Im Rahmen der vorliegenden Arbeit wurden Dibortetrahalogenide dargestellt, deren Eigenschaften strukturell sowie spektroskopisch analysiert und deren Reaktivität gegenüber Lewis-basischen Hauptgruppenelementverbindungen untersucht. Durch anschließende Reaktivitätsstudien konnten unter anderem neuartige Diborene dargestellt und analysiert werden. Weiterhin wurde die Verbindungsklasse der Elementhalogenide der Gruppe 13 in der Oxidationsstufe +2 (B, Ga, In) und +3 (In) bezüglich ihrer Reaktivität gegenüber Übergangsmetall Lewis-Basen untersucht. Die gebildeten, neuartigen Bindungsmodi der Gruppe 13 Elemente am Übergangsmetall wurden strukturell, spektroskopisch sowie quantenchemisch analysiert. / As a part of the present work diborontetrahalides were synthesized, analyzed and their reactivity was investigated towards Lewis-basic main group compounds. Subsequent reactivity studies were performed and novel Diborenes were synthesized and analyzed. Furthermore the reactivity of group 13 elemental halides in the oxidation state +2 (B, Ga, In) and +3 (In) was investigated towards Lewis-basic transition metal complexes. The novel bonding motifs of the group 13 elements at the metal center were investigated structurally, spectroscopically and by quantum chemical calculations.

Aldol addition reaction is one of the most important and most studied carbon-carbon bond forming reactions in organic chemistry. Recent studies focused on the catalytic version of this chemistry. Different from the classical Mukaiyama-type aldol reactions, chiral lewis bases have been used as promoters. In the presence of SiCl4, these reactions proceed through a cyclic transition state leading to anti aldol product as a major product with moderate-to-good diastereo and enantioselectivities. Phosphoramide derivatives, BINAPO, BINAPO derivatives, N,N-dioxides and N-oxides have been extensively used for this purpose. Recently, our group has designed new phosphine oxy aziridinyl phosphonates (POAP) as chiral Lewis bases. These promoters were used for the asymmetric aldol addition reaction between cyclohexanone and different aldehydes in the presence of SiCl4. Moreover, our previously designed phosphine oxy ferrocenyl substituted aziridinyl methanol (POFAM) ligands were also tested as Lewis bases. Among these 6 potential promoters, POAP-A gave the best results, and the aldol product were obtained in moderate to good yields up to 80%, and with moderate enantioselectivities (the highest, 66%) after standard optimization studies. Aldehyde screening experiments provided the highest enantioselectivity (68%) with 2- naphthaldehyde.

In der vorliegenden Arbeit werden M(II)-Formiat-Komplexe mit M=Cu, Ni, Zn beschrieben. Das themogravimetrische Verhalten dieser Komplexe wird vorgestellt. TG-MS-Untersuchungen geben erste Hinweise auf das Metallisierungsverhalten obiger Spezies. Die Charakterisierung der entsprechenden Komplexe erfolgte durch die Elementaranalyse, IR-Spektroskopie sowie in einzelnen Fällen durch die Einkristallröntgendiffraktometrie.

This thesis describes the development and rationalization of processes involved in a new methodology developed in our group, minor enantiomer recycling. The first part of the thesis addresses mechanistic studies of one of the reactions involved in minor enantiomer recycling, dual Lewis acid-Lewis base catalyzed acetylcyanation of aldehydes. The methodology uses a combination of a chiral titanium-salen  complex with a tertiary amine as a catalytic  system  in  the enantioselective  synthesis  of  O-acylated  cyanohydrins from aldehydes and ketonitriles. Mechanistic investigations revealed that the rate-determining step in the reaction changes, depending on the nature of the aldehyde that was used. It was also concluded that cyanohydrin is coordinated to the Lewis acid in the acylation step. The second part of the thesis deals with minor enantiomer recycling, a highly selective one-pot recycling system. In a first step the product is formed as a minor and a major enantiomer by asymmetric catalysis. Recycling of the minor enantiomer, by selective kinetic resolution, regenerates the starting material. Continuous addition of a second reagent, also involved in a coupled exergonic process, leads to an increase of both yield and enantiomeric excess. Recycling procedures for the synthesis of O-acylated and O-formylated cyanohydrins have been developed with high yield and high enantiomeric excess of the products. The study includes development of the systems, comparison to other methodologies in asymmetric catalysis, and attempts to understand the processes involved. / <p>QC 20141202</p>

Regensburg, Univ., Diss., 2007

Zugl.: Clausthal, Techn. Univ., Diss., 2009

In recent years, photoredox catalysis emerged as a privileged tool for small molecules activation via single-electron transfer mechanisms. Despite their ubiquity as reagents in organic synthesis, the use of boronic acid derivatives to generate carbon-centred radicals remains elusive. This dissertation explores the utilisation of photoredox catalysis to generate carbon radicals from boronic acid derivatives and subsequently engage them in C–C cross-coupling reactions. In the first chapter, an introduction to photoredox catalysis and organoboron reagents is provided, as well as a discussion on the key mechanistic aspects of photoredox catalysed C–C cross-coupling reactions. The second chapter presents our initial coupling strategy and how it evolved in understanding that pinacol boronic ester species can be used as a source of carbon radicals via single-electron oxidation from a photoredox catalyst. Coordination of the boronic esters with Lewis basic species was identified as a fundamental activating interaction. The synthetic utility of this discovery was highlighted by performing a wide range of photoredox catalysed arylations of pinacol boronic esters. The third chapter builds on our mechanistic understanding to identify a set of Lewis base catalysts that conveniently activates boronic esters and acids towards single-electron oxidation. The usefulness of this improved set of conditions was demonstrated by alkylating a wide range of boronic acid derivatives. The fourth chapter describes the application of this methodology in synthesising four active pharmaceutical ingredients from the GABA family. An emphasis was made on developing an efficient flow process and “transition metal free” conditions to survey the attractiveness of the method for the pharmaceutical industry. Finally, the fifth chapter describes the experimental procedures relevant to the results described in chapters 2 to 4.

