Thesis (M. Sc.)--University of Hong Kong. / Typewritten.

published_or_final_version / Chemistry / Master / Master of Philosophy

Graduate

Allenes are unique compounds in organic chemistry by virtue of their adjacent, orthogonal π-bonds. While of limited use in and of themselves, some classes of allenes have found use in organic synthesis as building blocks for more complex products. Previous work in the Fagnou group has identified a silver lewis acid-catalyzed enantioselective isomerization protocol for the synthesis of allenyl esters and amides. This protocol has been subject to reproducibility issues, the source of which is explored in this thesis. Initial work into the development of a phase-transfer catalytic process for the isomerization of alkynyl amides is also presented. The use of allenyl esters in lactonization reactions has become more common in recent years. The scope of the halolactonization of allenyl esters to form halobutenolides is explored here. The lactonization of allenyl carboxylic acids has also been demonstrated in the literature. The attempted synthesis of allenyl carboxylic acids via the oxidative deprotection of dimethoxybenzyl esters is also presented. Indole is an important and biologically and medicinally relevant compound in organic synthesis. Though many classical methods for its synthesis exist, the discovery of new, complex indole-containing compounds necessitates the development of efficient ways to synthesize indoles. Previous work in the Fagnou group has led to the discovery of a rhodium-catalyzed oxidative synthesis of indole with a key C-H functionalization step. This protocol has been applied to alkynyl esters to synthesize an array of 3-carboxylindoles in moderate to good yields. The competency of allenes as an intra- and intermolecular coupling partner in a similar rhodium-catalyzed hydroarylation reaction has also been explored, leading to the discovery that allenyl compounds are not tolerated in this reaction protocol.

Berlin, Freie Univ., Diss., 2001. / Dateiformat: zip, Dateien im PDF-Format. Computerdatei im Fernzugriff.

Berlin, Freie Univ., Diss., 2001. / Dateiformat: zip, Dateien im PDF-Format. Computerdatei im Fernzugriff.

Thesis--Wisconsin. / Vita. Includes bibliographical references.

Berlin, Freie Universiẗat, Diss., 2001. / Dateiformat: zip, Dateien im PDF-Format.

Allenes are unique compounds in organic chemistry by virtue of their adjacent, orthogonal π-bonds. While of limited use in and of themselves, some classes of allenes have found use in organic synthesis as building blocks for more complex products. Previous work in the Fagnou group has identified a silver lewis acid-catalyzed enantioselective isomerization protocol for the synthesis of allenyl esters and amides. This protocol has been subject to reproducibility issues, the source of which is explored in this thesis. Initial work into the development of a phase-transfer catalytic process for the isomerization of alkynyl amides is also presented. The use of allenyl esters in lactonization reactions has become more common in recent years. The scope of the halolactonization of allenyl esters to form halobutenolides is explored here. The lactonization of allenyl carboxylic acids has also been demonstrated in the literature. The attempted synthesis of allenyl carboxylic acids via the oxidative deprotection of dimethoxybenzyl esters is also presented. Indole is an important and biologically and medicinally relevant compound in organic synthesis. Though many classical methods for its synthesis exist, the discovery of new, complex indole-containing compounds necessitates the development of efficient ways to synthesize indoles. Previous work in the Fagnou group has led to the discovery of a rhodium-catalyzed oxidative synthesis of indole with a key C-H functionalization step. This protocol has been applied to alkynyl esters to synthesize an array of 3-carboxylindoles in moderate to good yields. The competency of allenes as an intra- and intermolecular coupling partner in a similar rhodium-catalyzed hydroarylation reaction has also been explored, leading to the discovery that allenyl compounds are not tolerated in this reaction protocol.

