Showing papers on "Intramolecular reaction published in 1997"

Intramolecular cyclization in hyperbranched polyesters

Abstract: The effect of monomer structure and catalyst on the synthesis of hyperbranched polyesters based on 4,4-(4′-hydroxyphenyl)pentanoic acid has been examined. The nature of the ester group and the catalyst have a significant effect on the molecular weight of the hyperbranched polyester but do not effect the degree of branching for these materials. The fate of the single ester group at the focal point of these hyperbranched macromolecules is probed by the synthesis and polymerization of 13C labeled methyl 4,4-(4′-hydroxyphenyl)pentanoate. Comparison of the molecular weights determined by 1H- or 13C-NMR spectra with those determined by osmometry suggest that intramolecular cyclization does not occur to a significant extent in these systems. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1627–1633, 1997

Intramolecular Reaction of (γ-Alkoxyallyl)stannane with Aldehyde: Origin of the Stereoselectivities

Abstract: The intramolecular cyclization of simple acyclic (γ-alkoxyallyl)stannane aldehydes 1, 2, and 12−15 was investigated to elucidate the relationship between the geometry of the double bond of the allylstannanes, the ring size of cyclic ethers produced by the cyclization, and the procedures for promoting the cyclization. The Lewis acid-mediated cyclization of 1-2, 12-13, and 14-15 gave the trans cyclic ethers 3, 39, and 41, respectively, either predominantly or exclusively irrespective of the geometry of the double bond and of the ring size of the cyclic ethers. The relationship in the thermal cyclization of 1 and 2, which gave the 6-membered cyclic ethers 4 and 3, was straightforward; the Z isomer 1 gave the cis product 4, and the E isomer 2 afforded the trans product 3. However, the relationship in the thermal cyclization of 12 and 13 which afforded the 5-membered cyclic ethers 39 and 40 was different from that expected from the cyclization via the well-accepted cyclic transition state, as observed in the c...

An Improved Synthesis of 1,2,3,4-Tetrahydroisoquinolines via Intramolecular Cyclization of N-Acyl-N-(aryl)methyl-2-(phenylsulfinyl)ethylamine by Pummerer Reaction.

Abstract: Pummerer reaction of the sulfoxides 5 of N-acyl-N-(aryl)methyl-2-(phenylthio)ethylamines (4) on treatment with trifluoroacetic anhydride (TFAA) effectively caused intramolecular cyclization under a mild condition to give N-acyl-4-phenylthio-1,2,3,4-tetrahydroisoquinolines (TIQs) (7). The reaction of the N-formyl sulfoxide 5c without a methoxy group in the benzene ring using a formyl group for N-protection is particularly efficient. Treatment of the N-formyl sulfoxide 5f with TFAA did not give any TIQ, but a sequential treatment using TFAA and BF 3 . Et 2 O afforded N-formyl-4-phenylthio-TIQ (7f) in quantitative yield. The efficiency of this method of preparing TIQs was demonstrated in the synthesis of 1,4-dideuterio-TIQ (10D) and its N-methyl derivative (11D).

Asymmetric total syntheses of hydroxylated piperidine alkaloids via the intramolecular reaction of γ-aminoallylstannane with aldehyde

Abstract: Asymmetric total syntheses of (+)-desoxoprosopinine and (−)-desoxoprosophylline were accomplished using L-glutamic acid as the chiral source, in which the intramolecular reaction of a γ-aminoallylstannane with an aldehyde was used as a key step.

Total Synthesis of Kealiiquinone, an Imidazole Marine Alkaloid

Abstract: The total synthesis of kealiiquinone (1), a highly substituted imidazole marine alkaloid isolated from sponge, was achieved via nine reaction steps starting from 1-methyl-1H-imidazole (5). The synthesis is based on the selective introduction of appropriate carbogenic substituents and protecting groups into the imidazole ring followed by an intramolecular cyclization of the substituents on the C4- and the C5-positions. The structure of the synthesized kealiiquinone was confirmed by X-ray crystallographic analysis.

