Kengo Hyodo

Catalytic enantioselective allylation of ketimines by using palladium pincer complexes with chiral bis(imidazoline)s.

Get selective! Enantioselective allylation of ketimines derived from isatins by using chiral 1,3-bis(imidazolin-2-yl)benzene (Phebim)-Pd(II) complexes afforded products with good enantioselectivity (see scheme). The reaction was applied to a wide variety of ketimines. The obtained product can be converted to homoallylic amines and a spirocyclic amine without the loss of enantiopurity.

Catalytic enantioselective decarboxylative cyanoalkylation of imines by using palladium pincer complexes with C2-symmetric chiral bis(imidazoline)s.

Manifold products: The enantioselective decarboxylative Mannich-type reaction of cyanoacetic acid with N-(2-pyridinesulfonyl)imines catalyzed by chiral 1,3-bis(imidazolin-2-yl)benzene (Phebim)-Pd(II) complexes afforded products with good enantioselectivity (see scheme). The reaction was applied to a wide range of imines with good yield and enantioselectivity. The obtained products can be converted into various compounds without the loss of enantiopurity.

Desymmetrization of meso-aziridines with TMSNCS using metal salts of novel chiral imidazoline-phosphoric acid catalysts.

Highly enantioselective desymmetrization of aziridines with TMSNCS has been developed. Good yield and enantioselectivity were observed by using novel chiral imidazoline-phosphoric acid catalysts. The obtained product can be converted to a chiral β-aminothiol and a β-aminosulfonic acid.

Fractal Surfaces of Molecular Crystals Mimicking Lotus Leaf with Phototunable Double Roughness Structures

Double roughness structure, the origin of the lotus effect of natural lotus leaf, was successfully reproduced on a diarylethene microcrystalline surface. Static superwater-repellency and dynamic water-drop-bouncing were observed on the surface, in the manner of natural lotus leaves. Double roughness structure was essential for water-drop-bouncing. This ability was not observed on a single roughness microcrystalline surface showing the lotus effect of the same diarylethene derivative. The double roughness structure was reversibly controlled by alternating irradiation with UV and visible light.

Photosalient Effect of a Diarylethene with a Perfluorocyclohexene Ring.

Crystals of a diarylethene with a perfluorocyclohexene ring exhibit a remarkable photosalient effect upon UV light irradiation that is attributed to the structural changes that occur when going from open- to closed-ring isomers in the crystalline state, together with the existence of two conformers with different photoconversions compared with those of a perfluorocyclopentene derivative. Our current results give a design principle for molecular structures so as to achieve the photosalient effect for photochromic crystals.

Iron-Catalyzed Dehydration of Aldoximes to Nitriles Requiring Neither Other Reagents Nor Nitrile Media.

The dehydration of aldoximes is an environmentally benign reaction affording the desired nitrile and water as a by-product. However, most of the reported catalytic dehydration reactions of aldoximes require a solvent containing nitrile to synthesize the corresponding nitrile compounds. Inspired by recent reports on the enzymatic synthesis under nitrile-free conditions, we here describe that a simple iron salt catalyzes the dehydration of aldoximes requiring neither other reagents nor nitrile media. Our method can be applied to the one-pot synthesis of nitiriles from aldehydes.

Photosalient Phenomena that Mimic Impatiens Are Observed in Hollow Crystals of Diarylethene with a Perfluorocyclohexene Ring

A diarylethene with a perfluorocyclohexene ring formed hollow crystals by sublimation under normal pressure. Upon UV irradiation of the crystals, they showed remarkable photosalient phenomena and scattered into small pieces. The speed of the flying debris released from the crystal by UV irradiation exceeded several meters per second. To clearly show a photosalient effect resembling the scattering behavior of Impatiens on a smaller scale, small fluorescent beads (1-μm diameter) were inserted into the hollow crystal. Consequently, scattering of the beads was observed as UV irradiation caused deformation and bursting of the hollow structure. This phenomenon is unique to hollow crystals, and the ability to effectively induce remarkable photosalient phenomena is similar to the behavior of hollow-structured Impatiens in nature.

Brønsted acid catalyzed transoximation reaction: synthesis of aldoximes and ketoximes without use of hydroxylamine salts

The transoximation reaction enables the transfer of an oxime to a carbonyl compound and is catalyzed by transoximase in the pupae of the silkworm. Inspired by this bio-synthetic pathway, we achieved the transoximation of oximes to aldehydes and ketones catalyzed by a Bronsted acid under mild conditions. Hydroxylamine salt, which necessitates a stoichiometric amount of base, was not required. NMR analysis clarified that this reaction proceeded through hydroxylamines generated by the successive hydrolysis of the oxime in situ. In addition, an environmentally benign method for catalytic transoximation was demonstrated in aqueous medium on a one hundred gram scale and the reaction filtrate containing the catalyst was recovered and reused over 10 times.

Brønsted Acid Catalyzed Nitrile Synthesis from Aldehydes Using Oximes via Transoximation at Ambient Temperature

The Brønsted acid-catalyzed synthesis of nitriles is described via transoximation under mild conditions using an O-protected oxime as a more stable equivalent of explosive O-protected hydroxylamines. The nitrile was generated via an O-protected aldoxime produced from the aldehyde and an O-protected oxime through transoximation. The reaction could be performed on a 1 g scale.

Photoinduced topographical changes on microcrystalline surfaces of diarylethenes

By alternate irradiation with UV and visible light, reversible topographical changes were observed on the microcrystalline surfaces of diarylethene derivatives above the glass transition temperatures (Tg) of their open-ring isomers. For the photogenerated closed-ring isomers, the crystal growth proceeded at the surface softened by molecular movement. This is the self-aggregation of the closed-ring isomers. The photogenerated surface topographies appear depending on the crystal habits of the closed-ring isomers. Reflecting the properties (crystal habits) of diarylethene derivatives, we obtained cubic, needle, and plate-shaped crystals of the closed-ring isomers on the microcrystalline surfaces of the open-ring isomers by irradiation with UV light. Even a derivative having one isopropyl group at a reactive carbon atom, whose closed-ring isomer is thermally unstable, showed photoinduced topographical changes, because the Tg of the open-ring isomer is around ambient temperature.