Symmetry‐Driven Strategy for the Assembly of the Core Tetracycle of (+)‐Ryanodine: Synthetic Utility of a Cobalt‐Catalyzed Olefin Oxidation and α‐Alkoxy Bridgehead Radical Reaction

Ryanodine ( 1 ) is a potent modulator of intracellular calcium release channels, designated as ryanodine receptors. The exceptionally complex molecular architecture of 1 comprises a highly oxygenated pentacyclic system with eleven contiguous stereogenic centers, which makes it a formidable target for organic synthesis. We identified the embedded C₂‐symmetric tricyclic substructure within 1 . This specific recognition permitted us to design a concise synthetic route to enantiopure tricycle 9 by utilizing a series of pairwise functionalizations. The four tetrasubstituted carbon centers of 9 were effectively constructed by three key reactions, a dearomatizing Diels–Alder reaction, the kinetic resolution of the obtained racemic 14 through asymmetric methanolysis, and the transannular aldol reaction of the eight‐membered diketone 10 . A new combination of cobalt‐catalyzed hydroperoxidation and NfF‐promoted elimination enabled conversion of the hindered olefin of 9 into the corresponding ketone, thus realizing the desymmetrization. Finally, the tetrasubstituted carbon was stereospecifically installed by utilizing the α‐alkoxy bridgehead radical to deliver the core tetracycle 7 with the six contiguous tetrasubstituted carbon centers. Consequently, the present work not only accomplishes efficient assembly of four out of the five fused rings of 1 , but also develops two new powerful methodologies: two‐step ketone formation and bridgehead radical reaction.     

An asymmetric synthesis of (+)-monomorine I

The synthesis of (+)-monomorine I, an indolizidine alkaloid isolated from Monomorium pharaonis, has been achieved. The 2,6-cis-piperidine ring moiety of (+)-monomorine I was constructed using diastereoselective aminopalladation. Chain elongation via cross-metathesis using Hoveyda-Grubbs 2nd catalyst followed by deprotection of the Cbz group and cyclic reductive hydroamination afforded (+)-monomorine I.     

A Tightly Stretched Ultralong Supramolecular Multiporphyrin Array Propagated by Double‐Strand Formation

A shape‐programmed linearity through supramolecular polymerization is demonstrated by a step‐growth double‐strand formation of a telechelic oligomeric porphyrin array in which two alternating pyridyl‐porphyrin sequenced units are held together by self‐complementary ligand‐to‐metal coordination. The stiff rod‐like structure and sufficiently large binding constant of the double‐strand unit considerably extended a supramolecular array in the one dimension, which produced a tightly stretched string with a length that exceeded several micrometers.     

Assembly of an Achiral Chromophore into Light‐Responsive Helical Nanostructures in the Absence of Chiral Components

The chirality found in living organisms is one of unsolved mysteries on Earth. It is crucial to understand the manner in which small achiral molecules evolve into helical superstructures in the absence of chiral components because this process can provide important insights regarding the origin of chirality in nature. 1) the uncommon helical assembly of an achiral trigonal chromophore into helical nanostructures with aggregation‐induced emission enhancement (AIEE) characteristics and 2) the tunability of the helical pitch and fluorescence intensity in response to light is reported. The Rietveld refinement of X‐ray diffraction (XRD) patterns and the growth process suggest that a striking transformation from an achiral to an asymmetric molecule can occur as a result of specific interactions with certain solvents, presumably leading to the unique helical assembly. More importantly, exposure to UV or visible light promoted not only the formation of irregular helical structures with a wide range of pitch lengths but also an increase in fluorescence intensity.     

An H2O2 Molecule Stabilized inside Open-Cage C60 Derivatives by a Hydroxy Stopper

An H₂O₂ molecule was isolated inside hydroxylated open-cage fullerene derivatives by mixing an H₂O₂ solution with a precursor molecule followed by reduction of one of carbonyl groups on its orifice. Depending on the reduction site, two structural isomers for H₂O₂@open-fullerenes were obtained. A high encapsulation ratio of 81 % was attained at low temperature. The structures of the peroxosolvate complexes thus obtained were studied by ¹H NMR spectroscopy, X-ray analysis, and DFT calculations, showing strong hydrogen bonding between the encapsulated H₂O₂ and the hydroxy group located at the center of the orifice. This OH group was found to act as a kinetic stopper, and the formation of the hydrogen bonding caused thermodynamic stabilization of the H₂O₂ molecule, both of which prevent its escape from the cage. One of the peroxosolvates was isolated by HPLC, affording H₂O₂@open-fullerene with 100 % encapsulation ratio, likely due to the intramolecular hydrogen-bonding interaction.     

Design and fabrication of bismith-silicate photonic crystal fiber

The process of design and fabrication of bismuth-silicate photonic crystal fiber (Bi-PCF) is reported. The Bi-PCF was fabricated by stack and draw method. This is the first trial of the fabrication of photonic crystal fiber made of bismuth-based glass with stack and draw method. The Bi-PCF structure was designed to reduce group-velocity-dispersion (GVD) in a plausible process. Thermal properties of the glass are investigated to establish the fabrication process. The applying pressure and pumping in fiber preform preparation were effectively utilized to control the air-hole diameter and arrangement. The fabricated Bi-PCF shows the well reduced GVD as the numerical calculation predicted. Fusion splicing between Bi-PCF and SMF-28 was also demonstrated.