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Catalytic and photochemical cycloadditions of alkynes
Fadeev, Aleksandr ; Kotora, Martin (advisor) ; Pour, Milan (referee) ; Parkan, Kamil (referee)
Novel approaches to utilizing alkynes in transition metal-catalyzed [2+2+2] cycloadditions and photochemical [2+2] cycloadditions were investigated with respect to the potential applications of these transformations. First, a chemo- and regioselective fully intermolecular cocyclotrimerization of internal alkynes with a commercially available ethynyl boronate was developed using Ru-catalysis and its mechanism was examined using DFT calculations. The established method allows for a straightforward preparation of various 1,4-diborylated benzenes, which can serve as multifunctional building blocks in organic synthesis. In particular, the products can be used in cross-coupling, carbonylation and oxidation reactions to access a broad variety of contiguously substituted arenes, such as natural products mirandamycin and violaceoid C. Second, a comparative study of catalytic and uncatalyzed photocycloadditions between alkynes and quinones was undertaken. Contrary to the recent reports, irradiation with visible light alone is sufficient to obtain not only the [2+2] cycloaddition products, but also several products of cascade transformations. Thus, depending on the structure of the quinone used, either carbo- or heterocycloaddition pathway is mainly realized, giving rise either to annulated cyclobutenes or...
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Reactions of Alkenes Iniciated by Transition Metals Alkyls and Hydrides
Nečas, David ; Kotora, Martin (advisor) ; Jindřich, Jindřich (referee) ; Starý, Ivo (referee) ; Mazal, Ctibor (referee)
l0 5. Conclusion 1) The first and practical catalýic method for smooth deallylation of 2-substituted-2-allylmalonates to 2-substituted malonates via selective cleavage of the C-C bond under mild reaction conditions has been developed' The reaction seems to be general with respect to the transition-metal complexes; however, the comparison of Ru and Ni catalysts indicates considerable differences in their specific activity and selectiviý. Last but not least, the smooth deallylation offers an opportuniý to use the allyl group as an effective protective group for acidic hydrogen of malonic esters. 2) It has been shown that it is possible to re-route the course of the reaction from c{ bond cleavage (deallylation) to c{ bond formation (cyclization) in Ni hydride cataryzed, reactions by a change in the amount of organoaluminium. It proceeded in high yields even in cases where deallylation could compete with cyclization (e.g. diallylmalonate, etc.) in high selectiviý. In addition, generation of Ni hydride species in sinr provides an effective means for fast and selective cyclization of variously substituted 1,6- heptadienes to cyclopentanes. Moreover, it is possible exert certain level of control for the preferential formation of methylidene(methyl)cyclopentanes or cyclopentenes by the appropriate choice of thb...
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Development of New Syntheses of Azaaromatic Compounds with Extended π-System
Ulč, Jan ; Kotora, Martin (advisor) ; Hrdina, Radim (referee) ; Tobrman, Tomáš (referee)
Azapolyaromatic compound are a class of heterocyclic compounds, which contains at least one nitrogen atom. A subclass of these compounds are quinolizinium salts, which contains nitrogen atom in bridgehead position. These salts usually have interesting photophysical properties. Naphthoquinolizinium salts are a group of quinolizinium salts, but their synthesis as well as their photophysical properties haven't been studied in detail yet. This work is about development of a new modular method for preparation of naphthoquinoliziniu salts. This method is based on catalytic C-C and C-H bond activations by transition metal catalysts. 1-Azabiphenylene was used as a starting material, which reacted in catalytic C-C bond cleavage followed by insertion of various alkyne to form benzo[h]quinolines. These benzo[h]quinolines then reacted in catalytic C-H bond activation reaction followed by insertion of another alkyne to form final tetrasubstituted naphthoquinolizinium salts. Photophysical properties of the prepared salts was studied. The developed method was used on a more complex starting material such as linear 1- 1-aza-[3]triphenylene, which was converted to phenanthroquinolines and eventually to the corresponding azonia salts. Key words: azapolyaromatic compounds, catalysis by transition metal complexes, C-C...
