No description available.

Julian A Cooper This work describes the functionalisation of carbon-hydrogen bonds in saturated hydrocarbons via free radical addition to fluorinated alkenes. For example, hexafluoropropene can be added to produce a mono-adduct:- A range of fluoroalkenes have been used. These adducts can be functionalised by elimination of hydrogen fluoride to give new fluoroalkenes whose chemistry has been investigated. This has resulted in new fluorinated building blocks.

A catalytic organometallic addition-ring opening sequence of cyclopropenes that enables the efficient and highly stereoselective synthesis of multisubstituted alkenes has been developed. A possible mechanism of organoaluminium reaction is proposed. The metalloenolate resulting from ring opening can be trapped with various electrophiles, enabling a rapid increase in molecular complexity in a one-pot operation. Also, in the presence of stoichiometric magnesium halides, a range of bis-activated cyclopropenes undergo highly stereoselective ring-opening reactions to produce multisubstituted alkenyl halides. The halogen nucleophile promotes Lewis-acid mediated regioselective SNVσ attack at the sp2-carbon of cyclopropene, resulting in the formation of acyclic conjugate enolate, which can be trapped with enones to furnish more highly functionalised products. At last, copper-catalysed asymmetric conjugate reductions of β,β'-disubstituted 2-alkenylheteroarenes are reported. A range of nitrogen-containing aromatic heterocycles are able to provide effective activation of an adjacent alkene for highly enantioselective catalytic conjugate reduction reactions. Extension of the general concept to other classes of heteroarenes has been proven successful. Further manipulation of the condition is required to tolerate more hindered heteroarene substrates.

Dortmund, Universiẗat, Diss., 2001.

Universiẗat, Diss., 2002--Marburg.

Techn. University, Diss., 2004--Berlin.

No description available.

No description available.

