• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 143
  • 40
  • 17
  • 15
  • 5
  • 4
  • 2
  • 2
  • 2
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 282
  • 87
  • 60
  • 53
  • 41
  • 40
  • 35
  • 30
  • 21
  • 20
  • 20
  • 20
  • 20
  • 19
  • 19
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

(Rh(CO)₂Cl)₂-catalyzed allylic substitution reactions and domino sequences and application of the Pauson-Khand reaction to the synthesis of azabicyclic structures total synthesis of (-)-alstonerine /

Miller, Kenneth Aaron, January 1900 (has links)
Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

A comparison of in vivo and in vitro alkylation by ethyl methanesulfonate in Vicia faba

Engle, James Buck, 1948- January 1972 (has links)
No description available.

Investigations into the reactions of enamines and imines.

Rae, Bruce. January 1990 (has links)
The alkylation of 2-methylcyclohexanone imines using methyl acrylate has been investigated with a view to optimising the reaction conditions. The mechanism of this alkylation reaction has been investigated and it has been shown that the alkylation does not proceed via a 2,6-intermediate which subsequently undergoes a rearrangement to the 2,2-product, but rather proceeds directly to the 2,2-product. As it had been shown that the alkylation of 2-substituted cyclohexanone imines in dry methanol occurred at the more substituted position, it was decided, in the light of certain apparently anomolous patent work, to investigate the alkylation of unsubstituted cyclohexanone imines using a variety of electrophilic alkenes. The results show that in certain instances, 2,2-bis-alkylation occurs and in others, mono-alkylation and that it is the strength of the electron-withdrawing group attached to the alkene which determines whether 2,2-bis-alkylation occurs or not. The reasons for this are discussed in the text. The preparation of a number of novel 2,2-bis-eyclohexanones and an octahydroquinoline are described. The reaction of I-phenyl-2-propen-l-one (phenyl vinyl ketone) with the benzylaluine imines of 2-butanone and I-phenyl-2-propanone in methanol gave gave two novel bicyclic diones, whereas the reaction between the benzylamine imine of 3-pentanone with I-phenyl-2-propen-l-one gave only mono-eyclic products only even though there appeared to be no impediment to the formation of the bicyclic compound. The structures were determined using nuclear magnetic resonance and confirmed by X-ray crystallography. The reaction between I-phenyl-2-propen-l-one and N-(l-phenyl-l-ethylidene)benzylamine gave after hydrolysis only the mono-substituted product, 1,5-diphenyl-l ,5-pentandione. / Thesis (Ph.D.)-University of Natal, Durban, 1990.

Studies of Hydrogenations and Isomerizations of Olefins and Alkylations of Amines Using Iridium Catalysts

Li, Jia-Qi January 2012 (has links)
This thesis describes three types of reactions that were carried out using iridium catalysts. The first type is the iridium-catalyzed asymmetric hydrogenation of olefins. In paper I, the preparation of a new type of bicyclic thiazole-phosphine based iridium complex was described. The new catalysts have displayed high activity and enantioselectivity in the asymmetric hydrogenation of unfunctionalized olefins. Papers II and III focus on the expansion of the substrate scope for the iridium catalyzed asymmetric hydrogenation in which a number of heterocyclic olefins were evaluated. In paper IV, the enantioselective asymmetric hydrogenation of α, β-unsaturated esters was described. The chiral products bearing tertiary stereogenic centers obtained by hydrogenation have great synthetic value and have been used in the synthesis of pharmaceuticals as well as in the total synthesis of natural products. The second type is the asymmetric isomerization of allylic alcohols. In paper V, both cis and trans primary allylic alcohols were isomerized to the corresponding β-chiral aldehydes in high enantioselectivities by an N,P-chelating iridium complex. The third type is the selective mono-N-alkylation of amines with alcohols. In paper VI, a phosphine/NHC based iridium catalyst was synthesized and applied in the alkylation of amines. It is the first time that this type of transformation is carried out at room temperature.

Synthesis of compounds of natural and unnatural origin by intramolecular alkylations /

Shirley, Neil John. January 1987 (has links) (PDF)
Thesis (Ph. D.)--University of Adelaide, 1987. / Includes bibliographical references (leaves 213-223).

The Morita-Baylis-Hillman cycloalkylation reaction

Brookover, Kimberly A. Krafft, Marie E. January 2005 (has links)
Thesis (M.S.)--Florida State University, 2005. / Advisor: Dr. Marie E. Krafft, Florida State University, College of Arts and Sciences, Dept. of Chemistry and Biochemistry. Title and description from dissertation home page (viewed Sept. 15, 2005). Document formatted into pages; contains xvii, 123 pages. Includes bibliographical references.

Asymmetric α-alkylation reactions / Asymmetric [alpha]-alkylation reactions

Klein, Rosalyn January 2000 (has links)
A novel camphor-derived hydroxy ketal 138 has been developed as a crural auxiliary, and used to prepare a series of six carboxylic esters of increasing steric bulk. The α-benzylation of this series of esters was achieved with diastereoselectivities of 59 - 83% d. e. and in 39 - 48% material yield. These results compared very favourably with those obtained in earlier studies using a regioisomeric analogue as the chiral auxiliary. Computer.modelling studies of the putative enolate intermediate has provided some insight into the possible mode of electrophilic attack at the α-carbon and the roles of the ketal protecting group and the lithium cation in these asymmetric transformations. In a related investigation, based on earlier work, a camphor-derived imino lactone has provided convenient access to α-alkyl α-amino acids, the imino lactone serving as a masked glycine equivalent. Using straight chain primary alkyl iodides [RI; R = Me, Et, Pr, Bu, CH₃(CH₂)₄ and CH₃(CH₄)₅], alkylation of the potassium enolate of the camphor-derived imino lactone was effected with 54 - 89% d.e. and in 54 - 87% material yield. Four novel alkylated derivatives were synthesised using isopropyl iodide, sec-butyl iodide and allyl iodide, the latter reagent resulting in both the monoallylated and diallylated products. While very good diastereoselectivities were achieved (83 - 88% d. e.) in these reactions, the material yields from reaction with the secondary alkyl iodides were low (31- 35%) due, presumably, to their decreased electrophilicity. Computer modelling studies of the enolate were carried out and support the hypothesis of endo attack by the electrophile on the enolate intermediate. These studies also indicate the possibility of coordination of the postassium cation to the endocyclic ester oxygen, thus effectively anchoring the bulky cation away from the reaction site.

