Chiroptical Inversion of Europium(III) Complexes by Changing a Remote Stereogenic Center of a C2-Symmetric Bispyrrolidinoindoline Manifold

Rapid Synthesis of Chiral Figure-Eight Macrocycles Using a Preorganized Natural Product-Based Scaffold

Chiral D2 -symmetric figure-eight shaped macrocycles are promising scaffolds for amplifying the chiroptical properties of π-conjugated systems. By harnessing the inherent and adaptable conformational dynamics of a chiral C2 -symmetric bispyrrolidinoindoline (BPI) manifold, we developed an enantio-divergent modular synthetic platform to rapidly generate a diverse range of chiral macrocycles, spanning from 14- to 66-membered rings, eliminating the need for optical resolution. Notably, a 32-membered figure-eight macrocycle showed excellent circularly polarized luminescence (CPL: |glum |=1.1×10-2 ) complemented by a robust emission quantum yield (Φfl =0.74), to achieve outstanding CPL brightness (BCPL : ϵ×Φfl ×|glum |/2=480). Using quadruple Sonogashira couplings, this versatile synthetic platform enables precise adjustments of the angle, distance, and length among intersecting π-conjugated chromophores. Our synthetic strategy offers a streamlined and systematic approach to significantly enhance BCPL values for a variety of chiral D2 -symmetric figure-eight macrocycles.

Strategies for total synthesis of bispyrrolidinoindoline alkaloids

Covering up to 2021Complex cyclotryptamine alkaloids with a bispyrrolidino[2,3-b]indoline (BPI) skeleton are an intriguing family of natural products, exhibiting wide systematic occurrences, large structural diversity, and multiple biological activities. Based on their structural characteristics, BPI alkaloids can be classified into chimonanthine-type BPI alkaloids, BPI diketopiperazines, and BPI epipolythiodiketopiperazines. These intricate molecules have captivated great attention soon after their isolation and identification in the 1960s. Due to the structural complexity, the total synthesis of these cyclotryptamine alkaloids is challenging. Nevertheless, remarkable progress has been achieved in the last six decades; in particular, several methods have been successfully established for the construction of vicinal all-carbon quaternary stereocenters. In this review, the structural diversity and chemical synthesis of these BPI alkaloids were summarized. BPI alkaloids are mainly synthesized by the methods of oxidative dimerization, reductive dimerization, and alkylation of bisoxindole. The purpose of this review is to present overall strategies for assembling the BPI skeleton and efforts towards controlling the stereocenters.

Coordination-Directed Self-Assembly of Functional Polynuclear Lanthanide Supramolecular Architectures

Lanthanide supramolecular chemistry is a fast growing and intriguing research field due to the unique photophysical, magnetic, and coordination properties of lanthanide ions (Ln^III). Compared with the intensively investigated mononuclear Ln-complexes, polymetallic lanthanide supramolecular assemblies offer more structural superiority and functional advantages. In recent decades, significant progress has been made in polynuclear lanthanide supramolecules, varying from structural evolution to luminescent and magnetic functional materials. This review summarizes the design principles in ligand-induced coordination-driven self-assembly of polynuclear Ln-structures and intends to offer guidance for the construction of more elegant Ln-based architectures and optimization of their functional performances. Design principles concerning the water solubility and chirality of the lanthanide-organic assemblies that are vital in extending their applications are emphasized. The strategies for improving the luminescent properties and the applications in up-conversion, host-guest chemistry, luminescent sensing, and catalysis have been summarized. Magnetic materials based on supramolecular assembled lanthanide architectures are given in an individual section and are classified based on their structural features. Challenges remaining and perspective directions in this field are also briefly discussed.

Self-assembled lanthanide-based helixes: synthetic control of the helical handedness by chirality of the ligand

The control of the self-assembly of lanthanide helical chain and their helical handedness have been investigated for the first time. Δ- and Λ-form lanthanide chain complexes were obtained by introducing thiazolidine ligands that were synthesised from L- and D-cysteine, respectively, and shared the same formula: [Ln₂(L)₃(H₂O)₅]_∞·3H₂O (Ln: Sm and Eu) (L: 2-(2-hydroxy-3,5-dinitrophenyl)thiazolidine-4-carboxylic acid). The crystallographic, circular dichroism, and luminescence properties of these novel lanthanide chain complexes were studied.

