Eine rotationsgehinderte und dadurch stereogene Biarylachse ist das strukturell und stereochemisch entscheidende Element einer ständig wachsenden Zahl von Naturstoffen, chiralen Auxiliaren und Katalysatoren. Daher ist es nicht überraschend, dass im letzten Jahrzehnt bedeutende Fortschritte in der asymmetrischen Synthese axial‐chiraler Biaryle erzielt worden sind. Neben dem klassischen Zugangsweg, der direkten Aryl‐Aryl‐Kupplung, sind innovative Konzepte entwickelt worden, in denen die asymmetrische Information in ein schon vorhandenes, aber nicht optisch aktives – symmetrisches oder konfigurativ labiles – Biaryl eingeführt oder eine Aryl‐C‐Einfachbindung stereoselektiv in eine Achse umgewandelt wird. In diesem Aufsatz werden die Strategien nach den zugrunde liegenden Konzepten klassifiziert, und ihre Anwendungsbreite und ihre Beschränkungen werden anhand ausgewählter Beispiele kritisch beurteilt. Ferner werden die Voraussetzungen für das Auftreten von Axialchiralität diskutiert.

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photon management. SF enables multiple excitons to be generated after the absorption of just a single photon. [1-9] By integrating SF materials into solar-cell architectures, it is feasible to increase the overall efficiency of solar cells by pushing the Shockley-Queisser limit from 32% to approximately 45%. Several requirements must, however, be met to allow for efficient SF well beyond 100%. [10,11] Thermodynamically, the energy level of the singlet excited state (S 1) must be equal to or higher than twice that of the triplet excited state (T 1); (S 1) ≥ 2(T 1). [2,3,12] In addition, the energy levels of higher-lying triplet excited states (T 2) should exceed twice the energy of the lowest-lying triplet excited state; (T 2) ≥ 2(T 1). [2,3,12] The latter avoids (T 2) population as a product of triplet-triplet annihilation up-conversion (TTA-UC). [2,3,12] Sufficient electronic interaction between two or more chromophores is essential, and is usually realized for monomers by overlaps in the crystal packing or high concentrations in the solid state or solution, respectively. [12-16] Dimers, in which different spacers are employed to link the chromophores, rather than monomers, represent yet another strategy to adjust and fine-tune, for Three diketopyrrolopyrrole (DPP) dimers, linked via different dithienylphenylene spacers, ortho-DPP (o-DPP), meta-DPP (m-DPP), and para-DPP (p-DPP), are synthesized, characterized, and probed in light of intramolecular singlet fission (i-SF). Importantly, the corresponding DPP reference (DPP-Ref) singlet and triplet excited state energies of 2.22 and 1.04 eV, respectively, suggest that i-SF is thermodynamically feasible. The investigations focus on the impact of the relative positioning of the DPPs, and give compelling evidence that solvent polarity and/or spatial overlap govern i-SF dynamics and efficiencies. Polar solvents make the involvement of an intermediate charge transfer (CT) state possible, followed by the population of 1 (T 1 T 1) and subsequently (T 1 + T 1), while spatial overlap drives the mutual interactions between the DPPs. In o-DPP, the correct balance between polar solvents and spatial overlap leads to the highest triplet quantum yield (TQY) of 40%. Notable is the superimposition of CT and triplet excited states, preventing an accurate TQY determination. For m-DPP, poorer spatial overlap correlates with weaker CT character and manifests in a TQY of 11%. Strong CT character acts as a trap and prevents i-SF, as found with p-DPP. The DPP separation is decisive, enabling a symmetry-breaking charge-separated state rather than CT formation, shutting down the formation 1 (T 1 T 1).

The chemical constituents and biological activities of Corydalis crispa (Fumariaceae) were investigated for the first time. The phytochemical study resulted in the isolation of nine known isoquinoline alkaloids: protopine (1), 13-oxoprotopine (2), 13-oxocryptopine (3), stylopine (4), coreximine (5), rheagenine (6), ochrobirine (7), sibiricine (8) and bicuculline (9), with complete NMR data for 2 and 3 provided here for the first time. Crude extracts exhibited significant anti-inflammatory (p<0.01) activity against TNF-α production in LPS activated THP-1 cells. The acetylcholinesterase inhibitory activity of compounds 2, 4 and 7 and the antiplasmodial activity of compound 5 against P. falciparum strains TM4/8.2 and K1CB1 (multidrug resistant strain) are reported here for the first time. Stylopine (4) did not show antimalarial activity against the K1CB1 strain in contrast to a previous report. This study generated a scientific basis for the use of this plant in Bhutanese traditional medicine, either individually or in combination with other medicinal ingredients to treat a broad range of disorders. This study also identified compound 5 as potential new antimalarial lead compound.