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Results for “Alkenes”

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PubMed2004

Cross-coupling of sp(3) C-H bonds and alkenes: catalytic cyclization of alkene-amide substrates.

We herein present a new oxidative cyclization of alkene-amide substrates under neutral and catalytic conditions. This overall transformation requires tandem sp3 C-H activation (at the position adjacent to the amide nitrogen) and C-C bond formation. Specifically, pyrrolidine 1 was converted to pyrrolizidinone 3 and indolizidinone 4 in 66% and 17% yield, respectively, in the presence of [Ir(coe)2Cl]2, the carbene ligand IPr (1:1 metal/ligand ratio, 5-10 mol % of Ir), and the hydrogen acceptor (NBE or TBE, 3-10 equiv). The results presented in this study suggest that complex 10 [IPr-Ir(Cl)(substrate)] is the key intermediate in the catalytic cycle. On the mechanistic front, the key advance was the ability to facilitate C-H activation and alkene insertion in tandem, and in preference to beta-hydride elimination, in the context of amide substrates. With respect to complex synthesis, catalytic and neutral conditions of this method unlock new exciting opportunities as illustrated by regioselective cyclization of the proline-derived substrate 16.

Alkenes↗
PubMed2005

Stereoselective cross-coupling reaction of 1,1-Diboryl-1-alkenes with electrophiles: a highly stereocontrolled approach to 1,1,2-triaryl-1-alkenes.

Palladium-catalyzed cross-coupling reaction of 1,1-diboryl-1-alkenes with aryl and alkenyl iodides was found to proceed stereoselectively, giving rise to the corresponding mono-coupled product as a single diastereomer with E-configuration. Second coupling of the initial product with another aryl iodide affords diverse triarylalkenes in their stereochemically pure form. This highly stereoselective approach for triarylalkenes allows one to synthesize both diastereomers in one pot from 1,1-diboryl-1-alkenes.

Alkenes↗
PubMed1987

Lipid peroxidation and cellular damage caused by the pyrrolizidine alkaloid senecionine, the alkenal trans-4-hydroxy-2-hexenal, and related alkenals.

Lipid peroxidation was examined as a possible mechanism for cell injury by trans-4-OH-2-hexenal, the macrocyclic pyrrolizidine alkaloid senecionine and related alkenals in isolated rat hepatocytes. Each compound elicited a positive dose response for peroxidation of cellular lipids as measured by the formation of thiobarbituric acid-reactive products. The addition of the anti-oxidant N,N'-diphenyl-p-phenylenediamine to the hepatocyte suspensions inhibited the production of thiobarbituric acid-reactants. However, the presence of the anti-oxidant had no protective effects on the cell membrane integrity as evidenced by the leakage of lactate dehydrogenase from the cells into the surrounding media. These results suggest that lipid peroxidation which occurs in the presence of senecionine, trans-4-OH-2-hexenal or related alkenals is not entirely responsible for the cellular damage in isolated rat hepatocytes.

Aldehydes↗
PubMed2001

Correlation of ionization potentials and HOMO energies versus relative reactivities of Cl2, of Br2, and of I2 with representative acyclic alkenes. comparison with other additions to alkenes.

Plots of log k(rel) versus IP or versus HOMO for the title reactions are presented; similarities and differences among the reactions are discussed. The Cl2 and Br2 data each show a single line of correlation with positive slope for all alkenes regardless of the steric requirements; increasing substitution at the double bond increases the reaction rate, indicating an electrophilic reaction. Each plot of the I2 data calculated for adsorption exhibits a natural separation into groups of similarly substituted alkenes, in which increased substitution reduces the rate. Within each group, a good-to-excellent correlation is observed, with a lower IP generally corresponding to a higher relative rate. The results indicate that the relative magnitude of the steric requirements about the double bond is similar to that of the electronic effects in iodination. Plot shapes for iodination are compared to those of other reactions, such as hydroboration, oxymercuration, complexation with Ag+, and complexation with MeHg+.