Alkylation of rat lens crystallins with iodoacetamide

Haynes, Linda Rose 28 July 2010 (has links)
Alkylation of lens proteins with iodoacetamide during homogenization of tissue (50 millimolar excess) immediately followed by gel-permeation chromatography yielded a crystallin population devoid of βH-crystallin. This result occurred in lens homogenates from both young (100 g) and older (400 g) male rats. BetaH-crystallin was not converted to insoluble protein with alkylation. Each crystallin fraction reacted with radioactive iodoacetamide in proportion to sulfhydryl content; at a ratio of 1 mg iodoacetamide/mg protein total free-sulfhydryl of the crystallins had reacted after 1 hr at pH 8, 25°C. Alkylated α-, βL-' and y-crystallin fractions demonstrated no altered chromatographic behavior on Sephacryl S-200; only alkylated βH-crystallin was altered so that it co-chromatographed with control or alkylated βL-crystallin. / Master of Science

Adaptation to Alkylation Mutagenesis in Escherichia coli

Muller-Meloche, Monique 05 1900 (has links)
This thesis is missing a page between pages 60 and 70, and three pages between pages 70 and 81. Since the pages are not all numbered, the specific page numbers cannot be determined. Theses missing pages are not in the other copies of the thesis. -Digitization Centre / Replicate isogenic populations of E. coli were propagated and maintained for over 4000 generations in order to investigate the adaptation of E. coli to increased levels of the mutagen methanesulfonic acid ethyl ester (EMS). Control "C" cell lines were propagated through daily serial culture in the absense of any mutagenic treatment. EMS adapted cell lines "E" / "e" were propagated through daily serial culturing and treated daily with 25Jul of EMS following serial dilution. Mutation frequency and survival assays conducted in this investigation strongly suggest that prior long-term low dose exposure to EMS results in significantly higher levels of resistance to the lethal and mutagenic effects of larger challenge doses of EMS relative to long-term evolved control cell lines "C". In addition, both survival and inhibition disk assays suggest a cross adaptive response between EMS and MNNG, showing enhanced survival and reduced growth inhibition zones in cells adapted to EMS and challenged with MNNG. Preliminary competition experiments suggest relative fitness for the EMS adapted cell lines ( "E" / "e") compared to the "C" control cell lines in both the presence of EMS. Unexpectedly the fitness estimates also suggest a higher relative fitness for the "E" / "e" EMS adapted cell lines in the absence of EMS treatment, suggesting that the EMS specific adaptation may also result in improved fitness in novel environments. Despite the adaptive advantage for the "E" / "e" cell lines suggested by the fitness estimates, the results from the competition experiments are insignificant due to the high degree of variability among replicate fitness estimates. Attempts to induce the adaptive response repair pathway were not successful in either the control "C" or the EMS adapted "E" / "e" cell lines suggesting that enhanced resistance seen in the adapted "E" / "e" cell lines could likely be a result of enhanced activity of the constitutive transferase Ogt and the constitutive glycosylase Tag. The ada and the ogt genes encode the induced and the constitutively-active DNA methyl transeferases in E. coli. As such they appeared to be the most likely candidates for genetic changes responsible for the enhanced resistance to the lethal and mutagenic effects of large doses of alkylating agents in the long-term EMS adapted "E" / "e" cell line. However, the DNA sequences analyzed for the ogt and the ada genes for both the long-term evolved control E. coli cell line "C" and the long-term-evolved EMS adapted "E" / "e" cell line indicate no sequences differences between these two cell lines. Previous studies have primarily observed E. coli's ability to phenotypically acclimate over very short time intervals to EMS. This analysis has shown that long-term genetic adaptation to low doses of EMS results in enhanced resistance to both the lethal and mutagenic effects of larger challenge doses of EMS. / Thesis / Master of Science (MS)

Investigations into the reactions of imines and enamines.

Mahomed, Hamdani Ahmed. January 1993 (has links)
Recent work in our laboratory has led to a new synthesis of the 2-oxo-a8'&-hexahydroquinoline ring system. This involved the condensation of B-alkylaminopropanoates with 2-methylcyclohexanone. Further reactions of B-aminopropanoates with other cyclic ketones and acyclic ketones have been investigated and are now reported. These reactions are found to be sensitive to steric effects, the stability of the ketone and the presence of molecular sieves and have led not only to the synthesis of the quinolone ring system but also to the inden-7-one and pyridone ring systems. A new one pot synthesis of the bicyclo[2.2.2]octan-5-one ring system from acyclic precursors has recently been reported. Reaction of" two equivalents of phenyl vinyl ketone with one equivalent of N-2-butylidenebenzylamine has lead to the synthesis of 2-benzoyl-4-methyl-l-phenylbicyclo[2.2.2]octan-5one as a mixture of two isomers. This reaction has now been extended to N-2-(4-phenylbutylidene)propylamine and ethyl N-propyl-4-iminopentanoate and our findings are reported. / Thesis (M.Sc.)-University of Natal, Durban, 1993.

Page generated in 0.1047 seconds