Institut für Organische und Analytische Chemie

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    Item-typ:Veröffentlichung,
    Synthesis of a chlorin with annelated lactam ring as subunit for artificial photosynthetic reaction centres
    (2018)
    Montforts, Franz-Peter
    ;
    Haake, Elmar
    ;
    Haake, Elmar
    A chlorin with an annelated cyclic ketone moiety was synthesized from a tricyclic nickel complex and appropriate pyrrole building blocks. Ketone functionality of the target chlorin allows Beckmann rearrangement to yield chlorin lactams. Lactam moieties on the chlorin represent masked amino acid structures which should allow formation of peptide-like backbones, along which chlorin pigments are arranged. Due to the natural chlorin chromophores and the peptide backbone the devices should represent artificial mimetics of natural photosynthesis systems.
    Wissenschaftlicher Artikel
      416  232
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    Item-typ:Veröffentlichung,
    Light and strain responsive polymeric materials
    (2025-05-15)
    Colaco, Ruchira Ashleyn
    ;
    Staubitz, Anne
    ;
    Spiteller, Peter
    ;
    Staubitz, Anne
    Stimuli-responsive polymers have garnered significant attention for their ability to undergo reversible changes in response to external cues. This thesis contributes to the development of smart materials by the covalent incorporation of molecular switches into two categories of polymers: linear elastomers and crosslinked thermoresponsive polymers, known as hydrogels. In thermoresponsive hydrogels, two types of azobenzene derivatives were co-polymerized to add light as a remote stimulus for controlling the phase transition behaviour. The first type is a hydrophobic azobenzene which can modulate the phase transition temperature by 6 °C and induce light-driven hydrophilicity in the network. This hydrogel formulation was further used to develop precise photo-actuating micropillars for cell sorting applications. The second type, an amphiphilic azobenzene resulted in broadening of the phase transition temperature enabling super swelling and super deswelling in the hydrogels. Through a combination of synthesis, characterization, and functional analyses, the work compiled in this thesis advances the understanding of photo-, mechano- and thermos-sensitive polymeric systems (linear and crosslinked) and paves the way for their future applications in responsive and adaptive materials. This thesis focuses on processing spiropyran functionalized elastomers into mechanchromic microfibers. The strategy of polymer blending is used to stabilize the micro-fibers, improving their durability, functionality, and reliability for advanced applications. Mechanochromic polymers exhibit color changes in response to mechanical stimuli, offering potential applications in stress sensing and smart materials. Additionally, the covalent integration of diazocine units into polymers via an atom transfer radical polymerization (ATRP) led to photochromic elastomers. The significant changes in the π-systems, resulting in color and size changes in the respective molecular switches, were utilized for developing mechano- and photo-sensitive smart materials.
    Dissertation
      57  50
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    Item-typ:Veröffentlichung,
    Synthesis and reactivity of Chiral N-Heterocyclic Iodanes
    (2021-09-20)
    Abazid, Ayham
    ;
    Spiteller, Peter
    ;
    Nachtsheim, Boris Johannes
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    Nachtsheim, Boris Johannes
    Hypervalent iodine compounds, in particular aryl-ʎ3-iodanes, have found widespread applications for many organic transformations. Their reactivities are comparable to highly oxidized period-6 metals, in particular Hg(II), Tl(III), and Pb(IV), with less toxicity. All these merits make hypervalent iodine compounds suitable reagents to perform a wide range of oxidative transformation reactions. The first part of this thesis describes the efficient synthesis of novel triazole substituted chiral hypervalent iodine catalysts. It also describes the reactivity and selectivity of these new catalysts in different stereoselective oxidative transformations, such as Kita-spirocyclizations, the α-tosyloxylation of propiophenone, oxidative lactonizations, oxidative dearomtization of phenols and the oxidative rearrangement of allyl alcohols. The second part of the thesis describes the development of a novel enantioconvergent benzylic hydroxylation by employing a chiral iodine catalyst that fulfills a dual purpose as both oxidant and chiral ligand for a Cu co-oxidant. Finally, the enantioselective cyclization of unsaturated amides using chiral aryl iodides has been described, which has the facility to synthesize oxazoline derivatives. This method can be used to prepare natural products and biologically active compounds efficiently. Also, the asymmetric oxidative cyclization of naphthol compounds for the synthesis of chiral spirooxazolines has been described. These compounds have many applications in drugs and industrial applications.
    Dissertation
      351  244
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    Cyclic diaryliodonium salts – from synthesis to halogen bond catalysis
    (2026-05-22)
    Damrath, Mattis
    ;
    Nachtsheim, Boris Johannes
    ;
    Wagner, Philipp
    ;
    Huber, Stefan M.
    ;
    Nachtsheim, Boris Johannes
    Cyclic diaryliodonium salts have emerged as highly adaptable building blocks in organic synthesis and, more recently, as particularly powerful halogen bond (XB) donors in organocatalysis. In the present thesis, both newly designed and previously known cyclic diaryliodonium salts are prepared and examined in a systematic manner with respect to their structural features, their chemical reactivity, and their performance as catalysts. As a basis for this work, two efficient one‑pot procedures were established that provide access to oxygen‑ and nitrogen‑bridged cyclic diaryliodonium salts. Their utility as synthetic intermediates is illustrated by a broad set of mono‑ and difunctionalization reactions. On this foundation, a broader series of cyclic diaryliodonium salts was investigated in previously unexplored XB‑mediated transformations. In a Pictet–Spengler reaction, a simple dibenzoiodolium salt displayed remarkable catalytic activity even at very low loadings, thus offering an XB‑driven alternative to classical Brønsted or Lewis acid catalysis. In addition, highly strained N‑sulfonyl aziridines were activated by N‑heterocyclic iodonium salts and transformed, via formal [3+2] cycloadditions, with a variety of dipolarophiles, into diverse N‑heterocyclic products. Computational analyses uncovered an unusual dual activation mode involving simultaneous I–N and I–π interactions. In another part of the thesis, novel chiral triazole-substituted diaryliodonium salts were designed for enantioselective XB catalysis. A series of these chiral iodonium salts was synthesized and evaluated in a vinylogous Mannich reaction, affording up to 99% yield and an outstanding enantiomeric ratio (>99:1). Moreover, these catalysts enabled the efficient functionalization of ketimines with alcohols to form N,O-acetals in up to 99% yield and 90:10 e.r. Computational investigations provided mechanistic insight into the origin of enantioselectivity, validating the concept of asymmetric induction via σ-hole-stabilized chiral moieties in iodine(III)-based XB catalysts.
    Dissertation
      62  62