The reaction of Rh(OEP)(H) (OEP - 2,3 J,8,12,13,17,18-octaemylporphyrin) with O₂ in organic solvents was examined by visible, proton and phosphorus nuclear magnetic resonance spectroscopy (nmr) as a candidate system for the net insertion of O₂ into the metal-hydride bond. The nmr data for a thermally unstable Rh[superscript]Ⅲ(OEP)(OOHXH₂0) mtennediate were obtained at -40 °C in CD₂C1₂- Addition of O₂ to CH₂CI₂ solutions of Rh(OEP)(H) with triphenylphosphine resulted in reaction with solvent forming Rh(OEP)(Cl)(PPh₃) and Rh(OEP)(CH₂Cl)(PPh₃) as the major species (in equimolar amounts), without concomitant formation of OPPh₃. The sensitivity of the reaction of Rh(OEP)(H) with O₂ to initial conditions, and the observation of products containing Rh (Ⅱ) and Rh-CH₂Cl, suggest a radical mechanism. Initiation/tenniriation: 2Rh(OEP)(H) ⇌ [Rh(OEP)]₂ + H₂ [Rh(OEP)]₂ ⇌ 2Rh(OEP)- and in the presence of PPh₃ [Rh(OEP)]₂+ PPh₃ ⇌ -Rh(OEP)(PPh₃) + Rh(OEP)- Propagation: Rh(OEP)- + O₂ ⇌ Rh(OEP)(O₂) Rh(OEP)( O₂) + Rh(OEP)(H) → Rh(OEP)(OOH) + Rh(OEP)- Teimination: Rh(OEP)(OOH) + Rh(OEP)(H) →[Rh(OEP)]₂ + H₂O +½O₂ and in the presence of PPh₃ •Rh(OEP)(PPh₃) + CH₂CI₂ ⇌ Rh(OEP)(Cl)(PPh₃) + ∙CH₂C1 Rh(OEP)∙ + ∙CH₂C1 ⇌Rh(OEP)(CH₂Cl) The reaction of Et₃N with Rh(por)(a)(L) (por = OEP or 5,10,15,20-tetramesitylporphyrin(TMP), L = H₂O, (CH₃)₂CHOH, CH₃CN) gave products, identified by visible (scanning and stopped-flow) and proton nmr spectroscopy to be Rh(por)(CH(Me)NEt₂), Et₂NH as Rh(por)(Cl)(Et₂NH), and Rh(por)(CH₂CHO). This indicated amine C-H and C-N cleavage and net one-electron reduction of Rh(Ⅲ) to Rh(Ⅱ) species ([Rh(OEP)]₂). Of other amines examined, aniline, N-methyl-diphenylamine and N-ethyl piperidine all formed complexes of the type Rh(OEP)(Cl)(amine). Proton Sponge and tributylamine with Rh(OEP)(Cl)(H₂O) give [Rh(OEP)]₂ as a major product under anaerobic conditions. Only the mechanism of the Et₃N system was examined in detail. Stopped-flow data indicated that Et₃N initially replaced L in the Rh[superscript]Ⅲ(por)(Cl)(L) species to form a Rh[superscript]Ⅲ(por)(Cl)(Et₃N) complex. An equilibrium involving reduction of Rh[superscript]Ⅲ to Rh[superscript]Ⅱ resulted and, in aromatic solvents under anaerobic conditions, slow reaction of Rh[superscript]Ⅱ(por) with Et₃N occurred to give Rh(por)(CH(Me)NEt₃). In CH₂CI₂, reaction of Et₃N with Rh(por)(Cl)(L) was fast, giving a mixture principally of Rh(por)(CH₂Cl)(amine) and the ɳ¹-ylidic enamine complex, Rh(por)(Cl)(CH₂CH=NEt₂) with minor mounts of Rh(por)(CH(Me)NEt₃). The Rh(por)(Cl)(CH₂CH=NEt₂) and Rh(por)(CH(Me)NEt₃) species were unstable, both ultimately giving Rh[superscript]Ⅲ(por)(Cl)(Et₂NH). The synthesis, along with characterization by visible, proton and phosphorus nmr spectroscopy, of the previously structurally characterised, mono-phosphine complex Rh(OEP)(Cl)(PPh₃) are presented. Additionally, spectroscopic evidence is presented for solution equilibria of Rh(OEP)(Cl)(PPh₃) involving formation of Rh(OEP)(L)₂+ (L = PPh₃, P[superscript]nBu₃) via thermal reactions, and Rh(OEP)(Cl)(L') (L'= CO, THF, CH₃CN) via photochemical processes. Thermodynamic data (ΔH⁰ = -33 ± 2 kJ mol⁻¹ and ΔS⁰ = -146 ±8 J K⁻¹mol⁻¹) have been estimated for formation of the bis(triphenylphospnine) species in CH₂CI₂: Rh(OEP)(Cl)(PPh₃) + PPh₃ [symbol omitted] [Rh(OEP)(PPh₃)₂]+ + Cl- Some complexes of Rh[superscript]Ⅲ(OEP) containing l,4-bis(diphenylphosphino)butane (dppb), l,2-bis((diphenylphospliino)ethane (dppe), bis(diphenylphosphino)methane (dppm) and 1,3-bis(diphenylphosphho)propane (dppp) have been characterized in situ using visible, proton and phosphorus nmr spectroscopy. The diphosphines (PP) are bound to Rh(Ⅲ) porphyrins in a monodentate dangling fashion (Rh[superscript]Ⅲ(OEP)(Cl)(PP) and [Rh[superscript]Ⅲ(OEP)(PP)₂]+), or a bridging mode between two metal centers ([Rh[superscript]Ⅲ(OEP)(Cl)]-μPP-[Rh[superscript]Ⅲ(OEP)(Cl)]). / Science, Faculty of / Chemistry, Department of / Graduate