Eberhardt Herdtweck

Bio: Eberhardt Herdtweck is an academic researcher from Technische Universität München. The author has contributed to research in topics: Carbene & Catalysis. The author has an hindex of 56, co-authored 332 publications receiving 10785 citations. Previous affiliations of Eberhardt Herdtweck include Jordan University of Science and Technology & Ludwig Maximilian University of Munich.

Pd(II)-Catalyzed Regioselective 2-Alkylation of Indoles via a Norbornene-Mediated C–H Activation: Mechanism and Applications

Abstract: A palladium-catalyzed direct 2-alkylation reaction of free N-H indoles was developed based on a norbornene-mediated regioselective cascade C–H activation. The detailed reaction mechanism was investigated by NMR spectroscopic analyses, characterization of the key intermediate, deuterium labeling experiments, and kinetic studies. The results indicate that a catalytic cycle operates, in which an N-norbornene type palladacycle is formed as the key intermediate. Oxidative addition of alkyl bromide to the Pd(II) center in this intermediate is the rate-determining step of the reaction. The synthetic utility of this indole 2-alkylation method was demonstrated by its application in natural product total synthesis. A new and general strategy to synthesize Aspidosperma alkaloids was established employing the indole 2-alkylation reaction as the key step, and two structurally different Aspidosperma alkaloids, aspidospermidine and goniomitine, were synthesized in concise routes.

Organocatalysis by Neutral Multidentate Halogen-Bond Donors†

Abstract: Over the last 15 years, hydrogen-bond donors, such as thiourea derivatives, have been used as noncovalent organocatalysts with ever-increasing sophistication. Yet, despite the large structural variety of the currently known noncovalent organocatalysts, virtually all are based on the same interacting atom: positively polarized hydrogen. Although it has been known for a long time that compounds featuring electrophilic halogen substituents also form adducts with Lewis bases, the corresponding interaction (“halogen bonding”) 4] was mostly ignored until the 1990s. An important difference between these two noncovalent interactions is the invariably high directionality of halogen bonds, with R X LB angles that are close to 1808 (X = Cl,Br,I; LB = Lewis base). Most studies involving halogen bonds are related to the solid state and to crystal engineering, but in recent years an increasing number of applications in solution-phase have been published, including fundamental studies and reports on anion receptors. In organocatalysis, the involvement of halogen bonds has only been postulated in two cases. Bolm et al. reported that iodoperfluoroalkanes catalyze the reduction of quinoline derivatives. The participation of halogen bonds in this reaction was derived from experimental observations. In a second example, iodine trichloride was reported to catalyze the ring-opening polymerization of l-lactide. The elucidation of the exact mode of action of this highly reactive interhalogen compound is not trivial, though, and in both reported cases the analysis is further complicated by the possible presence of traces of acid. One particular application of hydrogen-bonding organocatalysts is based on the coordination to anions and/or the abstraction of the latter from organic substrates (“anion binding mechanism”). Recently, we could show that halogen-bond donors may also serve as activators in a halide-abstraction benchmark reaction. To date, however, only dicationic compounds (based on either imidazolium, pyridinium, or 1,2,3-triazolium backbones) proved to be active, and stoichiometric amounts of the halogen-bond donor needed to be employed. As the use of cationic compounds comes along with several limitations (for example, concerning solubility, synthetic accessibility, and the presence of counteranions), our next goal was to design neutral halogen-bond donors for use as activators or, ideally, organocatalysts. At present, our studies have primarily proof-of-principle character to demonstrate the feasibility of halogen-bondbased organocatalysis. In the long term, we envision that halogen-based organocatalysts and hydrogen-bond donors will complement each other. Halogen-bond donors might be especially suitable for Lewis basic substrates featuring heavier elements (such as sulfur, phosphorous, or the halogens) or for certain reaction conditions. Furthermore, neutral fluorinated halogen-bond donors will likely allow the use of very nonpolar or fluorinated solvents in organocatalysis. Finally, the high directionality of halogen bonds might prove advantageous in future halogen-bond-catalyzed enantioselective transformations. In analogy to thiourea organocatalyst 1, we strove to develop multidentate halogen-based Lewis acids without further functional groups to study the isolated effect of halogen bonding. The 2,6-diiodo-3,4,5-trifluorophenyl group (Scheme 1) was chosen as building block for several reasons,

Phd by thesis

Abstract: Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Multicomponent Reactions with Isocyanides.

Abstract: Multicomponent reactions (MCRs) are fundamentally different from two-component reactions in several aspects. Among the MCRs, those with isocyanides have developed into popular organic-chemical reactions in the pharmaceutical industry for the preparation of compound libraries of low-molecular druglike compounds. With a small set of starting materials, very large libraries can be built up within a short time, which can then be used for research on medicinal substances. Due to the intensive research of the last few years, many new backbone types have become accessible. MCRs are also increasingly being employed in the total synthesis of natural products. MCRs and especially MCRs with isocyanides offer many opportunities to attain new reactions and basic structures. However, this requires that the chemist learns the “language” of MCRs, something that this review wishes to stimulate.

N-heterocyclic carbenes: a new concept in organometallic catalysis.

Abstract: N-Heterocyclic carbenes have become universal ligands in organometallic and inorganic coordination chemistry. They not only bind to any transition metal, be it in low or high oxidation states, but also to main group elements such as beryllium, sulfur, and iodine. Because of their specific coordination chemistry, N-heterocyclic carbenes both stabilize and activate metal centers in quite different key catalytic steps of organic syntheses, for example, C-H activation, C-C, C-H, C-O, and C-N bond formation. There is now ample evidence that in the new generation of organometallic catalysts the established ligand class of organophosphanes will be supplemented and, in part, replaced by N-heterocyclic carbenes. Over the past few years, this chemistry has been the field of vivid scientific competition, and yielded previously unexpected successes in key areas of homogeneous catalysis. From the work in numerous academic laboratories and in industry, a revolutionary turning point in oraganometallic catalysis is emerging.