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Articles 1 - 25 of 25

Full-Text Articles in Organic Chemistry

Structure And Stability Of Hexacoordinated Sila Dianions, Mark S. Gordon, Marshall T. Carroll, Larry P. Davis, Larry W. Burggraf Oct 1990

Structure And Stability Of Hexacoordinated Sila Dianions, Mark S. Gordon, Marshall T. Carroll, Larry P. Davis, Larry W. Burggraf

Mark S. Gordon

The structures and stabilities of hexacoordinated silicon-containing dianions SiX6 2- have been investigated by using both ab initio (X= H, F) and semiempirical AMI (X= H, F, OH, Me, Cl) calculations. Both methods predict the hexacoordinated structures to be minima on the potential energy surfaces, although the semiempirical barriers for the reactions SiX6 2- -+ Six5- + x- appear to be rather overestimated based on the ab initio results for X = H, F. The positive charge on the central silicon atom actually increases as the number of ligands increases, and the role of d orbitals on that atom appears to be one ...


Structural And Energetic Evidence For Oxygen-Lithium-Nitrogen Chelation In A Model For Asymmetric Induction., Edward Arnett, Michael Nichols, Andrew Mcphail Sep 1990

Structural And Energetic Evidence For Oxygen-Lithium-Nitrogen Chelation In A Model For Asymmetric Induction., Edward Arnett, Michael Nichols, Andrew Mcphail

Michael A Nichols

No abstract provided.


Rearrangements Of Bridgehead Bromides. A Direct Synthesis Of Epi-Modhephene, George A. Kraus, Jianmin Shi Sep 1990

Rearrangements Of Bridgehead Bromides. A Direct Synthesis Of Epi-Modhephene, George A. Kraus, Jianmin Shi

Chemistry Publications

Summary: The reaction of nucleophiles with bridgehead bromides 3 and 4 affords rearrangement products resulting from addition of the nucleophile to the carbonyl group followed by ring contraction. This rearrangement has been employed in a direct synthesis of epi-modhephene.


A New Synthesis Of Aryl Mono C-Glycosyl Derivatives Of Dialdehyde Sugars, George A. Kraus, Jianmin Shi Aug 1990

A New Synthesis Of Aryl Mono C-Glycosyl Derivatives Of Dialdehyde Sugars, George A. Kraus, Jianmin Shi

Chemistry Publications

A new synthesis of mono C-glycosyl derivatives of dialdehyde sugars using a Michael additionlaldol condensation sequence has been developed. It is complementary to previously reported methods for the production of C-glycosyl compounds. The synthesis involves the Michael addition reaction of an enol silyl ether with acetylbenzoquinone followed by an aldol condensation and subsequent aromatization of the resulting hydroxy ketone. The aldol condensation proceeds only under select conditions and affords the unstable ketols 7 and 15.


A Total Synthesis Of Racemic Paulownin Using A Type Ii Photocyclization Reaction, George A. Kraus, Li Chen Apr 1990

A Total Synthesis Of Racemic Paulownin Using A Type Ii Photocyclization Reaction, George A. Kraus, Li Chen

Chemistry Publications

The lignan paulownin was prepared in a seven-step route from piperonal. The key step was a type I1 photocyclization reaction wherein two of the four stereogenic centers were introduced.


Synthesis Of A Pentacyclic Precursor To The Strychnos Alkaloids, George A. Kraus, P.J. Thomas, Dan Bougie, Li Chen Mar 1990

Synthesis Of A Pentacyclic Precursor To The Strychnos Alkaloids, George A. Kraus, P.J. Thomas, Dan Bougie, Li Chen

Chemistry Publications

An advanced intermediate for the synthesis of the Strychnos alkaloids was constructed by a sequence involving an intramolecular Diels-Alder reaction, alkylation of an enol silyl ether, and conversion of the alkylation product into a pentacyclic lactam.