Les travaux de recherche fondamentale présentés ici sont ancrés au cœur de la chimie organique de synthèse moderne, et plus particulièrement dans le domaine de la multi-organocatalyse énantiosélective. Dans ce manuscrit, nous avons identifié deux organocascades originales et démontré la pertinence synthétique de l'une d'elle par des applications en synthèse totale de produits naturels. L’originalité de ce travail repose sur l’utilisation d’un NHC de la classe des 1,3-imidazol-2-ylidenes comme base de Brønsted ou base de Lewis organocatalytique / The basic research work presented herein is anchored at the core of modern synthetic organic chemistry, and more specifically in the field of enantioselective multi-organocatalysis. In this manuscript, we have identified two original organocascades and demonstrated the synthetic relevance of one of these through applications in total synthesis. The originality of the work lies on the use of a 1,3-imidazol-2-ylidene NHC as an organocatalytic Brønsted or Lewis base.

Ce manuscrit présente le développement de nouvelles réactivités mettant en jeu des sources d’halogène électrophile et leur application dans les réactions de carbocyclisation de substrats possédant des fonctions carbonées insaturées. Le concept d’activation par une base de Lewis de l’agent d’halogénation a été étudié dans ce type de réactions, d’abord en version racémique, puis en version énantiosélective. L’efficacité des chalcogénures de phosphines et de phosphites a en particulier été démontrée dans les réactions d’iocarbocyclisation d’énynes-1,5 et d’iodoarylation d’oléfines. De nouveaux organocatalyseurs chiraux ont par la suite été synthétisés par analogie aux bases de Lewis achirales utilisées. Des molécules chirales de types chalcogénures de phosphoramidites et de phosphites ont ainsi été préparées et leur activité a par la suite été évaluée dans la perspective du développement d’une version asymétrique des réactions d’iodocarbocyclisation étudiées précédemment. En parallèle, de nouvelles méthodologies impliquant des substrats possédant une fonction allène ont été développées. En particulier, la réaction d’iodocarbocyclisation d’arylallènes a permis d’accéder à des 2-iodoindènes polysubstitués selon un procédé 5-endo avec des rendements allant jusqu’à 95%. / This manuscrit concerns the development of new reactivities, involving electrophilic halogen sources and their application in carbocyclization reactions of substrates bearing unsaturated carbon functions. The concept of Lewis base activation of the halogenation reagent was assessed in this type of reaction, first in a racemic version, then in an enantioselective fashion. In particular, the efficiency of phosphine and phosphite chalcogenides has been demonstrated in iodocarbocyclization reactions of 1,5-enynes and iodoarylation reactions of olefins. New chiral organocatalysts were afterwards synthesized by analogy with achiral Lewis bases previously employed. Thus, chiral molecules such as phosphoramidite and phosphite chalcogenides were prepared and their activity has been evaluated in the perspective of the development of an asymmetric version of these reactions. In parallel, new methodologies involving substrates bearing an allene function were developed. In particular, the iodocarbocyclization reaction of arylallenes was exploited to access polysubstituted 2-iodoindenes following a 5-endo process with yields up to 95%.

This thesis deals with the development of new methods for efficient synthesis and analysis in asymmetric catalysis. It focuses on the preparation of chiral cyanohydrins by enantioselective addition of cyanide to prochiral aldehydes. The initial part of the thesis describes the development of a dual Lewis acid– Lewis base activation system for efficient synthesis of chiral O-acylated and Ocarbonylated cyanohydrins. This system was used for the preparation of a variety of cyanohydrins in high isolated yields and with up to 96% ee. Activation of the cyanide by nucleophilic attack of the Lewis base at the carbonyl carbon atom was supported experimentally. Secondly, convenient procedures for the synthesis of polymer-bound chiral YbCl3-pybox and Ti-salen complexes are described. The polymeric complexes were employed in cyanation of benzaldehyde. A T-shaped microreactor was used for screening of reaction conditions for the enantioselective cyanation of benzaldehyde using trimethylsilyl cyanide and acetyl cyanide as cyanide sources. A microreactor charged with the polymeric Tisalen complex was used for enantioselective cyanation of benzaldehyde. Finally, an enzymatic method for high throughput analysis of ee and conversion of products from chiral Lewis acid–Lewis base-catalysed additions of α- ketonitriles to prochiral aldehydes was developed. The method could be used for the analysis of a variety of O-acylated cyanohydrins. Microreactor technology was successfully combined with high throughput analysis for efficient catalyst optimisation. / QC 20100809