Sorting Phenomena and Chirality Transfer in Fluoride-Bridged Macrocyclic Rare Earth Complexes

The reaction of fluoride anions with mononuclear lanthanide(III) and yttrium(III) hexaaza-macrocyclic complexes results in the formation of dinuclear fluoride-bridged complexes. As indicated by X-ray crystal structures, in these complexes two metal ions bound by the macrocycles are linked by two or three bridging fluoride anions, depending on the type of the macrocycle. In the case of the chiral hexaaza-macrocycle L1 derived from trans-1,2-diaminocyclohexane, the formation of these μ2-fluorido dinuclear complexes is accompanied by enantiomeric self-recognition of macrocyclic units. In contrast, this kind of recognition is not observed in the case of complexes of the chiral macrocycle L2 derived from 1,2-diphenylethylenediamine. The reaction of fluoride with a mixture of mononuclear complexes of L1 and L2, containing two different Ln(III) ions, results in narcissistic sorting of macrocyclic units. Conversely, a similar reaction involving mononuclear complexes of L1 and complexes of achiral macrocycle L3 based on ethylenediamine results in sociable sorting of macrocyclic units and preferable formation of heterodinuclear complexes. In addition, formation of these heterodinuclear complexes is accompanied by chirality transfer from the chiral macrocycle L1 to the achiral macrocycle L3 as indicated by CPL and CD spectra.

Cephalodiones A-D: Compound Characterization and Semisynthesis by [6+6] Cycloaddition

Cephalodiones A-D (1-4), the first example of C₁₉ -norditerpenoid dimers, were isolated and fully characterized from a Cephalotaxus plant. These new skeletal natural products shared a unique tricyclo[6.4.1.1^2,7 ]tetradeca-3,5,9,11-tetraene-13,14-dione core that was capped in both ends with rigid multicyclic ring systems either C₂ -symmetrically or asymmetrically. Compounds 1-4 were proposed to be biosynthetically produced by the [6+6]-cycloaddition of two identical C₁₉ -norditerpenoid troponoids, which was validated by the semisyntheses of dimers 2-4. Moreover, some compounds showed significant inhibition on Th17 cell differentiation.

Catalytic asymmetric preparation of pyrroloindolines: strategies and applications to total synthesis

Pyrroloindolines are widely present in natural products. In this review, we summarize state-of-the-art of catalytic asymmetric synthesis of pyrroloindolines, as well as related applications to natural products total synthesis.

Electronic strain effect on Eu(iii) complexes for enhanced circularly polarized luminescence

The structural and electronic strain of ligands promotes the enhancement of the magnitude of circularly polarized luminescence in chiral Eu(iii) complexes.

A Route to (Het)arene-Annulated Pyrrolo[1,2-d][1,4]diazepines via the Expanded Intramolecular Paal-Knorr Reaction: Nitro Group and Furan Ring as Equivalents of Amino Group and 1,4-Diketone

A straightforward protocol toward pharmacologically relevant (het)areno[x,y-b]pyrrolo[1,2-d][1,4]diazepines in good to high yields has been described. The designed approach consists of an acid-promoted furan ring opening in easily accessible N-(2-furylethyl)-2-nitroanilines or their heterocyclic analogues followed by the reductive cyclization of the corresponding nitro-1,4-diketones.

Off-off-on chiroptical property switching of a pyrene luminophore by stepwise helicate formation

Pyrene-based chiral ligands (LR and LS) consisting of two chiral imidazole sidearms at the 1,8-positions first form pyrene-bridged oligomers [(L(R or S))3(Zn2+)n], which are chiroptically inactive, with a low concentration of zinc ions (Zn2+). Upon addition of more Zn2+, chiroptically active coordination helicates ([(L(R or S))3(Zn2+)2]) are formed. The stepwise assembly process successfully facilitated an "off-off-on" chiroptical switching process of a pyrene luminophore controlled by the concentration of Zn2+. The resulting pyrene-bridged helicates exhibit high performance in terms of a dissymmetry factor of circular dichroism (|gCD| = 0.006) and circularly polarized luminescence (|gCPL| = 0.01).