A Versatile Intermediate For The Synthesis Of Pyranoquinone Antibiotics, George A. Kraus, Jianmin Shi, Don Reynolds Feb 1990

A Versatile Intermediate For The Synthesis Of Pyranoquinone Antibiotics, George A. Kraus, Jianmin Shi, Don Reynolds

Chemistry Publications

As a result of the sophisticated detection and isolation procedures developed by Omural and others, the family of biologically active pyranoquinones continues to grow rapidly. As a consequence of their interesting structures and useful activity, several synthetic approaches have already appeared.2


Structure-Energy Relations For The Aldol Reaction In Nonpolar Media., Edward Arnett, Franklin Fisher, Michael Nichols, Anthony Ribeiro Jan 1990

Structure-Energy Relations For The Aldol Reaction In Nonpolar Media., Edward Arnett, Franklin Fisher, Michael Nichols, Anthony Ribeiro

Michael A Nichols

No abstract provided.


Comparison Of The Molecular Structures Of Monovalent Cation Salets Of N,N-Dimethyldithiocarbamate. Novel Synthesis And Crystal Structure Of (Phi4)(S2cn(Ch3)2)2h2o, Mark Draganjac, David Minick, Elizabeth M. Holt Jan 1990

Comparison Of The Molecular Structures Of Monovalent Cation Salets Of N,N-Dimethyldithiocarbamate. Novel Synthesis And Crystal Structure Of (Phi4)(S2cn(Ch3)2)2h2o, Mark Draganjac, David Minick, Elizabeth M. Holt

Journal of the Arkansas Academy of Science

Crystals of the tetraphenylphosphonium N,N-dimethyldithiocarbamate dihydrate (C₂₇H₃₀NO₂PS₂; F.W. = 495.6) are monoclinic; P2₁/n; a = 13.349(6), b = 20,968(6), c = 9.800(4) Å, β = 109.01(3)°; Z = 4; V = 2593.4(16) Å^3; Dₓ = 1.269 gcm- 3 . Data were collected at ambient temperature using MoKα radiation (λ = 0.71069 Å).F(000) = 1048, linear absorption coefficient, n = 2.80 cm- 1. The structure was solved by direct methods and subsequently refined by full matrix least squares techniques. Final R value = 0.064 for 1 61 0 reflections and 298 varied parameters ...


Geochemistry Of Selected Maine Peat Deposits, Stephen A. Norton Jan 1990

Geochemistry Of Selected Maine Peat Deposits, Stephen A. Norton

Maine Collection

Geochemistry of Selected Maine Peat Deposits

by Steven Allen Norton

Maine Geological Survey, Department of Conservation, Augusta, Maine, 1990.

Contents: Introduction / Purpose of Study / Location of Study Sites / Methods / Acknowledgements / Results / Water Chemistry / Dating of Short Cores / Chemistry of Short Cores / Core Interpretations / Summary / References Cited


The Norrish Type Ii Reaction In Organic Synthesis , Mark Donald Schwinden Jan 1990

The Norrish Type Ii Reaction In Organic Synthesis , Mark Donald Schwinden

Retrospective Theses and Dissertations

The Norrish Type II photocyclization has been known to organic chemists for several decades. To the best of our knowledge, no effort has been made to exploit the reaction in synthesis. A study was undertaken to investigate the synthetic potential of the Norrish Type II reaction;Ultraviolet irradiation of certain [beta]-alkoxy ketones and aldehydes leads to the formation of dihydro- and tetrahydrofuranols via hydrogen atom abstraction by the excited carbonyl and cyclization of the resulting biradical. Type II photocyclization of a 2,6-disubstituted aryl ketone provided a dihydrobenzofuranol which is a precursor to aflatoxin M[subscript]2. This constitutes ...


Observation By Flow 1h Nmr And Dimerization Kinetics And Products Of Reactive Ortho-Quinodimethanes And Benzocyclobutadiene , David R. Fischer Jan 1990

Observation By Flow 1h Nmr And Dimerization Kinetics And Products Of Reactive Ortho-Quinodimethanes And Benzocyclobutadiene , David R. Fischer

Retrospective Theses and Dissertations

The reactive o-quinodimethanes, 1,2-dimethylene-1,2-dihydronaphthalene (9) and o-xylylene (1) were observed by flow [superscript]1H NMR spectroscopy at room temperature. The [superscript]1H NMR spectrum of 9, generated in acetonitrile-d[subscript]3 (CD[subscript]3CN) by fluoride ion induced 1,4-elimination from (1-(trimethylsilylmethyl)) trimethyl(2-naphthylmethyl)ammonium iodide (10), was obtained in the absence of precursor and dimers. However, the [superscript]1H NMR spectrum of the more reactive 1, generated in a similar manner from (o-((trimethylsilyl)methyl)benzyl) trimethylammonium iodide (5), could be obtained only in the presence of its stable (4 + 2) and (4 + 4) dimers;The ...


