphyrin.
Abstract: The association of pentaammineruthenium(II) with the reducible ligand 4,4[prime]-azopyridine leads to a pH-induced redox reaction in which ruthenium is oxidized to the III state, while 4,4[prime]-azopyridine is reduced to hydrazopyridine. In this process, the conjugated ligand is transformed in a nonconjugated one, with loss of its intramolecular electron-transfer properties. In order to exploit this control of an intramolecular electron transfer by a protonation process, the authors have prepared shish kebab oligomers by first inserting a ruthenium chloro carbonyl complex in tetrakis(3,5-di-tert-butyl-4-hydroxyphenyl)porphyrin. The resulting Ru(CO)(porphyrin) complex is photochemically decarbonylated in the presence of bridging ligands (4,4[prime]-azopyridine or pyrazine). Oligomers are thus obtained, which can be oxidized by iodine, giving rise to intervalence transitions between ruthenium(II) and -(III) in the near-infrared. This provides a convenient way to monitor electron transfer along the oligomer chain. In the case of 4,4[prime]-azopyridine, the pH-induced redox reaction is again observed. Starting from a homovalent ruthenium(II) chain, this gives the possibility to switch on or off the intervalence transition by a protonation/deprotonation reaction. 17 refs., 8 figs. 2 tabs.
TL;DR: In this paper, a series of halo substituted carboxylic acid derivatives were cyclized in excellent yield to the corresponding 4-, 5-, and 6-members carbocycles.
Abstract: Intramolecular nucleophilic acyl substitution reactions involving a broad range of halo substituted carboxylic acid derivatives have been accomplished in excellent yield employing samarium(II) iodide as the reductive coupling agent. Although particular substrates cyclized most effectively in THF in the presence of tripiperidinophosphine oxide, carboxylic acid esters, the focus of this report, cyclize equally well without such an additive in the presence of a catalytic quantity of iron(III) complexes. Thus a comprehensive series of halo substituted esters were cyclized in excellent yield to the corresponding 4-, 5-, and 6-members carbocycles. The reaction is extremely mild and selective as demonstrated by experiments wherein alkyl chlorides, acetals, and olefins remain completely intact under the reaction conditions. In addition to introducing a convenient procedure for preparing stereodefined spirocyclic systems, a new ring expansion sequence has been developed that appears extremely general for the preparation of various ring systems
TL;DR: In this paper, the reaction of lithium diisopropylamide (LDA) with (η 4 -1,3-cyclohexadiene)Fe(CO) 3 complexes bearing functionalized side chains at C-5, under an atmosphere of carbon monoxide, gives bridged bicyclo[3.3.2] octene and bicyclo [3.1]nonene systems after electrophilic quenching, whereas larger rings cannot be obtained in this series.
Abstract: Reaction of lithium diisopropylamide (LDA) with (η 4 -1,3-cyclohexadiene)Fe(CO) 3 complexes bearing functionalized side chains at C-5, under an atmosphere of carbon monoxide, gives bridged bicyclo[3.2.1]octene and bicyclo[3.3.1]nonene systems after electrophilic quenching, whereas larger rings cannot be obtained in this series. Under the same reaction conditions, intramolecular cyclization of acyclic (η 4 -1,3-butadiene)Fe(CO) 3 complexes with functionalized side chains at the terminal position of the diene ligands furnishes fused bicyclo[3.3.0]octanone and bicyclo[4.3.0]nonanone derivatives after acid quenching. The iron-mediated intramolecular nucleophilic addition allows for the direct stereocontrol of four stereogenic centers of these fused bicyclic skeletons
TL;DR: Treatment of substances possessing vinyltrimethystannane and vinyl halide (I or Br) functions with copper(I) chloride in N,N-dimethylformamide (DMF) constitutes a new effective method for the stereospecific synthesis of cyclic conjugated dienes as discussed by the authors.
Abstract: Treatment of substances possessing vinyltrimethystannane and vinyl halide (I or Br) functions with copper(I) chloride in N,N-dimethylformamide (DMF) constitutes a new effective method for the stereospecific synthesis of cyclic conjugated dienes
TL;DR: The type 2 imino Diels-Alder cycloaddition was used for the synthesis of a homologous series of bridgehead olefin-bridgehead lactams as mentioned in this paper.
Abstract: The type 2 imino Diels-Alder cycloaddition was used for the synthesis of a homologous series of bridgehead olefin-bridgehead lactams. The X-ray crystal structures of three members of this series, including the highly strained 2-carbomethoxy-8-oxo-2-azabicyclo[3.3.1]non-4-ene, were obtained. An analysis of the structural data permits evaluation of the response of the bridgehead double bond and bridgehead amide linkages to similar torsional distorsions
TL;DR: An 11-step approach to tricyclic compound ethanopyrrolo[2,3-c]pyridine derivative 42, which contains the alkaloidal nucleus of the marine natural product sarain A (1), has been developed as discussed by the authors.