Intramolecular [4+2] cycloaddition of a photogenerated o-quinone methide in aqueous solution

Abstract: Using a approrpriately substituted o-hydroxybenzyl alcohol precursor 5, it is shown that a photogenerated o-quinone methide can undergo efficient intramolecular [4+2] (Diels-Alder) cycloaddition in aqueous CH3CN solution at 15°C, to generate the hexahydrocannabinol ring system 11. The dienophile tether must be sufficiently electron rich, having at least three alkyl groups. Laser flash photolysis studies show the intermediacy of an o-quinone methide (λmax ≈ 400 nm) which has a lifetime > 2 ms. Quantum yields for reaction and fluorescence parameters are also reported which depend strongly on the proportion of water in the H2OCH3CN solvent mixture.

Reactivity in Monolayers versus Bulk Media: Intra- and Intermolecular Aminolysis of Esters

Abstract: Monolayers possessing reactive amino and p-nitrophenyl ester functional groups at the same or different levels with respect to the monolayer interface have been self-assembled on a gold surface. Intramolecular reactions in these monolayers are at least 1000 times slower than the same processes in the bulk medium. Control experiments with external reagents showed that the monolayer p-nitrophenyl ester group reacts readily with amines from solution, whereas nucleophilicity of the monolayer amino functionality is significantly suppressed. This unusually low reactivity of the amino group was tentatively assigned to its interaction with the gold surface.

Convenient synthesis of silyl substituted butadienes; a new route to silicon tethered intramolecular Diels–Alder reaction precursors

Abstract: The preparation of a series of silyl substituted butadienes is reported together with their application in the silicon-tethered intramolecular Diels–Alder reaction (IMDA).

Sulfones as Radical Progenitors: An Unprecedented Example of Homolytic Sulfone Cleavage Facilitated by o-Stannyl Substitution of Aryl Sulfones(1).

Abstract: Allylic aryl sulfones bearing an o-allyldialkylstannyl moiety (1b), when converted to stannyl radical 1a, suffer homolytic cleavage via intramolecular attack of the stannyl radical on the sulfone. Allyl radicals generated in this manner can be utilized for further intramolecular radical cyclizations; thus the overall transformation can be viewed as an alkylative desulfonylation reaction. Previously unknown sulfonyl stannane polymer 5 is generated as a byproduct. The o-dibutylstannyl radical derived from nonallylic aryl sulfone 15 does not suffer homolysis but instead forms 9-membered macrocycle 19 via an intramolecular reaction with the phenylacetylene group.

Intramolecular meta photocycloaddition of 3-benzyl(dimethylsila)prop-1-enes

Abstract: The regiochemistry of intramolecular meta photocycloaddition of 3-benzyl(dimethylsila)prop-1-enes is controlled by the silicon in the tether and the presence of an electron donor substituent on the phenyl ring For 1′,3′-addition, the preferred formation of the angular rather than the linear triquinane isomer is interpreted in terms of an asymmetric orientation of the S 0 ethene and S 1 benzene inducing a non-synchronous addition which then promotes specific 2′,4′-cyclisation to give the cyclopropane ring of the dihydrosemibullvalene skeleton

Flow effects in the polymer cyclization reaction

Abstract: We investigate the effect of shear and uniaxial extensional flows on the rate of the cyclization reaction in polymers. We find that for such an intramolecular diffusion-controlled reaction the flow always reduces the reaction rate, in contrast to the previously studied case of intermolecular reactions, where linear flows enhance the reaction rate.

Novel Bis (1,3-Dithiole) Electron Donors by Oxidative Intramolecular Cyclization of 2,2′-Bis(1,4-Dithiafulven-6-yl)-3,3′-Bithienyls

Abstract: 2,2′-Bis(1,4-dithiafulven-6-yl)-3,3′-bithienyls 6 were prepared by using either a Wittig or a Wittig-Homer reaction. The cyclic voltammograms of 6 revealed that they undergo an intramolecular cyclization by electrochemical oxidation. Chemical oxidation of 6 with tris(4-bromophenyl)aminium hexachloroantimonate gave intramolecular cyclization products 16 as dication salts. The hexachloroantimonate ion was found to act as an oxidizing agent in the reaction. Chemical reduction of the dication salts with zinc afforded the corresponding neutral bis (1,3-dithiole) donors 7 in high yields. The cyclic voltammograms of 7 showed reversible one-stage two-electron oxidation waves, and the potentials are fairly low. A conductive TCNQ complex was formed from one of them. X-ray analyses of the neutral and dication states of the donor show that there is a large conformational change between them.