Preparation And 13c Nmr Investigation Of 1,1-Dilithioalkenes, 1,2-Dilithioalkenes, 1-Lithiocyclopropenes And 1,2-Dilithiocyclopropenes , Hon-Wah Man Jan 1990

Preparation And 13c Nmr Investigation Of 1,1-Dilithioalkenes, 1,2-Dilithioalkenes, 1-Lithiocyclopropenes And 1,2-Dilithiocyclopropenes , Hon-Wah Man

Retrospective Theses and Dissertations

The syntheses of 1,1-dilithioalkene, 1,2-dilithioalkene, and 1,2-dilithiocyclopropene derivatives have been attempted. The generation of a 1,1-dilithioalkene via double lithium-bromine exchange on 1,1-dibromo-3-methoxy-2-methoxymethylpropene with alkyllithiums was not successful. Quenching experiments did not provide enough evidence to prove the intermediacy of the 1,1-dilithio-3-methoxy-2-methoxymethylpropene. Two other routes, lithiation of the corresponding butatriene and 1,1-dimercurioalkene, were also studied but without success. A mechanism of reduction of carbenoid by BuLi was proposed.;The 1,2-dilithio-polyalkoxyalkenes were likely generated by the reaction of polyalkoxyalkynes with lithium. However, the presumed 1,2-dilithio-polyalkoxyalkenes not only did not dissolve in hydrocarbon or ...


Kinetic And Equilibrium Study Of The 2,3-Furan Ortho-Quinodimethane - 4,5-Dihydrocyclobuta[B]Furan And 9,10-Phenanthrene Ortho-Quinodimethane - 1,2-Dihydrocyclobuta[L]Phenanthrene Interconversions And Related Studies , Craig Wilson Montgomery Jan 1990

Kinetic And Equilibrium Study Of The 2,3-Furan Ortho-Quinodimethane - 4,5-Dihydrocyclobuta[B]Furan And 9,10-Phenanthrene Ortho-Quinodimethane - 1,2-Dihydrocyclobuta[L]Phenanthrene Interconversions And Related Studies , Craig Wilson Montgomery

Retrospective Theses and Dissertations

Preparation of 4,5-dihydrocyclobuta(b) furan (I) and 4-tert-butyl-4,5-dihydrocyclobuta(b) furan (II) was achieved by irradiation ([lambda]>280 nm) of 2,3-dimethylene-2,3-dihydrofuran (III), and 2-methylene-3-tert-butylmethylene-2,3-dihydrofuran (IV), respectively. Compounds I and II were characterized by [superscript]13C NMR, [superscript]1H NMR, and IR spectroscopy. Diagnostic IR absorptions for 4,5-dihydrocyclobuta(b) furan (I) corresponded with published values. Kinetic analysis of the conversion of I to III (E[subscript] a = 24.4 kcal/mol; log A = 10.1 s[superscript]-1), and II to IV (E[subscript] a = 28.0 kcal/mol; log A = 13.4 s[superscript]-1 ...


Palladium-Catalyzed Arylation And Vinylation Of Cyclic Alkenes , William H. Gong Jan 1990

Palladium-Catalyzed Arylation And Vinylation Of Cyclic Alkenes , William H. Gong

Retrospective Theses and Dissertations

This dissertation is divided into four parts. The focus of all four parts is on the development of a useful palladium-catalyzed procedure for cross-coupling aryl or vinylic halides and cyclic alkenes;Part One will discuss the development of an improved procedure (procedure C) for palladium-catalyzed allylic arylation of cyclic alkenes. Procedure C is compared with existing procedures (procedures A and B), and the scope and limitation of this improved procedure will be discussed;Part Two will discuss the use of procedure C in the synthesis of a variety of 2-aryl-2,3-dihydrofurans, and the application of this procedure in a key ...