Journal Article↗
PubMed2000

Studies on the oxidative addition reaction of 1,1-dibromo-1-alkenes, alpha-dehalopalladation, and the intramolecular bis(carbopalladation) reaction of alkenes. An efficient entry to fused bicycles.

Twenty-three examples of 1,1-dihalo-1-alkenes were synthesized by the conventional alkylation methods. The oxidative addition reactions of 1,1-dibromo-2,2-diphenylethene or 1, 1-dibromo-2-phenylpropene with a stoichiometric amount of Pd(PPh(3))(4) afforded 1,2-diphenylacetylene and 1-phenylpropyne, respectively, indicating that alpha-dehalopalladation reaction occurred to afford vinylic carbene intermediates. However, alpha-dehalopalladation reaction was not observed in all 1, 1-dihalo-1-alkenes containing an extra C=C bond suitable for cyclic carbopalladation under the current reaction conditions probably due to the fast cyclic carbopalladation reaction of 40A-type of palladium intermediates; A series of bicycles, i.e., fused 5,6-, 6, 6-, 6,7-, and 7,7-bicyclic compounds, were prepared efficiently via this bicyclic carbopalladation protocol. Under condition A, within 0. 5 h, 10 afforded the monocyclic product 37 in 79%. With prolonged reaction time, 37 was converted to bicycle 36. Even with isolated 37, the corresponding reaction under condition A afforded 36 in 92% NMR yield, indicating a stepwise oxidative addition-cyclic carbopalladation-beta-elimination mechanism for this bicyclization reaction.

Journal Article↗
PubMed2003

Phenonium ions from the addition of phenyl cations to alkenes. Photochemical synthesis of (rearranged) aminoalkylanilines from haloanilines in the presence of alkenes and amines.

beta-Aminoalkylanilines are smoothly obtained by irradiation of 4-chloro- and 4-fluoroanilines (as well as the N,N-dimethyl derivatives) in the presence of alkenes (1-hexene, cyclohexene) and amines (butylamine, piperidine) in polar, protic solvents such as trifluoroethanol (yield 40-75%). The reaction involves photoheterolysis of the haloaniline, addition of the resulting phenyl cation to the alkene and trapping of the phenonium cation by amine. A fraction (up to ca. 20%) of aminoalkylanilines resulting from Wagner-Meerwein rearrangement of the phenonium cation is obtained in some cases. Reduction and direct trapping of the phenyl cation by the amine compete with the above three-component synthesis in a less stabilizing solvent such as acetonitrile, but not in CF(3)CH(2)OH.

Journal Article↗
PubMed2005

Mechanisms of reaction of aminoxyl (nitroxide), iminoxyl, and imidoxyl radicals with alkenes and evidence that in the presence of lead tetraacetate, N-hydroxyphthalimide reacts with alkenes by both radical and nonradical mechanisms.

1,2-dideuterio-cyclohexene, 1,2-dideuterio-cyclooctene, and trans-3,4-dideuterio-hex-3-ene were reacted with three >NO* radicals: 4-hydroxyTempo, di-tert-butyliminoxyl, both used as the actual radicals, and phthalimide-N-oxyl (PINO) generated from N-hydroxyphthalimide (NHPI) by its reaction with tert-alkoxyl radicals (t-RO*) and with lead tetraacetate. In all cases, except the NHPI/Pb(OAc)4 system, only mono >NO-substituted alkenes were produced. The 2H NMR spectra imply that 88-92% of monoadducts were formed by the initial abstraction of an allylic H-atom, followed by capture of the allylic radical by a second >NO*, while the remaining 12-8% appear to be formed by an initial addition of >NO* to the double bond followed by H-atom abstraction by a second >NO*. A substantial and sometimes the major product formed with the NHPI/Pb(OAc)4 system has two PINO moieties added across the double bond. Since such diadducts are not formed with the NHPI/t-RO* system, a heterolytic mechanism is proposed, analogous to that known for the Pb(OAc)4-induced acetoxylation of alkenes. A detailed analysis of the NHPI/Pb(OAc)4/alkene products indicates that monosubstitution occurs by both homolytic and heterolytic processes.