Dirhodium(II)-Catalyzed Intramolecular Carbon-Hydrogen Insertion Reaction of α-Diazoketones : Synthesis of 7-Silyloxyoctahydrobenzo[b]furan-2-ones

Abstract: A dirhodium(II)-catalyzed intramolecular C-H insertion reaction of 2-oxygen-substituted cyclohexyl diazoacetoacetates 1a-f was investigated. In contrast to the trans-2-methoxy- 1a and trans-2-(p-methoxybenzyloxy)-cyclohexyl derivatives 1b, which, upon treatment with 1 mol% dirhodium(II) tetraacetate in boiling benzene, gave a complex mixture, the trans-2-(tert-butyldimethylsilyoxy)cyclohexyl derivative 1c gave, in addition to the β-lactone 3c (16%), cis- and trans-fused octahydrobenzo[b]furan-2-ones 2c in 22 and 18% yields, respectively. Similar treatment of the cis-isomer 1d gave the β-lactone 3d as the major product (34%) and cis- and trans-fused γ-lactones 2d (7 and 18% yields, respectively) as minor products. The (1R*, 2R*, 3R*)-3-benzyloxy-2-(tert-butyldimethylsilyloxy)cyclohexyl derivative 1e gave the γ-lactones 2e in 75% combined yield as a 5 : 2 mixture of cis- and trans-fused isomers, while the (1R*, 2R*, 3R*)-isomer 1f afforded the trans-fused γ-lactone 2f in 62% yield as a single product.

Stereocontrolled Synthesis of Polycyclic Ethers and Related Heterocycles via the Intramolecular Reaction of Allylstannanes

Abstract: The synthetic reaction using functionalized allylstannanes is widely appreciated as one of the most useful methods for the stereocontrolled C-C bond formation. We now report the stereoselective synthesis of functionalized heterocycles via the intramolecular reaction of allylstannane with aldehydes and imines. The stereocontrolled total synthesis of hemibrevetoxin B was achieved by using the intramolecular reaction of γ-alkoxyallylstannane with aldehydes. The extension of this methodology led to a new strategy for the stereoselective synthesis of alkaloids such as (+) -desoxoprosopinine and (+) -preussin.

Intramolecular reactions. An explanation for [M−H]+ ions in the chemical ionization mass spectra of some ring C‐substituted methyl dehydroabietate derivates

Abstract: The formation of [M–H] ions in the chemical ionization mass spectra of ring C-substituted methyl dehydroabietates, when methane is used as reagent gas, has been investigated. Two mechanisms, one involving H2 loss from [M + H] + ions, and the other, hydride ion transfer reactions to the methane reagent ions, have been proposed to account for [M–H] ion abundances. For methyl 12,14-diaminodehydroabietate, protonation of the amino group on C-14, followed by the loss of H2 by an intramolecular reaction via a cyclic transition state, is proposed as the predominant mechanism. Hydride ion transfer from the benzylic C-7 has been suggested to provide a major contribution to the formation of [M–H] ions of methyl 12-amino-14-nitrodehydroabietate. These conclusions are also consistent with results obtained using ammonia as reagent gas. © 1997 by John Wiley & Sons, Ltd.

Intramolecular photocycloaddition of a vinyl ether to CF3-substituted 2-methoxy-5-phenylpent-1-enes

Abstract: 2-Methoxy-5-[3-(trifluoromethyl)phenyl]pent-1-ene undergoes 2,6- and 1,3- meta -photocycloaddition on irradiation ( λ = 254 nm). The methoxy group has the endo configuration in the photocycloadducts. Irradiation of the para - and ortho -CF 3 -substituted 2-methoxy-5-phenylpent-1-enes leads to intramolecular ortho -photocycloadducts. The difference in product formation is related to the free enthalpy of electron transfer.

