Current applications of porphyrins in medicine and optics, such as photodynamic therapy or nonlinear absorbers, increasingly require the use of far-red absorbing dyes. Modifications of the porphyrin structure to accommodate these conditions can be achieved by extending the conjugation of the porphyrin π-system, which causes a bathochromic shift in the absorption spectrum. Thus, conjugated porphyrin oligomers have found widespread use. However, past synthetic strategies have mainly targeted symmetric porphyrin dimers, trimers, and oligomers, which limit the practical use of such chromophores. Here, a series of symmetric and unsymmetric dimeric and trimeric porphyrin systems, which are connected by conjugated linkers, namely alkyne and phenylacetylene, were synthesized by palladium-catalyzed C-C coupling re-
Both, chiral and achiral basket-handle porphyrins were synthesized via a short, reliable, and efficient route in multigram quantities. Standard synthetic protocols such as metalation of the macrocycle, halogenation, and borylation of the porphyrin core or alkyl- and arylation with lithium organyls were successfully adapted. The planar-chiral representatives were resolved into their enantiomers, whose absolute configurations were determined by comparison of experimental CD spectra with TDCAM-B3LYP calculated ones.
Indaphyrins and indachlorins possess large chiral porphyrinoid π‐systems with particularly long‐wavelength absorption properties. All indaphyrin derivatives, including the indaphyrin MII complexes (M = NiII, CuII, ZnII, and PtII), adopt strongly ruffled conformations incorporating a helimeric twist, thus forming two stereochemically stable helimeric enantiomers. Their degree of ruffling is modulated by the coordination to metal ions or pyrrole ring modifications. Resolution of the racemic mixtures of the helimers of all derivatives was achieved by HPLC on a chiral phase and their absolute stereostructures were assigned. The much altered UV/Vis spectra of the indaphyrin derivatives, when compared to those of porphyrins, were rationalized using excited state calculations. The conformational stability of the conformers toward thermally induced racemization was also shown. The report forms the basis for future applications that exploit the chiral properties of the chromophores.
Chiral and achiral basket-handle porphyrins (BHPs) with different p-xylene straps and peripheral solubilizing groups were synthesized using a previously established synthetic approach. Subsequent modification, functionalization, and metalation of the tetrapyrrolic macrocycle yielded more than 80 BHPs. The chiral representatives were resolved into their enantiomers, whose absolute configurations were determined by comparison of their ECD spectra with other experimental or quantum chemically calculated spectra. NMR studies and coupled-cluster calculations proved that the free base BHPs, although highly symmetric, exhibited the phenomenon of "arrested tautomerism". Comparison of the solid-state structures of three metalated BHPs offered detailed insight into their three-dimensional shape. Finally, directly linked dimeric porphyrins with a BHP subunit were synthesized from functionalized BHPs to prove their value as synthetic building blocks.
The first total synthesis of mbandakamine A, an unsymmetrically coupled dimeric naphthylisoquinoline alkaloid with a high steric hindrance, is described. Key step was the phenol‐oxidative cross‐coupling of its two 5,8’‐linked monomeric units, 5‐epi‐korupensamine E and 8‐O‐methylkorupensamine A. These two naphthylisoquinolines were synthesized atroposelectively by applying the ′lactone method′. As an alternative to the largely separate synthesis of the two monomers, both of them were provided simultaneously, by the – intentionally non‐selective – O‐demethylation of a late joint precursor, thus shortening the synthesis substantially. Oxidative coupling of a 1:1 mixture of the two monomers provided mbandakamine A as a single atropisomer, along with four further naphthylisoquinoline dimers, nearly all of them based on new coupling types. Some of these new quateraryls showed excellent antiplasmodial activities, in particular the 6’‐6’’‐coupled main product.
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