Atmospheric Input Of Polycyclic Aromatic Hydrocarbons To The Sea Surface Microlayer, Lino J. Gallo Jan 1990

Atmospheric Input Of Polycyclic Aromatic Hydrocarbons To The Sea Surface Microlayer, Lino J. Gallo

Dissertations, Theses, and Masters Projects

Atmospheric input of polycyclic aromatic hydrocarbons (PAH) to water was studied and the effects of sea surface microlayer (SSM) determined. The York River system and the Perrin River areas were monitored with a drum skimmer and a high volume air sampler. Experiments were conducted in the laboratory under controlled conditions. The SSM extracted vapor phase PAH of low molecular weight from the air, and there, aromatic compounds went from dissolved into particulate phase very rapidly. Water covered with a natural SSM received much less atmospheric input of PAH than water without SSM in a given period of time. Henry's ...


Palladium-Mediated Cyclizations , Colleen Ann Fried Jan 1990

Palladium-Mediated Cyclizations , Colleen Ann Fried

Retrospective Theses and Dissertations

This dissertation is divided into three chapters. The first chapter deals with an unprecedented cyclization that occurs during the reaction of norbornadiene-palladium dichloride and 1-iodomercurio-2-butyne. This reaction yields two novel [sigma]-vinylpalladium compounds. The work in chapter one focuses on obtaining further support for the two proposed structures. The second chapter deals with palladium-catalyzed arylannulation of conjugated dienes. Appropriately substituted aryl iodides and 1,3-dienes undergo a one-step, palladium(0)-catalyzed reaction to furnish polycycles. During arylannulation two carbon-carbon bonds are formed under relatively mild conditions. Chapter three is an extension of the work in the second chapter. Palladium-catalyzed arylannulation ...


Exploring Novel Silicon-Containing Polymers: From Preceramic Polymers To Conducting Polymers With Nonlinear Optical Properties , Yi Pang Jan 1990

Exploring Novel Silicon-Containing Polymers: From Preceramic Polymers To Conducting Polymers With Nonlinear Optical Properties , Yi Pang

Retrospective Theses and Dissertations

Several new types of silicon-containing preceramic polymers, i.e., poly(diorganosilacetylene) and poly(diorganosilvinylene) have been synthesized with molecular weights from 10,000 to 120,000. These polymers could be thermally converted to SiC with a moderate to high char yields. Ready solubility and good processability made these types of polymers even more attractive in their applications to ceramics;First example of copolymer which contains alternate -SiMe[subscript]2-C≡C- and -SiMe[subscript]2-CH=CH- units was successfully synthesized. This copolymer had a dramatically lower decomposition temperature (300°C) and high char yield;The thermal polymerization of diethynyldiphenyl-silane, which was ...


Free Radical Reactions Of Allylic And Propargylic Derivatives , Yuh-Wern Wu Jan 1990

Free Radical Reactions Of Allylic And Propargylic Derivatives , Yuh-Wern Wu

Retrospective Theses and Dissertations

Addition of tert-butyl radical, generated from t-BuHgCl, to allyl or propargyl derivatives forms adduct radicals which can undergo [beta]-elimination with substituents such as halogen, PhS, PhSO[subscript]2 to form the alkyl-substituted propene or allene and an eliminated radical which regenerates the tert-butyl radical by displacement from t-BuHgCl. With [beta]-oxy substituents, such as O[subscript]2CR, OP(O)(OEt)[subscript]2, O[subscript]3SAr, the adduct radical can displace the alkyl radical from alkylmercurial to yield the [beta]-substituted alkylmercurials which spontaneously, or in the presence of nucleophiles, undergo an elimination reaction to yield the alkene or allene ...


Gas-Phase Generations And Rearrangement Of Silathiones, R2si=S , Chong Bok Kim Jan 1990

Gas-Phase Generations And Rearrangement Of Silathiones, R2si=S , Chong Bok Kim

Retrospective Theses and Dissertations

The generation of silathiones is shown to be possible by the retroene elimination of propene from allylthiodimethylsilane and 1-allylthio-1-hydrido-1,2,2,2-tetramethyldisilane. This retroene reaction of allylthiodimethylsilane has a very low activation energy (E[subscript] a = 36.3 kcal/mol, log A = 11.3), when compared with carbon, oxygen or nitrogen homologs. The low activation energy is probably due to the strong Si-S [pi] bond and the weak S-C bond. The low log A indicates that the formation of propene and silathione is via a 1,5-hydrogen shift from a six-centered transition state.;The trapping of (trimethylsilyl)methylsilathione by butadiene ...


