Photo-induced tungsten-catalyzed cascade synthesis of pyrrolo[2,1-a]isoquinoline-1,3-dicarboxylate and its reaction mechanism.

A pyrrolo[2,1-a]isoquinoline core structure is prevalent in marine and other natural products. This article describes a tungsten-catalyzed [3+2] cycloaddition aromatization of dihydroisoquinoline ester and maleic anhydride or an acrylate. The photochemical reaction tolerates a range of functional groups such as ester, cyano, ketone, bromide, and alkene. It is shown that the cycloaddition-aromatization of 2-substitued acrylate catalyzed by a tungsten photocatalyst can be used to evaluate the leaving ability of the leaving group. Experiments done to determine the reaction mechanism revealed that the formation of an ion-pair intermediate generated in situ from dihydroisoquinoline ester and (Z)-4-methoxy-4-oxobut-2-enoic acid via the solvolysis of maleic anhydride with methanol is crucial for the cascade process to occur. The key cycloadduct acid intermediate derived from [3+2] cycloaddition was isolated and determined by X-ray crystallography.

Chiral Hierarchical Architecture Induced by Confinement-Assisted Living Supramolecular Polymerization of Simple Achiral Molecules.

Chiral supramolecular assembly (CSA) based on achiral molecules has provided important clues to understand the origin of biological chirality. However, a simple achiral monomer faces the challenge of chiral stacking with the absence of a chiral resource. The difficulty is that simple achiral monomer lacks steric repulsion to provide asymmetry during hierarchical assembly, which is a prerequisite for chiral stacking with an angle. Moreover, during chiral stacking of achiral molecules or units, the right-handed and left-handed chiral supramolecular isomers (CSIs) are equally formed due to the mirror-imaged conformation, which leads to chirality silence. Here, with the benefit of two-dimensional confinement space of layered double hydroxide (LDH), simple achiral molecules can be arranged to staggered bilayer arrays by imprinting the topological structure of LDH. Once LDH is removed, these staggered arrays can form asymmetric living seeds, which can further elongate to living units with the advantage of living supramolecular polymerization (LSP) by following off-pathway. Due to the asymmetry of living units, the possible chiral stacking outcomes, CSIs, are not mirror-imaged. With the increase of the molecular number in living units, the energy difference between CSIs can be amplified by self-replication of LSP, leading to handedness preference. Thus, the detectable CSA is mainly derived from the CSI with energetically favored hierarchical structure. Thus, our strategy breaks the stereotype that the complex molecular structure and symmetry breaking mechanism are necessary for the formation of detectable CSA by achiral molecules.

Dynamic Control over Hierarchically Dendritic Architectures of Simple Heterogenous Monomers by Living Supramolecular Assembly.

The successful preparation of supramolecular block copolymers (SBCPs) by living supramolecular assembly technology requires two kinetic systems in which both the seed (nucleus) and heterogenous monomer providers are in non-equilibrium. However, employing simple monomers to construct the SBCPs via this technology is almost impossible because the low spontaneous nucleation barrier of simple molecules prevents the formation of kinetic states. Here, with the help of confinement from layered double hydroxide (LDH), various simple monomers successfully form living supramolecular co-assemblies (LSCA). LDH overcomes a considerable energy barrier to obtain living seeds to support the growth of the inactivated second monomer. The ordered LDH topology is sequentially mapped to the seed, second monomer, and binding sites. Thus, the multidirectional binding sites are endowed with the ability to branch, making the branch length of dendritic LSCA reach its maximum value of 3.5 cm so far. The strategy of universality will guide exploration into the development of multi-function and multi-topology advanced supramolecular co-assemblies.

Oriented arrangement of simple monomers enabled by confinement: towards living supramolecular polymerization.

The living supramolecular polymerization technique provides an exciting research avenue. However, in comparison with the thermodynamic spontaneous nucleation, using simple monomers to realize living supramolecular polymerization is hardly possible from an energy principle. This is because the activation barrier of kinetically trapped simple monomer (nucleation step) is insufficiently high to control the kinetics of subsequent elongation. Here, with the benefit of the confinement from the layered double hydroxide (LDH) nanomaterial, various simple monomers, (such as benzene, naphthalene and pyrene derivatives) successfully form living supramolecular polymer (LSP) with length control and narrow dispersity. The degree of polymerization can reach ~6000. Kinetics studies reveal LDH overcomes a huge energy barrier to inhibit undesired spontaneous nucleation of monomers and disassembly of metastable states. The universality of this strategy will usher exploration into other multifunctional molecules and promote the development of functional LSP.

Highly dispersed layered double oxide hollow spheres with sufficient active sites for adsorption of methyl blue.

The adsorption of dyes in contaminated water is an effective approach to solving the environmental crisis. Layered double hydroxide (LDH) and its calcinated product layered double oxide (LDO) show great potential as adsorbents. However, the conventional preparation of LDH or LDO typically suffers from aggregation and blocked active sites, hampering the adsorption efficiency of the adsorbent. Herein, three-dimensional, hollow MgFe-LDO spheres were constructed through the sacrifice of a carbon template. The hollow structure and the monodisperse state provided MgFe-LDO with sufficient microchannels and abundant active sites for adsorption. Through the memory effect of LDO, the anion methyl blue (MB) can be effectively adsorbed with a high uptake capacity of 398 mg g-1. Isotherm simulations demonstrated the monolayer adsorption of MB and the heterogeneous surfaces of the reconstructed LDHs. Moreover, the adsorbents can be recycled and reutilized at least five times through magnetic separation followed by calcination. Our proposed strategy is expected to provide new possibilities for the construction of adsorbents with well-controlled architecture and abundant active sites to deal with anionic pollutants.