Synthesis of Optically Active Vasicinone Based on Intramolecular Aza-Wittig Reaction and Asymmetric Oxidation(1)

Both optical isomers of a quinazoline alkaloid, vasicinone, were synthesized by two different methods. The first method used (3S)-3-hydroxy-gamma-lactam as a chiral synthon, which was, after O-TBDMS protection, o-azidobenzoylated followed by treatment with tri-n-butylphosphine to afford (S)-(-)-vasicinone via the tandem Staudinger/intramolecualr aza-Wittig reaction. The second method utilized asymmetric oxygenation of deoxyvasicinone with (1S)-(+)- or (1R)-(-)-(10-camphorsulfonyl)oxaziridine (the Davis reagent), respectively. The aza-enolate anion of deoxyvasicinone was treated with (S)-(+)-reagent to afford (R)-(+)-vasicinone in 71% ee, while the reaction with (R)-(-)-reagent gave (S)-(-)-vasicinone in 62% ee. The optical purity was analyzed by HPLC on specially modified cellulose as a stationary phase. These results provided a facile method to prepare both optical isomers of vasicinone and confirmed the recently reversed stereochemistry of natural (-)-vasicinone.     

Capability of a Liquid-Crystal Adaptive Optics System Based on Feedback Interferometry for Retinal Imaging

A modified arrangement of the adaptive optical retinal imaging system that we described previously is proposed to reduce the intensity loss in the system, so that it works properly even when the intensity of light incident on the eye is very weak. Experiments to verify the system performance were conducted using a conventional artificial eye with a specular reflector as a model retina. We observed that an image of a test target (mimicking a retina) blurred by an aberration plate (mimicking the ocular aberrations) was successfully restored in the adaptive optics fashion even when the intensity of the incident light probing the aberration of the eye became about 1.5% of that required in the previous system. Effect of a more realistic artificial eye with a scattering object as a model retina was also examined experimentally. We found that not only the ocular aberrations, but also the retinal scattering cause the wave-front deformations and that our adaptive optics system compensates for both of them simultaneously.     

Molecularly defined graphitic interface toward proton manipulation

Proton plays a critical role in electrochemical systems to control electrochemical reactivity or isotopic enrichment. Graphene is intensively investigated owing to its unique electronic structure and device fabrication. Through the structural tunability of graphitic materials by chemical or physical modification of the surface, graphene is revealed to be an ideal material for proton manipulation. Here, we review the use of graphene or graphitic materials toward the manipulation of proton with regard to the following three points. (1) Electronic properties of graphene: The electronic band structure of graphene can be modified by metal contacts owing to the interaction with a metal surface. (2) Molecular control of graphitic interface: The chemical structure of graphene can be modified, as is done in molecular chemistry, and can be used as a catalytic platform. (3) Proton conduction by graphene: Proton transport through a graphene layer occurs with a unique mechanism such as tunneling. We provide a perspective on the use of graphitic materials toward controlling the behavior of protons on the basis of the aforementioned points. From the above, graphene can be used as a platform for proton manipulation.     

Rhodium-Catalyzed Highly Diastereo- and Enantioselective Synthesis of a Configurationally Stable S-Shaped Double Helicene-Like Molecule

An S-shaped double helicene-like molecule (>99 % ee), possessing stable helical chirality, has been synthesized by the rhodium(I)/difluorphos complex-catalyzed highly diastereo- and enantioselective intramolecular double [2+2+2] cycloaddition of a 2-naphthol- and benzene-linked hexayne. The collision between two terminal naphthalene rings destabilizes the helical chirality of the S-shaped double helicene-like molecule, but the introduction of two additional fused benzene rings significantly increases the configurational stability. Thus, no epimerization and racemization were observed even at 100 °C. The enantiopure S-shaped double helicene-like molecule forms a trimer through the multiple C−H⋅⋅⋅π and C−H⋅⋅⋅O interactions in the solid-state. The trimers stack to form columnar packing structures, in which neighboring stacks have opposite dipole directions. The accumulation of helical structures in the same direction in the S-shaped double helicene-like molecule enhanced the chiroptical properties.     

Synthesis of Well‐Defined Polybenzamide‐block‐Polystyrene by Combination of Chain‐Growth Condensation Polymerization and RAFT Polymerization

Well‐defined diblock copolymers composed of poly(N‐octylbenzamide) and polystyrene were synthesized by reversible addition‐fragmentation chain transfer (RAFT) polymerization of styrene with a polyamide chain transfer agent (CTA) prepared via chain‐growth condensation polymerization. Synthesis of a dithioester‐type macro‐CTA possessing the polyamide segment as an activating group was unsatisfactory due to side reactions and incomplete introduction of the benzyl dithiocarbonyl unit. On the other hand, a dithiobenzoate‐CTA containing poly(N‐octylbenzamide) as a radical leaving group was easily synthesized, and the RAFT polymerization of styrene with this CTA afforded poly(N‐octylbenzamide)‐block‐polystyrene with controlled molecular weight and narrow polydispersity.

     

Enantioselective total synthesis of the potent anti-HIV nucleoside EFdA

A concise enantioselective total synthesis of 4'-ethynyl-2-fluoro-2'-deoxyadenosine (EFdA), an extremely potent anti-HIV agent, has been accomplished from (R)-glyceraldehyde acetonide in 18% overall yield by a 12-step sequence involving a highly diastereoselective ethynylation of an α-alkoxy ketone intermediate.     

Research on Liebeskind-Srogl coupling/intramolecular Diels-Alder reaction cascade

The Liebeskind-Srogl coupling/intramolecular Diels-Alder (IMDA) reaction cascade that stereoselectively affords a tricarbocyclic compound with a trans–trans-cis fused ring system including an all-carbon quaternary stereogenic center at the ring junction is described. The cascade reactions proceed quickly and stereoselectively afford the products within 2?h at room temperature in the presence of a suitable thioester. The developed protocol as well as the prepared chiral compounds are useful for the enantioselective total synthesis of terpenoids with the trans–trans-cis fused ring system.     

The first total synthesis of hibarimicinone,a potent v-Src tyrosine kinase inhibitor

The first total synthesis of hibarimicinone has been achieved. The polyhydroxydecalin moieties (AB and GH rings) have been synthesized from sulfonylenone 4 derived from d-arabinose. The chiral biaryl 20 was coupled with two polyhydroxydecalins 11 by Michael–Dieckmann type condensation to give the eight rings system. Aromatization and oxidation with Ag⁺ gave quinone 24, and the subsequential transannular etheration gave the hibarimicinone skeleton. Deprotection and tautomerization were performed in one pot to give hibarimicinone (1).     

Dumbbell-Shaped 2,2’-Bipyridines: Controlled Metal Monochelation and Application to Ni-Catalyzed Cross-Couplings

2,2’-Bipyridine ligands (dsbpys) with dumbbell-like shapes and differently substituted triarylmethyl groups at the C5 and C5’ positions showed high ligand performance in the Ni-catalyzed cross-electrophile coupling and the Ni/photoredox-synergistically catalyzed decarboxylative coupling reactions. The superior ligand effects of dsbpys compared to the conventional bpy ligands were attributed to the monochelating nature of dsbpys.