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Ammonium enolates for the stereoselective syntheses of carbo- and heterocycles / eingereicht von DI Lukas Roiser BSc
AutorInnenRoiser, Lukas
Beurteiler / BeurteilerinWaser, Mario ; Monkowius, Uwe
ErschienenLinz, 2018
Umfang253 Blätter : Illustrationen
HochschulschriftUniversität Linz, Dissertation, 2018
Bibl. ReferenzOeBB
Schlagwörter (EN)ylides / ammonium enolates / carbocycles / heterocycles / stereoselective
Schlagwörter (GND)Ylide / Enolate / Ammoniumverbindungen / Carbocyclen / Heterocyclische Verbindungen / Stereoselektivität
URNurn:nbn:at:at-ubl:1-22608 Persistent Identifier (URN)
 Das Werk ist gemäß den "Hinweisen für BenützerInnen" verfügbar
Ammonium enolates for the stereoselective syntheses of carbo- and heterocycles [24.98 mb]
Zusammenfassung (Englisch)

Ammonium enolates, formed by the reaction between several carbonyl-compounds and tertiary amines have been widely used in various transformations in the past decades. An advantage of this species of nucleophiles is the ready availability of enantiopure amines for the reactions in the “chiral pool”, as is for example the case for cinchona alkaloids. These compounds possess a catalytically active nitrogen atom in the quinuclidine ringsystem as well as a well-defined, sterically demanding chiral environment, making them an ideal class of amines to catalyze asymmetric transformations. The mentioned ammonium enolates can be divided into three main types. What these classes have in common is the generation from tertiary amines and (pro)-nucleophiles, which are then covalently bound in the enolate. These nucleophilic enolates can be either generated from amines with ketenes (TYPE 1 enolates), with -halo carbonyl compounds and bases (TYPE 2) or with ,-unsaturated carbonyl compounds (TYPE 3). For TYPE 1 enolates it is well-known that they react with aldehydes and imines in a formal [2+2] cycloaddition to -lactones or -lactams, respectively. In the first part of this thesis the reactions of these nucleophiles (accessed by different methods with either tertiary amines or other Lewis-bases as catalysts) with aziridines and epoxides were investigated. While a formal [3+2] cycloaddition via a ring-opening/ring-closure mechanism to the corresponding -lactones or -lactams was expected, these reactions remained unsuccessful despite any optimization and variation of the reaction systems most probably due to the low reactivity of the substrates towards carbon-nucleophiles. Furthermore, also different Michael -acceptors, potentially leading to synthetically interesting products were investigated using this type of enolates. Additionally, an enolate based on nitroacetic acid was tested, possibly giving access to -amino carbocycles. All these further tested reactions of TYPE 1 ammonium enolates remained also unsuccessful despite all efforts. The second part of this thesis focused on the reactions of TYPE 2 ammonium enolates and other types of ylides. In the case of benzylic ammonium ylides, the diastereoselectivity and (generally high) yield were strongly depended on the nature of the substrates used and the superior leaving group ability of trimethylamine could be confirmed. For amide-stabilized ammonium ylides a new group of proline-based tertiary amines was found, giving access to epoxides and aziridines (up to 89% yield, trans-selective, e.r. = 93:7). Furthermore, the amide-enolates could be generated also using cinchona-alkaloid based amines in the highly enantioselective spiro-cyclopropanation of p-quinone methides (up to 98% yield, d.r. > 20:1, e.r. > 99.9:0.1). In a similar fashion keto-stabilized ylides based on cinchona-alkaloids could be used in a highly selective synthesis of 2,3-dihydrobenzofuranes from o-quinone methides (up to 85% yield, d.r. > 95:5, e.r. = 99:1). Further formal [n+1]-cyclizations, leading to spirocyclopentenyl-p-dienones, trifluoromethylated cyclopropanes and various 2,3-dihydrofuranes were tested and are still being investigated in our group.

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