Abstract: An 11-step approach to tricyclic compound ethanopyrrolo[2,3-c]pyridine derivative 42, which contains the alkaloidal nucleus of the marine natural product sarain A (1), has been developed. Pivotal steps in the construction of 42 include stereospecific intramolecular dipolar [3+2]-cycloaddition of an azomethine ylide generated from aziridine 27 to afford bicyclic lactam pyrrolo[2,3-c]pyridine derivative 28, and a novel intramolecular allylsilane/N-tosyliminium ion cyclisation of 41 to produce the tricycle
TL;DR: Copper carbenoids undergo efficient intramolecular insertion into allyl ethers, and the resulting ylide-type species rearrange to furnish cyclic ethers (ring sizes 6-8) in high yield.
TL;DR: In this article, the parent skeletons of the CD and DE diphenyl ether 16-membered ring systems of vancomycin and ristocetin, bared on the implementation of an intramolecular Ullmann macrocyclization reaction are detailed.
Abstract: The preparations of 2 and 3, the parent skeletons of the CD and DE diphenyl ether 16-membered ring systems of vancomycin and ristocetin, bared on the implementation of an intramolecular Ullmann macrocyclization reaction are detailed. Additional studies which define the scope of substrates suitable for use in the Ullmann macrocyclization reaction are described including a limited study of those bearing centers capable of racemization. Within the limited series of agents examined, Ullmann macrocyclization closure of the DE ring system war found to occur at a faster rate and in higher overall yields than those providing the CD ring system. N-Methylation of the amide linking chain decelerates or inhibits Ulmann macrocyclization and α-substitution of the central amino acid of the linking chain significantly increases the cyclization conversions. Racemization of the central amino acid of the linking amide chain was found to be minimal (5%) under reaction conditions where the secondary amides are deliberately deprotonated prior to exposure of the substrate to the thermal, basic reaction conditions
TL;DR: In this paper, the presence of heteroatoms in these bicyclic fused 5-membered rings permits for the first time an evaluation of the conformation of this system by means of NMR.
Abstract: Thermal intramolecular oxime olefin cycloaddition of α-allylamino aldoximes and ketoximes 4 led stereospecifically to formation of oxadiazabicyclo[3.3.0]octanes 6. The presence of heteroatoms in these bicyclic fused 5-membered rings permits for the first time an evaluation of the conformation of this system by means of NMR. We found that some substituents in 6 restrict the conformational mobility of these five-membered rings to the extent that only one conformer was detected at 20 o C. In other cases an equilibrium between two major conformers was revealed by NMR. Equilibrium measurements indicated a free energy of conversion of 13.2-13.4 kcal/mol, apparently a manifestation of the N-inversion in the isoxazolidine ring. NMR studies also showed that the NH-proton in isoxazolidines 6 prefers an axial orientation. Empirical force field data were adjusted for MM calculations in these bicyclic heterocycles. The MM2 force field with AMBER charge gave the best fit between calculated and experimental coupling constants
TL;DR: The first total synthesis of (±)-scopadulcic acid A has been accomplished using an intramolecular bis-Heck cyclization to form the B-D rings of this tetracyclic diterpene with complete stereocontrol as discussed by the authors.
Abstract: The first total synthesis of (±)-scopadulcic acid A has been accomplished using an intramolecular bis-Heck cyclization to form the B-D rings of this tetracyclic diterpene with complete stereocontrol
TL;DR: In this paper, the photophysical and photochemical properties of phenyldisilanes having a trifluoromethyl substituent on a benzene ring as one of the most suitable substituents for stabilization of the OICT (σπ * orthogonal intramolecular charge transfer) state were investigated in detail.
Abstract: Photophysical and photochemical properties of phenyldisilanes having a trifluoromethyl substituent on a benzene ring as one of the most suitable substituents for stabilization of the OICT (σπ * orthogonal intramolecular charge-transfer) state were investigated in detail. The OICT mechanism for CT fluorescence in nonpolar solvents was supported by the remarkable dependence of absorption and fluorescence spectra of trifluoromethyl-substituted phenyldisilanes on the dihedral angle between benzene pπ orbital and the SiSi a bond
TL;DR: In this paper, a synthetic approach to the synthesis of highly oxygenated indolizidine alkaloids, stereoisomers of swainsonine, is described, where a key feature of the approach is intramolecular cycloaddition between an acylnitroso dienophile and a tethered diene moiety.
Abstract: A synthetic approach to the synthesis of highly oxygenated indolizidine alkaloids, stereoisomers of swainsonine, is described. A key feature of the approach is intramolecular [4+2] cycloaddition between an acylnitroso dienophile and a tethered diene moiety, followed by ring contraction of the 1,2-oxazine so formed to a pyrrolidine. The requisite intermediates were prepared in optically pure form from L-glutamic acid
TL;DR: In this paper, a one-pot procedure for the synthesis of the five-membered heterocycles from the corresponding amino sugars is also reported, with total regioselectivity and no need for protection of the secondary hydroxyl groups.
Abstract: Chiral, sugar-derived oxazolidine-2-thiones having a pseudo-C-nucleoside structure, as well as bicyclic 2-thioxotetrahydro-1,3-oxazines, have been prepared by intramolecular cyclization of 6-deoxy-6-isothiocyanatoaldoses or -aldopyranosides, respectively. The reaction proceeds with total regioselectivity and no need for protection of the secondary hydroxyl groups. A one-pot procedure for the synthesis of the five-membered heterocycles from the corresponding amino sugars is also reported. The six-membered analogs have a cis- or trans-decalin-type core depending on the configuration of the sugar precursor