Studies on Chiral Organosulfur Compounds. VI. The Use of a Chiral Diene Bearing an Optically Active Sulfinylmethyl Group in the Lewis Acid-Catalyzed Intramolecular Asymmetric Hetero Diels-Alder Reaction.

Abstract: An asymmetric Diels-Alder reaction with a diene bearing a chiral sulfinyl group is described. The Lewis acid-catalyzed intramolecular asymmetric hetero Diels-Alder reaction of a chiral α'-sulfinyl-α, β-unsaturated ketone derived from 3-methylcitronellal produced optically active 4a, 5, 6, 7, 8, 8a-hexahydro-1H-2-benzopyran derivatives. On the basis of the stereochemical results obtained, a plausible mechanism for the asymmetric induction is presented.

Formation, structure and properties of polymer networks

Abstract: The systematic study of intramolecular reaction and get points together with measurements of moduli of trifunctional and tetrafunctional end-linked networks show that get points are always delayed and network imperfections always result from the intramolecular reaction which must occur when such networks are formed. The quantitative interpretation and prediction of get points and moduli directly from reactant structures and reaction conditions are discussed.

Reactions of carbonyl compounds in basic solutions. Part 26.1The mechanisms of the base-catalysed cyclisation of 1,2-diacetylbenzene,1,8-diacetylnaphthalene, 4,5-diacetylphenanthrene and2,2′-diacetylbiphenyl

Abstract: Rate coefficients have been measured for the base-catalysed cyclisation of 1,2-diacetylbenzene 1, 1,8-diacetylnaphthalene 2, 4,5-diacetylphenanthrene 3 and 2,2′-diacetylbiphenyl 4 in a range of aqueous dimethyl sulfoxide (DMSO) compositions at 30.0 °C, as well as at 45.0 and 60.0 °C at certain concentrations, containing tetramethylammonium hydroxide. For three of the substrates, 1, 2 and 4, the di-[2H3]acetyl compounds were also studied. Studies of the relative rates, activation parameters, kinetic isotope and solvent isotope effects and correlation of the rates with an acidity function were made to give detailed mechanistic pathways. Thus, 2, 3 and 4 react with rate-determining base-catalysed ionisation to give the enolate anion, followed by relatively rapid intramolecular nucleophilic attack and dehydration to give the corresponding cyclic enones; whereas, 1 reacts by the same pathway but with rate-determining intramolecular nucleophilic attack. An intermolecular base-catalysed aldol reaction was also detected for the product of the intramolecular reaction of 2 at high DMSO contents.

Construction of AB-Ring System of Taxane Framework by A-Ring Annulation Strategy: Synthesis of 1-Hydroxy-8,11,11-trimethylbicyclo-(5.3.1)undec-7-en-9-one by Way of Intramolecular Aldol Cyclization to Form the C1-C10 Bond.

Abstract: Construction of the AB-ring system of the taxane framework via an A-ring annulation strategy was demonstrated by base-mediated intramolecular aldol reaction of (Z)-2,2-dimethyl-3-(1-methyl-2-oxopropylidene)cyclooctanone, affording the title compound, 1-hydroxy-8,11,11-trimethylbicyclo[5.3.1]undec-7-en-9-one. A cyclization precursor, the tetra-substituted (Z)-alkene, was prepared from the corresponding cyclooctanone derivative, 3-[(alpha,alpha- dimethylbenzyl)dimethylsiloxy]-2,2-dimethylcyclooctanone via a bicyclic alpha,beta-unsaturated lactone intermediate.

Novel Intramolecular Introduction of Nucleophiles To 2,2′-Anhydrouridine

Abstract: 2′-N-alkyluridine nucleosides are synthesized via intramolecular reaction of alkyl isocyanates with 5′-O-protected-2,2′-anhydrouridine.