Thesis advisor: Amir H. Hoveyda / Chapter 1. Development of Ru-Based Catechothiolate Complexes for Z-selective Ring-Opening/Cross-Metathesis and Cross-Metathesis. We have developed a broadly applicable Ru-catalyzed protocol for Z-selective ring-opening/cross-metathesis (ROCM). Transformations are promoted by 2.0–5.0 mol % of a Ru-based catechothiolate complex, furnishing products in up to 97 % yield and >98:2 Z:E ratio. The Z-selective ROCM processes are found to be compatible with terminal alkenes of different sizes that include the first examples involving heteroaryl olefins, 1,3-dienes, and O- and S-substituted alkenes as well as allylic and homoallylic alcohols. Reactions with an enantioenriched α-substituted allylic alcohol are shown to afford congested Z-olefins with high diastereoselectivity. The insights gained from these investigations provided the impetus to develop electronically modified Ru catechothiolate catalysts that are readily accessible from a commercially available dichloro-Ru carbene and an easily generated air-stable zinc catechothiolate. The new complex is effective in catalyzing Z-selective cross-metathesis (CM) of terminal alkenes and inexpensive Z-2-butene-1,4-diol to directly generate linear Z-allylic alcohols, including those that bear a hindered neighboring substituent or reactive functionalities such as a phenol, an aldehyde or a carboxylic acid. Transformations typically proceed with 5.0 mol % of the catalyst within 4–8 hours under ambient conditions, and products are obtained in up to 80% yield and 98:2 Z:E selectivity. Utility is highlighted through synthesis of a molecular fragment en route to anti-tumor agent neopeltolide and in a single-step stereoselective gram-scale conversion of renewable feedstock to synthetically valuable Z-allylic alcohols. Chapter 2. Kinetically Controlled Z- and E-Selective Cross-Metathesis to Access 1,2- Disubstituted Alkenyl Halides. We have discovered that previously unknown halo-substituted molybdenum alkylidenes are capable of participating in highly efficient olefin metathesis reactions that afford linear 1,2-disubstituted Z-alkenyl halides. Transformations are promoted by 1.0–10.0 mol % of a Mo-based pentafluorophenylimido monoaryloxide pyrrolide (MAP) complex that is generated in situ and used with unpurified, commercially available and easy-to-handle liquid 1,2-dihaloethene reagents, delivering a myriad of alkenyl chlorides, bromides and fluorides in up to 91% yield and >98:2 Z:E ratio. Through mechanism-based modification of the aryloxide ligand, a newly synthesized Mo-based MAP complex was shown to be effective in promoting kinetically controlled E-selective CM to access the corresponding thermodynamically less favored E-isomers of alkenyl chlorides and fluorides. Reactions typically proceed within 4 hours at ambient temperature with 1.0–5.0 mol % of the catalyst, which may be utilized in the form of air- and moisture-stable paraffin pellets. Utility of the aforementioned protocols is demonstrated through preparation of biologically active compounds and related analogues as well as late-stage site- and stereoselective fluorination of complex organic molecules. Chapter 3. Molybdenum-Based Chloride Catalysts for Z-Selective Olefin Metathesis. A new class of Mo-based monoaryloxide chloride (MAC) complexes for Z-selective olefin metathesis has been developed. The MAC catalysts are capable of promoting CM with commercially available, inexpensive and typically inert Z-1,1,1,4,4,4-hexafluoro-2-butene to furnish the higher-energy Z-isomers of trifluoromethyl-substituted alkenes in up to 95% yield and >98:2 Z:E selectivity. Furthermore, otherwise inefficient and non-stereoselective transformations with Z-1,2-dichloroethene and 1,2-dibromoethene can be accomplished with appreciably improved efficiency and Z-selectivity. The method enables synthesis of biologically active compounds and CF3-analogues of medicinally relevant molecules. Density functional theory (DFT) calculations shed light on the origins of the activity and selectivity levels observed in these transformations. Chapter 4. Stereoselective Synthesis of Z- and E-Trisubstituted Alkenes by Merging Cross-Coupling with Cross-Metathesis. We have discovered that challenging acyclic E- and Z-trisubstituted alkenes, particularly alkenyl chlorides and bromides, can be accessed efficiently and in high stereoisomeric purity (up to >98% E and 95% Z) through a sequence involving catalytic cross-coupling followed by stereoretentive CM promoted by Mo-based catalysts. Initial exploratory studies with 1,1-disubstiuted alkenes revealed crucial mechanistic features of the transformations that led us to utilize readily accessible trisubstituted olefins as substrates, in combination with commercially available 1,2-dihaloethenes as cross-partners for CM. Applications to synthesis of biologically active compounds and synthetic precursors underscore utility. The stereoretentive transformations may be extended to trisubstituted non-halogenated alkenes such as aliphatic olefins. / Thesis (PhD) — Boston College, 2017. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

This dissertation mainly contains two parts: one is C-X (C, O, S) bond formation through gold(I) catalysis, one is new applications via gold(I/III) redox catalysis. In first part, gold(I) catalysts would be introduced and their general applications, then the TA-Au species will be emphasized including the design, synthesis, characters and their application in catalysis. The applications are well developed during the past decade in our group, but here only involves three examples regarding C-C, C-O and C-S bond formations. From these effective applications, the unique stability and reactivity of TA-Au will be studied and explained, which is the reason and value of TA-Au discovery. In second part, gold(I/III) redox catalysis will be presented through two application examples: cross-coupling of terminal alkynes, multiple bond di-functionalization. The most challenging part for coupling reactions is the competition between homo-coupling and cross-coupling products, while in our project, we have successfully developed a new method to selectively obtain cross-coupling as major product to homo-coupling product (ratio 12:1). Later on, we found a new method to achieve gold (I/III) redox cycle by using mild oxidant diazonium salt instead of PIDA or Selectfluor strong oxidant. The new mild and efficient method have largely extended the application of gold(I/III) redox catalysis into organic synthesis. In sum, the new gold catalysts and catalysis methods reported here are important to the development of gold catalysis field, which are critical and useful to help people understand the reason of applying noble gold species as catalysts, and the advantages that other metals do not have.