Hajime Iwamoto

Convenient synthesis of [3]catenane by olefin metathesis dimerizations

Abstract [3]Catenane 5a and 5b were synthesized conveniently by olefin metathesis dimerization of pseudorotaxanes 3a and 3b . The yields of 5a and 5b were influenced by concentrations of 3a and 3b , and a ring size of a center wheel of [3]catenane.

Thermodynamic study on supramolecular complex formation of fullerene with calix[5]arenes in organic solvents

Abstract Thermodynamic parameters for the supramolecular complex formation of fullerene C 60 with calix[5]arene receptors are reported. The entropy change in chloroform is negative, but in toluene is positive, suggesting the tight solvation around the guest in toluene. Desolvation of the guest plays an important role in the supramolecular complex formation in toluene.

Noncovalent Isotope Effect for Guest Encapsulation in Self‐Assembled Molecular Capsules

Noncovalent isotope effects are often observed on substrate–enzyme complexes in nature. Isotopic substitution of a substrate alters its affinity towards an enzyme. The difference between the behaviors of isotopic molecules has been recently reported in supramolecular host–guest complexes. Cyclodextrins (CDs) include a variety of guests that are complementary to their interiors in H2O. The guest binding affinities increased in D2O owing to a solvent isotope effect. Tanaka, Thornton, and co-workers examined the separation of protiated and deuterated compounds by reverse-phase HPLC analysis to evaluate their hydrophobicity. The replacement of a molecule of hydrogen with deuterium made it less polar or hydrophobic. Aoyama et al. reported the noncovalent isotope effect on the formation of host–guest complexes in aqueous media. Their water-soluble resorcinarene included protiated guests that were slightly stronger than deuterated ones because of hydrophobic and CH···p interactions. In organic media, the binding manner of the protiated and deuterated guests to a host cavity contrasts with the binding manner in aqueous media. Rebek et al. discovered that cylindrical molecular capsules preferentially encapsulate deuterated p-xylene. A similar noncovalent isotope effect was detected on C H···X R hydrogen bonds in guests that were binding within a deepcavity cavitand. The physical basis of the deuteration effect is commonly ascribed to the change in the zero-point vibrational levels of C H stretching modes. The weak noncovalent interaction may reduce (or increase) the stretching force constants and the fundamental frequencies, and thus the total binding energy is isotope dependent. This mechanism may explain the isotope effect on the enthalpy change, but not on the entropy change. To gain insight into the isotope effect in noncovalent interactions, detailed studies on the supramolecular association are needed. We report herein thermodynamic studies on the noncovalent isotope effect of CH···p interactions derived from the guest inclusion within self-assembled capsule 1·4BF4 (Figure 1). We found large isotope effects on

Synthesis of Molecular Tweezers Bearing Two Porphyrins and Its Complexation toward Electron Acceptors

Synthesis of new flexible molecular tweezers 1.M 2 (M = 2H, Co, Zn, Cu, Ni) based on bis-dioxa[2.2]orthocyclophane bearing two porphyrins is presented. The molecular tweezers (1.(2H) 2 ) can bind not only planar π-electronacceptors, such as tetracyanoquinodimethane (TCNQ) and tetracyanohenzene (TCNB) but also a spherical guest C 6 0 .

Synthesis and binding behavior of a Zn(II)-porphyrin having calix[5]arene cap

Abstract The synthesis and binding behavior of a Zn(II)–porphyrin having a calix[5]arene cap are presented. In order to synthesize such a bridged porphyrin, 5,15-bis(7-carboxy-1-naphthyl)-10,20-diphenylporphyrin having the syn arrangement of two naphthalene rings has been prepared. Amidation of the porphyrin and calix[5]arene having two amino functions and subsequent treatment of Zn(OAc) 2 gave a calix[5]arene capped Zn–porphyrin. Calix[5]arene–Zn–porphyrin was found to bind 4-methylpyridine much stronger than TPP·Zn.

Metal-Free, One-Pot, Sequential Protocol for Transforming α,β-Epoxy Ketones to β-Hydroxy Ketones and α-Methylene Ketones

A new sequential, one-pot protocol for transforming 1,3-disubstituted 2,3-epoxy ketones to β-hydroxy ketones and α-methylene ketones has been developed. Reaction of epoxy ketones with boron trifluoride etherate (BF3·OEt2) generates the cationic intermediates by regioselective epoxide ring opening and an acyl shift. Then, a treatment of these cations with 2-aryl-1,3-dimethylbenzimidazolines (DMBIH) results in formation of 1,2-disubstituted 3-hydroxy ketones. DMBIH serves as a hydride donor in the second step of this process. Finally, the β-hydroxy ketones can be converted to 1,2-disubstituted 2-methylene ketones by treatment with methanesulfonic acid or a combination of methanesulfonyl chloride and triethylamine. Importantly, the sequential steps involved in formation of the α-methylene ketone products can be carried out in one pot.

Synthesis and Enantioselective Recognition of a Calix[5]arene-based Chiral Receptor

Calix[5]arene-based artificial receptor 1 capped with chiral macrocycle 6 was synthesized and showed strong binding towards ethyltrimethylammonium derivatives via cation/π and/or hydrogen bonding interactions. The calix[5]arene cavity provided the dissymmetric guest-binding environment in which chiral guests 9–19 were encapsulated in an enantioselective fashion. Thermodynamic studies for this chiral recognition gave an insight into the binding manner of the receptor: the enantioselective recognition is enthalpy favoured. Probably, the attractive interactions between the host and the guest gives rise to the enthalpy difference in enantioselection; however, the enthalpy gains of one of the enantiomers are compensated by entropy costs, reducing the enantioselectivity of the receptor.

Conformational analysis by chemical shift simulation: structure of 1,4,11,14-tetraoxa[4.4]metacyclophane

Abstract Conformational analysis of 1,4,11,14-tetraoxa[4.4]metacyclophane was carried out using a combination of the molecular mechanics calculation, analysis of the temperature dependent 1 H NMR signal change and the chemical shift simulation method. The molecular mechanics calculation with Amber* force-field gave the two structures, one is highly symmetric C 2 v and the other is C i symmetric. The latter is identical to the structure found in the crystal. Both of the structures were confirmed by the chemical shift simulation.

CONSTRUCTION OF A AND C RING INTERMEDIATES FOR TAXOL BY USING (3+2)-CYCLOADDITION OF NITRILE OXIDE

Abstract Syntheses of the A-ring and the chiral C-ring model of taxol by using the intramolecular nitrile oxide cycloaddition and its diastereoselectivity based on MM2 transition state model are described.

Estimation of magnetic anisotropy in polycyclic aromatics

Dihydro-dibenzophenanthrene derivatives 1a ( 1b ) were synthesised in order to obtain the NMR shielding parameters for naphthalene ring. The 1 H NMR assignment of 1a and substituent-induced shifts (SIS) from the corresponding androstanone ethylene ketal ( 2 ) are presented. A simple sum of the magnetic shielding of benzene rings can satisfactorily reproduced the observed SIS values due to the naphthalene ring of 1 .