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Synthesis of Cationic Helical N-Heterocycles
Hrubý, Samuel ; Kotora, Martin (advisor) ; Rýček, Lukáš (referee)
Diploma thesis concerns synthesis of hitherto unknown cationic helical heterocyclic compounds by catalytic processes from simple building blocks. The focus was on the utilization of a catalytic C-C bond cleavage in biphenylene followed by annulation with nitriles, a method that was developed in our research group. As an alternative approach was applied Suzuki- Miyaura cross-coupling. The prepared phenanthridines were used in catalytic C-H bond activation followed by annulation with alkynes giving rise to cationic helical heterocycles. These compounds have potential application in various fields of material chemistry. Key words: C-C bond activation, C-H bond activation, Suzuki-Miyaura cross-coupling, heterocycles, helical compounds, catalysis
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Delipment of a new synthetic approach for synthesis of isoquinoline alkaloids
Pašek, Dominik ; Kotora, Martin (advisor) ; Pour, Milan (referee)
This bachelor work is focused on synthesis of a specifically substituted isoquinoline core which is the fundamental structure of natural isoquinoline alkaloids. The main aim is development of a new method for a synthesis of molecules with the isoquinoline framework which could lead to a more efficient way of total synthesis of these important natural substances. The main subject of interest is a cyclization providing a substituted piperidine ring condensed with the tetrahydroisoquinoline core. Zirconocene-based chemistry is used as the crucial synthetic step. Following the development of this new synthetic method, the goal was to study possibilities of cyclization of substituted 1,7-dienes by using the Negishi's reagent. Effects of temperature, reaction time, amount of Negishi's reagent on the course of the reaction as well as stereochemistry of the cyclization were studied. Key words: alkaloid, isoquinoline, synthesis, cyclization, zirconocene, Negishi's reagent
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Development of New Approachs to Selaginpulvilins
Beytlerová, Nela ; Kotora, Martin (advisor) ; Baszczyňski, Ondřej (referee)
The objective of this diploma thesis was application of catalytic [2+2+2]cyclotrimerization of alkynes induced by transition metals complexes in synthesis of selaginpulvilins O and S -natural products with the fluorene scaffold. Selaginpulvilins are bioactive natural compounds present in the Asian plants from Selaginella genus. Their isolation and structure determination was reported for the first time by Yin et al. in 2014.1 The plants are used in traditional Chinese medicine for treatment of asthma and chronic pneumonia disease. The integral part of the project was a study to assess efficacy of various transition metal catalysts and catalytic systems, solvents, reaction temperatures and reaction time on the course of the cyclotrimerization reaction. Synthesis of a suitable precursor for the cyclotrimerization step was achieved from commercially available 2-bromo-5- hydroxybenzaldehyde (153) as that starting compound. The total formal synthesis of selaginpulvilins O and S were completed by conversion of cyclotrimerization product. Key words: [2+2+2]cyclotrimerization; selaginpulvilin O; selaginpulvilin S; fluorene core; transition metal catalysis
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Studium of 1,6-pinakol rearrangement
Vlčková, Gabriela ; Kotora, Martin (advisor) ; Kamlar, Martin (referee)
This bachelor work focuses on a study of 1,6-pinacol rearrangement in substances possessing the 1,4-phenylendimethanol moiety. The pinacol rearrangement was studied under various reaction conditions in the presence of different Brønsted and Lewis acids. The project consists of preparation of suitable starting material and a study of different reaction conditions. The goal is for one thing to assess the scope of the reaction with respect to the structure of the starting material (specifically indenofluorene-5,8-diols) and for another to exploit its synthetic application. Key words: 1,4-fenylennedimethanol, indenofluorendiol, rearrangement, Brønsted acids, Lewis acids
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Development of new pathways for syntheses of sesquiterpenoids
Topolovčan, Nikola ; Kotora, Martin (advisor) ; Dvořák, Dalimil (referee) ; Pour, Milan (referee)
This work consists of four consecutive parts, each dealing with syntheses of structurally diverse compounds. The syntheses were based on the methods within the domain of transition-metal catalyzed and/or mediated reactions with particular emaphasis on the application of organozirconium chemistry. 1. A method for synthesis of tricyclic condensed hydrocarbons possessing 5(6)-7-6(aryl) framework was developed. It is based on reaction of bicyclic zirconacyclopentenes, prepared by oxidative dimerization of enynes on a low-valent zirconocene species (Negishi's reagent), with ortho-halobenzaldehydes in the presence of various additives. The presence of two different centers of reactivity - the sp2 C-Zr and sp3 C-Zr bond - allowed sequential functionalization of each bond. Thanks to its higher nucleophilicity, the sp3 C-Zr bond reacted preferentially with the carbonyl carbon of the aldehyde yielding an oxazirconacycloheptene. The subsequent transmetallation of the remaining sp2 C-Zr bond with CuCl in the presence of other additives (catalysts) enabled an intramolecular cross-coupling reaction with the aryl halide moiety furnishing the desired tricyclic products in reasonable yields. The scope of the reaction with respect to differently functionalized reactants was assessed, as well as its mechanistic...
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