Studies Directed To The Total Synthesis Of Biologically Active Natural Products , Spiros I. Liras Jan 1990

Studies Directed To The Total Synthesis Of Biologically Active Natural Products , Spiros I. Liras

Retrospective Theses and Dissertations

The total synthesis of biologically active, naturally occurring substances is an ambitious task. Fascinating new methods have been developed for the synthesis of natural products. We discuss the following accomplishments: (1) The short and convergent synthesis of 4,1-Bisdeoxydaunamycinone by Claisen/Diels-Alder sequence. (2) The regiochemical studies on the Diels-Alder reaction of electron-rich dienes and activated dienophiles, and the effort toward the aza-tricyclic moiety of atisine-type alkaloids. (3) The formation of bicyclic and monocyclic intermediates via silyl radical induced cyclizations, and the first chemoselective studies on silicon radicals.


Mechanism Of Cyclopropylidenoid Ring Opening Reactions , Chyoan Wang Jan 1990

Mechanism Of Cyclopropylidenoid Ring Opening Reactions , Chyoan Wang

Retrospective Theses and Dissertations

As part of an effort to understand the chemistry of cyclopropylidenoid ring opening in solution, the enantiomeric ratio of resulting allenes have been measured by nuclear magnetic resonance;When treated with methyllithium, at various temperatures, using ether as the solvent, optically pure 1,1-dibromo-trans-2,3-diphenylcyclopropane yields 1,3-diphenylallene with about 60% enantiomeric excess;The base induced decomposition of optically pure ethyl-N-nitroso-N- (trans-2,3-diarylcyclopropyl) carbamates yields allenes with about 45% enantiomeric excess;From the relative enantiomeric excess of the allenes from these two methods, we conclude the ring opening of halolithiocyclopropyl is different and may have more carbene character at the ...


A Search For Thermal Isomerization Of Olefins To Carbenes. Thermal Generations Of The Silicon-Nitrogen Double Bond , Xianping Zhang Jan 1990

A Search For Thermal Isomerization Of Olefins To Carbenes. Thermal Generations Of The Silicon-Nitrogen Double Bond , Xianping Zhang

Retrospective Theses and Dissertations

Thermal isomerization of an olefin to a carbene is observed only in a few strained olefins. Attempts to observe a 1,2-silyl migration to form a carbene from a simple olefin were not successful. The olefins studied are stable at lower temperature and decomposed to smaller molecules at higher temperature probably via a radical process. The gas-phase thermal behavior of a series of organic and organosilicon compounds was studied by stirred-flow reactor (SFR) pyrolysis. Kinetic parameters were determined in the gas phase for various hydrocarbons and organosilicon compounds. The activation energies and log As of the compounds studied are in ...


Synthesis Of Polycyclic Natural Products , Jianmin Shi Jan 1990

Synthesis Of Polycyclic Natural Products , Jianmin Shi

Retrospective Theses and Dissertations

Pyranonaphthoquinones show characteristic biological activities and have in common the isochromanquinone skeleton. As a consequence of their interesting structures and useful biological activities, new synthetic approaches have been developed. Our generally useful three step (Michael addition, oxidation and reduction) sequence for pyranolactone subunits represents a valuable contribution to synthetic methodology. Efforts toward the synthesis of these natural pyranonaphthoquinones led us to generate a common intermediate by which the more complex pyranonaphthoquinones can be prepared. This extremely convergent approach will permit the direct synthesis of biologically active analogues and may also aid in the structure identification of quinone natural products. In ...


Approaches To Terpenoid Natural Products Using Reactive Intermediates , Steven Barse Laramay Jan 1990

Approaches To Terpenoid Natural Products Using Reactive Intermediates , Steven Barse Laramay

Retrospective Theses and Dissertations

Two attempted syntheses of a functionalized ring system common to kaurenoid natural products is presented. One of the attempts employed a bridgehead enone as a dienophile in a Diels-Alder reaction. One example in this series resulted in the synthesis of the tetracyclic ring system, but the angular C-8 (kaurene numbering) methyl group could not be added. Another example in this series resulted in the synthesis of a tricyclic intermediate containing the carbons to form the fourth ring, but this could not be cyclized. The other approach employed a Michael addition followed by an oxy-ene reaction for the synthesis of the ...