Journal Article↗
PubMed2001

Study on the reactivity of the alkene component in ruthenium-catalyzed [2 + 2] cycloadditions between an alkene and an alkyne. Part 1.

[reaction: see text] The ruthenium-catalyzed [2 + 2] cycloadditions of 7-substituted norbornadienes with an alkyne have been investigated. The cycloadditions were found to be highly regio- and stereoselective, giving only the anti-exo cycloadducts as the single regio- and stereoisomers in good yields. The results on the relative rate of different 7-substituted norbornadienes in the Ru-catalyzed [2 + 2] cycloadditions with an alkyne indicated that the reactivity of the alkene component decreases dramatically as the alkene becomes more electron deficient.

Journal Article↗
PubMed2001

Cytochrome P450-catalyzed metabolism of ezlopitant alkene (CJ-12,458), a pharmacologically active metabolite of ezlopitant: enzyme kinetics and mechanism of an alkene hydration reaction.

Experiments were conducted to characterize the metabolism of ezlopitant alkene (CJ-12,458), an active metabolite of ezlopitant, in human liver microsomes. In incubations with human liver microsomes and cofactors required for cytochrome P450 (CYP) activity, CJ-12,458 was converted to two metabolites: a diol (CP-611,781) and a 1 degrees alcohol (CP-616,762). In human liver microsomes, apparent K(M) values of 5.4 and 8.5 microM were determined for the formation of diol and 1 degrees alcohol metabolites, respectively. High K(M) activities were also observed for formation of these metabolites; however, the aforementioned low K(M) activities accounted for greater than 90% of the total intrinsic clearance. In pooled human liver microsomes, formation of both metabolites was partially inhibited by both quinidine and ketoconazole, suggesting that CYP2D6 and CYP3A enzymes are involved in the metabolism of CJ-12,458. This evidence was corroborated through the use of heterologously expressed CYP enzymes and correlation analysis with a panel of human liver microsomes. The data suggest that CYP2D6 is quantitatively more important than CYP3A in the metabolism of CJ-12,458 by a factor of about 2 to 1. The conversion of an alkene to a 1 degrees alcohol represents a novel biotransformation reaction. Incubations using (18)O(2), (2)H(2)O, [(2)H(5)]CJ-12,458, and [(2)H]NADPH were conducted and the 1 degrees alcohol product was characterized by ion trap mass spectrometry. From these data, a mechanism for this reaction is proposed involving epoxidation, an exocyclic hydride shift, and reduction at the benzylic position.

Benzylamines↗
PubMed2002

Et(2)Al(+) alumenium ion-like chemistry. synthesis and reactivity toward alkenes and alkene oxides.

Inert weakly coordinating carborane anions, CB(11)H(6)X(6)(-) (X = Cl, Br), allow access to the long sought, highly electrophilic diethylaluminum moiety in Et(2)Al(CB(11)H(6)X(6)). X-ray crystallography reveals ion-like structural features reminiscent of the corresponding trialkylsilylium species. Et(2)Al(CB(11)H(6)X(6)) is a potent catalyst for the electrophilic ethenation of benzene, the polymerization of cyclohexene oxide, and the oligomerization of ethene to a low molecular weight, highly branched product.

Journal Article↗
PubMed2006

Enzymatic approach to enantiomerically pure 5-alken-2,4-diols and 4-hydroxy-5-alken-2-ones: application to the synthesis of chiral synthons.

Enantiomerically pure 1,3-diols 1-3 were obtained by a chemoenzymatic approach (lipase PS from Burkholderia cepacia). These diols were converted into useful chiral synthons, which could be considered homologues of glyceraldehyde and glyceric acid acetonides. Applications of these synthons to the de novo synthesis of sugars and preparation of conagenin carboxylic moiety were shown. Hydroxy ketone 4 was chosen as a model system for another synthetic evolution: it was obtained in enantiomerically pure form by enzymatic resolution and converted into chiral tetrahydropyranes, such as the stereoisomers of the commercial fragrance Gyrane.

Alcohols↗