Preparation of [23]cyclophane-1,2-diones by the reaction of 3,6;12,15-Di-1,4-benzo[6.6](3,4)-1,2,5-thiadiazolocyclophanes with grignard reagents

3,6;12,15-Di-1,4-benzo[6.6](3,4)-1,2,5-thiadiazolocyclophanes 1a-c were prepared starting from 3,4-di-p-tolyl-1,2,5-thiadiazole 3 and converted into [2³]cyclophane-1,2-diones 2a-c by the reaction with Grignard reagents.     

Asymmetric mono-oxazine: an inevitable product from Mannich reaction of benzoxazine dimers

The Mannich reaction is detailed, which was carried out on benzoxazine dimers under various conditions, that is, temperature, reaction time, and solvents. Against our expectation, in any condition, instead of generating a disubstitution oxazine compound, the reaction gives a product with only a single oxazine ring, a mono-oxazine benzoxazine dimer, as characterized by FT-IR, 1H NMR, 13C NMR, 2D-NMR (1H-1H COSY, 1H-13C HMQC, and 1H-13C HMBC), and EA. The asymmetrical reaction is found to be based on the original structure of the benzoxazine dimer which has two phenol rings in a different stability as clarified by X-ray structure analysis of the single crystal. All types of benzoxazine dimers indicate the specific structure with a pair of inter- and intramolecular hydrogen bonds. The bond distance indicates that the intramolecular hydrogen bonding is very strong, while the packing structure emphasizes the high stability of the dimer unit and implies the deactivation of one phenol ring in the benzoxazine dimer. In this contribution, we demonstrate one of the quite rare examples, showing how the stereostructure of the reactant molecule is an important factor to control the reaction and give an asymmetric product which we never expected when considering only the chemical formula.     

Frequency structure in an electronically tuned Ti:sapphire laser: periodic appearance of static fringes in both homodyne and heterodyne Michelson interferometers

Static interference fringes were observed repeatedly with changes of path difference in both homodyne and heterodyne Michelson interferometers. This unique coherence property of an electronically tuned Ti:sapphire laser with an intracavity acousto-optic tunable filter (AOTF) has revealed the frequency structure and dynamics of the laser field. The fact that static interference occurred in a heterodyne interferometer with unequal path lengths indicates backscattering of the intracavity laser field, suggesting that Brillouin-enhanced four-wave mixing occurs in the intracavity AOTF.     

Chiral Bis(oxazoline) Ruthenium Complexes with Bipyridyl‐Type N‐Heteroaromatics: Comparative Stereochemical and Photochemical Characterization of their Λ‐ and Δ‐Diastereomeric Geminate Isomers

Diastereomeric geminate pairs of chiral bis(2‐oxazoline) ruthenium complexes with bipyridyl‐type N‐heteroaromatics, Λ‐ and Δ‐[Ru(L‐ L)₂(iPr‐biox)]²⁺ (iPr‐biox=(4S,4′S)‐4,4′‐diisopropyl‐2,2′‐bis(2‐oxazoline); L‐ L=2,2′‐bipyridyl (bpy) for 1 Λ and 1 Δ, 4,4′‐dimethyl‐2,2′‐bipyridyl (dmbpy) for 2 Λ and 2 Δ, and 1,10‐phenanthroline (phen) for 3 Λ and 3 Δ), were separated as BF₄ and PF₆ salts and were subjected to the comparative studies of their stereochemical and photochemical characterization. DFT calculations of 1 Λ and 1 Δ electronic configurations for the lowest triplet excited state revealed that their MO‐149 (HOMO) and MO‐150 (lower SOMO) characters are interchanged between them and that the phosphorescence‐emissive states are an admixture of a Ru‐to‐biox charge‐transfer state and an intraligand excited state within the iPr‐biox. Furthermore, photoluminescence properties of the two Λ,Δ‐diastereomeric series are discussed with reference to [Ru(bpy)₃]²⁺.     

Simple and efficient synthesis of highly functionalized cyclohexanes; formal total synthesis of ovalicin and fumagillin

Two chiral cyclohexanes 4 and 6, which are key intermediates for the total synthesis of ovalicin 1 and fumagillin 2, respectively, were synthesized from (2R,3S) 1,2-epoxy-4-penten-3-ol. The key steps involve an efficient construction of divinylalcohol 7 using methallyl Grignard reagent 9c, and an intramolecular olefin metathesis of 7.     

Efficient Transformation of Polymer Main Chain Catalyzed by Macrocycle Metal Complexes via Pseudorotaxane Intermediate

Post-synthesis modification of polymers streamlines the synthesis of functionalized polymers, but is often incomplete due to the negative polymer effects. Developing efficient polymer reactions in artificial systems thus represents a long-standing objective in the fields of polymer and material science. Here, we show unprecedented macrocycle-metal-complex-catalyzed systems for efficient polymer reaction that result in 100 % transformation of the main chain functional groups presumably via a processive mode reaction. The complete polymer reactions were confirmed in not only intramolecular reaction (hydroamination) but also intermolecular reaction (hydrosilylation) by using Pd- and Pt-macrocycle-catalyzed systems. The most fascinating feature of the both reactions is that higher-molecular-weight polymers reach completion faster. Various studies suggested that the reactions occur in the catalyst cavity via the formation of a supramolecular complex between the macrocycle catalyst and polymer substrate like pseudorotaxane, which should be of characteristic of the efficient polymer reactions progressing in a processive mode.     

Supramolecular Structure of N,N-Bis(2-hydroxy-benzyl)alkylamine: From Hydrogen Bond Assembly to Coordination Network in Guest Acceptance

N,N-Bis(2-hydroxybenzyl)alkylamine ( HBA ) was described as a model to simplify the supramolecular system of polybenzoxazines. The single crystal X-ray analysis revealed that HBA forms a dimeric assembly based on its simultaneous inter- and intramolecular hydrogen bond network. When the HBA accepted the copper ion, the dimeric assembly HBA changed its primary hydrogen bond network to charge transfer coordination as clarified by the single crystal analysis as well as the superimposed structure based on DMol³ calculation. The supramolecular structure of HBA and copper also exhibited the role of solvent molecules in the packing structure which is a rare example showing the host accepts not only the metal ions but also the neutral molecules in the same time. The cyclization of HBA with esters or ethers to macrocyclic compounds was also an important model reaction to show how the backbone molecules self-stabilized with the hydrogen bond network initiate the simple, effective and efficient macrocyclic reaction.