Limited natural resources and an increasing demand for enantiomerically pure compounds render catalysis and especially heterogeneous asymmetric catalysis a key technology. The field has rapidly advanced from the initial use of chiral biopolymers, such as silk, as a support for metal catalysts to the modern research areas. Mesoporous supports, noncovalent immobilization, metal-organic catalysts, chiral modifiers: many areas are rapidly evolving. This Review shows that these catalysts have more to them than facile separation or recycling. Better activities and selectivities can be obtained than with the homogeneous catalyst and novel, efficient reaction mechanisms can be employed. Especially fascinating is the outlook for highly ordered metal-organic catalysts that might allow a rational design, synthesis, and the unequivocal structural characterization to give tailor-made catalysts.

Chiral metal-organic frameworks with a three-dimensional network structure and wide-open pores (>30 Å) were obtained by using chiral trifunctional linkers and multinuclear zinc clusters. The linkers, H(3) ChirBTB-n, consist of a 4,4',4''-benzene-1,3,5-triyltribenzoate (BTB) backbone decorated with chiral oxazolidinone substituents. The size and polarity of these substituents determines the network topology formed under solvothermal synthesis conditions. The resulting chiral MOFs adsorb even large molecules from solution. Moreover, they are highly active Lewis acid catalysts in the Mukaiyama aldol reaction. Due to their chiral functionalization, they show significant levels of enantioselectivity, thereby proving the validity of the modular design concept employed.

A bifunctional imidazolium linker was used for the production of highly crosslinked element organic frameworks by Suzuki-coupling with tetrafunctional boronic acids. The resulting porous materials are good heterogeneous organocatalysts in the N-heterocyclic carbene-catalyzed conjugated umpolung of α,β-unsaturated cinnamaldehyde.

Abstract:The stereoselective hydrogenation of auxiliary-substituted quinolines was used to build up saturated and partially saturated heterocycles. In a first step, the formation and diastereoselective hydrogenation of 2-oxazolidinone-substituted quinolines to 5,6,7,8-tetrahydroquinolines is reported. In this unprecedented process, stereocenters on the carbocyclic quinoline ring were formed with a dr of up to 89:11. Platinum oxide as a catalyst and trifluoroacetic acid as a solvent were found to be optimal for high levels of chemo-and stereoselectivity in this step. In a second hydrogenation step, the completely saturated decahydroquinolines with 4 newly formed stereocenters were obtained with enantioselectivities of up to 99%. Rhodium on carbon as a catalyst and acetic acid as a solvent gave the best results for this hydrogenation and allowed a traceless cleavage of the chiral auxiliary. Thus, this new method allows an efficient stereoselective synthesis of valuable 5,6,7,8-tetrahydro-and decahydroquinoline products.Keywords: asymmetric synthesis; chiral auxiliaries; decahydroquinolines; heterocycles; hydrogenation Enantiomerically pure saturated or partially saturated heterocyclic compounds are important building blocks and fragments of many biologically active compounds like coniine, the poisonous alkaloid of hemlock, or the multiply substituted Lycopodium alkaloids.[1] The asymmetric hydrogenation of heteroaromatic substrates presents an attractive strategy for their preparation and the last years have seen many significant contributions to this field.[2] For example, several different approaches have been reported for the asymmetric hydrogenation of pyridines: e.g., Charette et al. developed a highly selective Ir-catalyzed homogeneous hydrogenation of pyridine ylides, [3d] Zhang and Lei used a sequential combination of heterogeneous and homogeneous hydrogenation,[3c] Rueping et al. reported an organocatalytic approach employing chiral Brønsted acids, using a Hantzsch ester as the reducing agent.[3b] Whereas all these methods employ chiral, enantiomerically pure catalysts, Glorius et al. developed an efficient hydrogenation of chiral oxazolidinone-substituted pyridines using achiral heterogenous hydrogenation catalysts like Pd(OH) 2 /C.[3e,f] In this latter reaction, the auxiliary was cleaved under the reaction conditions and fully saturated piperidines with up to 4 newly formed stereocenters and high ees (85-98%) were obtained. Significantly more methods have been reported for the asymmetric (partial) hydrogenation of quinolines. Since the aromatic stabilization of the second aromatic ring in bicyclic aromatics is somewhat lower, hydrogenation of the annulated ring is significantly facilitated. Most of these methods employ homogeneous iridium, rhodium or ruthenium complexes of chiral ligands [4a-n] together with molecular hydrogen or, alternatively, chiral Brønsted acids as organocatalysts [4o,p] in transfer hydrogenations (Scheme 1). [2] However, despite these advances in the area of asymmetric hydrogena...

Knapper werdende Rohstoffe und ein zunehmender Bedarf an enantiomerenreinen Verbindungen machen die Katalyse und insbesondere die heterogene asymmetrische Katalyse zu einer Schlüsseltechnologie. Von den Anfängen, der Verwendung chiraler Biopolymere wie Seide als Träger für Metallkatalysatoren, zu den modernen Forschungsfeldern hat sich das Gebiet rasant entwickelt. Mesoporöse Träger, nichtkovalente Immobilisierung, metall‐organische Katalysatoren, chirale Modifikatoren: viele Gebiete sind im Aufbruch. Dass hierbei von den Katalysatoren mehr geleistet wird, als nur leichte Abtrennung und Wiederverwendung zu ermöglichen, zeigt dieser Aufsatz. So können z. B. bessere Aktivitäten und Selektivitäten als bei der homogenen Katalyse und zudem neuartige, effiziente Reaktionsmechanismen erhalten werden. Besonders spektakulär ist aber der Ausblick auf hochgeordnete metall‐organische Katalysatoren, die “rational” entwickelt, synthetisiert und strukturell eindeutig charakterisiert werden können, um maßgeschneiderte Katalysatoren zu erhalten.